Reproductive, metabolic, and endocrine responses to feed restriction and GnRH treatment in primiparous, lactating sows.

Abstract

The current experiment was carried out to determine whether exogenous GnRH treatment in primiparous, lactating sows undergoing feed restriction would improve reproductive performance after weaning. Sows were allocated to one of three treatments: AA sows (n = 8) were fed to appetite throughout a 28-d lactation, AR (n = 12) and AR + GnRH (n = 12) sows were fed as AA sows from farrowing to d 21 of lactation, and feed intake was reduced to 50% of the ad libitum intakes from d 22 to 28. The AR + GnRH sows received 800 ng of GnRH i.v. every 6 h from d 22 to 28 of lactation, and AA and AR sows received saline. Sow weight, backfat, and litter weight were recorded weekly. Within 2 d after farrowing, litter size was standardized to 8 to 10. At d 17 of lactation, an indwelling jugular catheter was surgically implanted in each sow. Blood samples were taken for characterization of plasma LH, FSH, insulin, IGF-I, and leptin by RIA at d 21 and before and after weaning on d 28 of lactation. After weaning, all sows were given ad libitum access to feed, checked for onset of standing estrus twice daily with mature vasectomized boars, and inseminated 12 and 24 h after onset of standing estrus with pooled semen from the same fertile boars (3 x 10(9) sperm/AI). After breeding, feed allowance was reduced to NRC (1988) requirements for gestation. At d 28 +/- 3 of gestation, sows were killed and ovulation rate and embryo survival were determined. Restricted sows lost more weight during lactation than AA sows (P < .02). During the period of feed restriction, plasma IGF-I and postprandial insulin and leptin in AR and AR + GnRH sows, and LH pulse frequency in AR sows, were lower than those in AA sows (P < .04). Associations (P < .004) between plasma insulin and leptin and between leptin and mean LH concentrations were established. The LH pulse frequency in AR + GnRH sows did not differ from that in AA sows before weaning. After weaning, maximum, mean, and minimum LH concentrations in the AA and AR sows, and FSH concentrations in AR sows, increased (P < .05) in response to weaning. Paradoxically, GnRH treatment in lactation seemed to suppress the expected LH and FSH responses to weaning. Ovulation rate and embryo survival were not different among the three groups. In conclusion, although exogenous GnRH therapy restored LH secretion in feed-restricted sows, it did not improve overall reproductive performance.

Influence of feed intake during pregnancy and lactation on fat body reserve mobilisation, plasma leptin and reproductive function of primiparous lactating sows

“…In contrast to Mao et al [23] we did not show any effect of feed intake (M-AL vs. M-RE sows) on leptin concentrations measured after feeding. This discrepancy is probably due to a smaller difference in feed intake between experimental groups in our study.…”

“…Circulating concentrations of leptin were similar to those previously described in lactating sows [9,23]. In contrast to Mao et al [23] we did not show any effect of feed intake (M-AL vs. M-RE sows) on leptin concentrations measured after feeding.…”

“…However, contrary to Estienne et al [9], a high correlation was also maintained at day 25 of lactation in our sows. It should be noted that postprandial leptin may increase with feed intake [21,23]. Therefore, body fat reserves may have a negative influence on concentrations of plasma leptin through inhibition of appetite.…”

GH and IGF-I binding sites in adipose tissue, liver, skeletal muscle and ovaries of feed-restricted gilts

“…No significant differences (P > 0.1) between the two groups were observed for skeletal muscle and subcutaneous adipose tissue. has also been described by Mao et al [18]. The finding of a lower plasma IGF-I concentration in feed-restricted gilts is consistent with the response to feed deprivation or restriction previously reported in young growing pigs [5,8,9], prepubertal and mature gilts [1,6] and lactating sows [18,27].…”

“…has also been described by Mao et al [18]. The finding of a lower plasma IGF-I concentration in feed-restricted gilts is consistent with the response to feed deprivation or restriction previously reported in young growing pigs [5,8,9], prepubertal and mature gilts [1,6] and lactating sows [18,27]. Because the liver is considered as one of the major sites of IGF-I production, it has often been indicated that the low concentration of IGF-I results from a decrease in GH binding.…”