The impact of melatonin implants on the fertility of superstimulated donor heifers at subsequent insemination after embryo recovery

Superstimulation of ovaries results in oxidative stress (OS), which may disturb the subsequent fertility of donor cows. This research was carried out to evaluate whether melatonin implants could alleviate the effect of OS during the follicular development, subsequent to their ovarian superstimulation program, to maintain the oxidative balance and improve pregnancy outcomes. Twenty-four donor heifers (14 of which had received 18 mg/50 kg melatonin implants) were subjected to blood sampling at their first AI (artificial insemination) after ovarian superstimulation and embryo collection. Total Antioxidant Capacity (TAC), and Total Oxidant Status (TOS) in serum were assayed to calculate the oxidative stress index (OSI), and the fertility outcomes were followed up. The interval of Flushing to AI was 24.07 ± 0.68 and 25.55 ± 0.95 (p = 0.202), and that to pregnancy was 47.69 ± 7.71 and 63.11 ± 15.40 (p = 0.638) in treatment and control groups respectively. The rate of First AI pregnancy was 42.85% and 30% (p = 0.678), the Final pregnancy was 85.71% and 80% (p = 1.00), and the mean Services per conception was 1.85 ± 0.25 and 2.1 ± 0.31 (p = 0.51) in treatment and control groups respectively. TAC (mmol/L) was 9.13 ± 0.23 in treatment and 6.94 ± 0.39 in control group (p = 0.00). TOS (µmol/L) was 7.13 ± 1.01 in treatment and 11.78 ± 1.4 in control group (p = 0.01), and OSI (AU) was 0.79 ± 0.11 in treatment and 1.72 ± 0.21 in control group (p = 0.00). TOS in control group exhibited significant positive correlation with Flushing to AI (r = 0.688, p = 0.028), and negative correlation with First AI pregnancy (r =—0.800, p = 0.005). Melatonin implants improved TAC, and decreased TOS and OSI during the first insemination subsequent to the ovarian superstimulation and embryo collection in heifer donors; higher TOS in control group was correlated with greater Flushing to AI and lower First AI pregnancy. However, pregnancy outcomes were not significantly influenced by the treatment.