By Brad Haire
University of Georgia

In the heat stress of Georgia’s summers, dairy cows give less
milk. Some University of Georgia researchers are trying to help
cows cope by doing something they want to do anyway: eat.

Cows can be stressed when average daily temperatures rise above
77 degrees Fahrenheit. In Georgia, this happens up to six months
every year, said Joe West, a dairy nutritionist with the UGA
College of Agricultural and Environmental Sciences.

West and CAES graduate student Lani Pacetti are working on a
dairy feed study at the Coastal Plain Experiment Station in
Tifton, Ga.

Cows are less able than humans to get rid of excess heat, West
said, because they have less surface area compared to internal
body mass.

Dairy cows are most comfortable when outside temperatures are in
the 40s and 50s. Most Southeastern dairies have sprinklers and
fans to help cows stay cool. But it often isn’t enough during
Georgia’s summers, when the heat index can reach into the 80s at
night.

A hot cow will eat less and give less milk. Milk production can
drop in the summer by as much as 20 percent in Southeastern
states.
Heat stress can hinder reproduction, too, and lead to health
problems.

Part of the problem is that eating can heat up a cow, too. A
meal high in fibrous carbohydrates, West said, takes more energy
to digest, generating more heat inside the cow. A diet high in
fat, though, takes less energy to digest and generates less
heat.

West and Pacetti hope to mix common feed components like
cottonseed, alfalfa hay, soybean hulls and corn silage into a
ration that will keep cows from producing excessive heat during
digestion while still getting the nutrients they need.

The theory is that by simply adjusting feed rations, farmers
could help keep their cows cooler in summer. Cool cows produce
more milk.

Pacetti said the eight-week study, which began June 13, will use
three groups of 10 cows. She and West will monitor and track
each cow’s body temperature, weight variation, respiration and
blood components, as well as the milk volume and fat content.
They will also record the environmental conditions surrounding
the cows.

Each cow in the study wears a magnetic key around her neck that
lets that cow eat only from a certain trough, or gate, where she
gets her experimental diet.

Group 1 will be fed a diet high in fiber and carbohydrates and
low in fat. This should generate the most heat during
digestion.

“It would be like us eating a big bowl of bran flakes,” Pacetti
said. This group can eat as much as it wants during each
feeding. But cows should feel full with this diet and eat less
than they normally do in cooler weather.

Group 2 will get a diet high in fat and starch. This should
generate less heat during digestion. “This would be like us
eating ice cream,” Pacetti said.

This group can eat as much as it wants, too, which will probably
be more than Group 1, she said.

The cows in Group 3 will be fed Group 2’s high-fat-and-starch
diet but won’t be able to eat as much as they want. They’ll get
the same amount of calories that Group 1 decides to eat.

“The best outcome would be the cow producing less total body
heat,” West said. “This would make the cow comfortable and more
likely to consume more feed and use the nutrients more
efficiently, which would mean more milk.”

A dairy cow can eat 100 pounds of feed each day. A good cow
gives 11 gallons of milk daily. Georgia dairy cows produced more
than 16 million gallons of milk last year, worth about $200
million.