Interaction between season and culture with insulin-like growth factor-1 on survival of in vitro produced embryos following transfer to lactating dairy cows

Abstract

Culture of bovine embryos in the presence of insulin-like growth factor-1 (IGF-1) can increase pregnancy rates following transfer to heat-stressed, lactating dairy cows. The objective of the present experiment was to determine whether the effect of IGF-1 on post-transfer embryo survival was a general effect or one specific to heat stress. Lactating recipients ( n = 311) were synchronized for timed-embryo transfer at four locations. Embryos were produced in vitro and cultured with or without 100 ng/mL IGF-1. At Day 7 after anticipated ovulation (Day 0), a single embryo was randomly transferred to each recipient. Pregnancy was diagnosed at Day 21 by elevated plasma progesterone concentrations, at Days 27–32 by ultrasonography, and at Days 41–49 by transrectal palpation. Transfers were categorized into two seasons, hot or cool (based on the month of transfer). There was a tendency ( P < 0.09) for an interaction between embryo treatment and season for pregnancy rate at Day 21; this interaction was significant at Days 30 and 45 ( P < 0.02). Recipients receiving IGF-1 treated embryos had higher pregnancy rates in the hot season but not in the cool season. There was a similar interaction between embryo treatment and season for overall calving rate ( P < 0.05). There was also an interaction between season and treatment affecting pregnancy loss between Days 21 and 30; recipients that received IGF-1 treated embryos had less pregnancy loss during this time period in the hot season but not in the cool season. The overall proportion of male calves born was 77.5%. In conclusion, treatment of embryos with IGF-1 improved pregnancy and calving rates following the transfer of in vitro produced embryos into lactating recipients, but only under heat-stress conditions.