Volume 19: Issue 5 July 2017
BOTTOM LINE Sharing ideas, solutions, resources and experiences that help dairy producers succeed.
Manage dairy-calf heat stress GEOF SMITH
Page 4 High-producing cows: enhance their fertility
Page 7 Another Dairy Dialogue Day tour coming
Page 8 An ethical will; what is it?
Page 10 Discover tiled fields
Summer is in full swing now and we’re experiencing heat-stress conditions in many parts of the United States. Dairy producers are familiar with the effects of heat stress on cows. If they’re not kept cool, p ro d u c t i o n drops and so does the milk check. But not Geof Smith everyone is awa re t h a t heat stress also has negative effects on young calves. Although calves can tolerate more heat than adult cows, they do reach a point where they need to expend energy to cool themselves. True heat stress is caused not only by the outside temperature but also humidity. When those factors are combined, a temperature-humidity index can be calculated. When humans or animals become heat stressed, the body relies on thermoregulatory mechanisms like sweating and panting to release extra heat. Calves lose most of their extra heat through evaporative cooling and increased respiration. When the water-vapor content of the air is high, the elevated humidity can drastically decrease a calf’s ability to lose heat through its skin and lungs. Calves can tolerate higher temperatures at lower
– levels routinely seen during July and August in many parts of the Midwest – calves suffer severe heat stress. Producers need to take steps to help them keep cool. Calf heat stress = growth-rate decrease
The “Cool Cow” application is available at no charge for both Android and iPhones. With this app, enter outside temperature and relative humidity; it will then calculate the temperaturehumidity index to determine how severe heat-stress conditions are for calves.
humidity because they can release heat more efficiently by sweating and panting. At temperature-humidity-index values of 75 or less, heat production in calves has shown to be fairly constant – whereas this level is considered heat stress in adult cows. At temperature-humidity-index values of more than 75, water loss through breathing and sweating increases; the calf becomes stressed. At values of more than 85 or 90
Likely the most noticeable symptom in heat-stressed calves is a decrease in growth rates. A recently published study from Europe showed Holstein calves fed 6 liters — about 1.65 gallons — of milk a day had an average daily gain of 1.05 pounds during normal temperatures – versus 0.83 pounds per day during the summer, on the same diets. As a rule of thumb, for every 10-degree increase in air temperature at more than 70 degrees Fahrenheit, expect average daily gain to decrease by at least 5 percent. One of the main reasons for the decrease is because calfstarter intake decreases significantly in hot weather. When calves become cold their starter intakes increase to help generate heat, but calves eat less solid feed in hot weather. By eating less calf starter they generate less heat in their stomachs, which helps maintain a lower core body temperature. Heat stress also decreases blood flow to the intestines so calves also have lower nutrient absorption. See HEAT, Page 2
Professional Dairy Producers™ I 1-800-947-7379 I www.pdpw.org