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The dietary valine requirement for prolific lactating sows does not exceed the National Research Council estimate^1,2

A. M. Gaines^*, R. D. Boyd^,2,3, M. E. Johnston^,3, J. L. Usry, K. J. Touchette^*,4 and G. L. Allee^*

^* Department of Animal Science, University of Missouri, Columbia 65211; and Pig Improvement Company, Franklin, KY 42135; and Ajinomoto Heartland LLC, Chicago, IL 60631

	Abstract

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Two studies were conducted to determine the effect of increasing the valine:lysine (V:L) ratio in diets of lactating sows above the minimum proposed by the NRC (1998). The first experiment involved 189 PIC, Camborough product sows (parity 1 to 4) that were allotted to 1 of 3 dietary treatments. Diets were formulated to achieve total dietary V:L ratios of 0.90, 1.05, or 1.25:1, respectively, and were corn and soybean meal-based. The second experiment involved 279 PIC, Camborough sows (parity 1 to 5) that were allotted to 1 of 4 treatments. Diets 1 and 3 were formulated using corn and a fixed inclusion of soybean meal (16.7%), with 0.27% L-lysine HCl. The V:L ratios in diets 1 and 3 were 0.73 and 1.25:1, respectively. Diets 2 and 4 were typical corn-soybean meal diets containing 0.05% L-lysine HCl, with a fixed inclusion of soybean meal (22.7%). The V:L ratios in diets 2 and 4 were 0.86 and 1.25:1, respectively. In both experiments, each litter was standardized to a minimum of 10 pigs, which achieved litter growth rates of 2.22 and 2.56 kg/d in Exp. 1 and 2, respectively. In Exp. 1, increasing the dietary V:L ratio beyond 0.90:1 did not improve (P > 0.10) the number of pigs weaned, survival rate, or piglet growth rate, even though sows were nursing more than 10 pigs per litter for 19 d. In Exp. 2, total lysine intake was similar among treatments and ranged from 52.1 to 55.3 g/d. Valine intake increased as the diet valine concentration increased (diet 1 vs. 3 and diet 2 vs. 4, P < 0.001), ranging from 40.0 to 66.1 g/d. Litter gain tended to improve (P = 0.14) when the 0.27% L-lysine HCl control (0.73 V:L) was supplemented with valine to achieve a 1.25:1 V:L ratio. In contrast, no aspect of sow or litter response was improved when the practical control diet containing 0.05% L-lysine HCl (0.86 V:L) was supplemented with valine to achieve a 1.25:1 V:L ratio. Collectively, this research shows that a V:L ratio in excess of 0.86 does not conserve maternal tissue loss or improve piglet growth rate, but a V:L ratio of 0.73 may compromise litter growth rate.

Key Words: amino acid • lactation • valine

	INTRODUCTION

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The NRC (1998) proposed a minimum dietary ratio of valine:lysine (V:L) of 0.85:1 for high milk producing sows. This true ileal digestible ratio is greater than previously estimated by the ARC (1981) and Pettigrew (1993) but lower than in a prior NRC edition (1988). The estimate was based on evidence, at the whole-animal level and the tissue level (Boyd et al., 1995), that the valine requirement is greater than would be predicted from the amount secreted in milk (NRC, 1998). This estimate of absorbed V:L is in relative agreement with the initial mammary transmembrane transport ratio estimate by Trottier et al. (1997).

A number of empirical studies have been conducted evaluating valine nutrition of lactating sows, but there is too much disparity among these trials to reach a reliable conclusion. Richert et al. (1996; 1997a,b) reported that a V:L ratio of at least 1.15:1 was needed to maximize litter growth rate. Similarly, Moser et al. (2000) reported an improvement in litter growth rate as the V:L ratio increased from 0.89 to 1.33:1 in sows that were nursing large litters (10 pigs/litter). In contrast, Carter et al. (2000) reported that a V:L ratio of 0.89:1 was sufficient to meet the need for litter growth of sows nursing 10 or more pigs. Southern et al. (2000) also reported no improvement in sow productivity when the V:L ratio was increased from 0.85 to 0.94:1, using hydrolyzed feather meal as a source of valine. The 2 latter reports are in agreement with the NRC (1998); however, the reason for the discrepancy between these data and the earlier reports is not clear. With the exception of the data by Moser et al. (2000), the studies where an increase in the V:L ratio beyond 1:1 proved beneficial to litter growth involved diets containing substantial amounts of crystalline AA (Richert et al., 1996; 1997a,b).

This research was conducted to determine if a dietary V:L ratio in excess of that suggested by the NRC (1998) conserves maternal body tissue or increases litter growth rate in sows nursing more than 10 pigs. Practical corn-soybean meal diets were used. Two of the semi-synthetic diets, used by Richert et al. (1996), were reproduced to see if we could duplicate the response. The PIC pig research and care committee approved animal use protocols in this research.

	MATERIALS AND METHODS

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Experiment 1

One hundred eighty-nine PIC, Camborough product sows (parity 1 to 4) were used to determine the effect of increasing the V:L ratio (dose-response assay) for lactating sows. Crystalline valine was added to practical corn-soybean meal diets. Sows were assigned on d 112 of pregnancy, within parity, to 1 of 3 diets, which were fed throughout a 19-d lactation period. Sows were housed in conventional farrowing crates in an environmentally regulated research facility. Temperature was maintained at 21°C (21.6 ± 1.5°C), and lights were on from 0600 to 1500. Within 24 h of farrowing, all litters were standardized to a minimum of 10 pigs each.

Dietary treatments were formulated to achieve total dietary V:L ratios of 0.90, 1.05, or 1.25:1. The lysine concentration was slightly below the estimate of lysine requirement (0.90% total lysine) determined using a regression equation that was developed by regressing total lysine intake of lactating sows on litter growth rate (Pettigrew, 1993). Diets were based on corn and soybean meal and contained 12% wheat middlings and 0.068% crystalline L-lysine HCl (Table 1). Dietary valine concentration was increased by substituting L-valine for an equivalent amount of corn. Calculated ratios of other essential AA to lysine exceeded NRC recommendations (1998) for the level of litter growth that was anticipated and subsequently achieved. The respective ratios of threonine, methionine + cysteine, and tryptophan to lysine were 0.68, 0.61, and 0.22:1, respectively.

Experiment 2

Two hundred seventy-nine PIC, Camborough product sows (parity 1 to 5) were used to verify the adequacy of the NRC minimum recommended V:L ratio (0.86 to 1.25:1), using practical corn-soybean meal diets containing 0.05% L-lysine HCl. We also determined if we could duplicate the litter growth response to an increase in the analyzed V:L ratio (i.e., 0.73 increased to 1.25) that was reported previously by Richert et al. (1996), whose diets involved extensive crystalline AA addition to the initial diet (0.73 V:L).

Four dietary treatments were used with 2 diets (diets 1 and 3) composed as described by Richert et al. (1996) with a minor exception that valine replaced corn rather than cornstarch. The diets were formulated to contain 0.91% total lysine and 0.275% crystalline L-lysine HCl (Table 2). The level of soybean meal was held constant (16.7%) for both diets and crystalline L-valine was added to increase the dietary V:L ratio from 0.73 to 1.25:1, respectively. The dietary valine concentration was increased by substituting crystalline L-valine for an equivalent amount of corn. Crystalline L-threonine, DL-methionine, L-tryptophan, and L-isoleucine were added to achieve ratios to lysine of 0.72, 0.60, 0.22, and 0.70:1, respectively. Two diets (diets 2 and 4) were formulated similar to those of Exp. 1 and based on corn and soybean meal without extensive crystalline AA use (Table 2). The level of soybean meal was greater than for diets 1 and 3, and was held constant (22.7%), thus achieving dietary V:L ratios of 0.86 and 1.25:1 in diets 2 and 4, respectively. Dietary valine concentration was increased by replacing corn with L-valine.

Sow and Litter Criteria

To calculate sow weight change during lactation, sows were weighed on d 1 of lactation and at the time of weaning in both experiments. In Exp. 1, to calculate change in loin and backfat depth (wean value – d 1 value), loin depth and backfat depth at the 10th and last rib were measured by the same technician using real-time ultrasound (Aloka 500; Aloka, Ithaca, NY). Change in loin and fat depth were used as an indication of body protein and lipid mobilization, respectively, in support of lactation.

To calculate litter growth rate, piglets were weighed on d 1 of lactation and at weaning. All pigs were processed according to routine management practices, which included tail docking, subcutaneous iron dextran injection, and castration. The sow was the sole source of nutrients provided to the litter.

Diet Analysis

Crude protein was determined by Kjeldahl analysis (N x 6.25), with tryptophan used as the internal standard for nitrogen recovery (AOAC, 1996). The AA content of the diets was determined using gas liquid chromatography (Beckman Model 6300; Beckman Instruments, Inc., San Ramon, CA) and by AOAC procedure 994.12, alternative 1 (AOAC, 1996). Performic acid was used before hydrolysis to oxidize cysteine and methionine to cysteic acid and methionine sulfone, respectively. Amino acids were liberated from protein by hydrolysis with 6 N HCl at 110°C for 24 h. Samples were cooled to room temperature, titrated with 50% NaOH to a pH of 2.20, and diluted to the desired volume with sodium citrate buffer. Norleucine was added to the hydrolysate to achieve 0.1 mmol/L in the final sample. Samples were filtered through a 0.2-µm syringe filter before injection. Amino acids were separated using a 3-buffer gradient-elution system on an ion-exchange column (4.6 mm i.d. x 120 mm) packed with sulfonated polystyrene divinylbenzene. Detection was by postcolumn derivatization with ninhydrin, using ultraviolet spectroscopy at 440 and 570 nm. Tryptophan was determined using gas liquid chromatography after alkaline hydrolysis using 60% barium hydroxide under anaerobic environment for 16 h. Conditions and use of the internal standard were as described.

Statistical Analysis

Data were analyzed by ANOVA using GLM procedures of SAS (SAS Inst., Inc., Cary, NC), and LS mean comparisons were made using Fisher’s protected least significant difference test (P < 0.05). The statistical model included parity, diet, and parity x diet interactions. The initial analysis indicated that there were no parity x diet interactions (P > 0.10) in either experiment; thus, the interaction term was dropped from the models. Sow data involving BW and carcass measurements contained their respective initial values as covariates in the model. Litter growth data were adjusted for the number of pigs nursed and lactation length by covariate analysis. In Exp. 1, polynomial coefficients were used to determine linear and quadratic effects of increasing dietary valine. In Exp. 2, preplanned nonorthogonal contrasts were used to test the effects of increasing dietary V:L ratio (diet 1 vs. 3; diet 2 vs. 4) within diet type. The effect of diet type was also compared at the 1.25:1 V:L ratio (diet 3 vs. 4). Sow and litter were used as the experimental unit for respective data.

	RESULTS

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Experiment 1

Increasing the dietary V:L ratio beyond 0.90:1 did not affect the number of pigs weaned, survival rate, litter weight gain, or piglet growth rate even though sows were nursing >10 pigs per litter for 19 d (Table 3). Sow feed intake, corrected for feeding waste, was not affected by dietary valine concentration and averaged 7.22 kg/d (Table 4). Lysine intake was similar across treatments and averaged 65.0 g/d. Daily valine intake increased (linear, P < 0.001) from 58.5 to 78.1 g/d as dietary valine concentration increased. Despite an increase in relative valine intake, there were no differences in the amount of sow BW or loin depth loss (Table 4). Fat depth declined at both the 10th and last rib but was similar among treatments. The concomitant loss of loin and fat depth would suggest that sow BW loss consisted of both body protein and lipid.

Total litter gain tended to improve (P = 0.14) when the 0.275% L-lysine HCl control was supplemented with valine to achieve a 1.25:1 V:L ratio, diets 1 vs. 3, respectively (Table 5). It is noteworthy that the litter growth advantage for the 1.25 V:L group was achieved despite the latter having a lower estimated feed intake (P < 0.05). It is not clear whether the 0.73 V:L control group exhibited an increase in intake due to deficient AA intake or whether the 1.25 V:L test group simply consumed less. The former is sometimes observed in growing pigs but under more extreme protein or AA deficiencies. To the contrary, no aspect of sow or litter response was improved when the corn-soybean meal control diet (0.05% L-lysine HCl) was supplemented with valine to achieve a 1.25:1 V:L ratio, diets 2 vs. 4, respectively. The litter gains achieved by all treatments, except the 0.73 V:L control, were remarkably similar and averaged approximately 44.8 kg (ca. 257 g of gain·pig^-1·d^-1).

	DISCUSSION

Top Abstract INTRODUCTION MATERIALS AND METHODS RESULTS DISCUSSION IMPLICATIONS LITERATURE CITED

 
This research shows that a V:L ratio in excess of 0.86 does not conserve maternal tissue loss or improve piglet growth rate for the prolific, high milk production sow. This suggests that the NRC (1998) estimate is not too low, and it agrees with subsequent studies by Carter et al. (2000) and Southern et al. (2000). These results are in contrast to earlier reports suggesting that the optimum V:L ratio was in excess of 1.0 (Richert et al., 1996, 1997a,Richert et al., b; Moser et al., 2000). We do agree that piglet growth rate seems to be compromised by a dietary V:L ratio of 0.73. This apparent response is consistent with but less remarkable than previously reported by Richert et al. (1996). In total, there is now sufficient information in the literature to conclude that the dietary V:L ratio requirement does not exceed the NRC estimate (1998). It is not clear whether the NRC estimate can be further refined downward and whether the V:L relationship is dynamic over a wide range of body protein mobilization (Kim et al., 2001).

Lysine intake (g/d) was greater than anticipated in Exp. 1. A possible criticism of this experiment is that lysine intake was in excess of the requirement, which would result in an inaccurate estimate of the minimum V:L need. A fundamental tenet to establishing an ideal pattern among AA is that the reference AA, lysine, must be marginally deficient and in the linear portion of the response curve. This concern was addressed in Exp. 2 by setting an upper limit on feed intake of 7.27 kg/d, beginning on d 12 of lactation. It is noteworthy that sows in both experiments lost BW. The fact that both fat and loin eye depth was lost during lactation (Exp. 1) suggests that tissue mobilization involved a net loss from lipid and protein pools; the latter implies an AA deficit.

We concluded that the reference AA, lysine, was marginally deficient and is in the linear portion of the response curve for Exp. 1 and 2, using published estimates of lysine need. We calculated the lysine requirement using an updated equation (Boyd et al., 2000) that relates litter growth rate to lysine intake of the lactating sow in the following manner:

This relationship was originally proposed by Pettigrew (1993). Our estimate was computed using litter growth rate (indirect function of milk output) and maintenance (obligatory loss). However, we included maternal lysine mobilization (described by the negative intercept) in the calculated estimate. We did not consider maternal lysine mobilization to be obligatory unless dietary intake fails to adequately meet the lysine requirement. This outcome is both more important and more difficult to achieve for the first litter sow because conservation of body protein mass during the first lactation is important to second litter size (Boyd et al., 2000). In Exp. 1, the lysine required during lactation was estimated to be 66.9 g/d. This assumes 2.23 kg of litter growth/d (computed from Table 3) and that an additional 7.55 g of lysine/d was required to prevent body lysine mobilization for maintenance (intercept). This compares to an estimated lysine intake of 65.0 g/d (Table 4). In Exp. 2 the lysine requirement was computed to be 75.9 g/d (2.57 kg litter gain/d), which is considerably greater than actual lysine intake (<55 g/d).

The fact that there was no response by the addition of valine to diets having a marginal deficiency of lysine and other AA led to the conclusion that the valine content was adequate in the corn-soybean control diets that were used in Exp. 1 and 2. This line of reasoning is most convincing for Exp. 2 because average valine intake was less than 50 g/d (Table 5). The discrepancy between this and early studies on the requirement for valine cannot be attributed to extreme differences in either the number of pigs nursed or litter growth rate, because both are similar across studies. The level of valine provided by the corn-soybean control diet in Exp. 2 is relatively similar to that provided by the control diets of Richert et al. (1996, 1997a,b) and Moser et al. (2000), in the range of 40 to 48 g/d. The level achieved in the dose response assay (Exp. 1; Table 3) was also similar (60 to 70 g/d). The possibility that diet composition was involved was also considered. With the exception of the report by Moser et al. (2000), supplemental valine improved litter growth rate in trials involving high (0.24 to 0.38%) levels of L-lysine HCl (Richert et al., 1996, 1997a,Richert et al., b). Two of the diets were virtually duplicated in Exp. 2 (0.27% L-lysine HCl). Although valine addition (1.25 V:L) improved litter growth rate when compared with the 0.73 V:L control, it performed equivalent to the corn-soybean control (0.86 V:L) and test (1.25 V:L) diets, containing 0.05% L-lysine HCl.

The concept of a dynamic ideal AA pattern was extended to the lactating sow by the elegant work of Kim et al. (2001). The work of Kim et al. (2001) is relevant to the current study and to future AA research. They proposed that the order of limiting dietary AA may differ with increasing body protein mobilization (or weight loss). This is best illustrated with threonine, where the threonine:lysine ratio was estimated to increase in increments from 0.59 to 0.75 as the sow experienced progressively greater BW loss and protein mobilization. Substantial increases in BW loss occur with extreme heat stress, for example. It is noteworthy that the V:L ratio was estimated to increase from 0.77 to only 0.78 over this same range of weight loss. The weight loss that we observed for sows in Exp. 1 and 2 was moderate (9.7 and 9.1 kg respectively) and, based on their research, would require a minimum V:L ratio of 0.78. Further research is required to determine whether the V:L requirement is closer to the pattern in milk (0.78) or the NRC estimate (0.85). It seems that the ARC (1981) estimate of 0.70 for the V:L ratio is deficient, based on the report of Richert et al. (1996) and Exp. 2.

	IMPLICATIONS

Top Abstract INTRODUCTION MATERIALS AND METHODS RESULTS DISCUSSION IMPLICATIONS LITERATURE CITED

 
This research demonstrates that the dietary valine requirement is not greater than the NRC (1998) proposed minimum (0.855 total or true ileal digestible valine:lysine) for the sow that is nursing a large litter (greater than 10 pigs). This means that crystalline lysine can be added to grain, soybean meal diets for lactating sows containing approximately 0.90% total dietary lysine without compromise of maternal body tissue or litter growth. Further refinement of the minimum valine:lysine ratio (between 0.70 and 0.85) is required before we can predict the second limiting amino acid and to take advantage of greater crystalline amino acid use.

	Footnotes

 
¹ Research was conducted at the Pig Improvement Company Research Farm, Franklin, KY 42135. The authors recognize the technical assistance of E. Wilson and the financial support of Ajinomoto Heartland LLC. Amino acid analysis was conducted by C. Deimerly of the Ajinomoto Heartland analytical lab, for which we are grateful.

³ Present address: The Hanor Company, Inc., P. O. Box 881, Franklin, KY 42134.

⁴ Present address: Cargill Animal Nutrition, Elk River, MN 55330.

² Corresponding author: dboyd{at}hanorusa.com

Received for publication February 2, 2005. Accepted for publication December 15, 2005.

	LITERATURE CITED

Top Abstract INTRODUCTION MATERIALS AND METHODS RESULTS DISCUSSION IMPLICATIONS LITERATURE CITED

 


AOAC. 1996. Official Methods of Analysis. 16th ed. Assoc. Off. Anal. Chem., Arlington, VA.

ARC. 1981. Page 164 in The Nutrient Requirements of Pigs: Agricultural Technical Review. Rev. ed. Commonw. Agric. Bureau, Slough, England.

Boyd, R. D., R. E. Kensinger, R. Harrell, and D. E. Bauman. 1995. Nutrient uptake and endocrine regulation of milk synthesis by mammary tissue of lactating sows. Page 35 in Second Int. Lactation Biol. Symp. H. A. Tucker, and J. A. Pettigrew, ed. J. Anim. Sci. 73(Suppl. 3).

Boyd, R. D., K. J. Touchette, G. C. Castro, M. E. Johnston, K. U. Lee, and I. K. Han. 2000. Recent advances in amino acid and energy of prolific sows: Review. Asian Aus. J. Anim. Sci. 13:1638–1652.

Carter, S. D., G. M. Hill, D. C. Mahan, J. L. Nelssen, B. T. Richert, and G. C. Shurson. 2000. Effects of dietary valine concentration on lactational performance of sows nursing large litters. J. Anim. Sci. 78:2879–2884.[Abstract/Free Full Text]

Kim, S. W., D. H. Baker, and R. A. Easter. 2001. Dynamic ideal protein and limiting amino acids for lactating sows: The impact of amino acid mobilization. J. Anim. Sci. 79:2356–2366.[Abstract/Free Full Text]

Moser, S. A., M. D. Tokach, S. S. Dritz, R. D. Goodband, J. L. Nelssen, and J. A. Loughmiller. 2000. The effects of branched-chain amino acids on sow and litter performance. J. Anim. Sci. 78:658–667.[Abstract/Free Full Text]

NRC. 1988. Page 52 in Nutrient Requirements of Swine. 9th ed. Natl. Acad. Press, Washington, DC.

NRC. 1998. Page 40 in Nutrient Requirements of Swine. 10th ed. Natl. Acad. Press, Washington, DC.

Pettigrew, J. E. 1993. Amino acid nutrition of gestating and lactating sows. BioKyowa Technical Review No. 5. Nutri-Quest, Inc., Chesterfield, MO.

Richert, B. T., R. D. Goodband, M. D. Tokach, and J. L. Nelssen. 1997a. Increasing valine, isoleucine, and total branched-chain amino acids for lactating sows. J. Anim. Sci. 75:2117–2128.[Abstract/Free Full Text]

Richert, B. T., M. D. Tokach, R. D. Goodband, J. L. Nelssen, R. G. Campbell, and S. Kershaw. 1997b. The effect of lysine and valine fed during lactation on sow and litter performance. J. Anim. Sci. 75:1853–1860.[Abstract/Free Full Text]

Richert, B. T., M. D. Tokach, R. D. Goodband, J. L. Nelssen, J. E. Pettigrew, R. D. Walker, and L. J. Johnston. 1996. Valine requirement of the high-producing lactating sow. J. Anim. Sci. 74:1307–1313.[Abstract]

Southern, L. L., F. M. LeMieux, J. O. Matthews, T. D. Bidner, and T. A. Knowles. 2000. Effect of feather meal as a source of valine for lactating sows. J. Anim. Sci. 78:120–123.[Abstract/Free Full Text]

Trottier, N. L., C. F. Shipley, and R. A. Easter. 1997. Plasma amino acid uptake by the mammary gland of the lactating sow. J. Anim. Sci. 75:1266–1278.[Abstract/Free Full Text]

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