Every summer, farmers prepare their dairy facilities for the negative effects of heat stress to avoid losses in milk production, feed intake and reproductive performance.

Heat stress on dairy farms can be alleviated by a number of on-farm management practices and heat-abatement systems. Heat-abatement systems such as fans, sprinklers and shades are commonly used to reduce the negative effects of heat stress on the lactating cow. However, each heat-abatement system varies in its ability to control thermal conditions and minimize production losses. Furthermore, the type of heat-abatement systems varies depending on the facility type, such as freestall housing barns or the holding pen.

Many studies have identified specific heat-abatement systems that can alleviate heat stress in dairy cows; however, no studies have looked at all the different types of systems in a single analysis. Before the summer of 2007, the University of Wisconsin along with Alta Genetics teamed up to design a study and identify heat-abatement strategies and systems that were consistent among dairy farms for reducing heat stress.

The study
During the summer of 2007, 29 dairy herds participating in Alta’s progeny testing program were selected to participate in a heat stress study to determine the importance of different types of heat-abatement systems and facility designs for alleviating heat stress in lactating dairy cows. Herds participating in the study were located in California, Wisconsin, Illinois and Michigan. For each herd, intravaginal temperatures were recorded from lactating cows using a continuous temperature logging device (HOBO) attached to a blank intravaginal insert (CIDR). (See a photo of the device on the next page.)

Cow temperature was recorded over a 39-hour period at 2-minute intervals. Intravaginal temperatures were recorded for eight early lactation cows per herd. Over the same 39-hour period, ambient temperature (in degrees Fahrenheit) and relative humidity were collected at 2-minute intervals in the freestall barns on each dairy.

Thirteen factors related to facilities and heat-abatement systems were considered in this study (See Table 1 for a list of all the factors). The effect of shade was not considered since every dairy that was visited had shade over the holding area and feedbunk.

Factors affecting cow temperature
From the study, four factors were identified to be consistent among all dairy herds in regards to elevated cow temperatures.

1. As the temperature-humidity index (THI) increased, cows were significantly hotter.

2. Cows in north-south orientated barns were significantly hotter than cows housed in east-west orientated barns.

3. As airflow rate in cubic feet per minute per cow (cfm/cow) increased, cows were significantly cooler.

4. As cows spent more time in the holding area, they were significantly hotter.

Note that the presence of soakers in the holding area or over the feedbunk was not recognized as systems for effectively cooling cows in the herds that were visited during this study. This does not go to prove that such systems cannot be effective in cooling cows. There is a lot of variation among soaker and sprinkler systems among farms that can make it difficult to observe concrete findings across all herds. Temperature activation, duration of the soaking cycle and the effectiveness of the water droplet soaking the cow were the most common types of variation for soakers among the dairy herds visited during this study.

Factors affecting thermal conditions within freestall barns
Although no heat abatement systems and factors were found to be consistent in reducing the THI inside of freestall barns, pen stocking densities influenced the relative humidity within the freestall barns.

• As stocking densities (i.e. number of cows / number of freestalls) increased, the relative humidity within the freestall barn was higher.

During the summer months, I would avoid overstocking freestall pens to improve cows’ thermal environment.

Recommendations
The holding area is definitely one of the major risk areas when it comes to cow cooling. Therefore, a few rules should apply to holding area cooling.

• Limit the amount of time cows spend in the holding area. Cows should never have to wait more than 45-60 minutes in the holding area.

• The holding pen should allow adequate space – 15 square feet per cow is recommended.

• Size soaker fans in the holding area to deliver approximately 1000 cubic feet per minute (cfm) per cow.

For herds with north-south orientated barns, shade can be used on the west wall to reduce the amount of direct sunlight. Here are some thoughts to consider:

• Lower curtains at 1 p.m. each day and raise around 8 p.m.

• Though curtains protect from direct sunlight, it also blocks natural airflow, so only lower curtains when protection from direct sunlight is needed.

Final points
Though there are many ways to effectively cool cows, the four factors previously listed were consistent among the farms that were visited in the summer of 2007. I cannot stress enough the importance of proper cooling in the holding area. Increased airflow in cfm per cow and less time spent in the holding area were associated with cooler cows.

In addition, herds with north-south orientated barns were exposed to more direct sunlight during afternoon hours, thus leading to hotter cows. Thus, it is essential to protect cows in north-south orientated barns from direct sunlight when possible. Following the simple guidelines for proper holding area cooling and protecting cows from direct sunlight and radiation are just a few consistent practices that can be utilized to reduce the negative effects of heat stress. PD

Jon Schefers
Graduate student at the
University of Wisconsin
schefers@wisc.edu