Factors Affecting Pregnancy Rate Per Embryo Transfer of In Vivo Produced Embryos in Recipient Holstein Heifers

Abstract

The present study aimed to determine factors responsible for variation of pregnancy establishment after transfer of in vivo produced embryos into recipient Holstein heifers. Embryos were produced from 19 donor Holstein cows using two super-stimulation protocols, estradiol-based and GnRH-based. A total of 95 fresh transfers have been carried out into previously selected recipient heifers and the grade of transferred embryo was recorded. Pregnancy was diagnosed in recipients 30 days after transfer. Serum samples were obtained from recipients on day of transfer and their ovaries were scanned using ultrasonography to record the type of CL (compact vs cavitory). In addition, recipient data as age, body weight, body height, average daily gain as well as type of estrus (spontaneous vs induced) were retrieved from available automatic records. Pregnancy rate per embryo transfer (PR/ET) was compared among different recipient categories using chi square analysis. PR/ET did not vary between different age, body weight, body height or daily gain recipient categories (P>0.05). PR/ET was similar between recipient groups receiving embryos from GnRH-superovulated donors and those from estradiol-superovulated donors (P>0.05). Presence of cavitory CL in recipient did not affect the risk of pregnancy establishment after embryo transfer. Interestingly, PR/ET was higher (P<0.05) in recipients with induced estrus (72.73%), compared to 35.72% in those with spontaneous estrus. Similarly, PR/ET was higher in high progesterone recipients (79.50%) than that achieved by low progesterone recipients (55.40%). Further, first grade embryo achieved greater (P<0.05) PR/ET than that of second and third grade embryo (79.17 vs 48.94%, respectively). Conceivably, the type of recipient CL did not affect PR/ET, while heifers with higher blood progesterone at embryo transfer are better selected as embryo recipients.