Reproductive Response of Crossbred Heifers (Bos indicus × Bos taurus) Used as Embryo Recipients in Venezuela

Abstract

Plasma Progesterone (P4) concentrations were determined by Enzyme-Linked Immuno absorbent Assay (ELISA) in 47 crossbred recipients (Bos indicus x Bos taurus) in a commercial embryo transfer (ET) program in the savannas of Venezuela. This study was carried out to evaluate the reproductive response of these embryo recipient heifers. Pregnancy status was confirmed by rectal palpation 60 days after estrus. Pregnancy rates were 38.3% (18/47) while a 61.7% stayed open. There were no significant differences between plasma P4 concentration of females that remained pregnant and those that did not either on day 0 (estrus) or 7 (ET). On day 21, the mean concentrations of P4 in pregnant females was 12.2 ng/ml being significantly higher compared to non-pregnant females (0.82 ng/ml). Recipients having plasma P4 concentrations of 2 ng/ml or more on day 21 were considered pregnant. This type of early pregnancy diagnosis using as a discrimination criterion 2 ng/ml of P4 in plasma, had an efficiency of 75% in detecting pregnant recipients and 100% in detecting open heifers correctly, for day 21 post estrus. It was concluded that this type of heifers has a good reproductive response as recipients of embryos in the Venezuelan tropics. Evaluating the concentrations of P4 on day 21 after estrus gave a high percentage of certainty in the early diagnosis of pregnancy. This would allow us to reuse the open recipient for ET before 60 days post estrus, and reduce the cost for maintenance.