FR 29. Reproductive response of crossbred heifers (Bos indicus x Bos taurus) used as bovine embryo recipient in Venezuelan tropic. I. Racial type
To evaluate reproductive response and early diagnosis of pregnancy in venezuelan tropic, plasma Progesterone (P4) concentrations were determined by Enzyme Linked Immunosorbent Assay (ELISA) in 47 crossbred (Bos indicus x Bos taurus) recipient heifers in a commercial embryo transfer (ET) program in savanna area of Monagas state, Venezuela. Pregnancy status was confirmed by rectal palpation 60 days after oestrus. Pregnancy rates were 38.3% (18/47) while a 61.7 % stayed open. Simple linear regression and one way analysis of variance indicated that there were not significant differences (P>.05) between plasma P4 concentrations of females which remained pregnant and those which did not on either days 0 (estrus) or 7 (ET). On day 21, the mean ± SD concentrations of P4 in pregnant females was 12.2 ± 2.2 ng/mL being significantly higher (P<.05) compared to non-pregnant females (0.82 ± 0.42 ng/mL). Recipients having plasma P4 concentrations of 2 ng/mL or more on day 21 were considered as pregnant. The test accuracy for diagnosing pregnancy was 75 % and 100 % for open cows. These heifers have good reproductive response as recipient of embryos in the Venezuelan tropic. Evaluating the concentrations of P4 the day 21 after estrus gives a high percentage of safety in the early diagnosis of pregnancy and the open recipient to recycle for ET before 60 days post estrus, reducing their maintenance cost.