High environmental temperatures cause an increase in early death of the embryo. Although fertilization occurs, the embryo dies at an early stage of development. If this occurs before the 1 6th or 1 7th day of pregnancy, cows will usually cycle on schedule the following heat period. If death of the embryo occurs after implantation in the wall of the uterus, return to estrus may be delayed for several days or weeks. High environmental temperature reduces the intensity of estrus activity.
Bulls are especially vulnerable to heat stress.
Overheating can cause damage to semen quality that may last for up to six weeks. Provide artificial shade if ample natural shade is not available in areas where cattle spend most of their time during the heat of the day. It is especially important to have cows pregnancy tested in the fall after drought conditions. Short pastures can potentially increase parasite loads. It is known that parasite eggs tend to concentrate more in the lower part of the forage plants, thus short pastures due to drought conditions can increase the potential parasite load.