The effects of the in utero environment on gilt performance

Traditionally, the pork industry has focused most of its attention on the management of replacement gilts in the post-selection (16–21 weeks) phase. However, in many species it is now understood that the prenatal environment of an animal plays an equally important role as the pre-pubertal environment. In dairy cows, the age of the dam at first calving, the dam’s milk yield and body condition score during gestation accounted for a significant proportion of the total phenotypic variance of calving interval and non-return rate of the daughter cows (Banos et al. 2007). There is growing evidence to suggest more research is needed on the long-term effects of the maternal environment. The aim of this study was to determine the efficacy of easily identifiable, early predictors of a gilt’s lifetime reproductive performance. We hypothesised that the proportion of female to male fetuses would significantly affect the in utero environment in which a gilt develops, thereby affecting ovarian development and overall performance.

This study used 166 Large White × Landrace gilts, which were identified and weighed at birth, weaning, week 18 and week 21. Reproductive tracts were collected post slaughter at 21 weeks of age and antral follicles on both ovaries were counted and classified as either small (1–3.99 mm) or large (>4 mm). An analysis of variance (ANOVA), unbalanced design (Genstat 15, VSN International, Hemel Hempstead, UK) was used to determine the effect of proportion of females in the gestated litter (low, <40%; normal, 41–59%; high, >60%) on surface antral follicle counts, birthweight and growth rates.

The ovaries of gilts from female-biased litters contained a higher total number of surface antral follicles (P < 0.05) (Table 1) than those of gilts from litters with low proportions of females. The total small follicle counts were higher (P < 0.05) in gilts from female-biased litters. Large antral follicle counts did not differ between females from male-biased, normal or female-biased litters. Female birthweight was reduced in female-biased litters in comparison to litters with low proportions of females (1.16 ± 0.02 kg v. 2.09 ± 0.02 kg; P < 0.05). Female piglets born into litters with low proportions of females showed an increased average daily weight gain to weaning (P < 0.05) and remained significantly heavier until slaughter (P < 0.05).

Table 1.  Piglet d 1 weight, average daily gains from birth to weaning, number of small (1–3.99 mm) and large (>4 mm) antral follicles present on the ovaries of 21-week-old gilts from gestational litters with low (<40%), normal (41–59%) and high (60%) proportions of females

The results of this study support the hypothesis that the in utero environment in which a gilt develops significantly affects the birthweight, and subsequent growth performance of an individual animal. Sexual maturity appears to be occurring independently of the in utero sex ratios, as there was no significant difference observed in large antral follicle numbers. However, the significantly higher number of small antral follicles observed in gilts from female-biased litters, indicates that these animals may have a higher ovarian reserve in comparison to gilts from normally distributed or male-biased litters.