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Easing milking time heat stress

Jeff Reneau, Dairy Extension Specialist

July 28, 2012

A few weeks ago I was entering data into my computer at a dairy farm. Certainly not a very strenuous job! But at 95F with 53% humidity and a human heat index of 107.4F, sweat was dripping off my forehead. The human heat index is an indication of how hot it feels when both temperature and humidity are considered.

Just as I was beginning to feel sorry for myself, the cows were lining up in the holding pen to be milked, some already huffing and puffing. While I drove to the farm in air conditioned comfort, these cows had spent the whole day in the stifling heat and now were jamming into the close quarters of a holding pen to wait their turn to be milked. For them this combination of temperature and humidity represented a Temperature Humidity Index (THI) of 85. At these conditions, cows are not able to maintain normal body temperature (101.5F) and will have a drop in milk production of 6 to 8 pounds per cow per day. A quick study of the heat stress charts for cows and humans (below) shows that cows are much more sensitive to heat stress than people. By the time we are just beginning to feel heat stress (80F with 40% humidity), the cows have been suffering for some time. Cows begin to experience heat stress when the THI reaches 68. Heat stress at milking time can be hard on both the cows and the milkers. How can we make it easier on the cows and people at milking time?

What happens when a cow is heat stressed?

The first rule in heat stress prevention is getting an early start! Routinely follow weather trends and begin heat abatement BEFORE a heat wave hits.

Bovine milking time heat stress prevention and first aid:

Milker heat stress prevention and first aid:

Dairy cow temperature humidity index (194 K PDF)


Dairy cow temperature humidity index

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