May 27, 2025

The Impacts of Heat Stress on the Dry Cow and Her Fetus with Dr. Jimena Laporta, University of Wisconsin-Madison, and Dr. Brian Gerloff, Renaissance Nutrition, Inc

56 minutes

This episode was recorded in Fort Wayne, Indiana, during the 2025 Tri-State Dairy Conference.

Dr. Laporta gives an overview of her presentation, focusing on the impact of heat stress during the dry period on the cow, her daughters and her granddaughters. She covers heat stress impacts on mammary gland involution, as well as fetal programming effects on the daughter and granddaughter. (3:37)

Daughters of heat-stressed cows have fewer sweat glands located deeper in the skin, thicker skin and more sebaceous glands. This was observed at birth, weaning and puberty. They sweat more than heifers who weren’t heat stressed in utero, but have higher rectal temperatures during the preweaning phase. Dr. Laporta hypothesizes that if those calves were exposed to additional stress, they would be more susceptible to illness because of the higher core temperature. (6:34)

The panel discusses heat stress impacts on male fetuses and the potential for epigenetic changes to be transmitted through semen. Dr. Gerloff asks about differences in the impacts of heat stress on first-calf heifers compared to older cows. Dr. Laporta describes the survival rates of heifers who were heat-stressed in utero. Heifers are lost from the herd even before first calving, with more following in first and second lactation. (11:00)

Dr. Laporta outlines the differences between heat-stressed and cooled treatments in her experiments. They measure respiration rates and rectal temperatures to assess the physiological impacts of heat stress in the cows. Scott asks how long the heat stress period needs to be in order to observe negative effects. Dr. Gerloff asks about calf mortality rates between the two groups. Dr. Laporta estimates a 12% death loss in the heat stress groups, who seem to be more susceptible to the usual calf illnesses. It appears that gut closure might occur earlier in heat-stressed calves - maybe even before birth, which does not bode well for their immune systems. (16:49)

Dr. Laporta details how heat stress impacts mammary gland involution. Early in the dry period, you want a spike in cell death to build new cells for the next lactation. In heat-stressed cows, the spike in cell death early in the dry period is diminished, not allowing those cells to die. This results in less proliferation of the mammary gland, and the cow starts her next lactation with older cells that weren’t renewed in full. Thus, producing less milk. Dr. Gerloff shares some of his experiences with heat stress in his area of Illinois. (22:17)

Heat stress has negative impacts on other organs as well. Heifers who experienced heat stress in utero are born with larger adrenal glands with altered microstructure. Dr. Laporta describes some of the DNA methylation that has been observed in these heifers. The panel discusses whether the response would be similar for other types of stressors, like cold stress or social stress. (26:19)

What can we do to mitigate these impacts? Cooling dry cows so they can thermoregulate during gestation is critical. Altering diets to account for heat stress is also an important strategy. Unfortunately, there is no magic bullet to “fix” cows who were exposed to heat stress in utero, but these negative implications can be prevented. Dr. Laporta has also focused on what she calls perinatal programming - after the calf is born, what can we do? She has been working to develop cooling mechanisms for calves and is interested in further investigating early life mammary development. (33:41)

When a dry cow experiences heat stress, she has fewer and smaller alveoli. Daughters of those cows have smaller udders with altered tissue growth. Granddaughters of those cows have fewer estrogen receptors in their udders and negative impacts on mammary proliferation. (44:30)

Panelists share their take-home thoughts. (47:52)

Scott invites the audience to Bourbon and Brainiacs at ADSA in Louisville - a bourbon tasting with all your favorite professors! Sign up here: https://balchem.com/anh/bourbon/ (54:31)

Please subscribe and share with your industry friends to invite more people to join us at the Real Science Exchange virtual pub table.

If you want one of our Real Science Exchange t-shirts, screenshot your rating, review, or subscription, and email a picture to [email protected]. Include your size and mailing address, and we’ll mail you a shirt.

...more

View all episodes

By Balchem Animal Nutrition & Health

6464 ratings