by Jim Massey

Wisconsin and the Upper Midwest might not have the heat and humidity of places like Florida, but that doesn’t mean dairy cattle here don’t suffer from heat stress during the dog days of summer.

Jimena Laporta, an assistant professor of lactation physiology in the University of Wisconsin-Madison Department of Animal and Dairy Sciences, has been studying heat stress in dairy animals since she began her research and teaching career at the University of Florida in 2015. She was recruited to UW-Madison in 2020 and has continued her focus on trying to find ways to keep dairy animals cool when temperatures rise.

Laporta, originally from Uruguay, says her five years on staff in Florida — “the epicenter of heat stress” — were instrumental in piquing her interest in heat stress biology. She has gone beyond usual heat-stress studies with lactating animals to investigate how heat stress can also affect pre-weaned calves, growing heifers and dry pregnant cows.

To conduct her most recent study, Laporta used electric heat blankets, similar to those used to keep horses warm in the winter, to induce heat stress in 56 transition dairy cows for 70 consecutive days through the dry period and into the onset of lactation. She worked with a Canadian company that makes electric heat blankets and modified the design slightly so the blankets could stay securely on the animals throughout the study.

Graduate student Brittney Davidson was instrumental in the implementation of the heat blanket study, which was completed in December 2022, Laporta says.

Laporta says she is not the first dairy researcher to use electric heat blankets for a heat-stress study. There were six prior studies in peer-reviewed journals using the research method — primarily in Iowa — where blankets were originally validated for cattle, but those studies were for shorter periods of time and with relatively small cow numbers. Yet, as with other heat-stress studies, classical hallmarks of heat stress were successfully induced, including increased respiration frequency and reduced milk production.

However, those studies did not represent the heat-stress exposure time often experienced in a typical Midwest summer of about 60 days, Laporta says.

“The effects of heat stress on dairy cattle are profound and significantly contribute to lower overall welfare, productivity and profitability of the dairy sector,” Laporta says. “Here in the Midwest, we have a shorter period of heat stress than in the Southeast, but that doesn’t mean it’s not relevant or important. There are a lot more cows here, so even in two months of heat stress, you can have detrimental short- and long-term effects.”

Impact on productivity

Whether experienced during lactation or the nonlactating dry period, heat stress hinders animal productivity through decreases in milk yield and quality, fertility, health status, welfare, and longevity, Laporta’s studies have shown.

Keeping ahead of heat stress is vital to avoid welfare and production losses, she says, which means closely monitoring animals, the daily forecast and the cattle-housing microclimate to which the animals are exposed.

When dairy farmers think about ways to limit heat stress on their animals during the hottest summer months, they generally pay attention to their cows that are the highest producing. But Laporta says farmers should also consider the welfare of their calves, heifers and dry cows, because heat stress can affect those animals over the long haul.

“Just because we don’t see an impact right away doesn’t mean those animals aren’t being impacted,” she says. “We are looking at things we can do while dairy animals are young and vulnerable that will make them more resilient when they get older.”

Cooling techniques often used on lactating animals such as shade, fans and mist sprayers should also be considered for use on calves and nonlactating animals, Laporta says.

Her research on heat stress in dairy animals is likely to become more important in the future as the climate changes and the Midwest experiences more high-temperature days, Laporta says.

“The research we’re doing here is very relevant, with climate change and the increasing temperatures that we’re experiencing,” she says. “And the predictions of the next 50 to 100 years are not very favorable to us nor to cattle. Despite our collective and individual efforts to combat climate change, the Earth’s temperature is going to keep increasing. Even regions that typically don’t experience a huge amount of heat stress will and are experiencing warmer temperature, so we have to find ways to keep a step ahead.”

A focus of Laporta’s research group is establishing benchmarks at which dairy cattle of different ages begin to experience thermal discomfort with a goal of preventing heat stress from occurring in the first place. Laporta says dry pregnant cows should be closely monitored when or before the temperature and humidity index reaches 77 to avoid further heat-stress-related impairments during the dry period and subsequent lactation, and to mitigate potential carryover effects on the offspring being gestated. For pre-weaned dairy calves in the Midwest, ambient temperature alone is a good indicator of thermal discomfort, and calves should be closely monitored when it surpasses 70 degrees F.

Laporta and her research team are exploring the multigenerational effects of dry period heat stress that persist in the progeny several years after the heat stress event took place. Her group is pulling together data from the heat blanket study and will be submitting an abstract to the American Dairy Cattle Association, and they will also be offering informational seminars to other researchers in the UW-Madison Animal and Dairy Sciences Department. An Extension publication summarizing the findings will also be produced, and presentations will be offered to farmers across the state.

USDA grant

Laporta recently received notification that her research laboratory has been awarded a $650,000 grant from the USDA National Institute of Food and Agriculture. The research project will explore the synergistic effects of heat abatement methods and nutritional interventions in pre-weaned dairy calves on mammary gland development and milk production capacity.

Improving early-life nutrition of dairy calves has been shown to positively influence a variety of productive outcomes, including mammary gland development, Laporta says. Conversely, early-life exposure to heat stress can exert long-term detrimental effects on physiology, leading to poor growth and productive outcomes. One of the goals of the grant is to characterize the short- and long-term responses of the mammary gland to early-life management interventions.

Experiments will be conducted in parallel in Wisconsin and Georgia during summer months to strengthen the validity of the findings. Holstein female calves will be exposed to either heat stress or active cooling and fed a conventional or enhanced plan of nutrition from birth to weaning. The animals will be housed on farms that have close ties with UW-Madison.

“When calves are hot, they eat less, just like us,” Laporta says. “This is a universal involuntary response to hyperthermia in all mammals. At the same time, nutrient availability in early life is critical for many aspects of growth and health.”

She says feeding more milk during this critical life stage yields larger and more productive mammary glands, yet many producers are reluctant to make investments due to the delay in time it takes for returns to be realized. The goal of the study is to test nutritional interventions during hot and humid summer months to maintain body gains and mammary development despite the climate toll.

The fact that her lab received the competitive grant shows the “relevance and importance” of her heat-stress work, despite the geographic location, Laporta says.

Massey lives near Barneveld, Wis.