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Dairy Pipeline: August 2004
Robert E. James
Extension, Dairy Scientist
Dairy Nutrition
(540) 231-4770 email: jamesre@vt.edu
We've all seen that high producing dairy cow panting during the dog days of summer. Milk production and ration intake are down and it's obvious that she is really stressed. Calves are also affected by heat stress. Although their body mass isn't as large, they react just as negatively to high heat and humidity. Body temperature of calves may increase from a normal range of 101 - 102 to as high as 106°F when stressed. At these temperatures respiration rates increase and circulating antibodies decrease, Calves can become more acidotic. The net result is that calves are less able to resist disease and death comes more quickly if intervention doesn't occur promptly.
Calves also grow more slowly because maintenance requirements increase due to the extra effort expended in trying to stay cool. Higher maintenance requirements mean that less of the nutrients she consumes are available for growth. What can be done to minimize heat stress? Keep calves as cool as possible! Wooden or opaque hutches are cooler than the translucent variety. Exercise areas outside the hutch are imperative in the southeast. Opening the vents of the hutch and raising the back end of the hutch can assist in venting excess moisture and heat. Where excessive wind is not a problem, use of 80% shade cloths over hutches is effective. If calves are housed in greenhouses or permanent structures make sure that ridge vents, eaves and side walls are as open as possible. Dairy producers are frequently concerned about calves getting wet during summer thunderstorms, but the impact of heat stress is a far bigger problem. An adequate supply of clean, free choice water is an absolute necessity. Ad libitum water encourages dry starter intake and promotes earlier weaning. Look at those water buckets the next time you feed or are checking on calves. Are the buckets covered in green slime? Is there feed or manure contamination? Buckets should be positioned in an elevated position inside the hutch to prevent fecal contamination. Cleaning buckets frequently with a dilute solution of Clorox or chlorine will retard growth of plant material in the bucket and encourage water intake. Heat stress and water management for calves are one of the "little things" than can dramatically encourage calf growth and reduce disease.