Assessment of standardized ileal digestible lysine and sulfur amino acids to lysine ratio for weaned piglets fed antibiotic-free diets
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Amino acids (AA) are required for protein accretion and the need for a specific AA depends on the physiological status, breed, and the health of the pig. Inasmuch as the AA requirements for growing pigs are given in an ideal AA ratio for protein accretion, the utilization of all AA is beyond growth and at least 30% of the total dietary AA will be used by the splanchnic tissue. A ban in the use of antimicrobial growth promoters (AGP) in piglets’ diets is likely to increase incidences of disease occurrence and exert additional AA requirements. Immune challenge models were used to determine standardized ileal digestible (SID) Lys and sulfur amino acids (SAA):Lys requirements for piglets under an antibiotic-free feeding regime. The first objective was to establish the dietary Lys requirement for piglets raised under both clean and unclean sanitary conditions. The Lys requirement could not be determined in the first experiment. However, from the second and third experiments the dietary SID Lys content for optimal growth of 7 to 16 kg weaned piglets was estimated to be 1.32%. The objective of fourth experiment was to determine the optimum SID SAA:Lys ratio in piglets when reared under clean or unclean conditions. Based on performance parameters, the optimum SAA:Lys ratios were 58 and 61 for piglets raised under clean and unclean conditions, respectively. However, VH estimates were 60 and 66 SAA:Lys under clean and unclean sanitary conditions, respectively. The objective for the fifth experiment was to determine SID SAA:Lys ratio of piglets under an enterotoxigenic Escherichia coli challenge using genes for expression of key products in the Met metabolic pathway. Gene expressions of methionine adenosyltransferase 1 and 2-α, 5-methyltetrahydrofolate-homocysteine methyltransferase, and cystathionine γ-lyase was done for liver and ileal tissue. The gene expressions indicates that the dietary SAA:Lys ratio of 60 was enough to support piglet’s immune response and performance during an immune challenge. Therefore, under an antibiotic-free feeding regime, the Lys requirement recommended by NRC (2012) is sufficient, however, the SAA:Lys should be raised to 60 in diets of both healthy and immune challenged piglets.