Nutrition: Think Spring—and Heat Stress

07:32AM Jan 07, 2015

Its winter, but not too early to start thinking about gearing up for heat abatement strategies.

We conducted a study with Elanco this past August to monitor internal body temperatures in cows. Elanco provided and installed Thermochron temperature monitors or “iButtons” on 38 cows in two of my client’s dairies in South Florida.

The iButtons record temperature within 0.1°F accuracy every five minutes and were kept in the cows for 72 hours. Our main objective was to correlate body temperature and reproductive performance in the summer.

Fortunately for the study, but not for the cows, we happened to choose the hottest week of the summer. The average  temperature humidity index (THI) was in the severe, heat-stress range (over 80) throughout the entire period.

One of my clients had just completed a new, tunnel-ventilated barn, so we had a
simultaneous comparison with conventional freestall barns. Each barn was equipped with intermittent soakers over the cows behind the feed alleys.

In a previous article, I discussed the risk of early embryonic death when body temperature nears 103°F. If we allow the cow’s temperature to rise above this critical point at any time during the day or night, much of our heat abatement is wasted and we risk losing pregnancies. The eye opening results of this study explained our difficulty getting cows pregnant in the summer. But we were also a little surprised at the tunnel barn numbers.

Body temperatures followed a daily pattern: lowest early in the morning and peaking mid-afternoon. The average body temperature for cows ranged from 102° in the morning to 104.5° or higher each afternoon.

While ambient temperatures were similar in each barn, body temperatures were lower with less daily variation in the tunnel barn.

The pen average body temperature in the conventional barns was 103.4° compared to 102.8° in the tunnel barn.

More importantly from a reproduction standpoint is the percentage of time during the day the average temperature of cows in the pen was above 103.5°. During 46% of the day, cows in the conventional freestalls were over 103.5° versus only 2.2% of the day in the tunnel barn.  

Air velocity in this 660', 6-row tunnel barn was 10 to 12 mph along the feed lane, 6 to 8 mph over the head-to-head stalls and 4 to 6 mph over the outside stalls. I think higher and more consistent air movement contributed to more consistent body temperatures in the tunnel barn.

Since this is a nutrition column, I should mention there are several feed management and nutritional strategies to help minimize the affect of heat stress. But nutrition can’t overcome extreme heat stress.
Both production and reproduction of cows in the new tunnel barn are showing appreciably better numbers than the previous year.  

Click here to read more on heat stress from Rick Lundquist.

RICK LUNDQUIST,  of Lundquist & Associates and Nutrition Professionals, based in Duluth, Minn. You can email him at: [email protected].