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♦ Managing Calves in Summer Heat
♦ Managing Calves in Summer Heat


Kim Egan, DVM, Dairy Consultant Manager, Genex

Managing heat stress in calves begins with cooling of dry cows. According to articles by Tao, et al. in the Journal of Dairy Science (2011, 2012), calves born from dams housed with fans and sprinklers had higher birth weights and better colostral IgG absorption.

Focusing on the pre-weaned period, here are some basics for improving calf health and growth by minimizing stress during the summer heat.

It's important to recognize that calves experience heat stress at slightly higher temperatures than cows, and they can dissipate heat if the overnight low temperature is under 77°F. Calves can tolerate slightly higher daytime temperatures, with stress beginning at over 80°F.

Intake. Like people, calves' appetites are reduced during periods of heat stress. Calves born in the summer months have been shown to have lower average daily gains versus calves born in other seasons (Bateman & Hill, Progressive Dairyman, 2012). Reduced average daily gain means a delay in time to puberty, longer interval to first calving and ultimately delayed return on increased investment. One way to encourage intake, gain and rumen development is by making fresh starter feed available. Starter intake is directly related to water intake.

Fresh, clean and abundant water helps to cool calves, and it is crucial during periods of heat stress, especially for calves with scours. During seasons with ideal temperatures (50°-80°F), one- to two-month-old calves will normally consume 0.5-2.0 gallons of water per day. This amount increases exponentially with heat and humidity and can reach up to six gallons per day in young calves.

Rinsing water buckets out daily and frequent refills are also advisable. For calves that habitually spill their water, wire or zip tie bucket handles to holders.

Like scours, heat stress can lead to dehydration. Close attention should be paid to each calf's attitude and ability to suckle. Oral electrolyte solutions, like NuLife® Oral Electrolytes available from Genex, can be used to help replenish fluids. The amount to use is dependent on the amount of dehydration and the ambient temperature. For example, a 100-pound calf that has a weak suckle may be 5% dehydrated. At normal outdoor temperatures, this calf would require 2.5 quarts of electrolyte solution per day. However, if the outdoor temperature is over 100°F, the amount should be doubled to five quarts per day in addition to normal feedings of milk or replacer (Bentley, Iowa State University Extension).

Air and Shade. Air movement promotes cooling. As shown in a curtain sidewall barn, calves had a 23% increase in average daily gain when cooled with fans (Hill et al, Journal of Dairy Science, 2011). Air movement helps a calf maintain normal body temperature, reduces bacterial load and reduces noxious gases, like ammonia, in the air. The recommendations for airflow in the hot summer weather are over six times higher than for airflow in winter. Your local extension or veterinarian may be able to help you determine if airflow in your calf facilities is adequate for summer heat.

A simple way to improve air flow in calf hutches is to raise the rear end of the hutch (can be supported with a cement block). Recommendations for maximum airflow in hutches are to place them four feet apart with 10 feet between rows.

No matter the type of housing for calves, the ability for the calf to get out of direct sunlight is important. Shade cloth above hutches can reduce the temperature inside the hutch by three to four degrees and therefore reduce body temperature. Calves housed in barns need the ability to move out of sunlight coming through sidewalls or windows. Calves in group housing will "bunch" to move away from direct sunlight or flies, thereby limiting their individual airflow.

Flies. Expending energy to swat at flies adds to the detriment of heat stress. There are several fly control products available. Also, fly eggs need moisture to hatch, so dry inorganic bedding helps to limit flies in the calf rearing area. Drainage of fluids under hutches or pens is aided by four or more inches of gravel below the bedded surface. Keeping water buckets and the areas under feed clean and dry will reduce hatching of maggots. Finally, trimming weeds around calf housing improves ventilation and reduces moisture in soil.

In summary, providing measure to reduce heat stress in calves not only improves their health but the farm's profitability. The following are key factors for calf rearing in summer months:

• Provide fresh starter daily
• Offer large amounts of clean water
• Provide electrolyte therapy to dehydrated calves as needed
• Produce adequate airflow
• Furnish shade
• Supply dry bedding
• Undertake fly control measures

July 2015