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During their second lactation, 123 second-parity Yorkshire × Landrace sows were fed either 6 kg or 3 kg d −1 of a barley-soybean meal diet formulated to provide 12.5 MJ DE kg −1 and 16% crude protein (approximately 90 and 45% of National Research Council (NRC 1988) requirements). From 48 h after the onset of the post-weaning estrus, sows from each lactation feed treatment were allocated equally to receive the same diet at 3.6 kg or 1.8 kg d −1 (approximately 160 and 80% of NRC (1988) requirements), until slaughtered at 25 d of gestation. On days 4, 8, 12 and 16 of gestation, eight sows from each of the four feed level combinations were blood sampled at 15-min intervals for 4 h. Additionally, a further eight sows were sampled once on each of the above days. The lower plane of feeding during lactation resulted in a greater body weight and backfat loss (26.6 vs. 13.8 kg and 6.5 vs. 3.6 mm, respectively; P < 0.01 for both), an increased incidence of anestrus (21 vs. 8%; P < 0.05) and a longer and more variable interval to estrus (8.9 ± 0.4 vs. 6.0 ± 0.2 d; P < 0.01) than higher level feeding. There was no effect of lactation feeding level on ovulation rate (17.6 ± 0.3 vs. 17.7 ± 0.4 for sows having the higher and lower feed intakes, respectively). There was a main effect of lactation (P < 0.01), but not gestation, feeding level and an interaction between lactation and gestation feeding level (P < 0.02), on number of embryos and percent embryo survival. Embryo numbers and survival were reduced following lower plane feeding during lactation but were lowest following lower plane feeding during both lactation and gestation. There was no effect of sampling day on plasma LH concentrations but plasma LH was lower (P < 0.01) in sows on lower plane feeding during both lactation and gestation. The present data confirm an adverse effect of low plane feeding during lactation on subsequent sow reproductive performance and suggest that a reduction in plasma LH concentrations may be involved. These data fail to confirm any adverse effect on embryo survival of high plane feeding during the first 25 d of gestation. Key words: Sow, feed intake, LH, progesterone, reproduction
Kirkwood et al. (Sat,) studied this question.