Have you cooled your cows today?

If heat stress has invaded your dairy, you’ve probably taken measures to reduce the symptoms of heat stress among your lactating herd. While much attention is given to cooling lactating cows during the summer, cooling animals during the dry period is often neglected.

In fact, it can be quite easy to forget about cooling your dry and close-up cows. After all, these cows have taken a 60-day vacation, so to speak, from producing milk so you don’t immediately see reduced milk production, as you would in your lactating herd. However, if you fail to cool dry and close-up cows, it still hits you in the pocketbook when these cows enter their next lactation.

According to heat-stress research, milk production losses due to heat stress begin at a temperature-humidity index (THI) of 72 and accumulate as the THI increases.

Researchers at Mississippi State University used this index to measure the severity of heat stress during the dry period. Then, they used a statistical procedure known as a regression analysis to measure the effect of THI on milk production during the cows’ first 200 days of lactation. Based on this analysis, they predicted milk production would decline about 20.9 pounds per cow during the first 200 days of lactation for every 1 point increase in the THI.

So, for example, dry cows exposed to a THI of 80.2 — the average THI observed in this study and 8.2 points greater than a THI of 72 — would be expected to produce about 171.4 pounds less milk during their first 200 days of lactation compared to cows exposed to a THI of 72.

Meanwhile, the researchers recorded a maximum THI of 88.9 — a whopping 16.9 points greater than a THI of 72. Dry cows exposed to this extreme level of heat stress were expected to produce about 353 pounds less milk during the first 200 days of lactation than cows exposed to a THI of 72.

Bottom line: As the severity of heat stress increases during the dry period, so, too, do the milk production losses experienced by these cows during their first 200 days of lactation. In fact, a 171.4-pound drop in milk production amounts to a loss of about $22.28 per cow when milk is priced at $13 per hundredweight. Remember, that’s the amount of milk lost per cow during the first 200 days of lactation alone when the THI averages 80.2 during the dry period, as it did in this study. As the average THI increases beyond 80.2, the losses continue to escalate.

Cooling cows isn’t just limited to your lactating herd. If you haven’t already done so, implement a cooling system in your dry and close-up cow areas. Heat-stress experts recommend that you cool cows in the holding pen first, followed by areas which house your dry, close-up, maternity and sick animals. Then, provide supplemental cooling along the feed bunk, and finally, over the free-stalls.