Threonine Is More Limiting Than Valine in Diets of Lactating Sows with High Rates of Body Protein Loss

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1 Threonine Is More Limiting Than Valine in Diets of Lactating Sows with High Rates of Body Protein Loss Kevin T. Soltwedel, Robert A. Easter, and James E. Pettigrew Department of Animal Sciences University of Illinois, Urbana, IL, INTRODUCTION When voluntary feed intake is at a level that does not provide sufficient amino acids and energy for milk synthesis, the lactating sow compensates by mobilizing protein and fat from body tissues to provide additional amino acids, glucose and energy needed to sustain milk production (Mullan and Williams, 1990; Pettigrew et al., 1992a,b; Sauber et al., 1998; McNamara and Pettigrew, 2002a,b). A balance of nutrients must be provided to support the demand for milk production by the litter and to minimize weight loss in lactation. Therefore, knowledge of the balance of amino acids and level of energy required to maximize efficiency of milk production and minimize body weight loss is needed to provide optimal nutrition for the lactating sow. The profile of amino acids supplied to the mammary gland from mobilized protein is a key determinant of the limiting order of amino acids in the diet during periods of significant tissue mobilization. Recently, it has been suggested that ratios of certain essential amino acids relative to lysine required in the diet of lactating sows change significantly as the proportion of amino acids supplied to the mammary gland from mobilized body tissue increase relative to the proportion of amino acids supplied by dietary intake (Kim et al., 2001). This concept has also been applied to the lactating sow model (NRC, 1998) constructed for estimating amino acid requirements. However, because of differences in the estimated amino acid profile of mobilized body tissues, estimates of amino acid requirements of lactating sows mobilizing significant amounts of body tissue reported by Kim et al. (2001) are different from NRC (1998) estimates. As the proportion of amino acids supplied from the sow s body increases relative to the dietary supply, the impact of the amino acid profile of mobilized body protein on dietary requirements becomes greater. Prior to research conducted using lactating sows (Kim and Easter, 2001; Kim et al., 2001), estimates of the amino acid profile of protein mobilized from body tissue used for calculating amino acid requirements for the lactating sow have been derived from body composition data of growing pigs (Pettigrew, 1993; NRC, 1998). Kim and Easter (2001) measured differences in protein content of carcass, gastro-intestinal tract, liver and reproductive tract of sows at the end of a 21-d lactation, in response to increasing litter size in one pig increments from 6 to 12 pigs. Litter size was increased to stimulate a greater demand for milk production, and sow feed intake was restricted, to increase the rate of body tissue mobilization. The difference in protein content of each tissue 88

2 was regressed on litter size to estimate the quantity of protein mobilized from sow body tissues for each additional pig over the 21-d lactation period. In a subsequent report, the amino acid content of each body tissue reported by Kim and Easter (2001) was regressed on litter size (Kim et al., 2001). The slopes derived from these regression equations describing differences in amino acid content of each body tissue, were used to estimate the amino acid content of protein mobilized from sow body tissues over the 21-d lactation period (Kim et al., 2001). Calculation of amino acid requirements using these estimates of mobilized amino acids, suggest that the limiting order of amino acids in a cornsoybean meal diet changes, as the proportion of amino acids supplied from mobilized body tissues increases relative to dietary amino acid supply. Specifically, threonine was estimated to be first limiting, lysine second limiting, and valine third limiting in corn-soybean meal diets for sows with the highest rate of body tissue mobilization during lactation (Kim et al., 2001). For sows with a low rate of body tissue loss, lysine was estimated to be first limiting, valine second limiting, and threonine third limiting (Kim et al., 2001). In comparison, calculation of amino acid requirements using estimates of amino acids required for maintenance and milk production, and the amino acid profile of mobilized protein reported by NRC (1998), suggest that lysine and valine are co-first limiting, and threonine third limiting in diets of sows with a high rate of body tissue loss. Similarly, lysine is calculated to be first limiting, valine second limiting, and threonine third limiting in diets of sows with a low rate of body tissue mobilization. The objective of the current study was to test whether threonine or valine is more limiting in diets of lactating sows with high rates of body tissue loss using plasma urea nitrogen (PUN) as an indicator. MATERIALS AND METHODS Experimental Design: The study was conducted as a replicated Latin Square crossover design using a total of 12 animals; 3 squares with four animals per square. Sows were allotted to individual squares on the basis of parity. One square consisted of first-parity sows and two squares consisted of multiparous sows. Diets: A low protein basal diet containing corn and soybean meal as the only sources of intact protein was formulated to 0.60% lysine to induce a high rate of body protein loss during lactation. The basal diet was formulated by diluting reference corn-soybean meal lactation diet (0.90% lysine) with starch, sucrose, and soybean oil. L-lysine HCl and D,Lmethionine were included in the basal diet at and 0.016%, to ensure that these amino acids were not limiting. From this low protein basal diet, each of the four dietary treatments (Table 1) was formulated: 1) the low protein basal diet, formulated to be deficient in threonine and valine relative to lysine (LP), 2) the LP diet supplemented with 0.139% L- threonine (LP+T) 3) the LP diet supplemented with 0.174% L-valine (LP+V), and 4) the LP diet supplemented with 0.139% L-threonine and 0.174% L-valine (LP+T+V). Diets were made isonitrogenous by L-glycine supplementation at the expense of starch. 89

3 Experimental Approach: The study was initiated on d3, 4 or 5 of lactation, to allow time for appetite recovery postpartum. Litter size was standardized to 8 to 10 pigs per litter. Each diet was fed during a 4-d period to each sow at a level of 4.8 kg/d. This feeding level provided adequate energy intake (18.0 Mcal ME/d), and deficient protein intake (485 g CP/d) to induce a high rate of body protein loss during lactation, yet it did not exceed sow appetite. Sow and litter weights were recorded, and blood samples collected for analysis of PUN, on d-4 of each period over the 16-d study. RESULTS AND DISCUSSION The diets fed in this study were formulated to induce a high rate of body protein loss. Protein intake was restricted to approximately 50% of the lactating sow s requirement, whereas energy intake was maintained at a level close to the sow s requirement. Sows lost a significant amount of body weight, while supporting a high level of litter gain over the entire 16-d study (Table 2). Daily sow weight loss and litter weight gain averaged kg and kg, respectively. The PUN was lower (P<.01) for the threonine supplemented treatments, and was not affected by supplemental valine intake (Table 3). The results of this study demonstrate that threonine is more limiting than valine in corn-soybean meal diets fed to lactating sows with high rates of body protein loss in lactation, when PUN is used as an indicator. Kim et al., (2001) suggested that threonine is the first limiting amino acid in diets of sows with high rates of body protein loss in lactation, followed by lysine and valine. In contrast, the NRC (1998) lactation sow model predicts lysine and valine to be cofirst limiting, followed by valine. The results of this study support the hypothesis proposed by Kim et al. (2001) that threonine is more limiting than valine in diets of sows with high rates of tissue loss in lactation. CONCLUSIONS Considering that the basal diet used in this study was supplemented with crystalline lysine, we can not conclude that threonine is more limiting than lysine. However, the results of this study demonstrate that threonine is more limiting than valine in diets of lactating sows with high rates of body protein loss. REFERENCES Kim, S. W. and R. A. Easter Nutrient mobilization from body tissue as influenced by litter size in lactating sows. J. Anim. Sci. 79: Kim, S. W., D. H. Baker, and R. A. Easter Dynamic ideal protein and limiting amino acids for lactating sows: the impact of amino acid mobilization. J. Anim. Sci. 79: McNamara, J. P., and J. E. Pettigrew. 2002a. Protein and fat utilization in lactating sows: I. Effects on milk production and body composition J. Anim. Sci. 80:

4 McNamara, J. P., and J. E. Pettigrew. 2002b. Protein and fat utilization in lactating sows: II. Challenging behavior of a model of metabolism J. Anim. Sci. 80: Mullan, B. P., and I. H. Williams The chemical composition of sows during their first lactation. Anim. Prod. 51: NRC Nutrient Requirements of Swine. 10th ed. National Academy Press, Washington, DC. Pettigrew, J. E Amino Acid Nutrition of Gestating and Lactating Sows. Biokyowa Technical Review 5. Chesterfield, MO: Nutri-Quest. Pettigrew, J. E., M. Gill, J. France, and W. H. Close. 1992a. A mathematical integration of energy and amino acid metabolism of lactating sows. J. Anim. Sci. 70: Pettigrew, J. E., M. Gill, J. France, and W. H. Close. 1992b. Evaluation of a mathematical model of lactating sow metabolism. J. Anim. Sci. 70:3762 Sauber, T. E., T. S. Stahly, N. H. Williams, and R. C. Ewan Effect of lean growth genotype and dietary amino acid regimen on the lactational performance of sows. J. Anim. Sci. 76:

5 Table 1. Composition of low protein diets, as fed basis Ingredient, % LP LP+T LP+V LP+T+V Corn Corn starch Granulated sugar Soybean meal, dehulled Soybean oil Limestone Dicalcium phosphate Trace mineral mixture a Vitamin mixture b UI sow pak c L-Lysine D,L-Methionine L-Threonine L-Valine L-Glycine Total Calculated Composition Energy, Mcal ME/kg Calcium, % Phosphorous, available, % Analyzed composition, % Crude protein Lysine Threonine Valine Methionine Cysteine Tryptophan Leucine Isoleucine Histidine Phenylalanine Tyrosine Amino Acid Ratios Threonine:Lysine Valine:Lysine a Supplies per kilogram of complete diet: Fe, 90 mg; Zn, 100 mg; Mn, 20 mg; Cu, 8 mg; I, 350 µg; Se, 300 µg; NaCl, 3 g b Supplies per kilogram of complete diet: retinyl acetate, 2,273 µg; cholecalciferol, 17 µg; dlalpha-tocopheryl acetate, 88 mg; menadione sodium bisulfite complex, 4 mg; niacin, 33 mg; d-ca-pantothenate, 24 mg; riboflavin, 9 mg; vitamin B 12, 35 µg; choline chloride, 324 mg c Supplies per kilogram of complete diet: choline, 300 mg; biotin, 100 µg; folacin, 1 mg 92

6 Table 2. Means of sow (n=12) and litter traits. Item Mean Range Sow parity Initial Sow body weight, kg Litter size Litter weight, kg Final Sow body weight, kg Litter size Litter weight, kg Table 3. The effect of diet on plasma urea nitrogen concentrations in sows. LP LP+T LP+V LP+T+V S.E.M PUN, mg/dl * * Significant diet effect (P <.05) 93