Easing milking time heat stress
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 95°F with 53% humidity and a human heat index of 107.4°F, 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 (101.5°F) 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 (80°F 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?
- Dry matter intake declines. Rumen pH decreases and rumen fermentation is disrupted.
- Milk production is depressed.
- Water intake may increase up to 5 times.
- Key blood electrolytes are lost – sodium by increased urinary secretion, potassium through skin perspiration, and bicarbonate by hyperventilation.
- Respiration rate of more than 60 breaths per minute (BPM) indicates heat stress.
- Body temperature increases. At a THI of 80 or above, cows can no longer maintain normal body temperature. Each 0.9°F increase in body temperature results in a 12% decrease in conception rate.
- Immune system is depressed. Yet during heat waves exposure to mastitis pathogens increases many fold. As a result, cases of clinical and sub-clinical mastitis increase.
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:
- Reduce stocking rates in holding pens. Cows need more space to dissipate heat; reducing the cow numbers can help alleviate crowding. This will also reduce time spent away from feeding and resting.
- Boost air movement in the barn or milking center. A minimum of 5 mph air speed directed onto the cows is needed to accomplish cooling. In tie-stall barns, increasing air flow with tunnel ventilation has proven helpful.
- Intermittent sprinkling of cows with water (for 3 to 5 minutes every 10 to 15 minutes) coupled with circulating fans directed onto the cows helps turn the holding pen into an oasis to cool cows.
- Fly control also reduces un-necessary stress helping prevent the counterproductive heat stress behavior of bunching as well as the fly defensive stomping that causes splashing of lower rear legs and udders. This will improve udder hygiene. Anything that keeps cows cleaner eases pre-milking cow prep.
- Provide water in return alley or exercise lot spiked with electrolytes ("Gatorade" for cows). Early Florida studies (Collier et at., 1982) found that rumen concentrations of sodium and potassium were low in heat stressed cows. Since heat stressed cows markedly decrease feed intakes but do increase water intake, it seems logical that providing water spiked with electrolytes may help offset some of the electrolyte loss caused by heat stress.
Milker heat stress prevention and first aid:
- Increased air movement (5 mph or greater) in the parlor is not only good for the cows but essential for the milkers. During times of heat stress, if we expect milkers to up their game of cleaning and drying teat surfaces in order to reduce mastitis, then we need to be sure they are as comfortable as possible.
- Provide a "cool one"… chocolate milk or Gatorade of course. People working in heat stress conditions need to maintain their own fluid and electrolyte intakes. When the human heat index is 90+, drinking a cup of fluids every 30 minutes to maintain hydration is advisable. During very strenuous exercise in heat stress conditions, people can lose as much as 1 quart of perspiration per hour.
- Heat exhaustion symptoms need immediate attention. Move the person to a cool place, have them lie down with feet elevated, and provide mechanical ventilation and fluids to rehydrate. Heat stroke, where the individual has hot dry skin, body temperatures greater than 104°F, rapid heart rate and dizziness, etc., is a very serious matter and requires immediate medical attention.
Dairy cow temperature humidity index (194 K PDF)