12 Differences in pregnancy loss between <i>Bos indicus</i> and <i>Bos taurus</i> cattle

Abstract Infertility due to pregnancy loss is a major issue leading to economic losses in cow-calf beef production. Furthermore, undernutrition is linked to infertility in cattle and is of most concern during times of extended drought periods and ever-increasing feed costs, such as today. Approximately 30% of cattle in the U.S. contain a portion of their genetic background of Bos indicus origin, and approximately 40% of beef cows and 50% of the cow-calf producers in the country are located in the southern U.S. where Bos indicus cattle and their crosses are located. Our research group has investigated differences in fertility and conceptus development between Bos indicus and Bos taurus cattle and there is evidence for differences in embryonic development and pregnancy establishment processes between Bos taurus and Bos indicus. In similar studies performed in Brazil and in the U.S., d 15 Bos indicus embryos averaged at 2.4 cm in length, while Bos taurus d 15 embryos averaged 11.4 cm in length. In addition, we determined that cows containing primarily Bos taurus genetics had larger fetuses at d 53 of pregnancy than cows with at least 20% Bos indicus genetics. These differences highlight the importance of performing controlled studies with direct comparisons between the two subspecies. Recent findings from our group indicate that Bos indicus cattle have improved fertility and embryonic survival under nutritional restriction when compared with Bos taurus cattle. Angus embryo transfer recipients submitted to a 70% nutritional restriction have increased pregnancy failure compared with Angus recipients in a maintenance diet and Brangus recipients in both restricted and maintenance diets. In addition, embryo recipients in the restricted diet that received an Angus embryo experienced greater pregnancy failure than recipients in the restricted diet receiving Brangus embryos, regardless of the recipient breed. Collectively, our results indicate that the magnitude of the detrimental effect of nutrient restriction differs between Bos taurus and Bos indicus cattle. Bos taurus genotype in both maternal and fetal systems decreased the probability of pregnancy when nutrient restriction was superimposed, indicating that Bos taurus cows were more susceptible to experience embryonic loss when exposed to the same negative plane of nutrition. There is a critical need to understand how the fetal-maternal crosstalk during early stages of pregnancy as well as the uterine environment differ between Bos taurus and Bos indicus cattle.