Effects of the Standardized Ileal Digestible Methionine : Lysine Ratio on Milk Performance, Litter Growth and Plasma Indices of Lactating Sows

The objective of the study was to determine the effects of the dietary methionine (Met) to lysine ratio (Met:Lys) for lactating sows suckling more than 11 piglets on milk production, litter growth and plasma indices. 120 Large White sows (parity 1 to 4) were randomly allotted to 4 dietary treatments with 30 sows per treatment based on parity, back fat thickness and body weight from farrowing day. Litters were standardized to 12 piglets. The sows were fed corn-soybean meal based diets containing 0.27, 0.37, 0.47 or 0.57 SID Met:Lys from day of farrowing until day 21 of lactation. On all 120 sows, BW and back fat thickness (BF) were registered at day 110 of gestation and day 7 and 21 (weaning) postpartum. Piglets weight, ADG and litter weight were determined weekly during a 21 days experimental period. Blood samples were taken from sows at day of farrowing, day 7 and 21 for the measurement of the homocysteine (Hcy) and thiobarbituric acid reaction substances (TBARS) level and glutathione peroxidase (GSH-Px) activity. Milk yield, and the DM, lactose, protein and fat concentrations of milk, were similarly not affected by dietary treatments. The ADG increased quadratically during first week and third week (P < 0.001) with increasing SID Met:Lys level. The TBARS level was increased as SID Met: Lys elevated from 0.27 to 0.57 at day 7 of lactation (P < 0.05) and weaning day (P = 0.06). Moreover, at day 7 of lactation, GSH-Px showed the higher activity in SID Met: Lys 0.37 and 0.47 group compared to other groups (P < 0.01). Methionine metabolites Hcy and taurine both increased linearly (P < 0.01) as SID Met: Lys increased. These results showed that lactation diet with 0.37-0.47 SID Met: Lys is optimal to achieve the better litter growth. However, along with the increased level of dietary methionine during lactation, gradually increased plasma Hcy and TBARS indicated that the high SID met to lys ratio greater than 0.47 might increase the risk of oxidative stress, regardless of the increased GSH-Px activity.