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Effects of dietary tryptophan:lysine ratio on the reproductive performance of primiparous and multiparous lactating sows
The objective of this study was to determine the effects of dietary tryptophan (Trp) to lysine (Lys) ratio on the performance of lactating sows. Thirty primiparous and 195 multiparouslactating sows (Landrace × Yorkshire) were allocated on the basis of parity, body weight, and backfat to 5 dietary treatments according to a randomized complete block design with 5 blocks of farrowing date. The 5 experimental diets contained 0.16%, 0.19%, 0.23%, 0.26%, or 0.29% standardized ileal digestible (SID) Trp and SID Lys level was identical (0.87%) for all the diets, with the SID Trp:Lys ratio being 0.18, 0.22, 0.26, 0.30, and 0.33, respectively. Sows received their assigned lactation diets from day 109 of gestation to weaning. Litter size was standardized to 10 to 12 piglets within treatment within 2 days after farrowing. The average lactation length was 18 days and no creep feed was provided. Changes of sow body weight and backfat during lactation, weaning-to-estrus interval, litter size and weight, litter weight gain, preweaning piglet mortality, and performance of subsequent parity (total born alive, stillborns, and mummies) were recorded. Average daily feed intake of the primiparous sows showed a tendency (4.53, 5.63, 5.52, 4.92, and 4.81 kg/d; P < 0.10) to a quadratic dependency on the SID Trp:Lys ratio with the ratio of 0.22 being associated with the highest feed consumption. A quadratic pattern of body weight loss (-15.75, -8.28, -5.48, -16.41, and -15.67 kg; P < 0.05) and backfat loss (-5.6, -4.4, -4.2, -3.9, and -5.1 mm; P < 0.10) with increasing Trp level was observed for the primiparous sows during lactation and the losses were minimized with the SID Trp:Lys ratio of 0.25 according to the broken-line model. Nevertheless, preweaning piglet mortality of the primiparous sows increased linearly and quadratically (P < 0.05) as Trp level increased. On the contrary, piglet mortality of the multiparous sows decreased linearly (11.1, 11.8, 6.8, 10.2, and 7.2%; P < 0.05) with increasing dietary Trp and the mortality was noticeably reduced when the SID Trp:Lys ratio reached 0.26. No differences (P < 0.05) were observed for the remaining parameters. In conclusion, our results indicate that the optimal SID Trp:Lys ratio could be 0.22 to 0.26 for lactating sows.
Keywords: lactation; tryptophan; lysine; sow; reproductive performance