Evaluation of standardized ileal digestible threonine to lysine ratio and tryptophan to lysine ratio in weaned pigs fed antibiotic-free diets and subjected to immune challenge
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Date
2019-12-19
Authors
Jayaraman, Balachandar
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Abstract
In animals, dietary amino acids (AA) are primarily important for maintenance and protein accretion. However, under immune challenge conditions, AA metabolism was altered, resulting in AA being redistributed away from growth and production functions to immune functions. Moreover, the AA requirements for weaned piglets might be higher with antibiotic growth promoter (AGP)-free starter diets than the NRC requirements for piglets, particularly if they are exposed to immune challenge conditions. Therefore, this project aimed at determining the optimal standardized ileal digestible threonine:lysine ratio (SID Thr:Lys) and tryptophan:lysine ratio (SID Trp:Lys) in weaned piglets fed AGP-free diets and subjected to immune challenge conditions (sanitation and enterotoxigenic Escherichia coli K88 (ETEC K88) models). The objective of study one was to determine the optimal SID Thr:Lys of weaned piglets fed AGP-free diets and reared under clean (CL) or unclean (UCL) conditions using growth as response criteria. An estimated SID Thr:Lys of 65% and 67% optimized feed efficiency for weaned pigs under CL and UCL conditions, respectively. The second study determined the optimal SID Trp:Lys in weaned piglets reared under CL or UCL conditions. Under CL conditions, the estimated optimal SID Trp:Lys for ADG was 19.7%, whereas under UCL conditions, these values were 20.5% and 19.0% for ADG and G:F, respectively. The third study was conducted to determine the optimal SID Trp:Lys and immune responses in weaned piglets fed AGP-free diets and challenged with ETEC K88. The optimal SID Trp:Lys determined using the linear-broken-line regression analysis for ADG and G:F was 21.7% and 20.1%, respectively. The objectives of the final experiment were to determine the optimal SID Thr:Lys and evaluate the effects of SID Thr:Lys on mucin gene expression and immune responses in weaned piglets challenged with ETEC K88. Based on ileal histomorphology as response criteria, the estimated optimal SID Thr:Lys was 65.6% in weaned piglets challenged with ETEC K88. In conclusion, weaned piglets raised under sub-optimal health conditions (E. coli K88) and fed AGP-free diets need greater dietary Thr:Lys and Trp:Lys requirements than reported by NRC (2012). Ensuring enough AA in AGP-free starter diets would support in maintaining good performance under sub-optimal health conditions.
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Keywords
Threonine to lysine ratio, Tryptophan to lysine ratio, Weaned piglets