Most cows are heat stressed for at least a quarter of a year annually, according to Dr. Glenn Holub, Executive Technical Services Manager for Dairy with Phibro Animal Health.
Before joining Phibro, Holub spent years studying and advising producers about heat stress, first as an animal nutritionist and later as a professor at Texas A&M University.
Phibro Animal Health has published a highly useful Heat Stress Reference Guide that addresses the serious issues surrounding heat stress. In it, Holub notes 5 key indicators that cows are heat stressed:
- Increased respiration rates – Cows dissipate body heat by moving it away from their bodies and into the air via respiration. If you see your cows panting, you know they are expending a lot of energy trying to cool themselves.
- Metabolic pH changes – Increased respiration leads to a greater release of carbon dioxide from cows’ bodies. This makes their blood more alkalotic during the daytime and acidic at night, affecting rumen function and potentially causing laminitis.
- Reproductive issues, including more days open – Heat stress can interfere with conception and/or cause early embryonic death. “During a severe summer with no effective cooling, I’ve seen conception rates sink as low as single digits on some dairies,” noted Holub.
- Behavioral changes – Heat-stressed cows stand more, chew their cud less, eat less, and shift their eating to nighttime when conditions are cooler.
- Decreased milk production – The more energy cows utilize to cool their bodies, the less they are able to partition to milk production. Add this to the fact that their dry-matter intake is down, and the herd can take a significant hit in production, especially if the period of heat stress lasts more than a few weeks.
Evidence continues to mount that heat stress is one of the costliest issues in dairy operations, with far-reaching effects that can even influence future generations of animals. Holub said each year, heat stress tends to sneak up on producers. And healthy cows — those with strong immune systems — are better able to withstand periods of heat stress.
