Heat stress tune-up – don’t forget the dry cows

With a late February ice storm in parts of Texas its hard to believe its time to begin thinking about summer heat stress! But now is the time to make changes to your facilities if you are going to be ready for the summer heat.

The latest research from Arizona indicates that for cows summer heat stress starts at a temperature-humidity index (THI) of just 68. Many of our dairies have invested heavily in cooling their lactating herds with shade, fans and soakers. The payback has been in increased milk production and improved reproduction. Those systems need to undergo a tune-up now so they are ready once heat stress begins.

Now research from Florida is showing how critical dry cow cooling is for not only the cow but for her heifer. Dry cows that are cooled produce 8 to 10 pounds more milk per day after calving than their contemporaries that suffer heat stress during the dry period. And that advantage lasts for at least the first 40 weeks of the lactation.

Besides heat stress during the dry period negatively impacting production, it also impacts the cow’s immune function. When cows that are heat stressed are vaccinated they have a reduced antibody response, which could compromise their ability to fight disease. The reduction in immune response continues during early lactation, which could also mean she is more susceptible to metritis, mastitis and other diseases as well.

Disease and production aren’t the only performance indicators impacted. Reproduction suffers as well. Fewer services per conception and days open have been reported when comparing cows dry during the cool months and those dry during the hot months of the year.

Not only are there negative impacts on the cow, but her calf suffers from the heat stress. For many years we’ve known that calves born to heat stressed dams are lighter at birth. The Florida researchers have been following the impacts on the calves born to heat stressed dams throughout their productive life. The calves from heat stressed dams are not only lighter at birth, but lighter at weaning and at 12 months of age when compared to herdmates born to dams that were cooled during the dry period.

The calves born to heat stressed and cooled dams attain puberty at the same time; however, the calves from heat stress dams require more services per pregnancy. And the negative repercussions don’t stop there. The calves from heat stressed dams also produce about 10 pounds per day less milk during their first lactation. Research continues on whether the loss is seen during second and greater lactations as well.

Although many provide shade for the dry cows, the Florida research indicates that isn’t enough. These cows also need fans and soakers to receive adequate cooling to mitigate the impacts of heat stress during the dry period. If you are going to have your facilities ready for this summer’s heat stress now is the time to make those modifications on your dry pens.


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