HEAT STRESS IN CALVES: CALVES GET HOT, TOO

Written by: Grace Cun, PhD

As an industry, we’ve made significant investments in keeping cows cool. Numerous research studies have explored every aspect of heat stress in cows, from calving through dry-off. The heat a cow feels is a combination of temperature and humidity. Interventions abound to maintain cow comfort, including fans, sprinklers and feed ingredients designed to work from the inside out.

While there has been focus on alleviating heat stress in cows, pre-weaned calves are often overlooked. Calves will start feeling heat stress at as little as 70–74 degrees F. Heat stress in calves can still result in lower weight gain, compromised health and difficulty achieving liveweight targets for age at first calving. Implementing management protocols for pre-weaned calves during hot weather is worthwhile.

Here are a few management protocols to consider:

SHADE: When calves are outside in plastic hutches during the summer, they experience some level of heat stress. While the hutches provide shade from the sun, the temperature and humidity inside can escalate quickly. Research studies suggest that providing shade above the hutches reduces internal temperature and minimizes stress for calves. Don’t forget calves raised indoors may still be exposed to sunlight. In such cases, consider shade curtains to block sunlight.

VENTILATION: Good air movement is crucial year-round to maintain calf health and prevent respiratory issues. Think strategically about air movement and prevailing winds when you are determining where is the best place to position hutches. During summer months, ammonia can accumulate rapidly in calf hutches, negatively affecting calf respiration. To prevent ammonia buildup, place a block under the back of the hutch, creating a space between the hutch and the ground for better airflow. Make sure to keep bedding from building up in the open space and blocking air movement. Ensure fans are available and operational in calf barns to increase airflow. Consider automated controls that turn fans on and off as weather changes and explore exhaust fans to expel stale air. Remember when discussing ventilation and facilities to include bedding. Regardless of the bedding type, ensure it remains dry and clean.

WATER: Just as people need more water in hot weather, so do calves. As calves attempt to maintain body temperature, water is lost through faster respirations and evaporative cooling (sweat). Water intake in calves can double as they try to replace water lost through increased respiration and sweat. This is crucial for calves of all ages. While younger calves may not respire as much as older ones, they are more susceptible to scours, leading to dehydration and worsening heat stress. If young calves experience diarrhea (scours), be proactive in promptly providing electrolytes to prevent dehydration. Ensure clean, fresh water is introduced to calves during their first week of life and help them recognize its availability.

Research indicates that calves do not consume enough water from milk alone. Fresh clean water also helps promote intake of starter grain. During summer, consider either increasing bucket size or filling buckets with fresh water more frequently. Additionally, maintain clean buckets by rinsing them daily to remove debris and keep the water fresh. Remember, just like humans calves like cooler water in warm weather, and warmer water in cool weather. This helps manage core body temperatures.

FRESH STARTER GRAIN: Just as it is essential to keep water cool and fresh, pay attention to the freshness of starter grain. Calves tend to eat less starter when it is hot, which increases the risk of leftover starter heating up and developing mycotoxins or other bacteria. Offer only as much starter as the calf will consume in a day, and promptly remove any uneaten starter.

MORE MILK REPLACER: As calves experience heat stress, their maintenance energy requirements rise. Ensuring adequate energy and nutrient intake becomes crucial. Although starter consumption typically decreases in hot weather, prioritizing higher milk replacer levels may help maintain energy levels available for growth. Feeding calves more than one and a half pounds of milk replacer per day can contribute to better energy balance and reduce the effects of heat stress.

Remember that calves represent the future of your herd. Investing in their health and performance during growth and development pays off when they join the milking herd. Incorporate heat stress management into your regular protocols to keep calves comfortable during hot conditions.