Don’t stress heat stressby Emily Carey

All dairy farmers can agree that cow comfort comes first. If cows aren’t feeling their best, then the whole farm won’t be at its best. During the summer when temperatures rise into the 90s, the humidity skyrockets and animals feel sluggish, some run the risk of becoming severely ill.

“Heat stress occurs when cows are unable to maintain their body temperature,” Alycia Drwencke, of Cornell Cooperative Extension South West New York Dairy, Livestock and Field Crops Program explained in her presentation, “Managing and Abating Heat Stress on your Dairy Farm.”

Drwencke’s presentation was shown during the “Ventilation and Heat Abatement for Dairy Cattle from Calves in Utero to Mature Cows” event that took place at SUNY Morrisville and SUNY Cobleskill on July 21 and July 29, respectively.

Heat stress occurs when the temperature humidity index (THI) rises above 68º. The higher the THI, the more likely the cow is to become sick from heat stress. Although THI should be used as a starting point to determine potential heat stress, every farmer understands that cow’s bodies process heat differently. They should use cow-centered measures that look at individual cows to best determine levels of heat stress. To monitor for heat stress, pay attention to increased respiration rate, panting, increased body temperature and other signs of discomfort.

Cows suffering from heat stress can face drastic health defects and decreased productivity. In fact, dry cows that aren’t cooled have decreased milk production throughout lactation, decreased DMI pre-calving, decreased immunity pre- and post- calving and decreased gestation length and dry period length. Dry cows need to be cooled for the entire period, Drwencke explained. There are $810 million in milk losses annually from heat stress in the dry period, according to research she presented.

Implementing cooling isn’t just important for dry cows; springing heifers have been found to have increased milk production with cooling also. In general, providing fans and shade improves cow health and production for all animals.

Contrary to popular belief, calves can also experience heat stress, both in utero and after birth. Calves that experience heat stress in utero have decreased milk production throughout their life, lower body weight, decreased immunity and lower IgG absorption regardless of colostrum quality.

Pregnant cows that have access to fans and shade will have much healthier calves as providing cooling improves the thermoregulation response, growth and health.

Heat stress will continue to take a toll across generations of cows. Even if one cow doesn’t experience heat stress, it will still see decreased production due to the heat stress its mother or grandmother experienced – “decreased herd survival for two generations and decreased milk production for three lactations,” Drwencke said.

Due to the lack of production that occurs in later generations after heat stress happens, many farmers have turned to raising additional heifers to offset the loss. In fact, Drwencke said that, from research in her presentation, as a group, U.S. dairy farmers spend $134 million annually rearing additional heifers. Also, there is a $90 million loss per year for reduced productive life and $371 million per year reduced milk yield of daughters born to heat stressed dams.

In total, there are $1.5 billion in total losses annually from heat stress. New York dairy loses around $35 million each year.

It’s clear how important cooling is for dairy cows. There are many ways to properly cool and ventilate barns that will decrease the chance of heat stress occurring.

Drwencke said that cleaning and renovating existing equipment, such as fans, will improve equipment efficiency more cheaply than buying new equipment. However, some older barns are not set up to be sufficient at cooling. In that case, it may be more beneficial and cost effective to do research and determine whether or not it would be cheaper to just build a new barn rather than renovate an old barn.

Tim Terry, of Wyoming County CCE and Pro-Dairy, also presented on how to provide the best calf housing options. He discussed how there are five considerations when choosing calf housing: ventilation, comfort, labor efficiency, cost consideration and individual or group.

The goal of ventilation is “to provide fresh air to remove harmful airborne organisms, minimize dust, eliminate noxious odors and remove excess moisture and heat without causing a draft on the calf,” Terry said. “We need to ventilate two entities: one, the calves, and also the barn.”

Calves less than two months old need 100 cfm of air in hot weather and 50 cfm in mild weather, while calves two to 12 months need 130 cfm in hot weather and 60 cfm in mild weather. To do this, there are three options for ventilation systems: naturally ventilated barns, which use eaves or sidewall openings to allow prevailing winds to force fresh air into the building and have ridge openings that allow warmed air to rise and exit the building; natural assisted/mechanical assisted barns; and mechanically ventilated barns that are automated systems that do not rely on natural airflow and can be negative (sucking air out), positive (pushing air in) or neutral (pushing at one end and pulling at the other end) pressure systems.

Each system has its benefits and drawbacks and should be thoroughly researched before being implemented into a barn, Terry advised.

Calves have many requirements that need to be met. In addition to colostrum, milk, water, grain and forage, calves also need to have dry and clean bedding, protection from the elements, healthy air and draft-free spaces. All of these contribute to the calves’ comfort.

Clean and dry bedding should be provided for the calves to nest in to preserve warmth. Also, each calf needs a minimum of 30 square feet, which will increase with age, and feed and water should be provided away from the resting area. Drainage plays a crucial role.

Calves can fall victim to heat stress and cold stress. The optimal outdoor temperature for calves is around 70º F but “calves can maintain a relatively constant body temperature when the environmental temperatures range between 50º and 80º,” Terry presented. Below 60º, calves have a higher energy requirement and can get cold stress. On the other end of the spectrum, above 80º, heat stress can occur. High humidity increases heat stress. Relative humidity in calf facilities needs to stay between 50% and 70%.

Drwencke also discussed the importance of drinking water. In warm weather, cows will increase water intake so having clean, shaded water is important. Keeping the available water shaded and at a lower temperature will also help keep cow temperatures lower and encourage drinking.

There is the age-old debate about whether calves should be kept in a group or separated. While there are benefits and drawbacks for either option, whatever option is chosen plays a role in how calves are kept cool and how a barn should be set up. When deciding, things to consider are how many calves there are (there should be 12 to 16 in a group with a maximum of 24), the age of the calves, how much space is available (a minimum of 30 square feet per calf, more for older calves), weaning strategies, air quality and ventilation and water location and accessibility.

Terry summarized his presentation by explaining that there is no one size fits all solution. He said, “Calf facilities must be designed with the basic needs of the calf in mind – nonnegotiable with the builder… Management is key… Calf housing fundamentals need to be incorporated into the design.”

Although it can be scary to think of the impact heat can have on a herd, with simple cooling management, farmers can rest assured that their animals and livelihood are safe. Dairy farming is a “cool” profession if done carefully and thoughtfully.