Amino acid nutrition and ideal protein for reproductive sows
The purpose of raising sows is to produce healthy weaning pigs. Sows should be maintained in healthy, strong, and good condition. High-prolific lean type sows have large litter size and high milk production, but low appetite during lactation, and therefore, high culling rate. Providing accurate amounts and profiles of amino acids to gestating and lactating sows will allow more efficient sow production and reduce feed cost and N excretion. Currently, there are some problems in sow nutrition: 1) current available amino acid requirements for gestating sows were adapted from growing pig data; 2) dietary amino acid ratios for the efficient protein utilization are not known for sows; and 3) current amino acid requirements may not provide accurate estimations for gestating and lactating sows. The current feeding system for gestating sows (one drop, single diet) is not sufficiently flexible to adjust the nutrient allowance according to the nutritional status of sows. Therefore, the amino acid requirements and ideal dietary amino acid ratios for gestating and lactating sows need to be better characterized. This dissertation covers the areas of: 1) changes of body weight, backfat thickness, and chemical contents in various maternal and fetal tissues in pregnant gilts and estimation of protein needs in different gestation stages of gilts; 2) growth of mammary glands of gilts during gestation; 3) estimation of ideal protein for pregnant gilts; 4) validation of ideal protein for pregnant gilts; and 5) validation of ideal protein for lactating sows. In the first study, 35 gilts were randomly allotted to seven slaughter groups: d 0, 45, 60, 75, 90, 102, and 112 of gestation. Gilts were bred and fed 2 kg/d gestation diet (as fed basis) during gestation. The gestation diet contained 3.1 Mcal/kg ME and 0.56% lysine (as fed basis). Maternal tissues and organs and fetuses were separated and weighed. Compositions of maternal and fetal tissues were analyzed. The protein accretion rates in various tissues increased (P < 0.05) after d 70 of gestation. Considering the needs of maintenance and maternal and fetal gains, we suggest that the diet of pregnant gilts should provide 6.8 and 15.3 g/d true ileal digestible lysine, respectively, before and after d 70 of gestation. Feeding gestating gilts based on a two-phase feeding program reflects the real protein needs for tissue protein accretion that may improve protein utilization. In the second study, individual mammary glands were separated and weighed. The first two pairs of glands were pooled as "anterior." The 3rd, 4th, and 5th pairs of glands were pooled as "middle." The 6th, 7th, and 8th pairs of glands were pooled as "posterior." The CP content in middle accreted faster than that in anterior and posterior. At d 112 of gestation, the CP content in individual mammary glands in middle was heavier (P < 0.05) than that in anterior and posterior. This result was different from the generally recognized concept that anterior mammary glands are larger and produce more milk than middle and posterior mammary glands. In the third study, based on changes of CP in various maternal and fetal tissues during gestation, ideal amino acid ratios for protein accretion and protein accretion plus maintenance for pregnant gilts were estimated. Amino acid needs of pregnant gilts for maintenance and amino acid accretion rates in maternal and fetal tissues changed during gestation; therefore, lysine-based amino acid ratios also changed. The ideal amino acid ratios were different in the early and late gestation. In the fourth study, thirty-four pregnant gilts at d 30 of gestation were used in two experiments. In Exp. 1, 14 pregnant gilts were randomly allotted to a control group (Cl, seven gilts) and an ideal protein group (IPl, seven gilts). In Exp. 2, 20 pregnant gilts were randomly allotted to a control group (C2, ten gilts) and an ideal protein group (IP2, ten gilts). Pregnant gilts had two meals of gestation diet (2.0 kg/d, as fed). The IPl was formulated to provide an ideal dietary amino acid ratio for maternal and fetal tissue gains, whereas the IP2 diet for both tissue gains and maternal maintenance. In Exp. 1, performance of gestation and subsequent lactation did not differ between the IPl and Cl. In Exp. 2, body weight gain of the IP2 was higher (P < 0.01) than that of the C2 fi'om d 30 to 109 of gestation. Serum urea level of the IP2 was lower (P < 0.05) than that of the C2 at d 90 and 109 of gestation. Litter mortality of the IP2 was lower (P < 0.05) than that of the C2 during lactation. Performance of the IPl was not improved, suggesting that the ideal amino acid ratios for protein accretion were not balanced for pregnant gilts. The IP2 had higher body weight gain (P < 0.01) from d 30 to 109 of gestation and lower serum urea level at d 109 of gestation (P < 0.05), suggesting that ideal amino acid ratios in the IP2 decreased the oxidation of amino acids and increased maternal protein accretion. In the fifth study, 51 sows were grouped according to their body weight at farrowing and parities. Within each group, sows were randomly allotted to four dietary treatments: 1) low-protein control (17.5% CP; LPC); 2) low protein with ideal protein (LPI); 3) high-protein control (19.5% CP; HPC); and 4) high protein with ideal protein (HPI). Ideal protein for lactating sows was obtained from the TTU-Sow Model (Kim et al., 2002). Feed intake and body weight loss of sows did not differ among four dietary treatments. Sows fed ideal protein had increased (P < 0.05) litter weight gain overall three parity at the low-protein diets. Sows fed ideal protein had decreased (P < 0.01) serum urea concentration at the high protein level. Sows fed ideal protein had increased (P < 0.05) litter weight gain of the first parity sows at the low-protein level. Sows fed ideal protein improved litter weight gain in the low-protein diet during lactation, indicating that consideration of ideal dietary amino acid ratio in lactation diet may enhance milk production. The benefits may be maximal for the first-parity sows because they have lower voluntary feed intakes and limited body tissue reserves. Current available estimation of amino acid needs of gestating and lactating sows for maintenance was based on the data of non-pregnant gilts. Whether pregnancy and lactation affect amino acid needs of gestating and lactating sows for maintenance is unknown. Further research is needed in these areas of nutritional physiology. In addition, we assumed that the metabolic rates of various amino acids in the small intestinal mucosa were similar between nonpregnant and pregnant pigs or between d 1 and d 21 of lactation, but some studies form other species suggested that the rates of amino acid synthesis and/or catabolism in enterocytes may vary with physiological status.