THE INFLUENCE OF FEEDING LEVEL DURING LACTATION ON THE OCCURRENCE AND ENDOCRINOLOGY OF THE POSTWEANING ESTRUS IN SOWS

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Abstract
Two experiments were performed with 78 second parity Lacombe sows to determine the influence of nutrition on reproductive performance. During a lactation of 35 d sows were fed daily either 3 (L) or 6 kg (H) of a diet having 16% crude protein and 12.5 MJ DE kg−1. For exp. 1, six L- and six H-fed sows were given an intravenous injection of gonadotropin releasing hormone (GnRH) at 21 d of lactation and blood was sampled at −30, −10, 0, 10, 20, 30, 45, 90 and 120 min from the time of injection. Prestimulation luteinizing hormone (LH) levels were lower for L-fed than for the H-fed sows (1.34 ± 0.1 vs. 1.93 ± 0.2 ng mL−1' P < 0.02). Peak LH levels achieved after UnKH injection, however, did not differ significantly (5.0 ± 0.6 and 5.8 ± 0.5 ng mL−1 for L and H sows, respectively). In exp. 2, 38 sows were fed the H and 40 fed the L level of feed throughout a 5-wk lactation. As expected, low-level feeding in lactation resulted in a greater body weight and backfat loss (17.4 ± 1.6 vs 41.2 ± 2.3 kg and 3.2 ± 0.4 vs. 6.3 ± 0.1 mm; P < 0.001 for both). Low-level feeding also resulted in an increased incidence of anestrus (15.0 vs. 0.0%) and an extended remating interval (140.7 ± 11.7 vs. 103.4 ± 2.1 h; P < 0.05). At the postweaning estrus, sows were inseminated with either fresh (F) or thawed (T) semen. Treatment groups were thus HF, LF and LT. Pregnancy rate was influenced by both feed level and semen type (90, 72, 69 and 39% for groups HF, HT, LF and LT, respectively). Ovulation rate was unaffected by feed intake (18.7 ± 0.9 vs. 18.2 ± 0.5 for L and H sows, respectively) but embryo survival was influenced by both feed intake and semen type (82.7 ± 2.5, 46.4 ± 9.7, 68.3 ± 9.6 and 53.7 ± 9.8% for groups HF, HT, LF and LT respectively). Eight H and twelve L-fed sows were blood-sampled via indwelling vena caval cannulae at 6-h intervals from weaning until the end of estrus. No treatment effect was noted for plasma levels of LH, growth hormone, estradiol-17β or testosterone during this period. It was concluded that low-plane feeding in lactation and the consequent increased weight and backfat loss reduce reproductive performance of sows. However, the mechanism(s) controlling this effect remain to be fully elucidated. Key words: Sow, lactation, nutrition, estrus