Abstract
AbstractOne gilt from each of 24 littermate trios was assigned at birth to one of three treatments which were to adjust litter size to six, nine or 12 piglets. Plasma luteinizing hormone (LH) and follicle-stimulating hormone (FSH) were measured before and after stimulation with 1 ng gonadotrophin-releasing hormone (GnRH) per kg body weight at 55 and 140 days of age. At 150 days, oestrogen was administered and ovarian and uterine responses were measured at slaughter on day 160.Litter size significantly modified pre-weaning growth rate (P < 0·01) but did not influence gonadotrophin secretion or sexual maturity at slaughter. The family of origin significantly influenced ovarian and uterine development (P < 0·05) and the LH and FSH responses to GnRH at 55 days (P < 0·05). Family size (P < 0·01) and sex ratio of the litter at birth (P < 0·05) also influenced the ovarian response to oestrogen treatment. Significant sire effects on ovarian and uterine development were established (P < 0·05); for the progeny of individual boars significant differences in the response to oestrogen were associated with significant differences in growth rate (P < 0·001).Variations in family birth and litter weaning weights were negatively correlated with ovarian and uterine development (P < 0·05), whereas all measures of growth from weaning to slaughter were significantly and positively correlated with sexual maturity at slaughter (P < 0·05).Basal FSH and the responses of both LH and FSH to GnRH at 55 days were correlated with growth rate at day 55 (P < 0·05). Basal LH and FSH at day 140 were correlated with ovarian and uterine development at day 160 (P < 0·05).
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