Heat Stress Impacts the Unborn Calf as Well as the Dam

The negative impact of heat stress on lactating cows has been well established and researched with the most commonly discussed impacts being reduced dry matter intake, lower milk yield, and compromised immune function. Several research groups have devoted years and years of research to investigating cooling strategies for lactating cows; however, the same can’t be said for dry cows. Recently, the impact of heat stress on the dam and the unborn calf has become an increasingly popular topic. The effect of heat stress on the dam and unborn calf can be detrimental to the calf’s future performance and this is an area that deserves more attention.

In 2016, researchers out of the University of Florida and the University of Georgia, published research investigating the impact of heat stress during late gestation on immune function, growth, and performance of dairy calves. In summary, calves that experienced heat stress in the last 6 to 7 weeks of gestation had lower birth body weights and were born on average 4-5 days early compared to calves of cows that were cooled during gestation. A portion of the poorer growth was attributed to those heat stressed calves also having compromised ability to absorb IgG’s from the colostrum.

Future performance of calves is also negatively impacted by heat stress during gestation. Heifers from cooled dams experienced fewer services to conception and became pregnant at an earlier age compared to heifers from heat stressed damns. Furthermore, heifers born to heat stressed dams had lower first lactation milk yield compared to heifers of cooled dams.

The results of this research demonstrate the importance of providing heat abatement to both lactating and dry cows. While the impact on dry cows is not nearly as obvious as the decreased milk yield of lactating cows, it is just as important in the long run. The aforementioned results highlight the benefits of providing cooling on calf health and performance, but there is also a profound benefit on the dam’s performance and welfare. Cooling cows during the dry period can increase mammary growth, resulting in better production throughout her lactation, improves immune status, and can help promote dry matter intake during the dry period. When you consider your heat abatement strategies for your lactating cows, I encourage you to also think about what you can do for the dry cows to make sure that they are sufficiently cooled during their pregnancy. The results will be beneficial to both the cow and the calf and I can assure you, it will be worth it!

Reference: Dahl, G.E., S. Tao, A. P. A. Monteiro. 2016. Effects of late-gestation heat stress on immunity and performance of calves. J Dairy Sci. 99:3193-3198.