Effect of Low Protein Levels with L-Valine Supplemented in Weaning Diet on Growth Performance, Fecal Score, Blood Profiles, Nutrients Digestibility, Carcass Characteristics and Economic Analysis in Weaning to Finishing Pigs

Abstract

Supplying adequate nutrients to livestock not only can lower production costs, but also reduce the economic losses and environmental burdens caused by excess nutrients. The Korea government has enacted laws to regulate environmental pollution resulted by livestock manure. In this context, NRC (2012) revised and adjusted the protein requirement to a lower level compared to previous NRC requirement (1998). However, there is a lack of verification that it can be applied to the domestic swine industry. So the process of verifying whether changes in the protein requirements suggested by the NRC (2012) is indeed appropriate for domestic situation is needed. Therefore, this study was conducted to evaluate optimal crude protein levels with L-valine supplementation in weaning pig diet considering subsequent growth performance, fecal score, blood profiles, nutrient digestibility, carcass characteristics and economic analysis from weaning to finishing pigs. A total of 160 weaning pigs ([Yorkshire×Landrace]×Duroc), with an average body weight of 7.86±1.05kg, were used for 22 weeks feeding trial. Pigs were allotted into one of five treatments by body weight and sex in 4 replicates with 8 pigs per pen in a randomized complete block (RCB) design. The treatments were included 1) Corn-SBM based diet with L-valine supplementation + protein content suggested by NRC (1998) (HP), 2) Basal diet + protein content suggested by NRC (1998) - 1% (MHP), 3) Basal diet + protein content suggested by NRC (1998) - 1.5%, 4) Basal diet + protein content suggested by NRC (2012) and 5) Corn-SBM based diet without L-valine supplementation + protein content suggested by NRC (2012). In feeding trial, reducing crude protein (CP) level showed negative effect on body weight (BW) and average daily gain (ADG) during early growing phase (P<0.01). However, there was no significant impact of reducing CP level on BW and ADG at the end of experiment. Also, average daily feed intake (ADFI) decreased as dietary CP level decreased in 7-10 week (linear, P<0.05). On the other hand, L-valine supplementation in weaning diet increased BW in 22 week, ADG in 7-14 week and ADFI 11-14 week (P<0.01, P<0.01 and P<0.05, respectively). There was no significant difference in fecal score, but fecal consistency tended to decrease as dietary CP level decreased (linear, P<0.10). Likewise L-valine supplementation in weaning diet had no significant effect on fecal score. In blood analysis, there was a positive effect of reducing CP level and L-valine supplementation in weaning diet on BUN concentration in both weaning and growing-finishing period (P<0.01

linear, P<0.05). Nutrient digestibility and nitrogen balance was not affected by dietary treatments. In carcass characteristics, pH and water holding capacity (WHC) were decreased linearly as dietary CP level decreased (linear, P<0.05). However, crude fat, Hunter L* and b* value showed linear response as dietary CP level decreased (linear, P<0.05). The fatty acid composition of longissimus muscle was changed by feeding CP diet leading to increased MUFA concentration (linear, P<0.05). When pigs were fed low CP diet, feed cost per weight gain, total feed cost and days to market weight were diminished compared to higher CP treatment groups (P<0.05). Moreover, L-valine supplementation resulted in improving days to market weight. Consequently, lowering dietary CP level did not show any detrimental impact on growth performance and increase amino acids availability, crude fat content and MUFA concentration in muscle. Moreover, decreased dietary CP level reduce BUN concentration, feed cost per weight gain, total feed cost, pH and WHC in muscle. On the other hand, supplementation of L-valine in weaning diet resulted in improved growth performance, BUN concentration and numerically decreased days to market weight during growing and finishing period. Although much lower CP level diet was provided during weaning period compared to NRC (1998), there was no detrimental effect on the whole growth performance of pigs. When pigs were fed lowered dietary CP treatment diet, it is desirable to consider supplementing L-valine in weaning pigs diet.