Unproductive behavior: Heat-stressed cows
By Dr. Jamison Allen
Increased standing time/decreased resting time reduces milk production and adds to risks of lameness.
Despite advances in cow cooling systems, heat stress remains a critical stressor on dairy cattle. Both directly and indirectly, heat stress impacts feed intake, body temperature, maintenance requirements and metabolic processes, feed efficiency, milk yield, reproductive efficiency and disease incidence.
Researchers have also focussed on heat stress and its relationship to animal behavior, since an uncomfortable cow tends to be a less productive cow.
Behavior and productive measures are linked, as cows take physical and physiological steps to stay cool. Milk production will decrease at the same time energy and nutrient usage by the cow increases. Increased maintenance requirements, compounded by a decrease in nutrient intake, diverts nutrients for survival and away from production.
One behavior to maximize heat loss is to stand more, leaving more of the cow’s body surface exposed to dissipate heat. Unfortunately, there’s a correlation between longer standing time and decreased milk production and increased risk of lameness. That creates a vicious cycle, since lameness in turn negatively impacts resting and feeding behavior.
Predicting heat stress
According Dr. Jamison Allen, Assistant Professor of Animal Science at Northwest Missouri State University, predicting heat stress is vital for keeping cows healthy and productive. Cows will pant, eat less and produce less milk when their core body temperature increases.
“We knew from previous experiments that cows with higher average body temperatures stood for longer amounts of time during a 24-hour period,” Allen said. “We wanted to better describe this relationship between standing behavior and body temperature. At any given moment, there is a 50% chance a cow is standing, and another 50% chance that same cow is not standing. We wanted to see if that 50:50 ratio changed according to body temperature. It did.”
The Northwest Missouri State University and University of Arizona study was conducted by Allen, along with Drs. Robert Collier, John Smith and Laun Hall at the University of Arizona. The researchers used two tools to study the relationship between behavior and temperature. They fitted each cow with an intra-vaginal sensor to measure core body temperature; and a special leg sensor to measure the angle of the leg and track whether the cow was standing or lying.
After comparing data from cows in Arizona, California and Minnesota, the researchers concluded that standing behavior and core body temperature are strongly correlated.
“We can predict the animal’s likelihood to stand according to their core temperature,” Allen said.
By observing standing behavior, dairy producers could use cooling systems to target a specific core body temperature to alleviate the negative affects of heat stress, particularly in decreasing the amount of time a cow stands to dissipate body heat. By encouraging cows to lie down, producers will also help their cows conserve energy, be more productive, and reduce other health risks.
“We have yet to look at length of bout in relation to body temperature,” Allen added. “We did find that regardless of initial body temperature, standing bouts ended once the body temperature had decreased about 0.4° F.”
Allen recommended future studies to see how cows respond to different cooling systems. The are also planning to investigate behavior as it relates to ambient temperature, relative humidity, and thermal humidity index.
• To contact Dr. Jamison Allen, email .
• Study summaries are available in the Abstracts of the 2013 ADSA Midwest Branch/ASAS Midwestern Section Meeting, and the Proceedings of the 2013 Western Dairy Management Conference. The abstract will be published in the Journal of Animal Science and Journal of Dairy Science later this year.