Recipient mare factors influencing pregnancy rates and early embryonic loss rates after transfer of IVP embryos

Abstract

There are a lot of factors known that could influence a mare's fertility, and though there is research available, most of it is focussed on mares carrying their own pregnancies or on transfers of in vivo produced embryos. Therefore, the objective of this study is to determine how recipient mare associated factors can influence the pregnancy and early embryonic loss rates of recipient mares after the transfer of frozen-thawed in vitro produced embryos. For this, a total of 2207 transfers of embryos produced in vitro via ovum pick-up (OPU) and intracytoplasmic sperm injection (ICSI) were analysed. All transfer procedures were performed at the reproduction department of the University Clinic for Horses at Utrecht University. The aim of this analysis was to determine whether recipient mare associated factors had effect on the pregnancy rate at the first pregnancy check and their rate of early embryonic loss. These factors were 1) year of transfer; 2) month of transfer; 3) age of the recipient mare; 4) breed; 5) parity; 6) presence of a nursing foal; 7) history of early embryonic loss; 8) length of endometrial oedema; 9) induced heat; 10) induced ovulation; 11) Caslick procedure; 12) number of ovulations; 13) use of the first ovulation of the season; 14) number of transfers.

Statistically significant correlations were found between the year of transfer and the pregnancy rate at the first pregnancy check, between whether a mare had a foal nursing at the time of transfer and the pregnancy rate at the first pregnancy check and the length of endometrial edema and the rate of early embryonic loss. Other factors did not show a statistically significant correlation with either pregnancy rate at the first check or the rate of early embryonic loss, but may still have clinical relevance.