Can serum levels of anti-Müllerian hormone and oestradiol in juvenile gilts be used to predict future reproductive performance?

The current process for selecting breeding gilts results in significant economic loss for the pig industry. In Australia, it is estimated that around 40% of selected gilts are culled before Parity 3 (Plush et al. 2016). Thus, there is a need for effective markers of future reproductive performance in young gilts.

We previously tested whether serum levels of anti-Mullerian hormone (AMH) and oestradiol (E2) in 80-day-old juvenile gilts would be useful markers of future ovarian and uterine properties and found that AMH was indicative of uterine capacity while E2 marked puberty attainment at 160 days of age (Steel et al. 2016). We also examined whether AMH and E2 in juvenile gilts aged 60, 80 and 100 days were predictive of mating and litter parameters over three parities. It was found that basal levels of AMH were not associated with mating and litter parameters and while E2 was associated with the proportion of piglets born alive and proportion stillborn at Parity 1 (Steel et al. 2017). The present study was conducted to determine the repeatability of our previous experimental results across different herds. It was hypothesised that, similar to our previous studies, E2 levels in juvenile gilts could be used to predict Parity 1 reproductive performance and, in contrast to other species, AMH could not.

Blood samples were obtained from 80-day-old Landrace x Large White gilts from two Australian commercial piggeries located in South-Eastern QLD (Farm A: PIC Australia™ Genetics, Grong Grong, NSW, Australia; n = 101) and in Southern NSW (Farm B: PrimeGro™ Genetics, Corowa, NSW, Australia; n = 187). Sera AMH and E2 were measured via competitive inhibition ELISA kits, CEA228Po and CEA461Ge, respectively (Cloud-Clone Corp., Katy, TX, USA). The mean mating age of gilts was 227.8 ± 12.5 (s.d.) days of age at Farm A and 208.6 ± 19.6 days of age at Farm B. Age at first heat (only at Farm A), first mating outcomes, gestation length, number of mummified, stillborn, and live piglets from the first litter and any culling information were recorded. Data was analysed using regression, restricted maximum likelihood and generalized linear model methods, with Farm as a factor, via the statistical package R (v3.3.3, R Foundation, Vienna, Austria).

Our two previously mentioned studies (Steel et al. 2016, 2017), were conducted only at Farm B. Similar to previous results, a single sample of AMH at 80 days of age was not predictive of Parity 1 mating, litter or culling parameters at both farms (P > 0.05). In contrast to our previous findings at Farm B, serum E2 levels were negatively associated with age at first heat at Farm A (b = –0.021, P = 0.011, R² = 0.10), positively associated with proportion of piglets born alive at both farms (OR = 1.005, P < 0.001) and were negatively associated with the proportion stillborn at Farm A (OR = 0.991, P = 0.003), but not at Farm B (P > 0.05). The inconsistent results between farms could be due to genetic variation studies, but reasons for disparities between experiments on the same farm are currently unclear. However, it is evident that at a time in juvenile gilts when ovarian cells first become responsive to gonadotrophins, serum E2 levels, which likely influence the development of the female reproductive tract, are indicative of first parity outcomes. It should be noted that the sample size of the present study (n = 288) was much greater than that of the earlier studies (Steel et al. 2016: n = 48; Steel et al. 2017: n = 72).

The findings of the present study validate those obtained previously showing that serum AMH levels in 80-day-old gilts are not predictive of first parity outcomes. The relationship between serum E2 levels at 80 days of age and the proportion of stillborns and piglets born alive at Parity 1 warrants further investigation.