Effects of a near ideal amino acid balance diet on lysine mammary utilization, whole body protein turnover and muscle protein breakdown on lactating sows

Abstract Background The study objective was to test the hypothesis that low crude protein (CP) diet with crystalline amino acids (CAA) supplementation to meet a near ideal AA (NIAA) profile improves Lys utilization efficiency for milk and reduces protein turnover and muscle protein breakdown. Eighteen lactating multiparous Yorkshire sows were allotted to 1 of 2 isocaloric diets (10.80 MJ/kg net energy): control (CON; 19.24% CP) and reduced CP with a NIAA or “optimal” AA profile (OPT; 14.00% CP). Sow body weight and backfat were recorded on day 1 and 21 of lactation and piglets were weighed on days 1, 14, 18, and 21 of lactation. Between days 14 and 18, a subset of 9 sows (CON = 4, OPT = 5) was infused with a mixed solution of 3-[methyl-2H3] histidine (bolus injection) and [13C] bicarbonate (priming dose) 1 hour prior to a constant 2-hour [13C] bicarbonate infusion followed by a 6-hour primed constant [1-13C] lysine infusion. Serial blood and milk sampling were performed to determine plasma and milk Lys enrichment, Lys oxidation rate, whole body protein turnover, and muscle protein breakdown.Results Over the 21-day lactation period, compared to CON, sows fed OPT had greater litter growth rate (P < 0.05). Compared to CON, sows fed OPT had greater Lys mammary utilization efficiency (P < 0.05), Lys mammary flux (P < 0.01) and whole-body protein turnover efficiency (P < 0.05). Compared to CON, sows fed OPT tended to have lower whole body protein breakdown rate (P = 0.069). Muscle protein breakdown rate did not differ between OPT and CON (P = 0.197).Conclusion Feeding a diet formulated to meet a NIAA balance (i.e., OPT diet) increased Lys mammary utilization efficiency and reduced whole-body protein turnover and protein breakdown. Sows fed a OPT diet had greater protein turnover efficiency indicating greater AA utilization efficiency.