Evaluation of the optimal standardized ileal digestible valine:lysine ratio in lactating sow diets

Abstract

An experiment was conducted with 430 sows to evaluate the ideal standardized ileal digestible (SID) Val:Lys on sow and litter performance during an 18.6-d lactation period. The SID Val:Lys ratios measured were based on the previously published literature and then values above and below reported values. Sows were randomly allotted within parity block (parity 1, parity 2, and parity 3+) to one of five corn–soybean meal-based lactation diets formulated to contain different levels of SID Val:Lys (0.50, 0.62, 0.75, 0.88, and 1.00, respectively). All diets were formulated to be isocaloric (3.35 ME Mcal/kg) with 0.95% SID Lys and contained vitamins and minerals that exceeded recommendations (NRC, 2012). Experimental diets were given to sows from 112 d of pregnancy throughout the 23-d lactation period. Litters were standardized within 48 h after farrowing. Sows were fed with the Howema computerized feeding system that mixed the high and low diets to create the intermediate diets, weighed the feed for each sow and then delivered the feed to each individual feeding hopper to record daily sow feed intake during lactation. Data were analyzed as a randomized complete block design using the PROC MIXED procedure of SAS with sow as the experimental unit and treatment as a fixed effect and parity as the random effect. Results were considered significant at P ≤ 0.05 and considered a trend at P > 0.05 and P ≤ 0.10. Sow ADFI was not significantly different (5.2, 5.2, 5.2, 5.0, and 5.4 ± 0.15 kg/d, respectively). On average, sows consumed ~45 g of SID Lys per day. Sow wean to estrus (5.2, 4.7, 5.3, 5.5, and 4.5 ± 0.32 d, respectively) was not different as the Val:Lys ratio changed. Increasing the Val:Lys ratio resulted in no differences (2.66, 2.64, 2.76, 2.61, and 2.62 ± 0.08 kg; P > 0.10) in average daily litter gain. There were no differences in sow weight loss or subsequent total born across the dietary treatments. Overall, increasing levels of SID Val:Lys did not change sow reproductive performance or piglet growth rate.

INTRODUCTION

Valine is part of the branched-chain AA (BCAA) group. The BCAAs are known to regulate blood sugar, repair tissues, and help provide energy to the body. With the reduction of soybean meal in the diet, valine and the other BCAA (isoleucine and leucine) are reduced. While valine levels can be increased with co-products such as dried distiller’s grains, some diets will only consist of feed-grade AA to reduce feed costs and lower CP levels; therefore, creating a potential deficit in valine. Limited work has been conducted to understand the SID Val level in lactating sows, and the outcomes of the studies have been varied.

Research conducted by Boyd et al. (1999) and Gaines et al. (2006) estimated that the total Val:Lys ratio was determined to be between 73% and 86% for a lactating sow. Work conducted by Carter et al. (2000) reported that feeding a lactating sow a diet that containing a Val:Lys ratio of 76% to 122% resulted in no difference in sow or litter performance. Richert et al. (1996) reported that to maximize litter growth rate, the diet should contain a total Val:Lys ratio of 120%. Strathe et al. (2016) reported that there was no reproductive or litter improvement when sows were fed more than a total dietary Val:Lys ratio of 84%. With conflicting peer-reviewed published trials and few with higher number of piglets weaned per sow and larger litter growth rates of current litters, there is a need for additional evaluation of the Val:Lys requirement. With large litter size and longer lactation length today than 10 yr ago, it is hypothesized that a sow nursing a large litter will have a higher need for BCAA than previously documented. Therefore, the objective of the study was to further determine the Val:Lys ratio for lactating sows.

MATERIALS AND METHODS

The study was conducted in a commercial 6,000 sow farm located in Western Illinois of the United States. All animal care practices were conducted by following the routine farm management procedures and Pork Quality Assurance guidelines (National Pork Board, 2012). In addition, an internal Carthage Innovative Swine Solutions Animal Care Committee had approved dietary lactation trial protocols with standard measurements and criteria in 2017. The trial protocol complied with the approved standard protocol and was documented into the approved study list for the animal care committee.

Animals

The study was conducted in March through April 2017. Four hundred and forty-three multiparous and primiparous sows (PIC Camborough, PIC USA, Hendersonville, TN) were evaluated. Sows were blocked as parity 1 (81 animals), parity 2 (88 females), or parity 3+ (274 females). The females were porcine reproductive and respiratory syndrome virus (PRRS) negative and Mycoplasma hyopneumonaie stable. The piglets were PRRS and porcine epidemic diarrhea virus negative. Only PRRS antibodies were present from the infection 6 months prior to the start of the study. In addition, no clinical signs of Mycoplasma hyopneumonaie were present.

Diets

Diets consisted of corn and soybean meal (Table 1). Diets were held to a constant standard ileal digestible (SID) Lys level and all ratios except for SID Val:Lys were held constant. Five treatments to be fed to sows were designed with increasing SID Val:Lys ratios of 50, 62.5, 75, 87.5, and 100, respectively. Diets were formulated to be isocaloric (3.35 Mcal ME/kg) and contained vitamins and minerals that exceeded recommendations (NRC, 1998). Energy values for individual ingredients were calculated using the ME values from the NRC (1998).

Table 1.

Diet composition of lactation diets for the evaluation of the SID¹ valine:lysine ratio for lactating primiparous and multiparous sows

	SID valine:lysine ratio
Ingredient, %	50.0	100.0
Corn	78.45	77.96
Soybean meal, 48%	14.25	14.25
Limestone	1.03	1.03
Monocalcium phosphate, 21%	1.33	1.33
Corn oil	3.00	3.00
Salt	0.45	0.45
l-lysine HCl2	0.57	0.57
l-threonine	0.28	0.28
l-tryptophan	0.06	0.06
HMTBa3	0.08	0.08
l-valine	0.01	0.49
l-isoleucine	0.18	0.18
VTM with phytase4	0.23	0.23
Choline chloride	0.10	0.10
Planned composition
ME, Mcal/kg5	3.35	3.35
CP, %	12.96	12.96
SID lysine, %	0.95	0.95
SID valine, %	0.48	0.95
SID isoleucine, %	0.58	0.58
SID M + C:lysine6	0.53	0.53
SID threonine:lysine	0.68	0.68
SID tryptophan:lysine	0.19	0.19
SID valine:lysine	0.50	1.00
SID isoleucine:lysine	0.61	0.61

¹SID = standardized ileal digestibility; Ingredients are presented as percent inclusion in the diet and are reported on an “as-fed” basis.

²HCl = hydrochloride.

³HMTBa-ALIMET is a trademark of Novus International, Inc., and is registered in the United States and other countries. Methionine source. 88% 2-hydroxy,4-methylthio butanoic acid HMTBa.

⁴Vitamin trace mineral (VTM) premix supplied per kilogram of diet: vitamin A, 13,201 IU; vitamin D₃, 2,596 IU; vitamin E, 123.2 IU; vitamin K (menadione activity), 5.0 mg; riboflavin, 9.9 mg; d-pantothenic acid, 29.7 mg; niacin, 44.0 mg; vitamin B12, 0.04 mg; d-biotin, 0.85 mg; folic acid, 7.16 mg; thiamine, 8.8 mg; pyridoxine, 4.5 mg; chromium (chromium propionate), 0.40 mg; Zn (20% ZnSO₄, 30% zinc oxide, and 50% Mintrex Zn, Novus, St. Louis, MO), 150 mg; Cu (50% CuSo₄ and 50% Mintrex Cu, Novus), 15 mg; Fe (FeSO₄), 100 mg; Mn (50% MnSO₄ and 50% Mintrex Mn, Novus), 50 mg; I (ethylenediamine dihydriodide), 0.4 mg; and Se (50% Na₂Se and 50% organic Se)), 0.30 mg. Phytase was provided as Axtra (Danisco Animal Nutrition, Wiltshire, UK) and added 374 phytase units/kg diet.

⁵Calculated from NRC (1998).

⁶M + C = methionine + cysteine.

Lactation Feeding

Upon entering the farrowing room and prior to farrowing, sows were fed 1.8 kg/d of the respective lactation diet. After farrowing, sows were fed 1.8 kg on day 1, 2.7 kg on day 2, 3.6 kg on day 3 of lactation, and then allowed a maximum of 5.5 kg/d to provide sows no more than 52 g of SID Lys intake per day.

Feed was delivered to each sow through the automated Howema Feed System (Big Dutchman, Vechta, Germany). The low (50 SID Val:Lys) and high (100 SID Val:Lys) diets were manufactured at a local feed mill and delivered to the facility. The feed system on site blended the intermediate diets by delivering a set percentage of each diet into a mixing hopper and recording the actual weight of each diet as it was added to the hopper and then proceeded to mix the diet prior to delivering each batch of feed to the corresponding sow. At the time of delivery, the system recorded the amount of feed delivered and tracked total lactation consumption per sow. Feed was delivered to each sow via a cable system and was held in a 6.8 kg plastic hopper (Automated Production Systems, Assumption, IL) attached to an InTak feeder (Automated Production Systems). Sows had ad libitum access to water throughout lactation.

Animal Husbandry

Sows were moved into the farrowing house at 112 ± 2 d of gestation length and allocated to the experimental diets upon entry into the farrowing house and were fed the allotted treatments from the time of entry into the farrowing house until weaning. Sows were housed in conventional farrowing stalls in an environmentally regulated commercial farrow to wean facility (18 to 24 °C) with lights on from 0600 to 1500 hours. Sows were housed in a standard farrowing stall with a total dimension of 1.5 × 2.1 m. Sows farrowed at 114 ± 3 d of gestation, and piglets were cross-fostered within treatment within 24 h of birth. In addition, the number of piglets per sow was equalized across all treatment groups. Tails of piglets were clipped and 200 mg of iron dextran was injected at 3 d of age. Male piglets were surgically castrated on day 3. Piglets were not offered creep feed during the study, but did have access to water. In addition, rubber mats and heat lamps were provided as a source of supplemental heat to the piglets.

Sow/Sow and Litter Criteria

Sows were weighed at the time of entry into the farrowing house (Tru-Test, Mineral Wells, TX and J&H Automation, Gridley, IL) and again at the time of weaning. Sow 48 h postfarrow BW was determined using the prediction equation: postfarrow weight, kg = [(112 d gestation weight, kg) × 0.98) − 20.81 (R² = 0.93) (Greiner, unpublished data)]. In addition, piglet litter weights were recorded at 48 h of age and at weaning (Tru-Test, Mineral Wells, TX and J&H Automation). Piglets were cross-fostered within experimental treatment assignments within 24 h of birth to equalize litter size and weight across treatments. Any mortalities and morbidities were recorded along with the piglet weights as the piglets were removed from trial. The removal weights and nursing days were calculated back into litter growth rate [(total litter wean weight – total starting litter weight + mortality weights)/((number of piglets weaned × lactation length) + days moralities nursed)]. After weaning, sows were fed ad libitum a conventional gestation diet containing 3.17 Mcal ME/kg and 0.61% total Lys. Sows were checked daily for signs of estrus using a mature boar beginning day 3 after weaning. Estrus was recorded when sows stood to be mounted by a boar, and days from weaning to estrus were also recorded. In addition, the number of sows bred within 10 d of weaning was recorded. The gestation feed was consumed at ~3.6 kg/d from weaning to mating. After mating, feeding levels were adjusted for visual body condition based on a farm specific feeding scale that allowed body condition to be maintained at a 3.0 (scale of 0–5) during the remainder of the gestation period. Weaning to mating interval, farrow to subsequent farrow interval and subsequent litter size, total born, born alive, stillborns, and mummies were recorded. For subsequent litter characteristics, only sows mated within 21 d postweaning and farrowing as a result of first mating were used.

Diet Analysis

The low Val and high Val diets were submitted for dietary AA analysis after manufacturing. Diets were submitted to Ajinomoto Heartland, LLC (Chicago, IL) for AA and CP analysis (AOAC, 1995).

Statistical Analysis

Data were analyzed using procedures of SAS (SAS Institute, Inc., Cary, NC) and reported as least squares means. The statistical model included treatment and parity (block). The sow was the experimental unit. Overall trial averages were calculated using PROC MEANS. Evaluation of treatment effects was analyzed by ANOVA using MIXED procedures. Polynomial coefficients were used to determine linear and quadratic effects on increasing SID Val:Lys ratio. A value of P < 0.05 was considered significant.

RESULTS

In this study, the average days on study were 16.6 (P = 0.94) which resulted in a complete 18.6 d of lactation for the sow. The average parity by treatment ranged from 2.4 to 2.6 (P = 0.24). After farrowing, the estimated sow BW was 213 kg with the range between treatments of 208 to 217 kg (P = 0.64). Sows lost on average 3.06% of their BW with an ADFI of 5.2 kg/d. Sow wean to estrus interval was 5.14 d. Sows started the trial with an average of 13.0 piglets/sow and weaned 11.4 piglets/sow with a piglet ADG of 0.230 kg/d and a daily litter growth rate of 2.70 kg/d. Thirteen sows did not complete the lactation period of the study. Reasons for removal included mortality, illness, weaning 7 or fewer piglets as this can cause early onset of estrus, or feed valve failure resulting in incorrect feed delivery. The number of replications by treatment for the subsequent number of total born was 84, 82, 87, 88, and 81 sows, respectively, with reasons for removal such as failure to conceive, low weaning numbers, old age, or mortality.

Diet analysis demonstrated that the planned ratios were slightly lower than the actual ratios (Tables 2 and 3). Overall, increasing the SID Val:Lys ratio resulted in a no differences in wean to estrus, percent of sows bred by 10 d postwean, sow ADFI, or subsequent total born (P > 0.05; Table 4). Furthermore, piglet ADG, litter ADG, or percent of animals removed from study were not changed (P > 0.05; Table 4) when the SID Val:Lys ratio increased.

Table 2.

Planned vs. analyzed CP, total Lys, and total Val values of the low (50) and high (100) SID¹ Val:Lys diets

	SID Val:Lys ratio
Item	50	100
Planned
CP, %	12.96	12.96
Total Lys, %	1.05	1.05
Total Val, %	0.57	1.06
SID Lys, %	0.95	0.95
SID Val, %	0.48	0.95
Total Val:Lys	0.54	1.01
SID Val:Lys	0.50	1.00
Analyzed
CP, %	13.69	14.15
Total Lys	1.01	1.01
Total Val	0.69	1.05
SID Lys, %	0.91	0.91
SID Val, %	0.59	0.93
Total Val:Lys	0.69	1.04
SID Val:Lys	0.65	1.02

¹SID = standardized ileal digestible; Analyzed values represented as total percentage in the diet.

Table 3.

Analyzed AA values for individual dietary treatments¹

	SID Val:Lys2
Item	50.0	62.5	75.0	87.5	100.0
Alanine, %	0.719	0.712	0.736	0.737	0.705
Arginine, %	0.786	0.777	0.810	0.828	0.783
Aspartic acid, %	1.175	1.168	1.214	1.236	1.169
Cysteine, %	0.246	0.240	0.248	0.249	0.243
Glutamic acid, %	2.205	2.204	2.272	2.299	2.186
Glycine, %	0.540	0.529	0.552	0.558	0.531
Histidine, %	0.337	0.334	0.344	0.350	0.334
Isoleucine, %	0.688	0.703	0.708	0.713	0.717
Leucine, %	1.205	1.211	1.242	1.247	1.195
Lysine, %	1.013	1.018	1.029	1.039	1.013
Methionine, %	0.211	0.213	0.218	0.219	0.208
Met + Cys, %	0.458	0.453	0.466	0.468	0.447
Phenylalanine, %	0.664	0.653	0.675	0.683	0.651
Proline, %	0.832	0.829	0.865	0.864	0.828
Serine, %	0.633	0.614	0.637	0.643	0.610
Threonine, %	0.754	0.685	0.691	0.703	0.705
Tyrosine, %	0.378	0.357	0.383	0.384	0.354
Valine, %	0.694	0.752	0.843	0.939	1.045
Tryptophan, %	0.171	0.169	0.166	0.168	0.172

¹The analyzed AA values are represented as total percentage in the diet.

²SID = standardized ileal digestibility.

Table 4.

Evaluation of lactating primiparous and multiparous sow and litter performance as dietary SID¹ Val:Lys ratio increases in sow lactation diets

	SID Val:Lys ratio
Calculated ratio	50.0	62.5	75.0	87.5	100.0
Analyzed ratio	65.0	74.3	83.5	92.8	102.0	SEM	Trt	Linear	Quadratic
Sow
Number of sows	84	82	87	88	81
Total Val intake, g/d	36.2	40.9	45.3	47.6	56.6	1.3	0.001	0.001	0.14
SID Val intake, g/d	30.9	35.4	39.6	41.9	50.1	1.1	0.001	0.001	0.13
Days on test, d	16.5	16.8	16.7	16.7	16.6	0.29	0.94	0.88	0.50
Parity	2.4	2.4	2.5	2.5	2.6	0.09	0.63	0.13	0.80
ADFI, kg	5.2	5.2	5.2	5.0	5.4	0.15	0.24	0.96	0.18
Sow 48 h wt, kg	216.63	214.31	214.58	211.83	208.85	4.11	0.64	0.12	0.75
Sow wean wt, kg	211.71	208.49	208.26	204.62	204.72	4.04	0.57	0.12	0.81
Weight change, %	−2.59	−1.93	−2.43	−3.15	−2.42	1.01	0.90	0.76	0.97
Bred by 10 d, %	96.54	97.78	91.88	94.77	100.0	3.25	0.32	0.66	0.11
Wean to estrus, d	5.2	4.7	5.3	5.5	4.5	0.32	0.57	0.45	0.26
Subsequent total born, n	13.93	13.51	14.28	13.88	13.26	0.75	0.87	0.66	0.55
Piglet
Number of piglets started/sow, n	13.1	13.1	13.2	13.2	12.9	0.21	0.77	0.71	0.28
Number of piglets weaned/sow, n	11.8	11.7	12.0	11.7	11.5	0.26	0.64	0.36	0.39
Litter 48 h wt, kg	20.37	20.40	20.26	20.39	19.35	0.66	0.73	0.27	0.39
Litter wean wt, kg	64.40	64.75	66.78	64.70	62.70	1.84	0.54	0.51	0.14
Pig ADG, kg/d	0.220	0.219	0.226	0.214	0.221	0.005	0.51	0.85	0.88
Daily litter ADG, kg/d	2.66	2.64	2.71	2.61	2.62	0.08	0.48	0.63	0.43
Removal, %	2.41	3.71	3.64	2.87	3.45	0.79	0.57	0.58	0.41

¹SID = standardized ileal digestibility; Values for both the calculated and analyzed SID Val:Lys ratio is presented.

DISCUSSION

Recent studies in finishing hogs have indicated that the SID Val:Lys requirement for finishing hogs is between 63% and 73% (Goncalves et al., 2018). There have been multiple studies in the last 20 yr evaluating the SID Val:Lys ratio requirement in lactating sow diets. Some of these studies have indicated a similar SID Val:Lys requirement of a lactating sow to the finishing hog. While some of the studies demonstrate a required level for valine, others have failed to demonstrate a ratio requirement. NRC (2012) suggested SID Val:Lys requirement of 85% for sows nursing 11.5 pigs. In this current study, the sows weaned 11.7 pigs to ensure that sows were producing significant milk throughout the lactation period and to align with the NRC estimates.

In this study, there were parity effects on parameters such as ADFI, weight change percentage, wean to estrus interval, and litter performance, but not for the number of pigs weaned or the percent of piglets removed from the sow. There were no parity × treatment interactions indicating that the optimal SID Val:Lys ratio is the same for all animals.

The analyzed dietary analysis was slightly higher than the calculated values. Therefore, all discussion will be based on the analyzed values and not the calculated. The use of feed grade lysine at higher levels was allowed in the diets to both reduce the amount of soybean meal and to produce the low SID Val:Lys diet. Feed grade isoleucine was added back to the diet to ensure that the other BCAAs remained constant across the diets to meet the sow’s requirements and to ensure that any response would be associated with the increasing level of Val. Based on the NRC (2012) estimates for AA required for milk production, a sow would need 16.8 g Ile/d and 39.6 g Leu/d. Dietary feed requirements for the sows in this study with estimated piglet growth rates of 220 g/d would be 31.1 g total Ile/d and 62 g total Leu/d. Based on the analyzed dietary analysis and the ADFI in this study, sows consumed 36.4 g of total Ile/d and 62.4 g of total Leu/d; thereby meeting their daily requirements for these AA.

Furthermore, feed intake in this study was allocated to a maximum of 5.5 kg/d to minimize the variation in digestible Lys intake associated with sow ad libitum feed intake variation. Based on the litter growth rate of 2.70 kg/d, NRC (2012) SID Lys requirements for a sow per day would be 49 g. In this study, sows consumed on average 45 g of SID Lys/d. Research conducted by Touchette (1998) would indicate that the SID Lys requirement for the sows in this study would be around 56 g SID Lys/d. Furthermore, research conducted by Greiner et al. (2009, 2011) would indicate that 62 g of SID Lys/d is required for optimal sow reproduction. The sows in this study were consuming below the expected Lys requirement to support litter growth based on both the NRC, as well as other studies associated with SID Lys requirements for lactating sows.

Upon the evaluation of Val consumed per day based on the litter growth rate of 230 g/d, the NRC (2012) would recommend 38.4 g SID Val/d. In this study, piglet ADG was 220 g/d and sows in this study consumed between 33 and 52 g SID Val/d; therefore, indicating that the NRC recommendation was within the dietary treatments in the study. Another method of calculating the Val requirement is to estimate the need based on milk output by utilizing the litter size and the mean litter gain. In this study, the number of pigs per sow was initially started at 13 pigs per sow with a final weaning number of 11.7. Estimated CP milk output can be calculated using the following equation: [(0.0257 × mean litter gain (g)) + 0.42 × litter size)] × 6.38 (NRC, 2012). From milk CP output, calculations can then be made on gram of AA per day. Milk has ~7.01 g Lys/100 g CP and Val is 71 g/100 g of Lys (NRC, 2012). From these estimates, milk output was 33 g Lys/d and 23 g Val/d. The efficiency of the SID AA utilization for the lactating sow is 0.670 and 0.583 for Lys and Val, respectively (NRC, 2012) resulting in the estimated requirements of 49 g SID Lys/d and 40 g SID Val/d. Based on the milk output calculation, sows in this study were consuming slightly below the estimated Lys requirement for milk output and the test Val levels in this study were above and below the estimated requirements for the sows.

With the Val levels tested in this study being above and below the estimated NRC requirements for both piglet growth rate and estimated milk AA output, sow reproduction or litter growth rate should have been improved with the additional valine. However, there was no significant response associated with increasing valine.

In work conducted by Kim et al. (2001), a sow that mobilizes tissue during lactation has a different sequence of limiting order of AA compared with a sow that is not mobilizing tissue. According to Kim et al., a sow mobilizing tissue would have an order of limiting AA as Lys, Thr, and then Val; whereas as sow that is not mobilizing tissue would have Lys as the first limiting AA followed by Val. Based on the NRC (2012) estimates, total Thr intake should be 37.2 g/d (30.5 g SID Thr/d), whereas the sows in this study consumed 36.7 g of total Thr/d. Previous work conducted by Greiner et al. (2017), suggested that the dietary level of SID Thr:Lys is 65%. In the current study, sows consumed a diet of 0.91% SID Lys with an SID Thr:Lys ratio of 68%. With a feed intake of 5.2 kg/d, the sows consumed ~32 g of SID Thr/d. If the desired ratio for optimal performance is 65%, then the SID Thr requirement for the sows in this study should have been 30.8 g/d. This would suggest that the sows consumed more SID Thr than their requirement while losing weight. Since the sows in this study lost weight, then the limiting AA order would have been Lys, Thr, and then Val. If the NRC (2012) requirement is correct, then the first AA provided above the expected requirement would have been valine and a valine response would have been expected. However, if the Greiner et al. (2017) requirement is correct, then Thr would not have been limiting and potentially masked the Val response in the study.

Based on the calculated NRC (2012) SID Val and SID Lys requirements for the sows in this study, the optimal SID Val:Lys ratio would be 85. The dietary treatments ranged from 55% to 100% for SID Val:Lys. There was no reproductive or litter growth rate response associated with animals being above or below the NRC estimate; thereby concluding that the findings from this study suggest that the valine needs for a lactating sow may be lower than that the current NRC (2012) recommendation for daily SID Val intake.

Conflict of interest statement. None declared.