Weight gain potential affects pregnancy rates in bovine embryo recipients raised under pasture conditions

Abstract

The aim of the present study was to evaluate the effect of differences in body weight gain after embryo transfer on the pregnancy rates of crossbred heifers used as recipients and raised under a grazing system. The study was performed during the dry (April to September) and the rainy (October to March) seasons. The embryos transferred were produced by in vitro fertilization. The body weight of each recipient was measured immediately before the embryo transfer and 23 to 25 days later, when the diagnosis of pregnancy was performed by ultrasonography. The associations among initial body weight (IBW), daily body weight gain (DWG), season, and pregnancy rate were evaluated using a logistic procedure that included the effect of the IBW, season, and linear and quadratic effects of the DWG. Altogether, there was no effect of season and pregnancy rates did not change between the dry and rainy seasons (42.3 vs. 45.8%, respectively; P > 0.05). However, the pregnancy rate was greater in the recipients with daily body weight gains over 250 g/day, regardless of the season. In addition, the pregnancy rate of the recipients was better (P < 0.04) explained by a logistic regression model that included the linear and quadratic effects of the DWG. The probability of each heifer to become pregnant according to DWG is explained by the follow equation: P(y = 1) = (Exp((-1.06703 + 0.0108 * DWG - 0.00002 * DWG ^ 2)))/(1 + Exp((-1.6703 + 0.0108 * DWG - 0.00002 * DWG ^ 2))). In conclusion, body weight gain potential is a critical factor for the pregnancy rates of in vitro embryo recipients managed under grazing systems.

Towards Improving the Outcomes of Assisted Reproductive Technologies of Cattle and Sheep, with Particular Focus on Recipient Management

“…The control of body condition is achieved through the correct nutritional management of the animal, as nutritionally induced metabolic changes affect reproductive parameters. Progesterone production, uterine function and health, along with embryo survival, are all impacted as a result of nutritional management [77]. Recipient nutrition is generally considered more influential than donor nutrition in terms of ET success rate [45].…”

“…Recipient nutrition is generally considered more influential than donor nutrition in terms of ET success rate [45]. A negative energy balance at the time of ET or early pregnancy results in pregnancy termination due to insufficient nutrient supply to the developing embryo [77]. Straw based diets, mouldy grain and sudden changes in nutrient intake can negatively impact ruminal microbes and fermentation, with an associated effect on circulating metabolites and hormones [77].…”

“…A negative energy balance at the time of ET or early pregnancy results in pregnancy termination due to insufficient nutrient supply to the developing embryo [77]. Straw based diets, mouldy grain and sudden changes in nutrient intake can negatively impact ruminal microbes and fermentation, with an associated effect on circulating metabolites and hormones [77]. Recipients should be placed on an allocated diet six weeks prior to ET and the diet maintained until eight weeks of gestation.…”

“…Recipients should be placed on an allocated diet six weeks prior to ET and the diet maintained until eight weeks of gestation. This helps prevent early embryo mortality as a result of altered hormones due to change in diet [77].…”

“…Once pregnancy is established, the recipient diet can be altered in relation to energy requirements; however, any change should be gradual [76]. A daily weight gain of 250-350 g/day resulted in higher pregnancy rates in cattle, with growth rates in excess of 350 g/day reducing pregnancy rate, hence establishing the threshold of 350 g/day for optimal ET success in recipients [77]. Whilst de Brun and colleagues [41] observed no effect of donor nutritional status on pregnancy establishment following embryo transfer in sheep, the nutritional status of the recipient was found to be critical for successful embryo survival following transfer.…”