Effects of immunization against androstenedione or bone morphogenetic protein 15 (BMP15) on reproductive performance in sheep.

Partial neutralization of bone morphogenetic protein 15 (BMP15) bioactivity by immunization is known to increase ovulation rate in sheep. However, it remains uncertain whether BMP15 vaccination would be a suitable procedure for increasing lambing rate. The aim of this study was to compare the efficacy of a BMP15 vaccination treatment on lamb production to that of commercially-available androstenedione-based vaccines that are used for this purpose. Ewes were immunized for 3 yr against androstenedione, BMP15, or no antigen (control). Vaccination with androstenedione or BMP15 altered (P < 0.05) ovulation rate as well as litter size at midpregnancy, birth, and weaning compared with controls. No differences were detected in the proportions of ewes conceiving in the first cycle or partial failure of multiple ovulations. Both gender and litter size affected birth weight of the lamb (P < 0.05), but no effect of treatment was found. Growth rate was significantly affected (P < 0.05) by gender, birth weight, and the number of lambs raised, but not treatment. In conclusion, immunization against either androstenedione or BMP15 increased ovulation rate. Androstenedione vaccination also increased the number of lambs weaned (P < 0.05). Bone morphogenetic protein 15 vaccination altered the pattern of the number of lambs weaned, but no increase in lamb production was observed as more ewes produced zero or three lambs. Overall, androstenedione or BMP15 vaccination did not significantly affect embryo or fetal survival or lamb performance independently of the effects of these treatments on ovulation rate.