192 The apparent utilization of DL-methionine and the hydroxy-analog of methionine for whole-body nitrogen retention when cysteine is supplemented in the diets of lactating sows.

Abstract Fifty-eight sows [average parity: 1.48±0.50; body weight on lactation d9: 196.9±14.0 kg] were used to determine the apparent utilization of dietary Met sources for N retention during lactation when L-Cys-HCl was supplied to partially meet the estimated sulphur amino acid requirement (NRC, 2012), allowing Met sources to be evaluated independently of Cys limitation. On day 9 of lactation, sows were assigned to 1 of 4 dietary treatments (n=~14): a basal diet formulated at 0.17% standardized ileal digestible (SID) Met supplied via whole-protein sources (70% of estimated SID Met requirements; 0.25% SID Cys, 2,600 kcal/kg net-energy) supplemented with DL-Met to reach [1] 0.20% or [2] 0.23% SID Met (80% DLM and 90% DLM), or supplemented with HMTBa (equimolar) to reach [3] 0.20% or [4] 0.23% SID Met (80% HMTBa and 90% HMTBa). All other indispensable amino acids were supplied at estimated requirements (0.93% SID Lys). Litters were standardized to 13±1 piglets within 48 hours of birth. Sows received the dietary treatments between days 10 and 20 (weaning) of lactation following a standard feeding curve. A N balance was conducted between days 17±1 and 20±1 of lactation with total urine collection and fecal grab-sampling; TiO2 was used as an indigestible marker. A mixed model analysis was used to evaluate main effects of Met source (DL-Met or HMTBa) and level (80% or 90%). Neither dietary Met source or level influenced sow average daily feed intake, body weight or backfat depth change between days 10 and 20 of lactation. Though, piglet growth performance improved with the higher dietary SID Met level (P<0.05) for both sources. Milk dry matter and crude protein content on day 20 of lactation were not influenced by dietary Met source or level but crude fat tended to be higher in DL-Met than HMTBa fed sows (P=0.072). During the N balance, neither sow N intake or retention (N intake – N output in urine and feces) were influenced by dietary Met source or level. Milk N output increased with the higher dietary SID Met level (P<0.05) for both sources. Maternal N retention (N intake – N output in urine, feces, and milk) was not influenced by dietary Met source or level. Therefore, SID Met level but not source influenced N partitioning for milk output in lactation when L-Cys-HCl was included in the diet.