Keep dry cows cool too
- Cows exposed to heat stress calved seven days earlier than those that were cooled.
- Calf body weight was 28.7 pounds lighter for calves born from heat-stressed cows.
- Milk production up to 30 weeks of lactation was higher for cows cooled during the dry period. The average increase in 3.5-percent fat-corrected milk (FCM) in cooled cows was 18.7 pounds of milk per cow per day compared to cows exposed to heat stress.
Remember, the cows were heat-stressed only during the dry period. The magnitude of response in milk production is related to heat stress load and intensity. In other words, how high the temperatures rise and how long it stays hot influences how much milk production is affected. With such dramatic results in this experiment, we decided to delve into the topic further. Our second experiment was designed similarly to the first, but the ambient heat that summer was not as intense as the summer before. Here’s what we found the second time around:
- Rectal temperature was increased in heat-stressed cows.
- Heat-stressed cows showed greater respiration rates.
- Heat-stressed cows again calved seven days earlier than cooled cows.
- Calves born from heat-stressed cows were 11 pounds lighter.
This experiment also evaluated immune function of the cows. Neutrophils are specialized cells that act as the immune system’s “first line of defense.” Through a process called phagocytosis, neutrophils engulf foreign bacteria and “kill” them through oxidative burst. This experiment showed that heat stress reduced both neutrophil phagocytosis and oxidative burst ability. Furthermore, heat-stressed cows produced fewer antibodies to fight against disease. This means the immune system was compromised in its ability to fight infection when cows were heat stressed during the dry period. Our third experiment was again designed similarly to the first and looked at the effect of heat stress on mammary gland cell proliferation (the multiplying of cells). Through udder biopsies, we were able to see that heat-stressed cows had lower proliferation of epithelial cells (milk-producing cells), which may be a contributing factor to the low milk yield. So what’s the take home message here? Keeping dry cows cool – as much as possible – increases milk production, immunity and mammary cell proliferation in the subsequent lactation. Any cooling is better than nothing, and minimizing heat stress in dry cows is a valuable management tool to increase milk production in the subsequent lactation. About the author: Dr. Bruno Amaral earned his bachelor’s degree in animal sciences in 2001 and his master’s degree in animal production in 2003 from the Federal University of Lavras in Brazil. In 2008, he finished his Ph.D. at the University of Florida, focusing on the effects of supplemental fat sources on production, reproduction, immunity, and metabolism of periparturient dairy cows. That same year, he was awarded the Omega Protein Innovative Research Award from the American Society of Animal Science for his Ph.D. research. Amaral’s post-doctorate work in Dr. Geoffrey Dahl’s lab evaluated the effects of heat stress during the dry period on the subsequent lactation of dairy cows. Amaral previously worked with Vita Plus as a dairy nutritionist and technical support specialist for Michigan, Indiana and Ohio. His passion is to be on the farm working with dairy cows, supporting our team of nutritionists and helping farmers to be more profitable. He and his wife, Michelle, have a six-year-old daughter, Natalie, who also loves cows.
Transition and reproduction