Evaluation of intrinsic and extrinsic factors affecting pregnancy rate in dual-purpose cows under tropical conditions

Abstract

A total of 648 embryo transfer (ET) procedures were performed between January and December 2021 and were evaluated to assess the effect of these two types of factors on in-vitro produced ET programs carried out in tropical conditions. The intrinsic factors were size and location of the corpus luteum, body condition, genetic group, age and parity; while extrinsic factors were location of the farm, environmental comfort, season in which ET was carried out, prevailing weather conditions, and the preservation, quality, and development stage of embryos at the time of transfer. A χi2 was used for analysis of main effects, and logistic regression analysis for the combined effects in each factor (intrinsic or extrinsic); additionally, a multivariate analysis of data clusters were used to find a linkage between the effects. While age of the recipient female had a negative effect (Odds ratio = 0.179–0.870) on PR (p < 0.05), being higher in younger cows; the rest of the intrinsic factors did not affect (p > 0.05) the PR. The extrinsic factors significant (p < 0.05) were THI category, season of the year and type of embryo preservation during the ET, which indicates that the higher PR (p < 0.05) were obtained in the comfort THI category, winter season and the use of fresh semen during the ET. The clustering analysis did not show any linkage (p > 0.05) between PR and the intrinsic factors, while a linkage (p < 0.05) was found with yearly season and embryo preservation as extrinsic factors. It is concluded that age of the recipient cow and environmental conditions at the time of the transfer are key factors to be considered for successful in-vitro produced ET programs using dual-purpose cows under tropical conditions.