Dietary energy source at two feeding levels during lactation of primiparous sows: I. Effects on glucose, insulin, and luteinizing hormone and on follicle development, weaning-to-estrus interval, and ovulation rate

Our objective was to study the effects of dietary-induced insulin enhanceme nt during and after lactation on the reproductive performance of primiparou s sows. During a 21-d lactation period, 48 sows were allotted to a 2 x 2 fa ctorial experiment. Treatments were feeding level (high or low; 44 MJ or 33 MJ NE/d) and dietary energy source (fat or starch). After weaning, all sow s received the same amount of feed (31 MJ NE/d from weaning to estrus and 1 7.5 MJ NE/d from breeding until slaughter) of the same energy source as fed during lactation. On d 7, 14, and 21 of lactation and d 22 (weaning), bloo d samples were taken every 12 min for 12 h and analyzed for plasma glucose, insulin, and LH. Sows were slaughtered on d 35 of the subsequent pregnancy , and ovulation rate was assessed. During lactation, postprandial plasma gl ucose and insulin concentrations were higher for sows fed the starch diet t han for those fed the fat diet (P < .001), whereas feeding level had no eff ect. Basal and mean LH concentrations were not affected by treatments. The LH pulse frequency on d 7 of lactation was greater for sows fed the starch diet than for those fed the fat diet (.52 vs .17 pulses/12 h; P = .03). The high compared with the low feeding level resulted in a greater LW pulse fr equency on d 21 of lactation (.89 vs .47 pulses/12 h; P = .05) and on d 22 (8.63 vs 5.77 pulses/12 h; P = .02), in a higher percentage of sows that ex hibited estrus within 10 d after weaning (96 vs 63%; P = .01), and a tenden cy for a higher ovulation rate (18.0 vs 16.2; P = .09). Plasma glucose and insulin concentrations were not related to any of the LH traits. The LH pul se frequency after weaning was related to the weaning-to-estrus interval (W EI) and was best explained by a linear-plateau model. In sows fed the low f eeding level, follicle size after weaning was correlated with LH pulse freq uency after weaning and with the WEI, whereas in sows fed the high feeding level these correlations were not significant. Our results indicate that an improved dietary-induced insulin status during and after lactation does no t overcome the inhibitory effects of lactation on subsequent reproduction a t any of the feeding levels.