The problem in your herd is one seen throughout the Central Region of the United States. You likely live in the fescue belt, and your cows are consuming endophyte-infected tall fescue. Endophyte is a fungus that exists in most fescue. Some stands of fescue are highly infected, while others are marginal to lowly infected. The endophyte fungus produces a large number of chemical compounds, many of which have serious biological effects on an animal’s body. One of the compounds that is secreted by the fungus actually redirects blood flow, which leads to severe heat stress in animals. During the summer months, the capillary beds expand, which allows for more blood to flow to the exterior of the body so that it can be cooled. However, the blood pools in the internal regions of cattle consuming endophyte-infected tall fescue. This blood pooling reduces the animal’s ability to dissipate heat, and they remain heat stressed. Observe your herd to determine the level of infection. Cattle that do NOT shed their hair during the summer are in a highly stressful, endophyte-infected tall fescue environment. Additionally, if your cattle spend a majority of their time in ponds and shade, they are experiencing heat stress issues likely the result of consumption of endophyte-infected tall fescue. Observe the behavior of your cows on a perfect day?65-70°F. Cattle in a normal environment will NOT show signs of heat stress at this temperature. If the temperature is 65-70°F, and your cattle are standing in the shade panting or in the pond, then your cows are in a highly infected endophyte environment.
Once you have diagnosed the problem, the real question is how to improve the pregnancy rates of the cow herd in this environment. The best plan is to change your breeding and calving season. If you want to remain a spring-calving herd, then begin your breeding season in late April or early May. By moving the breeding season back, you allow your cows ample time to conceive before the worst heat stress begins. The best alternative is to calve in the fall (September-October). The reproductive rates of fall-calving cows consuming endophyte-infected tall fescue is high. If moving the breeding season is not possible, then feeding fat can help reduce the heat stress effects of cattle consuming endophyte. Other feedstuffs can also be used to help dilute the chemicals, but the cattle will still exhibit signs of extreme heat stress.
