125 Effects heat waves on the rate pregnancy in bovines, from local breeds, receiving embryos produced in vitro in a transferency program in tropicals areas in Mexico

The effects of a heat wave were analysed before, during and following bovine embryo transfer (n = 648) on the rate pregnancies, in bovines with a different racial kind, groups under pasture grazing conditions. The work was realise from January to December 2021. Was estimated the livestock weather comfort index, also known as temperature-humidity index, using meteorological data obtained in situ with portable hygro-thermometers. A heat wave was defined as, the period of 3 to 5 consecutive days with temperature and humidity levels above 74 points in the index; considered this as the limit of thermal comfort for cattle. Statistical analyses were done with the STATISTICA V10 and Sigma Plot V11 software programs, and logistic regression, was the nonlinear estimation model, used to determine the of rate gestation, in the presence (1) or absence (0) of a heat wave; as well as the effect, before (Days −4, −3, −2), during (Days −1, 0, +1) and after (Days +2, +3, +4) a heatwave. The Day 0 is taken, as the day on which the embryo transfer is performed. In addition, to this, a multivariate cluster and main component analysis was used, to find correlations between variables of the receiving cows and the transferred embryo. The variables that were taken into account in the case of the recipients cows were: Size of the corpus luteum (CL1, CL2, CL3), body condition score (BCS, scale 1–5), age (young 2–4, adult 5–8 and elderly 9+) and parity (0 birth, 1 birth). While, in the case of the embryo, they were preservation kind (fresh or frozen), developmental stage at the transfer (compact morula, expanded blastocyst or hatched blastocyst) and quality (good or excellent). The parameters of the logistic regression were the following: before the transferency, B0 (−0.247) and B1 (−0.445); during the transferency, B0 (−0.260) and B1 (−0.396); and after the transferency, B0 (−0.295) and B1 (−0.376). The confidence limits (95%) of the odds ratios were as follows: before the transfer (0.465–0.881), during the transfer (0.489–0.924), and after the transfer (0.497–0.946). The odds of rate gestation, before the transferency, and without a heat wave, were 0.467 ± 0.06; and with a heat wave, 0.296 ± 06. During the transferency, without a heat wave, 0.331 ± 0.08; and with a heat wave, 0.431 ± 07. After the transferency, without a heat wave, 0.399 ± 0.03; with a heat wave, 0.364 ± 04. The variables showing the strongest influence (r > 0.80) on the likelihood of a gestation in the absence of a heat wave were the size of the CL (CL1), and the age of the animal (young and adult animals). Among the embryo variables, preservation type (fresh embryos) was the most strongly correlated with gestation, in absence of a heat wave. Thus, it is concluded that heat waves could affect, the rate pregnancy in cows, that receiving embryos produced in vitro in tropical areas of México.