Effects of Dietary Tryptophan Levels on Performance, Blood Metabolites and Nutrient Digestibility in Sows

Abstract

In Korea, the sow reproductivity is relatively lower than that in EU countries and this trend is somewhat likely to affect the national competiveness in international pork industry like FTA. In 2010, PSY of Korea was 21.9, much lower than that of Dutch (PSY

27.2). Several nutritional strategies including feeding scheme, energy level, energy/Lys ratio and amino acids balance in sow diets have been developed to improve sow reproductivity. As one of essential AAs, Trp was metabolized in 3 different pathways, which are protein synthesis for protein deposition, kynurenine synthesis for immune response regulation, and serotonin synthesis for feed intake and stress reducer through the hydroxylase pathway. Consequently, three experiments were conducted 1) to investigate the dietary Trp levels in sows diet on reproductive performance in gestating and lactating sows, 2) to determine the optimal relative Trp level to Lys in gestating and lactating sows, and 3) to evaluate the nutrient digestibility in gestating sows by varying Trp/Lys ratios. In the first study, dietary Trp levels (ai Trp/ai Lys, 18%, 22% and 26%

ai Lys, 0.50%) were fed to gestating sows. From insemination to weaning of sow, there were no significant differences in BW, BF thickness, and their changes by dietary Trp treatments. Furthermore, dietary Trp levels in gestating sows did not affect ADFI, WEI, and litter performance of their progeny after cross-fostering. During gestation, higher Trp level in gestation diet increased Trp level and Trp/ LNAA ratio in blood plasma significantly. Although Trp and Trp/LNAA ratio in diet were higher, there were no significant differences on blood cortisol, melatonin and serotonin. Above 22% Trp/Lys ratio in gestation diet showed the higher feed consumption until d 12 post-parturition. However, there was no positive reproductive performance derived from high feed intake during early lactation. These results indicated that highly supplementation level of Trp (22~26%) over requirement of gestating sows had no additional effects on reproductivity and optimum range of daily ai Trp intake during whole gestation was 1.98 g - 2.16 g (ai Trp/ai Lys, 18%

ai Lys, 0.50%). The second experiment was conducted to evaluate the dietary Trp levels (ai Trp/ai Lys, 18%, 22% and 26%

ai Lys, 0.65%) in lactating sows diet on reproductivity. Among treatments, there were no differences significantly in BW, BF thickness, ADFI, and WEI. At farrowing of sows, dietary Trp levels did not affect number of piglets in total born, still born, mummy and born alive. Above 22% Trp/Lys ratio in lactation diet tended to increase litter weight and litter weight gain. And high Trp level in lactation diet showed significant difference in serotonin concentration at 24 h postpartum. Blood cortisol tended to decrease whereas blood melatonin was numerically increased as dietary Trp level of lactation diet was increased. Piglet weight, weight gain and BUN during lactation were not affected by dietary Trp level. Although blood Trp concentration increased numerically as Trp level increase in lactation feed, there was no linear or quadratic response by the effect of dietary Trp levels in Trp/LNAA. Above 22% Trp/Lys ratio in lactation diet, ADFI tended to increase in middle of lactation (d 8 - 14) numerically. In brief, high level of Trp in lactation diet improved the litter performance with reducing the delivery stress in farrowing sows. However except some criteria, excess supplementation of Trp (>18% ai Trp/ai Lys) had plateau effects to reproductivity of sows. These results indicated that the optimum ratio of ai Trp/ai Lys in lactation feed was 18%, when ai Lys content in lactation feed was 0.65% (as fed basis). The third study was conducted to evaluate the effect of dietary Trp levels (ai Trp/ai Lys, 18%, 22% and 26%

ai Lys, 0.50%) on nutrient digestibility in gestating sows. There were no significant differences in BW, BF thickness, and their changes during digestibility trial. In nutrient digestibility, dietary Trp levels had no effect on digestibility of dry matter, crude protein, fat and ash. Trp digestibility tended to increase linearly as high dietary Trp level and high dietary ai Trp/ai Lys level reduced the digestibility of Ile. Consequently, dietary ai Trp/ai Lys level over 18% increased Trp digestibility while it diminished the Ile digestibility and did not affect nutrient digestibility and nitrogen retention in gestating sows. In summary, dietary Trp level in sows might change Trp metabolism with LNAA metabolism and reproductive performance of sows. Some parameters of reproductivity, such as litter gain of whole lactation and daily feed intake during early-middle lactation, were improved by higher Trp level. However, over 18% ai Trp/ai Lys in sow diet is not recommendable due to the fact that beneficial effects for reproductivity of sows and low coherence with other parameters were not observed. Further studies would be required to demonstrate effects of lower dietary Trp levels than those in current studies for optimal dosage in sows.