Pattern of feed intake and associated metabolic and endocrine changes differentially affect postweaning fertility in primiparous lactating sows

Effects of differential patterns of feed intake during lactation, associated metabolic and endocrine changes, and reproductive status after weaning were investigated in 26 primiparous sows suckled by six piglets. Sows were fed to appetite (Group AA; n = 9) from d 1 to 28 of lactation or restricted to 50% from d 22 to 28 (Group AR; n = 9) or from d 1 to 21 (Group RA; n = 8). Sow weight, backfat, and litter weights were recorded weekly. After weaning sows were tested twice daily for onset of estrus and inseminated twice using pooled semen. At d 28 of gestation sows were slaughtered and reproductive tracts were recovered to determine ovulation rate and embryo number. Intensive blood sampling was carried out for 12-h periods on d 21 and before and after weaning on d 28 to characterize changes in plasma LH, FSH, insulin, and IGF-I by RIA. Litter growth rates did not differ among groups. Feed-restricted sows lost more (P < .01) body weight and backfat than those fed to appetite. During periods of feed restriction in AR and RA sows, postprandial insulin, mean IGF-I, and LH pulse frequency were less than in AA sows fed to appetite. All sows exhibited an increase (P < .001) in LH pulsatility in response to weaning. After weaning, no differences were observed in insulin, LH, or FSH, although IGF-I was still lower (P < .05) in AR sows. Weaning-to-estrus interval increased in AR and RA sows and ovulation rate was lower (P < .05) than in Al sows. Embryo survival did not differ between RA and AA sows but was lower (P < .01) in AR sows. These results demonstrate that the pattern of metabolic change in the primiparous lactating sow exerts differential effects on fertility after weaning.