Factors affecting the success of a large embryo transfer program in Holstein cattle in a commercial herd in the southeast region of the United States

Abstract

The objectives of this study were to evaluate factors affecting in vivo embryo production and pregnancy per embryo transfer (P/ET) in Holstein cattle in the southeast region of the United States. Data from a total of 516 embryo collections and 10,297 ETs performed from 2011 to 2014 were available. For embryo production, the effects of donor parity (nulliparous [N], primiparous [P], multiparous [M]), average temperature-humidity index (THI) at embryo collection, days in milk at embryo collection, occurrence of calving problems, and occurrence of metritis postpartum were evaluated. For P/ET, the effects of donor parity (N or parous), recipient parity (N, P, and M), embryo type (fresh, frozen, IVF, and IVF-frozen), embryo developmental stage (4–7), embryo quality (1–3), recipient estrous cycle day at ET (6–9), average THI at ET, days in milk at ET, milk yield at ET, occurrence of calving problems (abortion, dystocia, twins, fetal death, or retained placenta), and occurrence of metritis postpartum were evaluated. Pregnancy was diagnosed at 41 ± 3 days of gestation. Continuous and binary data were analyzed using the MIXED and GLIMMIX procedures of SAS, respectively. Parity affected embryo production; M had greater number and percentage of unfertilized embryos and lesser percentage of viable embryos than P and N. Recipient parity, embryo type, embryo stage, embryo quality, estrous cycle day at ET, and THI at ET affected P/ET. There was an interaction between recipient parity and THI at ET. P/ET was greater for N than P and greater for P than M, greater for fresh embryos than others, greater for stage 7 than others, greater for quality 1 than 2 and greater for quality 2 than 3, and greater for ET on estrous cycle Day 7 and 8 than 6. P/ET was decreased for THI ≥80 in N and THI ≥72 in P and M. Calving problems and metritis also affected P/ET in P and M and was lesser for cows that had calving problems and metritis. In conclusion, embryo production was affected by donor parity, and P/ET was affected by embryo type, embryo stage, embryo quality, recipient estrous cycle day at ET, THI, calving problems, and metritis.

Introduction

Embryo transfer (ET) is an important tool to disseminate individual with high genetic merit and potentially improve herd performance [1]. In addition, ET has the potential to increase fertility in cows under heat stress [2], [3], [4] and in repeat-breeder cows [5], [6]. In the past 40 years, there have been improvements in synchrony and hormonal protocols for ovarian superstimulation and synchronization of the estrous cycle and ovulation; however, the mean number of embryos produced via superstimulation or pregnancy per ET (P/ET) has not appreciably changed [1].

Reports from large-scale bovine ET programs have greatly improved our understanding of the factors that affect the success of such programs [7], [8], [9], [10], [11]. In regard to P/ET, these reports reported that surgical transfers resulted in greater P/ET than nonsurgical transfers, fresh in vivo produced embryos resulted in greater P/ET than frozen in vivo produced embryos, nulliparous (N) had better P/ET than parous cows, and higher quality embryos resulted in greater P/ET. The effect of stage of embryo development and donor-recipient synchrony were inconsistent. Whereas some studies reported greater P/ET for early blastocysts than other stages of development [7], [9], others reported greater P/ET for expanded blastocysts [8] or even no effect of embryo stage of development on P/ET [11]. Whereas some studies reported greater P/ET for more synchronous ET [7], [9], others reported greater P/ET when recipients were in estrus 12–48 hours before the donor [8]. Also, although the transfer of in vitro produced (IVF) embryos has been increasing worldwide [1], there are scant data comparing in vitro with in vivo produced embryos fresh and frozen [4], [12], [13]. Furthermore, with rising global temperature, understanding the effect of heat stress on embryo production and P/ET becomes paramount for the success of an ET program. Whereas most reports show decreased embryo production [11], [13] and P/ET in dairy cattle [13], [14], [15] under heat stress, one report found an increase in P/ET in dairy cattle as ambient temperature increased [8]. Another important consideration for embryo production and P/ET is postpartum health. Recent reports have pointed out to a large effect of postpartum health, particularly uterine health on pregnancy per artificially inseminated (AI) [16], [17] and P/ET [18].

Having a better understanding of the factors that affect embryo production and P/ET could help improve the success of ET programs. The objectives of this study were to evaluate environmental and cow donor factors affecting in vivo embryo production and environmental, cow donor, cow recipient, and embryo factors affecting P/ET in Holstein cattle in the southeast region of the United States.