Can Weather Affect Cows in Utah?

Dr. Allen Young
USU Extension Dairy Specialist

Ever since I came here, I have been told that weather, especially heat, is not a factor in Utah. If a dairy farmer lives in Cache Valley, I have been told it is never a factor because the cows can cool off at night. While I have never totally believed it, and it may even be partially true, research that we just completed at the university dairy suggests what I have suspected for a long time - weather is a major factor in determining production results.

I had a graduate student who was interested in the effects of environment and nutrition on production. As part of her thesis, she continuously measured the temperature, light, and humidity at the university dairy, at 15-minute intervals, from March 1, 2004 to April 30, 2005. At the same time she monitored milk production, milk composition, ration composition, dry matter intake and milk urea nitrogen. We used the actual temperature, temperature-humidity index (THI), and a measurement that the crops people use � evapotranspiration rate (Etp) � because our relative humidity is very low here. We thought this might be interesting because the only two measurements needed to calculate it are temperature and, without going into detail, the amount of sunlight for the day. We are beginning to analyze the data, but some of the results that are of interest are listed below.

In terms of milk production, the maximum THI and Etp calculations gave similar results. Basically, using the resulting regression equations, maximum THI above about 54 degrees F begins to cause decreased milk production at an accelerated rate as THI rises. This is surprising because most formulas suggest that the THI needs to be above 72 before production suffers. My feeling is that animals become acclimated to their environment, and the THI affects them differentially depending on the environment they are adapted to. For example, a cow in Cache Valley probably feels the effects of heat before a cow in a warmer climate would. Also, because the Etp calculation was such a good predictor, it may be more useful for the Intermountain West since we have lots of sunlight, but lower humidity than places such as Florida. Dry matter intake had a minor effect on milk production changes compared with environmental factors. The take-home message is that effects of environmental temperature on cows may be a function of what they are adapted to as much as its actual level. Feeling heat depends on where you live. Consider what a person who lives in Alaska would consider �hot� compared to one who lives in Arizona.

In terms of milk fat percent and milk protein percent, Etp was the best predictor for both. For example, comparing summer to winter, milk fat percent decreased by 1.1% and milk protein decreased by 0.3%. Comparison of milk urea nitrogen levels from a winter environment compared to a summer environment showed an increase of 0.8 units; however, increasing the CP percent of the ration by 1 percent increased MUN by 1.2 units. The Maximum THI and CP % in ration were two significant factors related to MUN. Dry matter intake has a lesser effect on milk fat percent compared to environment. Milk protein percent was significantly affected by ration CP percent � increased CP percent was related to increased milk protein. Milk protein percent appears to be inversely related to dry matter intake.

What does this all mean? In a nutshell, environment plays a large role in determining production responses. Even though these data were from only one dairy, I see the exact same changes in many other dairies I analyze. Even in Utah we can have negative effects due to heat. So what can you do? Consider ways to cool your cows. First, provide shade for your cows. Getting them out of the sun is my first recommendation, especially during a summer afternoon. Second, reduce time in the holding pen or place fans there. The holding area is a big problem for heat stress on most dairies. Third, consider installing misters and/or fans. The feedbunk, especially if it is uncovered, is a great place to put them. Fourth, if you plan on adding new freestalls, make sure you orient them east to west and especially make sure you put the roof high enough so that it provides summer shade plus winter sun on the north side of the stalls. Low roofs over freestalls tend to trap heat rather than remove it from the cow.

Summer is about here, but it is not too late to consider cooling your cows. It is important from a health and economic perspective on your dairy. There is a lot of information out there on how to set up these systems, so start now. If you have any questions, you can contact me at (435) 797-3763 or ©