– Rory Lewandowski, Extension Educator, Athens County
The shade for cattle question has been raised more than once on grazing council pasture walks. There is a range of opinions on the issue and really, at first glance it seems to make sense that shade on hot days will increase cattle comfort and performance. I spent a little time on the Internet looking for research articles dealing with cattle, heat stress and shade. With the time I could give to this I’m not going to claim to have the definitive answer to this question, but I did discover some factors that should be taken into account when attempting to answer the shade question.
First of all, how hot it is and how humid the weather is matters. There have been several studies that suggest cattle dry matter intake begins to decrease at temperatures above 77 degrees F. Although hot temperatures can make cattle uncomfortable due to the sun’s rays, it is a combination of high temperature and high humidity that can really be detrimental to cattle comfort and performance. It is under these weather conditions especially that shade might be of value to cattle. A study published by McIlvain and Shoop in 1970 entitled “Shade for Improving Cattle Gains and Rangeland Use” evaluated as part of the study summer shade use by cattle over a 4-year period in Oklahoma. Some of the steers in the study had access to shade, while others did not. Steers with access to shade outgained steers without shade by an average of 19 pounds during the summer across the 4 years of the study. The advantage in weight gain increased as the number of hot, humid days during the summer increased, which brings up a second factor to consider. It is not only the temperature and humidity, but also the length of time these conditions persist.
The McIlvain and Shoop study tracked the number of what they termed “hot muggy” days. These were defined as days when temperatures above 85 degrees F plus humidity in percent totaled 130 or more. They found that this combination of temperature and humidity had the severest effect upon steer weight gains. These conditions combined with the number of these types of days determined how much shade could benefit animal performance. In a year in which there were only 30 of these hot muggy days there was only a 4-pound weight gain advantage between the steers with access to shade vs. steers without shade. In years where hot muggy days accounted for 50 to 60 days over the summer, the weight gain advantage increased to 27 to 30 lbs for steers with shade compared to steers without shade.
At this point it is probably worth considering the quantity of shade that will be available to cattle under hot, humid conditions. It matters. Have you ever walked out among a bunch of cattle squeezed together under a single shade tree? It might be hotter and more humid in amongst those cattle than it is out in the open sun. Typically, it is suggested that shade be provided at between 40 to 60 square feet per cow. Cattle lose heat primarily by transferring it to cooler air, and by evaporation of water from sweat as well as from moist tissues in the respiratory system. Cattle crowded together under limited shade are not going to find conditions conducive to heat loss and evaporation.
Related to hot, humid conditions and the time for which they persist, is what happens at night. In an article by Steve Sharrow of Oregon State University entitled “Trees in Pastures: Do Cattle Benefit from Shade?” and published in a July 2000 issue of the Temperate Agroforester, he says, “Humidity is probably as important as temperature in summer heat stress on grazing livestock. We often think of the daily high temperatures as the main issue in heat stress. However, night conditions are equally important.” The reason that night conditions are important is because it is normal to have variation in body temperature. Generally there will be a slight increase in body core temperature during the heat of the day, but this temperature is then reduced during cool nights, allowing the animal to recover from the heat stress of the day. This is a condition common in many western states that may have higher daytime summer temperatures than we experience in Ohio, but they typically cool down at night. However, here in Ohio we get periods where it remains warm and humid throughout the night. This type of condition does not allow the animal (or the cattleman without air conditioning for that matter) to recover from the previous day’s heat stress and so the effects become cumulative and place greater stress upon the animal.
While shade provided and utilized correctly can aid in cattle comfort and performance, it should be recognized that there are limitations to shade and that cattle also employ other methods of coping with heat when shade is not available. Blackshaw and Blackshaw in 1994 published an article in the Australian Journal of Experimental Agriculture that was a review of the literature studying shade and heat stress in cattle. One of the points made is that shade can be very helpful in reducing the heat loading occurring from the sun’s rays but that is not the entire picture. Cattle also receive heat that is reflected from bare soil and nearby objects and shade does not protect cattle from this heat. Shade also has no effect upon the heat generated from the digestion and use of energy from feedstuffs. The Sharrow article estimates that shade may only directly affect 25% or less of the total heat energy cattle must deal with on a sunny, hot day. An article entitled “Shade-Seeking Behavior of Rotationally-Grazed Cows and Calves in a Moderate Climate” published in the proceedings of a Livestock Environment Symposium from 2001 in Louisville Kentucky mentioned both some detrimental effects of shade as well as alternative coping mechanisms. The detrimental effect is obvious to any cattleman; cattle congregating in shade result in manure accumulation in one area and reduced overall pasture fertility. The study found that cows without shade spend significantly more time at the water trough, especially as the humidity index increased, and more time out on pasture as compared to cows with shade. However, even though cattle with access to shade spent less total time out on pasture there was no reduction in actual grazing time between cows with shade and those without shade. Back to the Sharrow article where the author notes that there is also a behavioral and learned aspect to heat tolerance. “Cattle may successfully deal with lack of shade by restricting their grazing and traveling to the cooler hours of the day or night and by standing together in areas of good airflow.”
For many cattle producers shade may not be an issue because it is already part of the pasture system but for those who may be in the position to decide if shade is or is not provided to cattle, the possible advantages and disadvantages of shade must be considered, along with other methods that cattle might have to cope with heat stress.