Heat stress pre- and post-partum and its effect on calf performance – Dr. Sha Tao, University of Georgia
Click here to download Tao’s PowerPoint presentation.
When the summer heat rises, the best strategy on dairy farms is simple: Keep everyone cool.
Dr. Sha Tao, assistant professor at the University of Georgia at Tipton, has taken in-depth looks at heat stress effects from a variety of angles, starting with his research at the University of Florida. During his presentation at Vita Plus Calf Summit, Tao cited his recent research that quantified something dairy farmers have known for a long time: heat stress in lactating cows negatively impacts milk production. In addition, heat stress during the dry period also has negative effects on the entire subsequent lactation.
“It’s important to cool the cows,” Tao said. “It doesn’t matter if it’s dry cows or early or late lactation.”
But milk production isn’t the only thing affected by dry period heat stress – calf performance is also negatively impacted.
Tao said, according to a 2013 study (Monteiro et al., 2013), late gestation heat stress decreases birth bodyweight by 10 pounds and that carries through the entire first year of the calf’s life. In addition, recent research showed a calf heat-stressed in utero had a higher ability to absorb glucose (Monteiro et al., 2015). This could lead to greater fat deposition, which could, in turn, impact the breeding program.
The calf’s immune system can be impacted as well because the calf has less ability to absorb IgG from maternal colostrum and lower lymphocyte function. All of these factors lead to heifers leaving the herd before puberty or not completing their first lactation. Tao said research shows the offspring’s milk production is decreased as well (Monteiro et al., 2013).
With all this in mind, Tao said he recommends cooling during the entire dry period, if possible. Although research in heifers is limited, he said cooling spring heifers is also likely a very good strategy.
But not just adult animals are affected by heat stress. Tao said cooling the neonatal calf is also vital.
Work done by Bateman and Hill in 2012 showed that calf body temperatures, on average, are higher during summer months than the cooler months. This indicates that calves accumulate heat during hot weather; they aren’t able to easily dissipate the heat through evaporative cooling.
Tao cited several studies that showed heat stress in calves reduced starter consumption, average daily gain (ADG) and growth. Higher ambient temperatures at birth correlate with lower serum protein levels and heat-stressed calves are unable to mount as big of an immune response when challenged by a pathogen.
Tao encourages calf raisers to take several steps to limit heat stress in their young animals.
Providing shade can reduce hutch air temperature by 2 to 3 degrees C. Research conducted in the 70s showed shade can improve immune transfer and decrease mortality.
Tao said aluminized low-density polyethylene covers can also greatly reduce hutch temperature and the calf’s respiration rate. He said these covers have a nine-week lifespan and should be replaced every year (at a price of $8 to $10 per cover plus freight).
Ventilation is also key in promoting calf health. Using blocks to raise the backs of hutches can decrease ammonia and carbon dioxide levels and bacterial counts, leading to better air quality for the young animals. In pens or group housing systems, Tao said it’s worth investing in fans to cool calves. Research shows this practice improves ADG and feed efficiency (Hill et al., 2011).
Finally, Tao said a couple nutritional strategies can help limit the effects of heat stress as well. Calves should always have access to free-choice water. Many producers feed more milk or milk replacer (additional feedings, high volume or higher solids concentrations) during the winter, but this same practice may be beneficial in the summer as the calf’s body burns more energy to stay cool. Starter should always be fresh and Tao said a recent study indicates that higher moisture content of starter may improve ADG (Beiranvand et al., 2016), but more research needs to be done before we can say it’s an effective strategy to implement in calf programs.
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