Effect of wet/dry, fresh liquid, fermented whole diet liquid, and fermented cereal liquid feeding on feed microbial quality and growth in grow-finisher pigs

Abstract

Fermented liquid feeding has proved beneficial for weaner pigs; however, there is limited research on its effect on the growth and feed conversion efficiency (FCE) of grow-finisher pigs. Microbial decarboxylation of amino acids is associated with whole diet fermentation, while wet/dry and liquid feeding reportedly improve growth compared with dry feeding. The objective of this study was to determine the effect of wet/dry feeding and fresh, fermented whole diet, and fermented cereal liquid feeding on pig growth, feed efficiency, and carcass quality in grow-finisher pigs. Pigs were allocated to one of four dietary treatments in two experiments: 1) Single-space wet/dry feeders (WET/DRY), 2) Fresh liquid feeding (FRESH), 3) Fermented cereal liquid feeding where the cereal fraction (38% barley, 40% wheat) of the diet was fermented prior to feeding (FERM-CER), and 4) Fermented whole diet liquid feeding where the whole diet was fermented prior to feeding (FERM-WH). In exp. 1, pigs were fed the experimental diets for 68 d prior to slaughter (29.8 kg ± 0.92 SE to 102.3 kg ± 0.76 SE). Overall, average daily gain (ADG) was 1,094, 1,088, 1,110, and 955 g/d (SE = 13.0; P < 0.001) and FCE was 2.26, 2.37, 2.40, and 2.88 (SE = 0.031; P < 0.001) for treatments one through four, respectively. Pigs fed FERM-WH were lighter at slaughter than pigs fed the other three treatments (P < 0.001). In exp. 2, pigs were on treatment for 26 d prior to slaughter (85.3 kg ± 1.69 SE to 117.5 kg ± 0.72 SE). Overall, ADG in exp. 2 was 1,103, 1,217, 1,284, and 1,140 g/d (SE = 27.9; P < 0.01) and FCE was 2.78, 2.99, 2.95, and 3.09 g/g (SE = 0.071; P = 0.05), for treatments one through four, respectively. There were no significant differences observed between treatments for apparent total tract digestibility of dry matter, organic matter, nitrogen, gross energy, or ash. Higher lactic acid bacteria counts and lower Enterobacteriaceae counts and pH were observed in FERM-CER and FERM-WH compared with WET/DRY and FRESH. Ethanol concentrations were almost 4-fold higher in FERM-CER troughs than FRESH troughs and 5-fold higher in FERM-WH than FRESH troughs. To conclude, FERM-WH resulted in poorer growth and FCE compared with WET/DRY, FRESH, and FERM-CER, probably due to amino acid degradation and a loss in gross energy found in FERM-WH.

Introduction

Fresh liquid feeding involves mixing the diet with water just prior to feed-out, while fermented liquid feed (FLF) is prepared by soaking all or part of the diet with water for a period of time prior to feeding, with/without an inoculum (Scholten et al., 1999; Dung et al., 2005). Wet/dry feeding, where pigs mix dry feed with water at the point of feeding using a water nipple located in the trough, has resulted in improved growth compared with dry feeding (Gonyou and Lou, 2000; Bergstrom et al., 2008; Myers et al., 2013). Diet fermentation can be beneficial to pig gastrointestinal health due to reduced feed pH and the resultant lower gastric pH, proliferation of lactic acid bacteria (LAB), and decreased Enterobacteriaceae (Mikkelsen and Jensen, 2000; Lawlor et al., 2002; Canibe and Jensen, 2003). Fermenting the cereal fraction of the diet may be preferable to whole diet fermentation to avoid microbial decarboxylation of free amino acids (Canibe and Jensen, 2003; Canibe et al., 2007a, 2007b; Brooks, 2008). FLF has been proposed as an alternative to antibiotics for young pigs (Close, 2000; Stein, 2002) and to reduce Salmonella in grow-finisher pigs (van Winsen et al., 2002). However, lower feed intake and growth rates have been reported in grow-finisher pigs fed FLF than in pigs fed fresh liquid feed (Canibe and Jensen, 2003). Previous work has found improved growth rates and apparent total tract digestibility (ATTD) of nutrients by fermenting the cereal fraction of the diet compared to fresh liquid feeding (Torres-Pitarch, 2019). The aim of this study was to compare the effect of wet/dry, fresh liquid, fermented whole diet liquid, and fermented cereal liquid feeding on diet microbial quality and the growth, feed conversion efficiency (FCE), health, and carcass quality of grow-finisher pigs. It was hypothesized that whole diet fermentation would result in reduced growth due to decarboxylation of amino acids and that nutrient digestibility would improve in the fermented cereal diet compared with fresh and wet/dry diets.

Materials and Methods

Animal care and ethics

Ethical approval for this study was granted by the Teagasc Animal Ethics Committee (approval no. 107/2015). The experiment was conducted in accordance with Irish legislation (SI no. 543/2012) and the EU Directive 2010/63/EU for animal experimentation.

Experimental design and animals

The effect of wet/dry feeding and fresh, fermented whole diet, and fermented cereal liquid feeding on pig growth, feed efficiency, health, and nutrient digestibility was examined in two experiments. Experiment 1 used 216 Danavil Duroc × (Landrace × Large White) female and entire male pigs with an initial body weight (BW) of 29.7 kg ± 0.92 SEM and its duration was 68 d, following which pigs were slaughtered on days 69 and 70. Experiment 2 used 160 pigs with an initial BW of 85.3 kg ± 1.69 SEM and its duration was 26 d after which time, the pigs were slaughtered on days 27 and 28. In exp. 1, the pigs were penned in groups of six pigs per pen with a total of nine pen groups per treatment. In exp. 2, pigs were penned in groups of five pigs per pen with a total of eight pen groups per treatment.

In both experiments, all treatments were applied in the same room. Pen groups were blocked by sex and weight and assigned to one of four treatments, as follows: 1) Single space wet/dry feeders where pigs mixed water and meal at the point of feeding, using a water nipple located in the trough (WET/DRY); 2) Fresh liquid feeding (FRESH) where the diet and water were mixed immediately prior to feeding; 3) Fermented cereal liquid feeding (FERM-CER) where the cereal fraction of the diet was fermented and then mixed with balancer and water prior to feeding; and 4) Fermented whole diet liquid feeding (FERM-WH) where the whole diet was fermented prior to feeding. Pen groups were given a 1-wk adaptation period prior to the start of the experiment, during which pigs fed WET/DRY were fed meal via wet/dry feeders while the other three treatment groups received fresh liquid feed prepared at 2.5:1 water:feed on a fresh weight basis.

Pen groups were housed in pens (2.36 × 2.37 m) with concrete slatted floors and solid PVC partitions. Each pen group had access to supplementary water from a water bowl (DRIK-O-MAT, Egebjerg International A/.S, Egebjerg, Denmark) to comply with Council Directive 2008/120/EC (2008). Air temperature was maintained at 20 to 22 °C. The room was mechanically ventilated using ridge mounted exhaust fans and side inlets controlled by a Stienen PCS 8100 controller (Stienen BV, Nederweert, The Netherlands). Pigs were observed twice daily and pigs showing signs of ill-health were treated appropriately. All veterinary treatments were recorded, including pig identity, symptoms, medication, and dosage administered.

For the three liquid treatments (FRESH, FERM-CER, and FERM-WH), each pen was equipped with a solenoid valve over a short trough fitted with an electronic sensor. Sensors were checked four times per day increasing to six times per day and when the residual feed in the trough was below the sensor, additional feed was dispensed into troughs. Feeding was according to a feed curve for these three treatments that ensured ad libitum access to feed. The feeding curve allowed for 23 MJ digestible energy (DE)/pig/d at the start of exp. 1, increasing to 42 MJ DE/pig/d during the experiment, and for 36 MJ DE/pig/d at the start of exp. 2, increasing to 42 MJ DE/pig/d. The liquid feed level in the troughs was manually inspected daily prior to and after feeding and feeding curves increased or decreased accordingly to ensure ad libitum access to feed while minimizing wastage. The three liquid-fed treatments were fed from short steel troughs (100 × 32.5 × 21 cm) located on top of a rubber mat (1.5 × 1 m) to help minimize feed wastage.

The WET/DRY treatment was fed from single-space wet/dry feeders (Irish Dairy Services, Portlaoise, Ireland; 104.1 × 36.8 × 30.5 cm) that were fitted with a water nipple at the point of feeding. Wet/dry feeders were monitored twice daily with feed in the hopper replenished as required and adjustments to feed flow made to ensure ad libitum access to feed while minimizing wastage.

Feed preparation

All diets were formulated to contain 9.8 MJ net energy (NE)/kg and 9.97 g/kg standardized ileal digestible lysine. All other amino acids were formulated relative to lysine according to the ideal protein concept (NRC, 2012). The full ingredient specification and nutrient composition of the dietary components and the experimental diet are reported in Table 1. The dietary components and experimental diet were manufactured in meal form at the Teagasc feed mill facilities (Teagasc, Moorepark, Fermoy, Co. Cork, Ireland) as follows: 1) Complete meal diet for WET/DRY treatment; 2) Cereal fraction, milled through a 3-mm screen, composed of 38% wheat and 40% barley; and 3) Balancer fraction composed of soybean meal, soy oil, synthetic amino acids, phytase, minerals, and vitamins. Components 2) and 3) were stored in steel bins adjacent to the liquid feed preparation area during the experimental period and the complete diet was stored in 25 kg bags. Celite (2 g/kg) was added to the feed during the manufacturing process in order to measure the coefficient of apparent total tract digestibility (CATTD) of nutrients using the acid insoluble ash (AIA) technique (McCarthy et al., 1977).

Table 1.

Composition of the experimental diet and dietary components (on an as-fed basis, g/kg unless otherwise stated)¹

		Dietary components
	Experimental diet	Cereal	Balancer
Ingredient composition2
Wheat	400.0	400.0
Barley	382.7	382.7
Soybean meal	183.0		183.0
Limestone flour	11.0		11.0
Soy oil	9.7		9.7
Lysine HCl	3.8		3.8
Salt	3.0		3.0
l-Threonine	1.7		1.7
Celite	2.0		2.0
Vitamin and mineral premix3	1.0		1.0
Mono diCalcium phosphate	1.0		1.0
dl-Methionine	0.9		0.9
l-Tryptophan	0.2		0.2
Phytase4	0.1		0.1
Chemical composition
DM	875.0	871.0	900.0
CP	173.0	94.0	420.0
Ash	40.0	29.0	118.0
NDF	123.0	178.0	79.0
GE, MJ/kg	16.1	16.0	17.0
Lysine	9.8	8.4	33.2
Methionine	4.4	4.2	10.9
Threonine	7.2	6.5	20.0
DE, MJ/kg2	13.8
NE, MJ/kg2	9.8
Oil2	25.7
Standardized ileal digestible lysine2	10.0
Total calcium2	6.6
Total phosphorus2	2.6

¹Values are the mean of diets from 1 and 2 analyzed for DM, CP, ash, NDF, and GE. Values for amino acids are from exp. 2 only.

²Calculated values.

³Vitamin and mineral premix provided per kilogram of complete diet: Cu from copper sulfate, 15 mg; Fe from ferrous sulfate monohydrate, 24 mg; Mn from manganese oxide, 31 mg; Zn from zinc oxide, 80 mg; I from potassium iodate, 0.3 mg; Se from sodium selenite, 0.2 mg; retinyl acetate, 0.7mg; cholecalciferol, 12.7 μg; dl-alpha-tocopheryl acetate, 40 mg; Vitamin K, 4 mg; vitamin B12, 15 μg; riboflavin, 2 mg; nicotinic acid, 12 mg; pantothenic acid, 10 mg; vitamin B1, 2 mg; vitamin B6, 3 mg; and celite, 2,000 mg.

⁴The diet contained 500 phytase units (FYT) per kg feed from RONOZYME HiPhos (DSM, Belfast, UK).

The three liquid-fed treatments (FRESH, FERM-CER, and FERM-WH) were prepared and fed using a liquid feed system (HydroMix, Big Dutchman, Vechta, Germany) that had two fermentation tanks (2,000 liters) which were connected to two mixing tanks (500 liters) for feed preparation and feed-out. Liquid feed was mixed using an agitator (consisting of one vertical axis and six horizontal blades) installed in each tank. A high-pressure air system delivered liquid feed from the mixing tanks to the feed troughs.

The FRESH liquid dietary treatment was prepared by mixing the cereal and balancer components (at 0.784:0.216, cereal:balancer) with water. The diet was agitated for 120 s prior to delivery to the troughs. FERM-CER and FERM-WH were prepared by adding a starter culture containing Lactobacillus plantarum DSMZ16627 and Pediococcus acidilactici NCIMB3005 (Sweetsile, Agway, Cork, Ireland) to the cereal plus water or cereal plus balancer (mixed at a ratio of 0.784:0.216) plus water, respectively, and allowing an initial fermentation for 48 h, during which no cereal/feed was removed from the tank. Lactobacillus plantarum is facultatively heterofermentative while P. acidilactici is homofermentative. The starter culture was included at 20 g/2,000 liters feed mix in exp. 1 and 15 g/1,500 liters feed mix in exp. 2, giving an estimated inclusion level of 5.0 × 10⁵ CFU/mL of each strain in the fermentation tanks. Thereafter, to replace feed consumed by the pigs, the fermentation tanks were replenished once daily to a volume of 2,000 liters in exp. 1 and 1,500 liters in exp. 2 with either cereal or whole diet, according to treatment, at a water:feed ratio of 2.5:1 on a fresh matter basis. The contents of the fermentation tanks were agitated on a constant 30 min on/30 min off cycle for the duration of both experiments. The water:feed ratio (on a fresh matter basis) was 2.5:1 for each liquid feeding treatment. The WET/DRY treatment involved feeding meal from single-space wet/dry feeders as outlined above.

Records and sampling

Individual pig weights were recorded on days 0, 34, 48, and 68 in exp. 1 and on days 0 and 26 in exp. 2. Pen-group weights were also recorded on day 13 in exp. 1. Feed delivered to troughs was recorded daily for each pen and feed disappearance calculated for the periods between each pig weighing in each experiment. Average daily gain (ADG), average daily feed intake (ADFI), and FCE were calculated for each period and the entire experiment. To calculate carcass ADG and carcass FCE, a kill-out percentage of 65% was applied to the pig start weights in exp. 1 and a kill-out percentage of 75% to start weights in exp. 2 due to their heavier start weights (Lawlor and Lynch, 2005). The kill-out percentage at slaughter was then applied to the final BW of pigs prior to slaughter and carcass ADG and carcass FCE were calculated accordingly.

During the initial 48-h fermentation, feed samples were collected during agitation from a release valve at the base of each of the fermentation tanks at 0, 4, 8, 12, 16, 20, 24, 30, 36, and 48 h for exp. 1 and every 6 h for exp. 2 (0, 6, 12, 18, 24, 30, 36, 42, and 48 h). The pH and temperature of these samples were recorded at each time point (Mettler Toledo pH meter, Greifensee, Switzerland), and samples were analyzed microbiologically as explained below. The experiment began immediately at the end of the 48-h initial fermentation. Samples were also collected from each of the fermentation tanks and analyzed on days 2, 8, 26, and 62 of exp. 1 and on days 2, 6, 8, and 25 of exp. 2.

On days 26 and 62 of exp. 1 and on days 6 and 25 of exp. 2, feed samples were collected from the WET/DRY hopper, mixing tanks (FRESH, FERM-CER, and FERM-WH), liquid feed troughs (FRESH, FERM-CER, and FERM-WH), and WET/DRY troughs for microbiological analysis. Liquid feed trough samples were sampled ~30 min before a new feed mix was delivered to the trough, which was 3 to 4 h after the previous feed, and included two trough samples per treatment on each sampling occasion that were analyzed separately. On each sampling day, one sample was collected from the hopper (WET/DRY) or mixing tank (FRESH, FERM-CER, and FERM-WH) of each treatment and two trough samples were collected per treatment. All feed samples for microbiological analysis were put on ice and transported to the laboratory for analysis on the same day. All samples were analyzed separately.

On days 6 and 25 of exp. 2, feed samples (~20 g) were collected from the mixing tanks and troughs of FRESH, FERM-CER, and FERM-WH, as were samples from the fermentation tanks of FERM-CER and FERM-WH. These were stored at −20 °C for subsequent volatile fatty acid (VFA), ethanol, and lactate analysis. On day 26 of exp. 2, liquid feed samples were collected as follows for amino acid analysis; ~250 g from the mixing tanks of FRESH, FERM-CER, and FERM-WH and a dry feed sample (~250 g) from the WET/DRY hopper. These were frozen at −20 °C for subsequent drying (trough samples were freeze-dried and the mixing tank and fermentation tank samples were oven-dried at 55 °C for 72 h) and amino acid analysis. The dry dietary components from the mill (cereal and balancer) were also frozen at −20 °C prior to amino acid analysis.

Feed samples from each batch produced in the mill were collected during exp. 1 and exp. 2. These were pooled into one feed sample per component for each experiment (i.e., one full diet, one cereal, and one balancer) for proximate analysis. The full diet sample from exp. 2 was used for ATTD determination. In exp. 2, freshly voided fecal samples for ATTD determination were collected from three pigs per pen from 24 pens (six pens/treatment) on day 27. These fecal samples were frozen at −20 °C in aluminum foil trays for subsequent freeze-drying prior to chemical analysis.

Slaughter, carcass records, and blood sampling

On days 69 and 70 of exp. 1 and on days 27 and 28 of exp. 2, pigs were transported to a commercial abattoir. They were stunned using CO₂ and killed by exsanguination, during which blood samples were collected for hematology analysis from 36 pigs (9 pigs/treatment) in exp. 1 and 32 pigs (8 pigs/treatment) in exp. 2 using Vacuette tubes (Labstock, Dublin, Ireland) containing Ethylenediaminetetraacetic acid to prevent clotting.

The following measurements were taken: hot carcass weight was recorded 45 min after stunning, and back-fat thickness and muscle depth at 6 cm from the edge of the split back at the level of the third and fourth last rib were determined using a Hennessy Grading Probe (Hennessy and Chong, Auckland, New Zealand). Lean meat content was estimated according to the formula: Estimated lean meat content (%) = 60.3 – 0.847x + 0.147y where x = fat depth (mm); y = muscle depth (mm) (Department of Agriculture, 2001). Cold carcass weight was calculated as hot carcass weight × 0.98. Kill-out percentage was calculated from cold carcass weight and final BW.

Hematological analysis of blood samples

Hematological analysis as an indicator of pig health was performed on whole blood within 6 h of collection using a Beckman Coulter Ac-T diff analyzer (Beckman Coulter, High Wycombe, UK). The following parameters were measured: white blood cell (WBC) number, lymphocyte number and percentage, monocyte number and percentage, granulocyte number and percentage, red blood cell number, red blood cell distribution width, hemoglobin, hematocrit, mean corpuscular volume, mean corpuscular hemoglobin, platelets, and mean platelet volume.

Microbiological analysis of feed sampled from fermentation tanks, mixing tanks, and troughs

Approximately, 10 g of each liquid or dry feed sample was homogenized in a stomacher as a 10-fold dilution in maximum recovery diluent (MRD; Oxoid, Basingstoke, UK) and a 10-fold dilution series was performed in MRD. Relevant dilutions were plated in duplicate as follows: 1) pour-plated on de Man, Rogosa, and Sharpe (Merck, Darmstadt, Germany) agar, containing 50 U/mL nystatin (Sigma-Aldrich, Arklow, Co. Wicklow, Ireland), overlaid, and incubated at 30 °C for 72 h for enumeration of LAB; 2) pour-plated on violet red bile glucose (Oxoid) agar, overlaid, and incubated at 37 °C for 24 h for Enterobacteriaceae; 3) pour-plated on ChromoCult tryptone bile X-glucuronide (Merck) agar and incubated at 44 °C for 24 h for E. coli; and 4) spread-plated on yeast glucose chloramphenicol (Merck) agar and incubated at 25 °C for 5 d for yeasts and molds. Colonies were counted and the counts averaged and presented as log₁₀ CFU/g of the original sample.

Feed analysis and ATTD determination

Prior to analysis, feed and fecal samples were ground in a Christy Norris mill through a 2-mm screen. Dry matter (DM, AOAC.934.01) and ash (AOAC.942.05) concentration were determined according to methods of the Association of Official Analytical Chemists (AOAC) (AOAC, 2005). The Nitrogen content was determined using the LECO FP 528 instrument (Leco Instruments, UK LTD., Cheshire, UK) (AOAC.990.0). Crude protein (CP) was determined as Nitrogen × 6.25. The neutral detergent fiber (NDF) content was determined according to the method of Van Soest et al. (1991) using an Ankom 220 Fiber Analyzer (Ankom Technology, Macedon, NY, USA). Gross energy (GE) was determined using an adiabatic bomb calorimeter (Parr Instrument Company, Moline, IL, USA). Amino acid determination was carried out using cation exchange high-performance liquid chromatography (HPLC) as previously described by McDermott et al. (2016) (AOAC 994.12). The concentration of AIA in dry diets was determined according to the method of McCarthy et al. (1977) in order to measure the CATTD of nutrients using the AIA technique.

Preparation of liquid feed samples for ethanol and lactate analysis was carried out as described by van Winsen et al. (2000). Briefly, feed aliquots were defrosted prior to centrifugation at 2,000 × g for 10 min at 4 °C. The supernatant was then centrifuged at 18,500 × g for 10 min. The resulting supernatant was filtered through a 0.2-µm filter and stored at −20 °C until ethanol analysis by gas chromatography (GC) and lactate analysis by HPLC.

Samples were thawed slowly at room temperature prior to ethanol analysis by GC (Agilent 6890; Agilent Technologies, Waghaeusel-Wiesental, Germany) using a flame ionization detector. A 1 µL volume of each sample was injected by split injection 5:1 onto the column (AT-100 15 m × 0.53 mm i.d. × 1.2 microns) with a column flow rate of 3.4 mL/min helium. The temperature program was 40 °C for 3 min, ramped at 10 °C/min to 180 °C, and held at 180 °C for 3 min.

For lactate analysis, samples were thawed slowly at room temperature, diluted with water as required, and re-filtered through a 0.2-µm filter prior to analysis by HPLC (Waters, Milford, USA). A 10 µL volume of each diluted sample was injected onto a Phenomenex Chirex (5 µm Chiral IV [(ligand exchange] 3126-PA 150 × 4.6 mm) column under isocratic conditions. The column temperature was 22 °C, detector wavelength 254 nm, and flow rate 1 mL/min with a run time of 40 min.

For VFA analysis, extractions were carried out as described by McCormack et al. (2017) with some modifications. Briefly, a 3.5-g sample was weighed and the pH was recorded. Samples were diluted with 5% trichloracetic acid (at 2.5 × weight of sample) and centrifuged at 1,800 × g for 10 min at 4 °C. A 1.5 mL aliquot of the resultant supernatant was mixed with 1.5 mL internal standard (0.05% 3-methyl-n-valeric acid in 0.15 M oxalic acid dihydrate) and filtered through a 0.45-µm filter and stored at −20 °C until analysis by GC. An injection volume of 1 µl was injected into a Scion 456 gas chromatographer (SCION Instruments, Goes, The Netherlands) equipped with a EC 1000 Grace column (15 m × 0.53 mm I.D) with 1.20 µm film thickness. The temperature program set was: 75 to 95 °C increasing by 3 °C/min, 95 to 200 increasing by 20 °C per min, which was held for 30 s. The detector and injector temperatures were 280 °C and 240 °C, respectively while the total analysis time was 12.42 min.

Statistical analysis

Growth parameters (ADFI, ADG, FCE, and BW), carcass quality parameters, and blood hematology data were analyzed using the MIXED procedure of SAS 9.4 (SAS Institute, Inc., Cary, NC, US). For growth parameters, dietary treatment and sex and their associated interaction were included in the model as fixed effects. Initial BW was included as a covariate and day as a repeated variable in the model while pen was the experimental unit. For carcass ADG and FCE, dietary treatment and sex and their associated interaction were included in the model as fixed effects, with initial weight included as a covariate and pen as the experimental unit. For carcass quality parameters, dietary treatment and sex and their associated interaction were included in the model as fixed effects with pen as the experimental unit. Carcass cold weight was included as a covariate for the analysis of muscle and fat depth and lean meat percentage while initial BW was included as a covariate for the analysis of cold weight. For hematological analyses, data from both experiments were analyzed together with dietary treatment, sex and experiment, and their associated interactions included in the model as fixed effects. For ATTD determination, treatment, sex, and their associated interaction were included in the model as fixed effects with pen as the experimental unit.

The normality of scaled residuals was investigated using the Shapiro–Wilk and Kolmogorov–Smirnov tests within the UNIVARIATE procedure of SAS. Results are presented as LS means ± SEM. Significance was reported for P ≤ 0.05 and tendencies toward significance were reported for P > 0.05 but P < 0.10. The PROC MEANS procedure was used to obtain means and standard deviations for plate counts, lactate, ethanol, VFA, and proximate and amino acid analysis of the feed.

Results

Pig removals

There were no pigs removed from treatment during exp. 1. One pig was removed from the FERM-CER treatment on day 4 of exp. 2 due to lameness.

Microbiological analysis of fermented cereal and fermented whole diet during the initial fermentation

The initial fermentation refers to the first 48 h after inoculant addition, during which time no feed was added to or removed from the fermentation tanks. Figure 1 shows the changes in counts of key microbial groups, as well as pH, observed within each fermentation tank during exp. 1 (Figure 1A) and exp. 2 (Figure 1C) during the initial fermentation and throughout the experiment (Figure 1B and D).

Figure 1.

Lactic acid bacteria, Enterobacteriaceae, E. coli, yeast, and mold counts (log₁₀ CFU/g) and pH of the fermented cereal diet and the fermented whole diet during the initial 48-h fermentation (A, C) and for the duration of the experiments (exp. 1 [B] and exp. 2 [D]). ¹DL (i), detection limit 1: 2 log₁₀ CFU/g applies to lactic acid bacteria, Enterobacteriaceae, and E. coli.²DL (ii), detection limit 2: 3 log₁₀CFU/g applies to yeast and mold; ³Day 0 was when the initial 48-h fermentation ended.

A similar pattern was observed in each tank when experiments 1 and 2 were compared. During both experiments, the numbers of LAB increased steadily in both the cereal and whole diet fermentation tanks during the 48-h start-up period. However, counts at 48 h were marginally higher in FERM-WH compared with the FERM-CER (9.26 to 9.86 vs. 8.84 to 9.23 log₁₀ CFU/g).

Enterobacteriaceae counts behaved differently across experiments during the initial 48-h start-up period. In exp. 1, Enterobacteriaceae counts were stable in the fermented cereal component until they began to decline at 20 h up to 48 h, except for a small increase at 36 h. On the other hand, in FERM-WH, counts were stable up to 30 h into the fermentation, at which point they began to decrease. Final Enterobacteriaceae counts were similar in both fermentation tanks in exp. 1, with 3.33 log₁₀ CFU/g detected in the FERM-CER and 3.03 log₁₀ CFU/g in FERM-WH. In exp. 2, Enterobacteriaceae counts were stable in the FERM-CER for the first 12 h, before an increase to 7.18 log₁₀ CFU/g at 30 h was observed, but these were reduced by 36 h and counts in the tank at the end of the 48-h period were 2.81 log₁₀ CFU/g. Enterobacteriaceae counts in FERM-WH also began to increase at 18 h, reaching a peak of 7.54 log₁₀ CFU/g at 30 h, before decreasing to 3.74 log₁₀ CFU/g at 48 h.

E. coli counts during exp. 1 were below the detection limit at the start and at the end of the initial fermentation in the FERM-CER, despite some being detected between 16 and 24 h. However, in FERM-WH, E. coli was detected at 4.79 log₁₀ CFU/g at the start of the fermentation before a steady decline to below the detection limit was observed, except at 30 h when the E. coli count temporarily increased. In exp. 2, a similar result was obtained in the FERM-CER, except that the temporary increase was not as high. On the other hand, counts increased from just above the detection limit of 2.00 log₁₀ CFU/g at the start of the fermentation to 2.78 log₁₀ CFU/g at 48 h in the FERM-WH.

Yeasts grew similarly in both fermentation tanks during exp. 1 with a steady increase from ~5.8 log10 CFU/g in both tanks to 7.24 and 7.58 log10 CFU/g during the 48-h period in the FERM-WH and FERM-CER tanks, respectively. Both initial and final counts were lower in exp. 2 and differed between fermentation tanks, ranging from 4.72 to 5.01 log₁₀ CFU/g in the FERM-CER and from 3.74 to 6.61 log₁₀ CFU/g in the FERM-WH.

During exp. 1, mold counts declined from 4.22 and 5.18 log₁₀ CFU/g in the FERM-CER and FERM-WH tanks, respectively, to below the detection limit at the end of the initial fermentation in both tanks. A similar pattern was observed during exp. 2, although initial counts were lower (3.47 log₁₀ CFU/g in the FERM-CER and 3.53 log₁₀ CFU/g in FERM-WH).

The pH (Figure 1A and C) of the feed was recorded at each sampling during the initial fermentation. In exp. 1, the starting pH of the FERM-CER was 6.17, lower than that of FERM-WH which was 6.35. The pH declined steadily in both tanks, dropping to pH 4, 24 h into the initial fermentation in the FERM-CER and to 4.03 in the FERM-WH but after 48 h. In exp. 2, the starting pH was similar in each feed at 6.15 in the FERM-CER and 6.20 in FERM-WH. As in exp. 1, the pH of the FERM-CER decreased faster than that of FERM-WH with the pH of the FERM-CER dropping below 4, 30 to 36 h into the initial fermentation, while it was 42 to 48 h before the pH decreased below 4 in the FERM-WH.

Microbiological analysis of FERM-CER and FERM-WH in the fermentation tanks during the experiments

Day 0 began when the initial 48-h fermentation ended. Figure 1 shows the changes in counts of key microbial groups, as well as pH, observed within each fermentation tank throughout exp. 1 (Figure 1B) and exp. 2 (Figure 1D). Throughout the experimental period, counts of LAB in both the FERM-CER and FERM-WH remained relatively constant in the fermentation tanks for the duration of experiments 1 and 2 (days 2 to 62 and 2 to 26, respectively). However, Enterobacteriaceae counts were more inconsistent; during exp. 1, they increased to 4.80 and 4.22 log₁₀ CFU/g in the FERM-CER and FERM-WH, respectively on day 2 compared with the counts obtained at the end of the initial fermentation (i.e., the start of day 0). Thereafter, counts were similar in both fermentation tanks, decreasing initially and then increasing to reach final counts of 5.35 and 5.89 log₁₀ CFU/g, respectively on day 62 of exp. 1. In exp. 2, although Enterobacteriaceae counts had been very similar during the initial fermentation for the FERM-CER and FERM-WH, they behaved very differently during the feeding experiment. In the FERM-CER, counts remained just above the detection limit throughout the 26-d experiment, while in the FERM-WH, counts increased to reach 5.57 log₁₀ CFU/g at day 25 after a slight decrease at day 8.

E. coli were non-detectable in the FERM-CER during both experiments, while in the FERM-WH, counts increased to 4.74 and 3.35 log₁₀ CFU/g in the early stage of experiments 1 and 2, respectively, but subsequently declined and were non-detectable at the end of both experiments.

The levels of yeast in the FERM-CER varied only slightly during exp. 1, ranging from 6.34 to 7.51 log₁₀ CFU/g, while counts in the FERM-WH fluctuated more, ranging from 5.07 to 7.19 log₁₀ CFU/g. Nonetheless, counts were almost identical in both tanks at the end of the experiment. In exp. 2, yeast counts in both tanks were similar and remained relatively stable at 7.00 to 7.70 log₁₀ CFU/g throughout the experiment.

Mold counts fluctuated throughout both experiments, ranging from non-detectable to 5.20 log₁₀ CFU/g in the FERM-CER and from 3.33 to 5.14 log₁₀ CFU/g in the FERM-WH during exp. 1 and from non-detectable to 4.45 log₁₀ CFU/g in the FERM-CER and from non-detectable to 4.00 log₁₀ CFU/g in FERM-WH during exp. 2. Final mold counts were almost identical in both fermentation tanks at the end of exp. 1, but mold counts were below the detection limit in FERM-WH while 4.00 log₁₀ CFU/g was detected in the FERM-CER on day 25 of exp. 2. The pH of the FERM-CER in exp. 1 remained relatively constant at 3.54 to 3.71 up to day 26 and had dropped to 3.26 on day 62 of exp. 1, while the pH of FERM-WH remained ~4 up to day 26 after which it declined to 3.58 on day 62 of the experiment. In exp. 2, the pH of the fermented cereal component ranged from 2.92 to 3.20 throughout the experiment, while FERM-WH ranged from 3.24 to 3.74 throughout the 25-d experimental period.

Microbiological analysis of dietary treatments in hoppers, mixing tanks, and troughs

Mean microbial counts in wet/dry hoppers, mixing tanks, and troughs are presented in Figure 2A (exp. 1) and Figure 2B (exp. 2). It should be noted that these results are not based on statistical evidence, but give an indication of the microbiological differences between treatments.

Figure 2.

Lactic acid bacteria, Enterobacteriaceae, E. coli, yeast, and mold counts (log₁₀ CFU/g) of the four experimental diets sampled from the hopper/mixing tank and feed troughs during exp. 1 (A) and exp. 2 (B) The data from exp. 1 (A) are the mean of data from counts performed on days 26 and 62 and the data shown for exp. 2 (B) are the mean of data from counts performed on days 6 and 25. In both experiments, on each sampling day, one sample was analyzed from the hopper or mixing tank per treatment and two trough samples were analyzed per treatment. Therefore, in each experiment the data represent the mean of two hopper or mixing tank samples per treatment and four trough samples per treatment. The error bars represent the standard deviation. 1DL, Detection limit.

In WET/DRY, counts of all microbes enumerated were higher in the trough than in the dry feed sampled from the hopper in both experiments 1 and 2, except for Enterobacteriaceae counts in exp. 2 which were similar in both locations.

In FRESH, LAB, E. coli, and yeast counts were higher in the trough than in the mixing tank in exp. 1. Mold counts were slightly higher in the trough than in the mixing tank and there was a slight decrease in Enterobacteriaceae counts in the trough compared with the mixing tank. In exp. 2, counts of all microbes enumerated in FRESH were higher in the trough than in the mixing tank. The pH of FRESH in exp. 2 decreased slightly from 5.99 ± 0.120 in the mixing tank to 5.75 ± 0.278 in the trough and the temperature increased from 18.1 ± 2.05 °C in the mixing tank to 19.2 ± 1.90 °C in the trough (data not shown).

In FERM-CER in exp. 1, LAB and Enterobacteriaceae counts were similar in the mixing tank and the trough, but counts of E. coli, yeast, and mold increased in the trough when compared with the mixing tank. In FERM-CER in exp. 2, LAB counts and temperature of feed (19.7 ± 0.78 °C in the mixing tank and 19.6 ± 0.91 °C in the trough, data not shown) were similar in the mixing tank and trough. However, counts of Enterobacteriaceae, E. coli, and feed pH increased slightly (pH was 3.56 ± 0.184 in the mixing tank and 3.98 ± 0.139 in the trough, data not shown) and counts of yeast and mold decreased slightly from the mixing tank to the troughs.

In FERM-WH in exp. 1, counts of LAB were similar in the mixing tank and trough while counts of all other microbes increased in the trough compared with the mixing tank (albeit only slightly for molds). In exp. 2 in FERM-WH, yeast counts remained similar and only a slight decrease in LAB counts was noted; however, counts of Enterobacteriaceae, E. coli, and mold increased in feed troughs compared with counts found in the mixing tank. Feed pH also increased slightly (3.38 ± 0.028 in the mixing tank and 3.46 ± 0.028 in the trough, data not shown).

Effect of dietary treatment on the lactic acid, ethanol, and VFA concentrations in liquid diets during exp. 2

The results of lactate, ethanol, and VFA analysis of the liquid diets are shown in Table 2. The total lactic acid concentration in FRESH varied greatly between the two analyzed samples; nonetheless, lactic acid concentration increased while feed resided in troughs compared with that sampled from the mixing tank. Concentrations of lactic acid in FERM-CER and FERM-WH were less variable across samples, as indicated by the smaller standard deviations. Lactic acid concentrations were lowest for FERM-CER sampled at all locations compared with the other two liquid treatments. There was a decrease in lactic acid concentration in FERM-CER from the fermentation tank to the mixing tank, most likely due to the addition of balancer and fresh water followed by an increase once again while this diet resided in troughs. Total lactic acid concentration in FERM-WH was highest in the mixing tank but only marginally, decreasing slightly in the trough. The highest concentration of lactic acid in the tanks (fermentation tank and mixing tank) was in FERM-WH but in the troughs it was in FRESH.

Table 2.

Effect of dietary treatment on the lactic acid (mMol/kg), ethanol (mMol), and VFA (mMol/kg) concentrations in liquid diets from exp. 2¹

	FRESH		FERM-CER			FERM-WH
	Mixing tank	Trough	Ferm. tank2	Mixing tank	Trough	Ferm. tank	Mixing tank	Trough
d-Lactate	164 ± 187.9	478 ± 313.7	128 ± 11.0	873	101 ± 8.8	166 ± 3.8	179 ± 42.9	163 ± 18.7
l-Lactate	166 ± 173.2	518 ± 305.1	127 ± 2.0	923	96 ± 1.7	225 ± 14.0	232 ± 30.4	217 ± 19.1
Total LA4	330 ± 361.2	996 ± 616.6	255 ± 9.1	1793	197 ± 9.8	392 ± 10.2	411 ± 73.3	381 ± 37.3
Ethanol	7 ± 5.9	10 ± 6.8	50 ± 8.7	41 ± 9.8	37 ± 11.3	63 ± 5.2	63 ± 1.9	51 ± 3.6
VFA
Acetate	8.14 ± 2.000	14.76 ± 3.336	12.47 ± 0.513	7.96 ± 0.488	11.98 ± 2.330	18.07 ± 2.135	20.29 ± 2.300	18.64 ± 2.773
Propionate	0.06 ± 0.008	0.16 ± 0.057	0.20 ± 0.221	0.14 ± 0.129	0.19 ± 0.119	0.14 ± 0.129	0.23 ± 0.221	0.22 ± 0.077
Isobutyrate	0.24 ± 0.008	0.5 ± 0.151	0.02 ± 0.001	0.17 ± 0.202	0.41 ± 0.037	0.28 ± 0.017	0.35 ± 0.028	0.41 ± 0.042
Butyrate	0.02 ± 0.008	0.05 ± 0.022	0.04 ± 0.011	0.03 ± 0.016	0.02 ± 0.003	0.02 ± 0.011	0.04 ± 0.011	0.02 ± 0.009
Isovalerate	0.02 ± 0.010	0.046 ± 0.015	0.03 ± 0.004	0.03 ± 0.009	0.05 ± 0.015	0.02 ± 0.008	0.03 ± 0.000	0.03 ± 0.007
Valerate	0.03 ± 0.020	0.08 ± 0.019	0.06 ± 0.025	0.06 ± 0.000	0.08 ± 0.006	0.07 ± 0.080	0.05 ± 0.044	0.10 ± 0.023
Total VFA	8.51 ± 2.020	15.24 ± 3.400	12.82 ± 0.703	8.37 ± 0.151	12.73 ± 2.25	18.60 ± 1.940	20.99 ± 2.493	19.41 ± 2.667
A:P ratio	134.7 ± 50.67	108.0 ± 52.40	169.6 ± 188.29	99.4 ± 94.19	97.8 ± 73.56	231.4 ± 226.39	147.8 ± 129.49	97.58 ± 47.70
Protein-der5	0.29 ± 0.021	0.28 ± 0.144	0.11 ± 0.020	0.25 ± 0.192	0.54 ± 0.046	0.37 ± 0.055	0.43 ± 0.016	0.54 ± 0.054

¹Mean ± standard deviation of samples collected on days 6 and 25 of exp. 2 are presented at each location. Tank samples (Mixing tank and Ferm. tank) represent the mean of two samples (one sample from each sampling day; except for FERM-CER from the mixing tank where insufficient supernatant prevented the analysis of a second sample) while trough samples represent the mean of four samples (two samples from each sampling day).

²Ferm. tank, fermentation tank.

³Value for one analyzed sample; therefore, no standard deviation available.

⁴LA = lactic acid (sum of d-lactate and l-lactate).

⁵Protein-der = Protein-derived VFA.

Ethanol concentrations were notably lower in both the mixing tank and trough samples of FRESH compared with the same locations for FERM-CER and FERM-WH. Concentrations in FERM-CER were lowest in the feed trough. The highest concentrations recorded across treatments were in the FERM-WH at all three locations, with the lowest concentration again observed in the trough.

A noticeable increase in acetate, propionate, isobutyrate, butyrate, isovalerate, and valerate concentrations from the mixing tank to the trough was observed for the FRESH treatment, while a decrease in the acetate:propionate (A:P) ratio was observed. Acetate and propionate concentrations in FERM-CER decreased in the mixing tank compared with the fermentation tank, most likely due to the addition of fresh balancer, before increasing once again in the trough samples. Concentrations of butyrate decreased slightly (as did the A:P ratio) in the trough of FERM-CER compared with the fermentation tank and mixing tank, while isobutyrate, isovalerate, and valerate concentrations were higher in the trough than at the other two sampling locations.

Concentrations of acetate in the mixing tank of FERM-WH were slightly higher than in the fermentation tank and trough, but generally remained quite constant. Increases in isobutyrate and valerate were observed in the trough when compared with the fermentation tank and mixing tank, while butyrate and isovalerate remained quite constant. The concentration of propionate was higher in the mixing tank and trough compared with the fermentation tank. The A:P was highest in the fermentation tank and decreased in the mixing tank and again in the trough. Although data were limited, the highest levels of acetate across all treatments were observed in FERM-WH at all three sampling locations.

Effect of dietary treatment on the GE, CP, ash, and amino acid content of the diets

The results of these analyses are presented in Table 3. There was no decrease in GE from the dry bagged diet to WET/DRY troughs or from the FRESH mixing tank to FRESH troughs; however, there does appear to be a loss of GE when the values in the respective mixing tank and troughs of FERM-CER and FERM-WH are compared. The limited amino acid analysis performed indicates a noteworthy reduction in lysine concentration in the mixing tank and trough in FERM-WH when compared with the lysine content of the dry diet and that in the troughs of the other three treatments. Methionine and threonine concentrations also appear lower in the troughs of FERM-WH than in troughs of the other three treatments.

Table 3.

Effect of dietary treatment on the gross energy, CP, ash, and amino acid content of the diets (presented on a DM basis)

	Dry1			Mixing tank2			Trough3
	Bagged	Cereal	Balancer	FRESH	FERM-CER	FERM-WH	WET/ DRY	FRESH	FERM-CER	FERM-WH
GE, MJ/kg	18.3	18.5	18.8	18.9	18.9	18.9	18.2 ± 0.18	18.9 ± 0.62	18.3 ± 0.02	18.0 ± 0.26
CP, %	20.4	20.8	44.9	23.1	20.8	20.7	21.0 ± 0.63	23.6 ± 0.09	23.2 ± 0.11	20.3 ± 2.30
Ash, %	4.6	4.6	14.4	3.4	3.7	3.2	4.8 ± 0.36	3.4 ± 0.11	4.5 ± 0.13	4.4 ± 1.24
Amino acids, g/kg
Lysine	11.1	9.6	36.7	12.1	10.8	9.7	12.4 ± 0.14	13.5 ± 0.49	13.3 ± 0.14	9.4 ± 2.05
Cysteic acid	5.1	5.0	8.8	5.4	5.3	5.7	5.6 ± 0.07	6.3 ± 0.00	5.9 ± 0.35	5.5 ± 0.35
Taurine	1.5	1.4	1.2	1.7	0.7	0.6	0.7 ± 0.28	0.7 ± 0.21	0.6 ± 0.14	0.5 ± 0.28
Methionine	5.0	4.9	12.0	5.4	4.7	4.9	5.8 ± 1.13	5.4 ± 0.14	5.1 ± 0.21	4.5 ± 0.28
Aspartic acid	16.3	15.8	48.5	20.8	16.3	18.0	17.0 ± 0.49	20.7 ± 0.64	21.6 ± 0.78	16.0 ± 1.77
Threonine	8.3	7.4	22.2	9.5	7.9	8.3	8.1 ± 0.35	9.5 ± 0.28	9.2 ± 0.21	7.6 ± 0.71
Serine	8.9	8.9	21.2	10.8	8.7	10.1	9.4 ± 0.49	11.3 ± 0.28	10.9 ± 0.35	9.1 ± 0.78
Glutamic acid	42.0	42.8	78.6	46.2	37.0	44.5	43.6 ± 0.85	50.1 ± 0.49	45.1 ± 0.99	41.0 ± 5.09
Glycine	7.9	7.7	17.9	9.6	8.1	8.9	8.1 ± 0.21	9.6 ± 0.14	9.3 ± 0.21	7.8 ± 0.64
Alanine	7.3	7.2	17.8	9.1	8.3	9.1	7.7 ± 0.14	9.2 ± 0.21	9.6 ± 0.21	8.8 ±1.48
Cysteine	0.9	1.1	1.0	1.2	1.2	1.5	0.3 ± 0.07	0.7 ± 0.07	1.0 ± 0.07	1.0 ± 0.57
Valine	8.8	8.9	20.5	10.8	9.5	10.6	9.1 ± 0.21	11.4 ± 0.07	11.0 ± 0.07	9.1 ± 1.06
Isoleucine	7.3	7.3	19.0	9.0	7.5	8.5	7.6 ± 0.14	9.3 ± 0.07	9.3 ± 0.21	7.4 ± 0.64
Leucine	13.2	13.2	32.2	16.3	13.2	14.9	13.8 ± 0.42	16.6 ± 0.28	16.2 ± 0.49	13.2 ± 1.20
Tyrosine	3.8	3.7	12.3	5.5	5.1	6.0	4.9 ± 0.07	6.2 ± 0.14	6.4 ± 0.14	5.1 ± 0.57
Phenylalanine	9.2	9.3	21.7	11.0	9.2	10.4	9.6 ± 0.21	11.5 ± 0.21	11.0 ± 0.07	9.3 ± 0.92
Histidine	6.7	6.6	13.4	6.6	5.1	5.7	6.1 ± 0.49	6.8 ± 0.14	6.1 ± 0.14	5.3 ± 0.64
Arginine	11.1	10.9	29.5	13.7	10.8	11.6	11.8 ± 0.35	14.0 ± 0.21	13.7 ± 0.21	10.3 ± 1.41
Proline	13.5	13.9	19.4	15.2	12.4	14.0	13.1 ± 0.07	14.9 ± 0.07	13.1 ± 0.35	12.3 ± 0.28

¹Dry samples pooled from three feed batches manufactured in the feed mill during exp. 2 and pooled prior to analysis (n = 1/treatment).

²Mixing tank samples pooled from three samples at collection on day 26 of exp. 2 prior to analysis (n = 1/treatment).

³Trough samples collected from two pens per treatment on day 26 of exp. 2 and analyzed separately (n = 2/treatment). Standard deviations are included for trough data because a mean of the two samples is presented.

Effect of WET/DRY, FRESH, FERM-WH, and FERM-CER feeding on growth and carcass quality of grow-finisher pigs from exp. 1

The effect of treatment on BW, ADFI, ADG, FCE, and carcass quality is presented in Table 4. Pigs on all treatments had similar BW at the start of exp. 1. At the end of the experimental period, pigs fed FERM-WH were significantly lighter than those fed the other three treatments (P < 0.001). Overall, pigs fed WET/DRY had a similar ADFI to pigs fed FRESH, but significantly lower than those fed FERM-CER and FERM-WH (P < 0.01). Overall, pigs fed FERM-WH had a lower growth rate than those fed the other three treatments (P < 0.001). This resulted in a significantly poorer FCE in FERM-WH-fed than pigs fed the other three treatments, while pigs fed WET/DRY also had a significantly better FCE than those fed FRESH (P < 0.001). Pigs fed FERM-WH had a significantly poorer carcass ADG (P < 0.001) and carcass FCE (P < 0.001) than pigs fed the other three treatments. The coefficient of variation (CV) of BW in pens was similar across all treatments on day 1, while pigs fed FERM-WH had a greater CV than all other treatments on day 68 (P < 0.001).

Table 4.

Effect of WET/DRY, FRESH, FERM-CER, and FERM-WH on the growth, feed intake, feed efficiency, BW, and carcass characteristics of grow-finisher pigs in Exp. 1¹

	Treatment					P-value
	WET/DRY	FRESH	FERM-CER	FERM-WH	SEM	Treatment	Sex	Treatment × sex
No. pens/trt2	9	9	9	9
BW, kg
Day 1	30.0	30.4	29.0	29.7	0.92	0.15	<0.01	0.09
Day 13	41.5a	41.8a	41.1a,b	37.5b	0.76	<0.001	0.80	<0.01
Day 34	63.2a	64.2a	65.6a	56.4b	0.76	<0.001	0.40	<0.001
Day 48	81.9a	80.9a	83.1a	71.6b	0.76	<0.001	0.44	<0.001
Day 68	103.7a	103.9a	105.7a	95.8b	0.76	<0.001	<0.001	<0.001
ADFI, g/day
Day 1 to 13	1,801	1,851	1,841	1,799	72.1	0.93	0.05	0.59
Day 14 to 34	2,326b	2,519a,b	2,691a	2,606a,b	72.3	<0.01	0.13	0.02
Day 35 to 48	2,808b	2,814b	3,096a,b	3,148a	71.6	<0.001	0.36	<0.01
Day 49 to 68	2,878b	3,108b	3,087b	3,518a	71.6	<0.001	0.72	<0.001
Overall	2,453b	2,573a,b	2,679a	2,768a	62.4	<0.01	0.24	0.77
ADG, g/day
Day 1 to 13	941a	954a	893a	613b	28.2	<0.001	0.03	<0.001
Day 14 to 34	1,027b,c	1,063a,b	1,168a	905c	28.2	<0.001	0.97	<0.001
Day 35 to 48	1,325a	1,188a,b	1,249a	1,086b	28.2	<0.001	<0.001	<0.001
Day 49 to 68	1,081b	1,146a,b	1,130a,b	1,217a	28.2	0.01	<0.001	<0.001
Overall	1,094a	1,088a	1,110a	955b	13.0	<0.001	<0.001	0.08
FCE, g/g
Day 1 to 13	1.92b	1.95b	2.07b	2.92a	0.056	<0.001	0.50	<0.001
Day 14 to 34	2.27b	2.41b	2.30b	2.81a	0.057	<0.001	<0.01	<0.001
Day 35 to 48	2.13c	2.39b,c	2.49b	2.90a	0.055	<0.001	<0.001	<0.001
Day 49 to 68	2.71	2.73	2.75	2.89	0.055	0.09	<0.001	<0.001
Overall	2.26c	2.37b,c	2.40b	2.88a	0.031	<0.001	<0.001	0.09
CV3 of BW, %
Day 1	4.7	4.2	6.2	5.0	0.69	0.21	0.09	0.96
Day 34	5.8b	4.4b	6.1b	9.1a	0.67	<0.001	0.06	<0.001
Day 48	4.9b	4.6b	5.7b	9.6a	0.67	<0.001	0.09	<0.001
Day 68	4.9b	5.1b	5.8b	9.6a	0.67	<0.001	0.35	<0.001
Carcass
ADG4, g/day	890a	893a	924a	788b	12.0	<0.001	0.16	0.15
FCE5, g/g	2.80a	2.99a	2.95a	3.59b	0.065	<0.001	0.04	0.10
Cold-weight, kg	79.5a	79.7a	81.8a	72.9b	0.86	<0.001	0.28	0.14
Kill-out, %	77.0a,b	77.0a,b	77.5a	75.8b	0.33	0.01	0.13	0.63
Muscle, mm	49.6A	49.3A,B	49.1A,B	46.8B	0.67	0.09	0.74	0.31
Fat, mm	12.0b	12.3a,b	12.6a,b	13.4a	0.30	0.04	0.10	0.84
Lean meat, %	57.4a	57.1a	56.9a,b	55.8b	0.30	0.02	0.15	0.77

¹Least square means and pooled standard errors of the mean are presented.

²No. pens/trt: pen replicates per treatment; six pigs per pen replicate.

³CV, coefficient of variation as a measure of within pen pig weight variation.

⁴Carcass ADG: From weight at start of experiment to slaughter = ((carcass weight in kg – BW on day 1 × 0.65) × 1,000) / number of days on treatment (Lawlor and Lynch, 2005).

⁵Carcass FCE: From start of experiment to slaughter = total average daily feed intake / carcass ADG (g).

^a,b,cWithin each row, values that do not share a common superscript are significantly different (P < 0.5).

^A,B,CWithin each row, values that do not share a common superscript tend to be different (0.05 < P < 0.10).

At slaughter, pigs fed FERM-WH had lighter carcasses than those fed the other three dietary treatments (P < 0.001). Pigs fed FERM-WH also had a lower kill-out percentage than those fed FERM-CER (P < 0.01), tended to have less muscle depth than pigs fed WET/DRY (P = 0.09), had a greater fat depth than those fed WET/DRY (P < 0.05), and had a lower lean meat percentage than WET/DRY- and FRESH-fed pigs (P < 0.05).

Effect of WET/DRY,FRESH, FERM-WH, and FERM-CER feeding on growth and carcass quality of grow-finisher pigs from exp. 2

The effect of dietary treatment on BW, ADFI, ADG, FCE, and carcass quality is presented in Table 5. Following the adaptation week, pigs fed WET/DRY were lighter at the start of the experiment than those fed the other three dietary treatments (P < 0.001). At slaughter, pigs fed FERM-CER were heavier than those fed FERM-WH and WET/DRY but similar in weight to those fed FRESH (P < 0.01).

Table 5.

Effect of WET/DRY, FRESH, FERM-CER, and FERM-WH on growth and carcass quality traits of grow-finisher pigs from exp. 2¹

	Treatment					P-value
	WET/DRY	FRESH	FERM-CER	FERM-WH	SEM	Treatment	Sex	Treatment × sex
No. pens/trt2	8	8	8	8
BW, kg
Day 1	81.2	86.6	86.5	86.7
Day 26	115.4c	118.3a,b	120.1a	116.3b,c	0.72	<0.01	<0.001	0.07
ADFI,g/day	3,068c	3,602a,b	3,743a	3,510b	57.3	<0.001	0.42	0.50
ADG, g/day	1,103c	1,217a,b	1,284a	1,140b,c	27.7	<0.01	<0.001	0.07
FCE,g/g	2.78b	2.99a,b	2.95a,b	3.09a	0.071	0.05	<0.001	0.25
CV3 of BW, %
Day 1	4.8	4.0	3.5	4.1	0.67	0.33	0.01	0.32
Day 26	5.3	6.1	5.1	4.2	0.69	0.29	0.77	0.56
Carcass
ADG4, g/day	917c	1,002b	1,086a	967b,c	20.9	<0.001	0.24	0.19
FCE5, g/day	3.35b	3.61a,b	3.46a,b	3.64a	0.078	0.04	0.24	0.47
Cold-weight, kg	89.1b	91.0b	93.7a	90.1b	0.62	<0.01	0.22	0.42
Kill-out, %	76.8b	76.9b	77.6a	77.4a,b	0.19	<0.01	0.16	0.17
Muscle, mm	52.1A,B	52.5A	52.7A	51.3B	0.39	0.06	0.47	0.28
Fat, mm	11.7b	13.3a	13.4a	13.0a	0.32	0.02	0.47	0.58
Lean meat, %	58.1a	56.8b	56.7b	56.8b	0.29	0.02	0.41	0.52

¹Least square means and pooled standard errors of the mean.

²No. pens/trt = pen replicates per treatment; five pigs per pen replicate

³CV, coefficient of variation as a measure of within pen pig weight variation.

⁴Carcass ADG: From weight at start of experiment to slaughter = ((carcass weight in kg – BW on day 1 × 0.75) x 1,000) / number of days on treatment (Lawlor and Lynch, 2005). A higher kill-out percentage was used in exp. 2 due to the heavier BW on day 1.

⁵Carcass FCE: From start of experiment to slaughter = total average daily feed intake / carcass ADG (g).

^a,b,cWithin each row, values that do not share a common superscript are significantly different (P < 0.5).

^A,B,CWithin each row, values that do not share a common superscript tend to be different (0.05 < P < 0.10).

Overall, pigs fed FERM-CER had a higher ADFI than those fed FERM-WH and WET/DRY but similar to pigs fed FRESH (P < 0.001). Pigs fed FERM-CER had the highest overall ADG which was similar to those fed FRESH and higher than those fed WET/DRY and FERM-WH (P < 0.01). The FCE of pigs fed WET/DRY was better than those fed FERM-WH (P = 0.05). Pigs fed FERM-CER had a higher carcass ADG than all other treatments, while FRESH also had a higher growth rate than WET/DRY (P < 0.001). Pigs fed WET/DRY had better carcass FCE than those fed FERM-WH but similar to those fed FRESH and FERM-CER (P < 0.05).

At slaughter, pigs fed FERM-CER had heavier carcass weights than those fed the other three treatments (P < 0.01). Pigs fed FERM-CER had a higher kill-out percentage than those fed WET/DRY and FRESH but similar to those fed FERM-WH (P < 0.01). Pigs fed FRESH and FERM-CER tended to have greater muscle depth than pigs fed FERM-WH (P = 0.06). Pigs fed WET/DRY had less fat depth (P < 0.05) and a lower lean meat percentage (P < 0.05) than those fed the other three dietary treatments.

Effect of dietary treatment on apparent total tract nutrient and energy digestibility

The effect of dietary treatment on ATTD of nutrients is shown in Table 6. There were no treatment differences in the total tract digestibilities of DM, organic matter (OM), nitrogen, GE, or ash (P > 0.05).

Table 6.

Effect of dietary treatment on apparent total tract nutrient (%) and energy (%) digestibility in grow-finisher pigs in exp. 2¹

	Treatment					P-value
	WET/DRY	FRESH	FERM-CER	FERM-WH	SEM	Treatment	Sex	Treatment × sex
DM digestibility	87.5	86.2	86.9	87.6	0.53	0.29	0.23	0.31
OM digestibility	89.8	88.5	89.0	89.7	0.49	0.29	0.21	0.35
Nitrogen digestibility	87.0	84.8	87.4	87.8	0.84	0.11	0.33	0.15
GE digestibility	86.7	85.4	86.0	86.7	0.61	0.42	0.15	0.42
Ash digestibility	61.1	58.9	63.9	64.5	1.85	0.18	0.76	0.28

¹Least square means and pooled standard errors of the mean. Apparent total tract digestibilities were calculated from analysis of the experimental diet and feces collected from a minimum of 3 pigs/pen from 24 pens (6 pens/treatment) on day 27 of exp. 2.

Effect of dietary treatment on the hematological profile of pigs at slaughter

The impact of dietary treatment on the hematological profile of pigs at slaughter is shown in Supplementary Table S1. Pigs fed FERM-WH tended to have a lower (P = 0.06) percentage of lymphocytes and had a higher (P < 0.05) percentage of granulocytes than those fed FRESH.

Discussion

To our knowledge, this is the first study to compare WET/DRY, FRESH, FERM-WH, and FERM-CER feeding of grow-finisher pigs under the same environmental and management conditions. Such a study is essential to help inform the decision-making process of pig producers when choosing the most efficient feeding system to install for grow-finisher pigs. The carcass growth rate and carcass FCE of pigs fed FERM-WH were significantly poorer than for pigs fed the other three treatments in exp. 1 of the current study. Although based on a limited number of samples, this is most likely due to the degradation of amino acids and a loss of energy in FERM-WH when compared with the other treatments. Although based on a low number of samples, reduced levels of lysine, methionine, and threonine were observed in the troughs of FERM-WH compared with troughs of the other three treatments. Amino acid degradation in FLF has previously been reported (Pedersen et al., 2002; de Lange et al., 2006; Niven et al., 2006; Canibe et al., 2007a; Shurson, 2009). It is generally accepted that microbes in the liquid feed use free amino acids and losses are greater when coliforms predominate compared with Lactobacillus (de Lange et al., 2006; Niven et al., 2006). In the present study, greater microbial growth was observed in both fermented liquid diets (FERM-CER and FERM-WH); however, because the synthetic amino acids and soybean meal were added to the FERM-CER just prior to feeding, the level of microbial decarboxylation of amino acids in this treatment appears to have been lower. It is also interesting to note that E. coli counts in the early stages of both experiments were higher in FERM-WH than in FERM-CER when fermentation tank samples were compared, most likely due to the faster decrease in pH in the FERM-CER tank.

Pigs fed FERM-CER and FRESH had similar carcass ADG and carcass FCE which were better than FERM-WH. This further suggests that amino acid degradation was responsible for the poorer growth and feed efficiency in FERM-WH, as synthetic amino acids and soybean meal were added just prior to feed-out in FRESH and FERM-CER, and they produced similar results. Similar to the results of the current study, Canibe and Jensen (2003) found improved growth rates in grow-finisher pigs fed fresh liquid feed compared with those fed a fermented whole diet. Likewise, fermenting only the cereal fraction and adding synthetic amino acids just prior to feeding is preferable to whole diet fermentation (Canibe and Jensen, 2003; Canibe et al., 2007a, 2007b; Brooks, 2008). However, the current study would suggest that there is little additional benefit for FERM-CER over FRESH in terms of growth or feed efficiency. Previous work also reported no advantage of fermentation of the cereal fraction of the diet compared with fresh liquid feeding on growth rate in the finisher phase and, in fact, a significantly lower growth rate was reported for this practice during the grower-phase (MLC, 2005).

In the fermentation tank, the pH of the FERM-CER dropped faster (20 to 24 h into the fermentation in exp. 1 and 24 to 30 h in exp. 2), and, as a result, its final pH was lower than that of the FERM-WH after the initial 48-h fermentation. This is likely due to the fact that cereals have a lower buffering capacity than whole diets (Scholten et al., 2001; Lawlor et al., 2005). A similar result was reported by Canibe et al. (2007a) in that the pH of a FERM-CER was lower than that of a FERM-WH. The pH of the FERM-CER also remained lower than the FERM-WH in the fermentation tanks throughout both experiments. Counts of Enterobacteriaceae were lower in the mixing tank and troughs of FERM-CER and FERM-WH than FRESH in both experiments, most likely due to the lower pH in these treatments, which in turn was probably due to the higher LAB counts. It would appear that FERM-CER and FERM-WH had reached phase 2, the steady phase of fermentation, as indicated by the low pH, high LAB counts, and low Enterobacteriaceae counts (Canibe and Jensen, 2003). However, feed in the troughs of FRESH and WET/DRY were still at fermentation phase 1, with spontaneous fermentation occurring, as described by Canibe and Jensen (2003); this was evidenced in the FRESH by high Enterobacteriaceae and pH compared with FERM-CER and FERM-WH. The concentration of lactic acid in FRESH troughs varied greatly by sample as evidenced by the large standard deviation; however, the lactic acid concentrations in both fermented diets were much more uniform. The liquid feed collected from troughs in the current study was residual feed collected 3 to 4 h after feeding. This highlights the unpredictability of spontaneous fermentation in the fresh liquid feed while it resides in the feeding trough. It would seem reasonable to suggest that a stable feed pH of ~ 4.0 should be sustained for some time before phase 2 of fermentation is reached, which consequently causes a reduction in Enterobacteriaceae populations.

It has been well documented that ethanol is produced along with acetic acid and amylic alcohol when yeasts dominate the fermentation of liquid feed (Brooks et al., 2001, 2003; Canibe et al., 2007b; Missotten et al., 2009, 2015). Yeasts convert starch to alcohol and CO₂ resulting in a loss of energy in the feed (Brooks et al., 2001). It is, therefore, not surprising that because yeast counts were higher in the mixing tank and troughs of the FERM-WH and FERM-CER than the FRESH, ethanol concentrations were also higher in these treatments and acetate concentrations were highest in the FERM-WH. Ethanol concentrations in the mixing tank were 83% higher in FERM-WH than FRESH and 89% higher in FERM-CER than FRESH, while concentrations in the trough were 80% higher in FERM-WH than FRESH and 73% higher in FERM-CER than FRESH in the current study. The ethanol concentrations in FERM-CER and FERM-WH reported in the current study were higher than those reported by Canibe et al. (2007a) despite similar yeast counts in both studies.

Standard values for fresh liquid feed have been reported as 0 to 10 mmol/kg liquid feed for both lactic and acetic acids (Vils et al., 2018), which suggests that lactic acid concentrations in FRESH in the current study were extremely high, whereas acetic acid concentrations were within range in the mixing tank and were just outside the standard range in the trough. However, the huge variation in lactic acid measured in FRESH must be taken into consideration as previously discussed. In the mixing tank LAB counts were also within the standard ranges of 10⁶ to 10⁸ log¹⁰ CFU/g reported by Vils et al. (2018) but increased to above the range in the trough in FRESH. In contrast to the current study, Canibe et al. (2007a) found lower yeast counts and ethanol concentrations in a fermented whole diet than in a fermented cereal diet; however, in agreement with the current study, they did find higher levels of acetic and lactic acids in a fermented whole diet than the fermented cereal diet.

Most work on fermented liquid feeding, to date, has been conducted with weaned pigs (Geary et al., 1999; Lawlor et al., 2002; Canibe et al., 2007a; Rudbäck, 2013) in which the immature digestive tract may benefit most from the physical, microbial, and chemical properties of FLF. Nonetheless, reduced feed intake in weaned pigs fed fermented whole diets has been linked to a reduction in diet palatability (Brooks et al., 2001; Pedersen, 2001; Canibe et al., 2007a). Despite the elevated ethanol and acetate concentrations found in the fermented diets in the current study, feed intake was not adversely affected, suggesting that the negative impact of fermented whole diet feeding on feed palatability is greatest in younger pigs.

In the current study, no differences in the ATTD of nutrients and energy were found in response to treatment. In contrast, our group previously found that cereal fermentation improved DM, OM, GE, and CP digestibility compared with fresh liquid feeding resulting in improved ADG (Torres-Pitarch, 2019). It should be noted that the dietary energy value of 9.4 MJ NE/kg in the latter study was lower than the 9.8 MJ NE/kg used in the current study and because of this, pigs fed the fermented cereal treatment in their study likely benefitted more from the increased digestibility and fermentation. Increased protein and OM digestibility were also previously reported with fermented liquid feeding compared with dry feeding of grower pigs (Dung et al., 2005).

As carcass feed efficiency of pigs fed WET/DRY was numerically better than all other dietary treatments, increased physical feed wastage associated with liquid feeding was likely an issue in the FRESH, FERM-CER, and FERM-WH treatments. Physical feed wastage during liquid feeding resulting in poorer feed efficiency has previously been reported (Russell et al., 1996; Han et al., 2006; Missotten et al., 2010; l’Anson et al., 2012) and improved feeding management during liquid feeding must be implemented if this is to be minimized.

In conclusion, this study shows that FERM-WH feeding results in poorer carcass growth rate and feed efficiency in grow-finisher pigs compared with WET/DRY and FRESH or FERM-CER feeding. It would appear that fermentation of the whole diet reduces GE and results in amino acid losses from the diet and that this contributes to the decreased growth and feed utilization on this treatment. Based on the results of the current study, whole diet fermented liquid feeding is not recommended for grow-finisher pigs.

Glossary

Abbreviations

ADFI

average daily feed intake

ADG

average daily gain

AIA

acid insoluble ash

AOAC

Association of Official Analytical Chemists

A:P

acetate:propionate

ATTD

apparent total tract digestibility

BW

body weight

CATTD

coefficient of apparent total tract digestibility

CP

crude protein

DE

digestible energy

DM

dry matter

FCE

feed conversion efficiency

FERM-CER

fermented cereal liquid feeding

FERM-WH

fermented whole diet liquid feeding

FLF

fermented liquid feed

FRESH

fresh liquid feeding

GC

gas chromatography

GE

gross energy

HPLC

high performance liquid chromatography

LAB

lactic acid bacteria

MRD

maximum recovery diluent

NDF

neutral detergent fiber

OM

organic matter

NE

net energy

VFA

volatile fatty acid

WBC

white blood cells

WET/DRY

wet/dry feeding

Conflict of interest statement

The authors declare no conflict of interest.