Effects of feed conditioning temperature on pellet quality, growth performance, intestinal development and blood parameters of geese from 1 to 28 d of age

Abstract

A 28-d experiment was conducted to investigate the effects of feed-conditioning temperature on the pellet quality, growth performance, intestinal development, and blood parameters of geese. A total of 180 one-day-old White Yuzhou goslings were randomly allotted to 5 treatment groups, with 6 replicates containing 6 birds each. Five diets were conditioned at 65, 70, 75, 80, and 85°C. Body weight and feed intake per pen basis were recorded from the arrival to the end of the trial. Blood and small intestine samples were collected on d 28 for analysis. The results showed that the pellet durability index (PDI), pellet hardness, and gelatinisation degree of starch (GDS) increased with increasing conditioning temperature (P < 0.05). The final body weight (FBW), average daily gain (ADG) and average daily feed intake (ADFI) of goslings significantly increased when conditioning temperature increased from 65 or 70°C to 80 or 85°C (P < 0.05), accompanied by unaffected feed conversion ratio (FCR) (P > 0.05). The villus height to crypt depth ratio (VH/CD) in the duodenum and ileum improved with increasing conditioning temperature (P < 0.05). Additionally, trypsin and amylase activity were enhanced when the conditioning temperature increased from 65 to 85°C (P < 0.05). No significant differences in the carcass traits and blood parameters of goslings were observed among the groups (P > 0.05). Overall, under the present experimental conditions, increasing the steam-conditioning temperature of pelleted feed improved pellet quality, growth performance, intestinal morphology, and digestive enzyme activity in goslings. Based on broken-line regression analysis, the lower critical conditioning temperature for ADG in geese from 1 to 28 d of age was 80.95°C.

INTRODUCTION

Feed is the most expensive item, accounting for approximately 60–70% of the total production cost, in poultry production (Abdollahi et al., 2013). Pelleting is a feed processing technology widely used in poultry feed production. Feeding pelleted diets to poultry improves the economics of production by improving growth rate and feed conversion efficiency (Heywang and Morgan, 1944; Runnels et al., 1976; Engberg et al., 2002; Skinner-Noble et al., 2005; Abdollahi et al., 2010b; Abdollahi et al., 2011; Abdollahi et al., 2018). Conditioning, a hydrothermal method applied to the mash before pelleting, is a crucial step in the pelleting process that allows for increased production rates and improved pellet durability during the handling and transportation of finished feeds (Skoch et al., 1981; Abdollahi et al., 2010b).

The effect of pelleting on poultry performance largely depends on the conditioning temperature. A lower conditioning temperature can reduce pellet quality and pellet mill efficiency and increase frictional heat as the feed is extruded through the pellet die (Skoch et al., 1981). High conditioning temperatures can reduce the availability of nutrients, lower enzymatic activity, damage vitamins and heat-labile amino acids, and reduce mineral digestibility, thus negatively affecting bird performance (Silversides and Bedford, 1999; Kirkpinar and Basmacioglu, 2006; Abdollahi et al., 2010a; Loar et al., 2014; Boney and Moritz, 2017). Moderate steam-conditioning temperatures increase the pellet quality of feed (Abdollahi et al., 2011) and improve the digestibility of starch, nitrogen (Abdollahi et al., 2020) and amino acids (Boltz et al., 2020) in broilers. Therefore, it is necessary to maintain an appropriate conditioning temperature during poultry feed processing.

With the rapid development of indoor goose rearing in China, commercial pellet diets are being used extensively. Hence, controlling the conditioning temperature has become increasingly crucial. A multi-phase feeding strategy is generally adopted in goose production when considering the long raising period of the geese. Goslings are more sensitive to nutrient digestibility than adult geese; however, the conditioning temperature of pellet feed for each rearing stage in geese has not yet been reported. It was speculated that geese fed diets steam-conditioned at various temperatures before pelleting may show diverse responses and that there is a threshold value in the steam conditioning temperature for geese pellet feed. Therefore, the objective of the current study was to investigate the effects of conditioning temperature on pellet quality, growth performance, intestinal development, and blood parameters in geese from 1 to 28 d of age.

MATERIAL AND METHODS

Diets, Birds, and Housing

The experiments were approved by the Animal Care and Welfare Committee of Chongqing Academy of Animal Science (CAAS), China. All geese used in this study were obtained from the CAAS goose-breeding center.

The ingredient compositions and nutrient contents of the experimental diets are listed in Table 1. The diets were manufactured by Chongqing Zhongxin Nongmu Co., Ltd (Chongqing, China). Whole corn was ground using a hammer mill equipped with a 2.0 mm screen. The formulated diet was divided into five equal batches, conditioned at 5 different temperatures (i.e., 65, 70, 75, 80 and 85°C) by adjusting the steam flow rate. The steam-conditioning time of the mash was 35 seconds, and the conditioned temperature was measured at the conditioner outlet using a thermal imager infrared camera (Tis60+, Fluke, WA). Then, the mash feed was pelleted through a 2 mm pellet die with an effective length of 24 mm (length/diameter ratio = 12).

Table 1.

Composition and nutrient levels of basal diet for 1 to 28 d of age (as-fed basis).

Items	%
Ingredients
Maize	32.00
Rice bran	18.00
Wheat flour	15.00
Wheat bran	4.00
Corn DDGS	5.00
Soybean meal	20.80
Limestone	1.20
Calcium hydrogen phosphate	1.80
Sodium chloride	0.30
L-Lysine HCl	0.50
DL-Methionine	0.20
Threonine	0.10
Choline chloride	0.10
Soybean oil	0.70
Mineral and vitamin premix1	0.30
Total	100.00
Nutrient levels2
Metabolizable energy (MJ /kg)	11.50
Crude protein	18.00
Calcium	0.97
Total phosphorus	0.96
Lysine	1.02
Methionine	0.43

¹Premix provided the following per kg of diet: Cu (CuSO₄•5H₂O) 8 mg; Fe (FeSO₄•H₂O) 96 mg; Zn (ZnSO₄•H₂O) 80 mg; Mn (MnSO₄•H₂O) 100 mg; Se (Na₂SeO₃) 0.3 mg; I (KI) 0.4 mg; Vitamin A 6,000 IU; Vitamin D₃ 1,500 IU; Vitamin E 10 IU; Vitamin K₃ 2.4 mg; Vitamin B₁ 1.5 mg; Vitamin B₂ 5 mg; Vitamin B₆ 3 mg; Vitamin B₁₂ 0.02 mg; Pantothenic acid 10 mg; Nicotinic acid 50 mg; Folic acid 0.5 mg; Biotin 0.15 mg.

²Analyzed values except for metabolizable energy.

A total of 180 one-day-old White Yuzhou goslings were randomly allotted to five treatment groups with 6 replicate pens per group and 6 birds per pen and provided with one of the five diets. All pens had similar average initial body weight (86.08 ± 0.65 g). Goslings were reared in wire-floored pens in the same house, equipped with ventilation and heating facilities. The stocking density was 6 birds/m². The ambient temperature was 31°C and then decreased by 1°C every second day until a temperature of 26°C was reached. Lighting was continuous from 1 to 3 d of age and then gradually reduced to 16 L (light):8 D (dark). Geese had access to water and pelleted feed throughout the experimental period.

Pellet Quality

Pellet durability was determined using a Holmen Pellet Tester (New Holmen NHP100 Portable Pellet Durability Tester, TekPro Limited, Willow Park, North Walsham, Norfolk, UK) according to the method described by Abdollahi et al. (2012) with some modifications. The 100 g pellet samples containing no fines were rapidly circulated in a perforated test chamber for 30 s. The pellet remaining on the sieve mesh was weighed. The pellet durability index (PDI) was calculated using the following equation: PDI (%) = (remaining pellet weight / 100) × 100.

Hardness was measured using a texture analyzer (TVT7600, PerkinElmer Ltd., Waltham, MA, USA) according to the methods of (Samuelsen and Oterhals, 2016) with some modifications. The peak force before breakage is expressed in Newtons (N). The pellets were treated individually for both measurements, and the reported values were based on an average of 20 analyses.

Starch gelatinization was performed according to the approved MARA method (NY/T4125-2022; MARA, 2022) using a microplate reader (SpectraMAX Plus384, Molecular Devices, San Francisco, CA).

Growth Performance and Carcass Traits

Body weight (BW) and compound feed were measured and recorded per pen at 1 and 28 d of age. Body weight gain (BWG), average daily gain (ADG), average daily feed intake (ADFI), feed conversion ratio (FCR), and European production index (EPI) were calculated for all trials. Mortality was recorded, and the percentage liveability was calculated using the obtained data. The following formulae were used:

$$\text{BWG}\left(\mathrm{g}/\text{bird}\right)=\text{final}\text{body}\text{weight}\left(\mathrm{g}/\text{bird}\right)-\text{initial}\text{body}\text{weight}\left(\mathrm{g}/\text{bird}\right)$$

$$\text{ADG}\left(\mathrm{g}/\text{bird}\text{per}\text{day}\right)=\text{BWG}/\text{rearing}\text{time}\left(\mathrm{d}\right)$$

$$\text{ADFI}\left(\mathrm{g}/\text{bird}\text{per}\text{day}\right)=\text{cumulative}\text{feed}\text{intake}\left(\mathrm{g}/\text{bird}\right)/\text{rearing}\text{time}\left(\mathrm{d}\right)$$

$$\text{FCR}\left(\mathrm{g}\text{feed}/\mathrm{g}\text{gain}\right)=\text{ADFI}/\text{ADG};$$

$$\text{Liveability}(\%)=\text{birds}\text{remaining}\text{at}\text{the}\text{end}\text{of the}\text{study}\text{period}(\%)$$

$$\text{EPI}=\text{liveability}(\%)\times \text{BW}\left(\text{kg}\right)\times 100/\text{FCR}\left(\mathrm{g}\text{feed}/\mathrm{g}\text{gain}\right)\times \text{rearing}\text{time}\left(\mathrm{d}\right)$$

One bird was selected from each pen based on the average body weight of the corresponding pen and slaughtered for carcass assessments. The breast meat, thigh meat and abdominal fat percentages and the heart, liver, and glandular-gizzard stomach indices were calculated based on live body weight.

Intestinal Development and Morphology

The goslings were sacrificed after blood collection, and the intestinal segments were excised. The duodenal, jejunal, and ileal segments were collected and analyzed as described in our previous study (Liu et al., 2021). The lengths of the duodenum, jejunum, and ileum were measured using a flexible tape measure (± 0.01 cm). Sections (1 cm) from the middle portion of the duodenum, jejunum, and ileum tissues were fixed in 10% formaldehyde phosphate buffer after being washed with 0.1 M phosphate-buffered saline. The fixed sections were processed, dehydrated, and embedded in paraffin wax, sectioned into 5 μm-thick slices and stained with the hematoxylin-eosin. Histological sections were examined with villus height (VH), crypt depth (CD), and muscularis thicknesses (MT), which were performed on 10 well-oriented villi and 10 muscularis thicknesses from each segment, using a digital camera microscope (BA400 Digital, McAudi Industrial Group Co., Ltd., Xiamen, China) and the Motic Advanced 3.2 digital image analysis system. The ratio of villus height to crypt depth (VH/CD) was calculated.

Digestive Enzyme Activity

The mucosa of the duodenum from geese was gently scraped with a slide and carefully collected in 1.5 mL sterile tubes, frozen in liquid nitrogen, and then stored at −80°C. The activities of amylase, lipase, and trypsin in the duodenal mucosa were measured using detection kits from the Nanjing Jiancheng Bioengineering Institute (Nanjing, China), following the manufacturer's guidelines.

Blood Parameters

At the end of the trial, one bird per pen with a weight close to the average weight of the pen was selected and blood samples were collected from the neck veins using a heparinized anticoagulation vacuum tube. Whole blood was centrifuged at 3,000 × g for 20 min to separate the plasma and were then stored at −70°C until analysis.

According to Liu et al. (2022), the colorimetric method was used to determine total protein (TP), albumin (ALB), globulin (GLO), creatinine (CRE), urea nitrogen (UN), uric acid (UA), cholesterol (CHOL), triglyceride (TG), high density lipoprotein (HDL), and low density lipoprotein (LDL) in plasma using an automatic biochemical analyser (AU680, Beckman Coulter, Tokyo, Japan) with corresponding commercial kits (Nanjing Jiancheng Bioengineering Institute, Nanjing, China), following the manufacturer's instructions.

Statistical Analysis

Data were subjected to one-way ANOVA using the GLM procedure of SAS (SAS Institute Inc., 2003), with a pen used as the experimental unit for analysis. When differences among groups were significant (P < 0.05), the means were compared using Duncan's multiple comparison procedure in SAS (SAS Institute Inc., 2003).

The conditioning temperatures were estimated using a broken-line regression model and the NLIN procedure of SAS (SAS Institute Inc., 2003): y = l + u × (x−r); where y = goose response (weight gain), x = conditioning temperature (°C), r = breakpoint between 2 lines which was defined as the conditioning threshold temperature, u = the slope of the curve, l = maximum or minimum response if x < r and y = l + u × (x − r) if x ≥ r.

RESULTS AND DISCUSSION

Pellet Quality

The effects of conditioning temperature on pellet quality are shown in Table 2. PDI, pellet hardness, and GDS increased with increasing conditioning temperature (P < 0.05). Diets conditioned at 65°C had lower PDI, pellet hardness, and GDS than those conditioned at 80 and 85°C (P < 0.05). Steam-conditioning at 70 and 75°C reduced PDI, pellet hardness, and GDS in comparison with that conditioned at 85°C (P < 0.05). In addition, diets conditioned at 80°C had lower PDI and GDS than those conditioned at 85°C (P < 0.05).

Table 2.

Effects of conditioning temperature on pellet quality.

Items1	Conditioning temperature°C					SEM	P value
	65	70	75	80	85
PDI (%)	87.61c	88.80bc	88.62bc	89.70b	91.65a	0.417	<.0001
Hardness (N)	24.01c	29.80b	32.89b	39.77a	43.56a	1.469	<.0001
GDS (%)	20.95d	23.04c	24.04c	26.09b	29.22a	0.359	<.0001

¹Abbreviation: PDI, pellet durability index; GDS, gelatinization degree of starch.

^a,b,cIn the same row, values with different small letter superscripts indicate a significant difference (P < 0.05), whereas values with common or no letter superscripts represent no significant difference (P > 0.05).

The results obtained in current study agree with those from previous studies in broilers, which reported that both PDI and hardness increased in maize-, wheat- or sorghum-based diets as the conditioning temperature increased from 60 to 90°C (Abdollahi et al., 2010a;b; Abdollahi et al., 2011; Abdollahi et al., 2012; Teixeira Netto et al., 2019; Abdollahi et al., 2020). Rueda et al. (2022) also found that corn-based diets conditioned at 82 and 88°C had higher PDIs than those conditioned at 71 and 77°C. Gelatinized starch content increased in maize- or wheat-based diets when conditioning temperature increased from 60 to 90°C, while it initially declined and subsequently increased in sorghum-based diets (Abdollahi et al., 2010a; Abdollahi et al., 2011; Abdollahi et al., 2012). Therefore, we concluded that conditioning temperature has different effects on nutrient availability in different types of diets. The pellet quality enhancements that were observed as the conditioning temperature increased can be attributed to the increased injection of moisture into feed particles, thereby enhancing adhesion among the pellet components (Teixeira Netto et al., 2019). Furthermore, the improved durability of pellets resulted in higher nutrient density and less feed waste, resulting in increased nutrient intake per unit of expended energy, which may explain the improvements in growth performance.

Growth Performance and Carcass Traits

The effects of conditioning temperature on the growth performance of the goslings are presented in Table 3. Birds those were fed the diet conditioned at 80 and 85°C had greater FBW and ADG and higher ADFI than those fed the diet conditioned at 65 and 70°C (P < 0.05), while no significant on FCR effects were observed (P > 0.05), indicating that appropriately elevated conditioning temperature improves growth performance. The improvement in growth performance observed in the present study is presumably attributable to the improved pellet quality through the gelatinization of starch and gelation of proteins (Buchanan et al., 2010). Broken-line regression was used to estimate the dietary conditioning temperature in our study. According to this regression, the conditioning temperature was 80.95°C for ADG {y = 46.23 + 0.25 × (x − 80.95);R² = 0.9681, P = 0.0319}. The assessment of liveability and economic efficiency of EPI were not affected by the conditioning temperatures, but numerically higher values were observed in the geese that were fed the diet conditioned at 80°C.

Table 3.

Effects of conditioning temperature on growth performance of goslings from 1 to 28 d of age.

Items1	Conditioning temperature°C					SEM	P value
	65	70	75	80	85
IBW (g/bird)	86.08	85.99	85.78	86.33	86.22	0.271	0.646
FBW (g/bird)	1276c	1288bc	1343ab	1375a	1380a	21.64	0.006
ADG (g/bird per day)	42.48c	42.94bc	44.91ab	46.03a	46.23a	0.778	0.007
ADFI (g/bird per day)	78.71bc	77.06c	82.61ab	84.83a	85.88a	1.616	0.005
FCR (g/g)	1.854	1.794	1.840	1.835	1.858	0.207	0.487
Liveability (%)	86.67	91.67	94.44	95.83	94.44	0.057	0.728
EPI	227.8	246.1	243.3	250.7	239.2	15.41	0.827

¹Abbreviation: IBW, initial body weight; FBW, final body weight; ADG, average daily gain; ADFI, average daily feed intake; FCR, feed conversion ratio; EPI, European production efficiency factor.

^a,b,cIn the same row, values with different small letter superscripts indicate a significant difference (P < 0.05), whereas values with common or no letter superscripts represent no significant difference (P > 0.05).

Previous studies have shown that high conditioning temperatures impair the growth of poultry. Steam-conditioning temperature at 88°C decreased the weight gain and increased the FCR in broiler starters compared to that at 60°C and 70°C (Perera et al., 2021). Kirkpinar and Basmacioglu (2006) reported that pelleting a maize-soybean meal diet at 65°C resulted in higher weight gain compared to diets pelleted at 75 and 85°C. Abdollahi et al. (2010b) showed that broiler starters fed with maize-based diets conditioned at 60°C and 90°C had higher weight gain and feed intake than those fed with the diet conditioned at 75°C, while increasing conditioning temperature decreased the weight gain and feed intake in wheat-based diets, and FCR increased in both grain-type diets. Another similar study found that broiler starters fed maize- or sorghum-based diets conditioned at 60°C had a similar weight gain to those fed diets conditioned at 90°C and higher than those fed diets conditioned at 75°C; however, there were no changes in FCR (Abdollahi et al., 2010a). Abdollahi et al. (2011; 2020) reported that broiler starters fed diets steam-conditioned at 60 and 90°C had similar ADG, ADFI and FCR. A similar trend was observed in another study, in which steam conditioning at low (47°C) and high temperature (90°C) prior to pelleting did not affect the growth performance of broiler starters (Lundblad et al., 2011).

Carcass traits are presented in Table 4. Breast muscle, thigh muscle, and abdominal fat percentages and the heart, liver, and proventriculus-gizzard indices were unaffected by the various steam conditioning temperatures (P > 0.05). These results are consistent with that from previous studies (Loar et al., 2014; Rueda et al., 2022; Hernandez et al., 2024). However, Abdollahi et al. (2010a;b) found that conditioning at 60°C prior to pelleting caused a reduction in the relative gizzard weight of broiler starters fed maize-, sorghum-, or wheat-based diets when compared to those conditioned at 75°C and 90°C.

Table 4.

Effects of conditioning temperature on carcass traits of goslings at 28 d of age.

Items1	Conditioning temperature°C					SEM	P value
	65	70	75	80	85
BMP (%)	1.258	1.283	1.316	1.318	1.320	0.001	0.555
TMP (%)	12.90	12.85	13.13	13.23	13.38	0.005	0.949
AFP (%)	1.587	1.870	1.842	1.816	1.896	0.002	0.765
HI (%)	0.576	0.609	0.630	0.637	0.618	0.000	0.418
LI (%)	2.580	2.528	2.714	2.906	3.061	0.002	0.424
PGI (%)	4.186	4.131	4.127	4.287	4.077	0.002	0.959

¹Abbreviations: BMP, breast muscle percentage; TMP, thigh muscle percentage; AFP, abdominal fat percentage; HI, heart indice; LI, liver indice; PGI, proventriculus-gizzard indice.

The inconsistent results of steam-conditioning temperature on birds' growth performance and carcass traits may be attributed to differences in breeds, diet formulations, and other processing parameters, such as conditioning time. Consequently, further research on this topic is necessary to provide better references for practitioners.

Intestinal Development and Morphology

The results of intestinal development results are listed in Table 5. Goslings that were fed diets conditioned at 65 and 70°C had a lower VH/CD in the duodenum compared to those that were fed diets conditioned at 80 and 85°C (P < 0.05). Additionally, diets conditioned at 65, 70, and 75°C decreased the VH/CD of the ileum compared to that conditioned at 85°C (P < 0.05). No significant differences were observed in the MT and length of the duodenum, jejunum, and ileum among the different groups (P > 0.05).

Table 5.

Effects of conditioning temperature on intestinal development of goslings at 28 d of age.

Items1	Conditioning temperature°C					SEM	P value
	65	70	75	80	85
Duodenum
VH (μm)	1137	1117	1186	1189	1196	45.28	0.653
CD (μm)	172.1	166.9	164.5	158.8	151.0	5.579	0.111
VH/CD	6.616b	6.716b	7.246ab	7.481a	7.926a	0.223	0.002
MT (μm)	317.2	318.2	342.4	323.9	343.2	15.81	0.624
Length (cm)	28.30	28.33	29.50	29.40	27.92	1.129	0.782
Jejunum
VH (μm)	1404	1364	1464	1622	1672	86.56	0.061
CD (μm)	172.3	164.6	167.8	186.1	176.0	9.346	0.612
VH/CD	8.137	8.334	8.850	8.891	9.535	0.512	0.317
MT (μm)	280.4	293.6	312.3	315.9	310.9	18.98	0.644
Length (cm)	63.80	69.40	69.97	68.07	64.65	2.648	0.221
Ileum
VH (μm)	890.8	912.8	960.3	927.0	1061	50.73	0.111
CD (μm)	172.7	162.8	169.1	161.0	167.0	6.626	0.675
VH/CD	5.192b	5.548b	5.644b	5.810ab	6.373a	0.232	0.011
MT (μm)	308.5	322.7	320.9	328.1	312.2	12.22	0.788
Length (cm)	56.73	56.60	59.23	59.47	56.10	2.341	0.641

¹Abbreviation: VH, villus height; CD, crypt depth; MT, muscularis thicknesses; VH/CD, villus height to crypt depth ratio.

^a,bIn the same row, values with different small letter superscripts indicate a significant difference (P < 0.05), whereas values with common or no letter superscripts represent no significant difference (P > 0.05).

The small intestine plays an essential role in the digestion and absorption of nutrients, and the morphological indicators of the small intestine (VH, CD, and VH/CD) are directly associated with the digestive capacity and intestinal health of animals (Zhang et al., 2024). However, studies on the effects of steam-conditioning temperature of pelleted feed on small intestine morphological indicators in poultry are lacking. A study on meat-producing rabbits exhibited that the VH, CD, and VH/CD in the duodenum, jejunum and ileum were similar between groups that were fed diets conditioned at 80 and 90°C. In the present study, the increased VH/CD in the duodenum and ileum with increasing steam-conditioning temperature indicated enhanced digestive capacity, which might be one of the reasons for improved growth performance.

The small intestine length is an essential and direct indicator in the development of the digestive tract (Wang et al., 2019; Wen et al., 2022). However, findings on the effects of steam-conditioning temperatures on small intestine length of birds are not consistent. The limited effect of steam-conditioning temperatures on the length of the duodenum, jejunum and ileum in the current study was supported by Abdollahi et al. (2011), who found that birds that were fed diets conditioned at 60, 75, and 90°C had similar relative small intestine lengths. However, another study showed that the length of the jejunum, ileum, and entire small intestine in broilers fed diets conditioned at 60°C was shorter than those fed diets conditioned at 75 and 90°C (Abdollahi et al., 2010a).

Digestive Enzyme Activity

The effects of conditioning temperature on the digestive enzyme activity of geese at 28 d of age are presented in Table 6. Geese fed diets conditioned at 65°C had lower trypsin activity than those fed diet conditioned 75, 80, and 85°C (P < 0.05), but there were no significant differences between 65 and 70°C or among 75, 80, and 85°C (P > 0.05). In addition, diets conditioned at 80 and 85°C increased the amylase activity when compared to those conditioned at 65, 70, and 75°C (P < 0.05). There were no significant changes in the activities of trypsin, chymotrypsin, or lipase (P > 0.05). The enhanced digestive enzyme activity observed in our study may be attributed to the increasing gelatinization degree of starch, which suggests that the digestive capacity of goslings for starch and protein has improved, thus facilitating their growth. These results are in contrast with those by Hu (2011), who reported that steam-conditioned temperatures (70, 80, and 90°C) did not influence the trypsin and amylase activities of duodenum and jejunum in broilers. A recent study in meat-producing rabbits found no significant difference in trypsin, amylase and lipase activities in the duodenum, jejunum and ileum when diets were conditioned at 80°C and 90°C (Zhang, 2023). These contradictions in results may be due to breed difference.

Table 6.

Effects of conditioning temperature on digestive enzymes activity of goslings at 28 d of age.

Items1	Conditioning temperature°C					SEM	P value
	65	70	75	80	85
TRY (U/mgprot)	833.8c	1059bc	1208ab	1362a	1240ab	99.66	0.004
CHY (U/mgprot)	0.659	0.656	0.657	0.678	0.687	0.117	0.999
LPS (U/gprot)	4.136	4.211	4.204	4.361	4.637	0.558	0.944
AMS (U/mgprot)	1.453b	1.433b	1.268b	1.766ab	2.190a	0.189	0.013

^a,b,cIn the same row, values with different small letter superscripts mean significant difference (P < 0.05), while with common or no letter superscripts mean no significant difference (P > 0.05).

¹Abbreviations: TRY, trypsin; CHY, chymotrypsin; LPS, lipase; AMS, amylase.

Blood Parameters

As shown in Table 7, there were no significant differences in plasma TP, ALB, GLO, TG, HDL, LDL, CRE, UN, or UA concentrations among the groups (P > 0.05), indicating that steam conditioning temperature did not affect the protein and lipid metabolism of goslings. No reports on the effects of conditioning temperatures on blood metabolites in poultry are available. However, our results resembled those reported in fattening lambs by Ran et al. (2020), who reported that no significant change was observed in TP, ALB, GLO, TG, and UN, while total cholesterol concentration was lower with medium (75°C) conditioning temperatures than with low (65°C) or high (85°C) conditioning temperatures.

Table 7.

Effects of conditioning temperature on blood biochemistry of goslings at 28 d of age.

Items1	Conditioning temperature°C					SEM	P value
	65	70	75	80	85
TP (g/L)	40.58	40.92	39.42	39.63	41.48	1.025	0.425
ALB (g/L)	11.00	11.33	11.10	11.13	11.63	0.247	0.246
GLO (g/L)	29.58	29.58	28.32	28.50	29.85	0.847	0.460
CHOL (mmol/L)	3.918	3.793	3.782	3.983	3.882	0.168	0.903
TG (mmol/L)	1.558	1.315	1.528	1.547	1.420	0.242	0.931
HDL (mmol/L)	1.860	1.995	1.937	1.980	2.018	0.122	0.900
LDL (mmol/L)	1.498	1.325	1.368	1.548	1.363	0.091	0.362
CRE (μmol/L)	55.88	59.10	56.50	56.28	59.17	2.377	0.707
UN (mmol/L)	0.538	0.528	0.540	0.508	0.498	0.075	0.987
UA (μmol/L)	168.5	170.2	173.4	172.0	178.0	19.71	0.997

¹Abbreviation: TP, total protein; ALB, albumin; GLO, globulin; CHOL, cholesterol; TG, triglyceride; HDL, high density lipoprotein; LDL, low density lipoprotein; CRE, creatinine; UN, urea nitrogen; UA, uric acid.

CONCLUSIONS

In conclusion, increasing the steam conditioning temperature of pelleted feed improves pellet quality, growth performance, intestinal morphology, and digestive enzyme activity in goslings. Taking into account the ADG, liveability, and EPI, we recommend that the suitable conditioning temperature for the diet of gosling should not be below 80°C. However, when referring to the results of this study, producers should consider the composition of the diet.

DISCLOSURES

There are no conflicts of interest to declare.