Prenatal and neonatal gilt management and anti-Müllerian hormone: effects on the ovary and response to the boar

Sub-optimal sow reproductive performance constrains breeding herd efficiency and causes premature sow culling. In cattle, the capacity of ovaries to respond to gonadotrophins and produce high quality embryos is determined in the neonatal period and is positively related to circulating concentrations of anti-müllerian hormone (AMH) (Ireland et al. 2011). Further, more gilts reared in small compared to large litters survived to parity six (Flowers 2012). The current study had two objectives: first, to determine the effect of prenatal and neonatal environment on ovarian development and response to boar stimulation, and second, to determine relationships between plasma AMH and ovarian characteristics, and response to boar stimulation.

A total of 101 gilts (Camborough 29 × PIC 400) was selected from small or large birth litters. At 12–24 h after birth, male pigs were cross-fostered into small litters to achieve suckled litter sizes of 9 or 12 piglets creating a 2 × 2 factorial arrangement of treatments with main effects being gestated litter size (≤9 vs ≥12 piglets; Small and Large, respectively) and suckled litter size (9, Small vs 12, Large). A plasma sample was collected at weaning (20 ± 0.1 days; mean ± SEM) and at 20 weeks of age, and assayed for concentrations of AMH using a pig AMH ELISA kit (CUSABIO Biotech, China). From 20 weeks of age, gilts received daily exposure to a mature boar for 14 days. Thereafter, gilts were marketed at 102 ± 0.5 kg and 169 ± 1.5 d of age, and ovaries recovered. The number of corpora lutea (CL) and surface antral follicles <1 mm were recorded for a subset of gilts (Table 1). Puberty attainment was defined as the presence of CL. Gilts were allocated to a high or a low weaning or 20 week AMH group with the cut off being the median value for the population. Treatment and AMH group effects were analysed using ANOVA (Genstat, 15th Edition; UK). Differences between proportions were analysed by Chi-square.

Table 1.  Interaction effects of gestated litter size (Small or Large) and suckled litter size (Small or Large) on ovarian characteristics at 169 d of age, puberty attainment and plasma AMH levels at weaning and 20 weeks of age. Values are mean ± SEM

Total surface follicle number and the number of CL were not statistically influenced (P > 0.05) by gestated or suckled litter size (Table 1). Puberty attainment showed a trend (P < 0.1) to be higher in the Large-Small compared to the Small-Small treatment group (Table 1). Gilts reared in a small litter had higher (P < 0.05; main effect) AMH concentrations at weaning (Table 1). There was a weak trend (P < 0.2) for puberty attainment in gilts with high ( >8.3 ng/mL) compared to low ( < 8.3 ng/mL) AMH at weaning (62% vs 45%, respectively). Within the large gestated litter size treatment, puberty attainment was higher (P < 0.05) for gilts with a high compared to low AMH concentration (74% vs 42%, respectively) (data not shown).

These data tend to suggest that higher concentrations of AMH at weaning are associated with improved capacity to ovulate in response to boar contact, with this relationship stronger for gilts born into a large litter. If earlier puberty indicates greater potential fertility, the effect of gestated and reared litter size on puberty attainment suggests a possible impact of the Large-Small litter combination on subsequent fertility.