With hot summer days officially upon us and rainfall falling short in several areas of the state, it is stressful time for producers trying to get cows bred, hay made and silage chopped. While we can’t control what Mother Nature will bring us tomorrow, there are some steps that can be utilized to help minimize stress on the cow herd and manage the reproductive performance to aid embryo retention during this period of drought and heat stress.
Heat Stress & Embryo Loss
Breeding season for spring calving herds is in full swing and it is important to consider what impacts the summer heat is having not only on the cow/calf pair in the pasture, but also the embryo that is developing in utero. Heat stress is caused by a combination of temperature, humidity, radiant heat and wind. When these factors combine and lead to an increase in rectal temperature above normal (102.2º F), this can cause conception rates to decrease due to heat reducing the oocyte quality as well as sperm viability. In addition, for cows that have already conceived, embryo development can be compromised as the early stages of development (day 1 – 4) is also when embryos are most susceptible to increased temperatures.
How do we combat embryo loss?
- Breed once a day: Animals under heat stress will be less likely to show visible signs of estrus, and if they do it is likely occurring between midnight and 6 am when the heat of the day has subsided. If using heat detection, spend as much time as possible watching for heats between 6 PM – 6 AM. Breeding cattle in estrus during the morning hours can be an effective way of avoiding breeding during hot summer afternoons and evenings.
- Timed – AI: Fixed-Time AI is one way to increase pregnancy rates of animals under heat stress. By setting the time all cows are bred, this breeding system eliminates the need for heat detection and may be the best protocol to use when animals are too hot to move around and show estrus.
- Embryo Transfer: High-quality embryos can adapt to elevated temperatures better than oocytes and sperm. Therefore using ET can be a way to increase pregnancy rates during periods of heat stress.
- Avoid Nutrient Shortage: If drought conditions affect pasture quality to where it becomes inadequate to meet the nutrient needs of the lactating dam, supplementing 0.5% - 1.0% of the cow’s body weight on pasture may be necessary. Research has shown that heifers fed 85% of requirements had reduced embryo development compared to counterparts fed 100% of requirements. Note: Provide a balanced supplement of protein and energy in order to also avoid a nutrient imbalance, which can affect the uterine environment and also decrease conception rates.
- Increase Bull Power: Heat can have a negative effect on sperm motility and morphology, causing the semen to be less concentrated. Increasing the number of bulls or rotating new bulls into the pasture during peak heat may help get cows bred on time while minimize heat stress.
Other Management Considerations
However, there are also ways to physically control environmental heat that may be easier than trying to control the biological factors of reproductive function. Heat-reducing strategies such as not working cattle during periods of extreme heat (after 10 AM) and avoid transporting them between day 4 – 42 after breeding, increase water availability, provide cool areas to escape radiant heat (fans, misters, trees, shade structures, and fly control programs can all be utilized to minimize heat stress and its negative effects on the performance of the cow herd going into the fall.
- Effects of Shipping and Heat Stress on Embryonic Mortality in Cattle
- What’s Ahead for Cows on Drought-stricken Pastures?
- Drought Management Tips for Beef Cattle Producers