Something to Ruminate On

Cooling dry cows is a sound investment


Much of the Midwest has seen a rise in heat and humidity in the past couple of weeks. The effects of summer heat and humidity are well-documented in lactating dairy cows as we see decreases in dry matter intake and subsequent production losses. Newer research points to the value of heat abatement and cooling practices for dry cows.

Three University of Florida research trials showed that heat stress during the dry period negatively impacted cows during the next lactation as well as the unborn calves. In these studies, cows were moved to a freestall barn at dry off and exposed to either heat stress or cooling with fans and sprinklers. Both treatment groups received the same dry cow ration from dry off until calving. After calving, the animals from both groups were moved to one common sand-bedded freestall with fans and sprinklers, and all received the same milking cow ration.  

Improved milk production

Results showed cows that were cooled during the dry period yielded significantly more milk through the first 20-30 weeks of lactation. The average across all three Florida studies was 11 pounds more fat-corrected milk per cow per day in early lactation. Heat stress during the dry period significantly reduced DMI prior to calving compared to cooled cows. The trend of higher feed intakes by cows that were cooled continued post calving and progressively increased to the end of the trials.  

During the dry period, udder cells from the previous lactation are replaced with new milk secretory cells to support milk production in the next lactation. Mammary tissue biopsies were conducted in the third University of Florida study to determine the impact of heat stress on mammary cell turnover. Results indicated heat stress decreased the creation of mammary epithelial cells, which may be a contributing factor to lower milk yield.  

Immune function and calf growth

Heat stress during the dry period has a negative effect on animal health and immune function during the transition period. Neutrophils, specialized immune cells responsible for fighting infections, do not function well in heat-stressed cows.  

On average, cows exposed to heat stress had a dry period that was seven days shorter than those cooled. Calves born from heat-stressed cows had significantly lower birth weights, ranging from 12%-42% lower birth weight. University of Florida researchers have continued to follow the calves born from these two dry cow treatment groups and have found significant improvements in milk production, not only for the calves born to the cooled cows but also for the granddaughters. 

Watch for signs of heat stress

Although we do not have milk yields to monitor the severity of heat stress in dry cows, we can observe other cow behavior signs. Dry cows under heat stress will have lower-than-usual feed intakes, rumination and chewing times. They will also stand for more hours of the day to promote heat loss, leading to issues in cow comfort. Activity systems can be used to monitor some of this behavior. Elevated respiration rates can also be observed by visually monitoring the breathing pattern on a subset of dry cows within a group. If respiration rates exceed 60 breaths per minute, the cows are likely to experience some level of heat stress. As numbers rise above that target threshold, heat stress becomes more severe. Similar to lactating cows, dry cows under more severe heat stress may be seen open-mouth panting and bunching around shade or water sources.  

Return on investment

Heat abatement in dry cows may require significant investment in facilities or equipment, but the research shows it can be worth the investment. Not only does it support greater DMI, improved mammary cell growth, better immune function and subsequent milk production, but it also lends itself to healthier, more productive calves for multiple generations. 

Barry Visser is a nutritionist for Vita Plus.


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