In-Utero Heat Stress: Dry Period Heat Stress Effects on the Calf

Many studies within the last ten years have shown that heat stress during the dry period of the dam negatively impacts the calf. We know that the last 60 days of a cow's pregnancy are the most important for fetal development; this is when a lot of fetal programming and growth occurs (Bauman et al., 1980). When a cow's body temperature is raised because of heat stress, it also increases the temperature of the placenta, raising the body temperature of the calf (Laburn et al., 2000). Research has shown that this raised placental temperature affects that animal as a calf and as she becomes a cow and starts producing milk.

Impacts on the Newborn Calf

Heat-stressed cows during their dry period typically have shorter gestation lengths, resulting in smaller calves because they do not have adequate time to grow. This late gestation heat stress also lowers dry matter intake of the cow, limiting nutrients for the calf to develop (Tao et al., 2013). While smaller calves may have a calving ease advantage, they may be limited in their growth potential.

It is well known that calves are born with an impaired immune system and need high-quality colostrum to begin building it. Calves who experience in-utero heat stress cannot absorb IgGs as well, compromising their immune system (Tao et al., 2012). They cannot absorb IgGs as well as calves who had in-utero cooling because their gut closes earlier (Ahmed, 2017). Calves who experience in-utero heat stress have lower survival rates and are more likely to be culled before they ever have a calf (Monteiro et al., 2016).

Impacts on the Heifer

It has been seen in several studies that in-utero heat stress impacts the growth rate of heifers. One study showed that average daily gain was low from birth until weaning (Tao et al., 2012). A recent study showed that heifers who experienced in-utero heat stress were smaller at a year of age and had smaller follicles and corpus lutea, which may impact reproduction in the future (Davidson et al., 2025). Adequate growth is crucial to ensure that animals are large enough to be bred on time and have their first calf between 22 and 24 months. Animals that take longer than this to get to breeding weight cost farms money.

Lifelong Impacts

A groundbreaking meta-analysis showed lifelong effects of in-utero heat stress. Not only did animals that experienced in-utero heat stress have lowered milk production, but so did their daughters and granddaughters (Laporta et al., 2020). It is theorized that in-utero heat stress impacts the formation of the mammary gland, so these animals never reach their full potential (Skibiel et al., 2018).

What can you do to prevent these negative impacts?

While most people provide some form of heat abatement for their lactating animals, heat abatement for dry cows is essential too. Lactating cows are more easily heat-stressed because they put lots of energy into milk production, but dry cows can also get easily heat-stressed. Lactating cows experience heat stress at a Temperature-Humidity Index value of 68. This may not feel very hot to us, but it is to the cows, so it is important to remember to turn the fans on early.

Not only does cooling during the dry period increase milk production of the dam, but it also increases the milk production of the calf by 19% (Dahl et al., 2017). Cows must be provided heat abatement for their entire dry period, not just the far-off or close-up period, for the best results (Fabris et al., 2019). To learn more about this, check out this article: Dry Cow Heat Stress Abatement.

It is also important to remember bred heifers, as they are carrying calves that can experience in-utero heat stress. Bringing them into the barn 60 days before calving to get them in some sort of heat abatement is a good idea. Heifers who are provided with cooling before calving produce more milk (Davidson et al., 2021).

Heat stress can impact every age of animal in different ways. Set your calves up for success and provide cooling for dry cows.

References

Ahmed, B. M. S. 2017. Elevated in utero temperature: a suppressor of fetal development and ruminant fitness? Ph.D. Dissertation. Department of Animal Science, University of Florida, Gainesville, FL.

Bauman, D. E., and W. B. Currie. 1980. Partitioning of Nutrients During Pregnancy and Lactation: A Review of Mechanisms Involving Homeostasis and Homerhesis. J. Dairy Sci. 63:1514-1529.

Dahl, G. E., S. Tao, and J. Laporta. 2017. Triennial Lactation Symposium/BOLFA: Late gestation heat stress of dairy cattle programs dam and daughter milk production. J. Anim. Sci. 95:5701-5710.

Davidson, B. D., B. Dado-Senn, N. Rosa Padilla, T. F. Fabris, L. T. Casarotto, V. Ouellet, I. M. Toledo, G. E. Dahl, and J. Laporta. 2021. Late-gestation heat stress abatement in Dairy heifers promotes thermoregulation and improves productivity. J. Dairy Sci. 104:2357-2368.

Davidson, B. D., S. L. Field, B. Dado-Senn, A. D. Beard, P. L. J. Monteiro, K. A. Risgraf, A. R. Guadagnin, M. C. Wiltbank, G. E. Dahl, and J. Laporta. 2025. In utero heat stress compromises whole-body growth and mammary development from postweaning through puberty. J. Dairy Sci. Articles in Press, May 09, 2025.

Fabris, T. F., J. Laporta, A. L. Skibiel, F. N. Corra, B. D. Senn, S. E. Wohlgemuth, and G. E. Dahl. 2019. Effect of heat stress during early, late, and entire dry period on dairy cattle. J. Dairy Sci. 102:5647-5656.

Laburn, H., A. Faurie, and D. Mitchell. 2000. The thermal physiology of the ruminant fetus. P.B. Cronje (Ed.). Pages 295-310 in Ruminant Physiology: Digestion, Metabolism, Growth and Reproduction, CABI Publishing, Wallingford, UK.

Laporta, J., F. C. Ferreira, V. Ouellet, B. Dado-Senn, A. K. Almeida, A. De Vries, and G. E. Dahl. 2020. Late-gestation heat stress impairs daughter and granddaughter lifetime performance. J. Dairy Sci. 103:7555-7568.

Monteiro, A. P., S. Tao, I. M. Thompson, and G. E. Dahl. 2016. In utero heat stress decrease calf survival and performance through the first lactation. J. Dairy Sci. 99:8443-8450.

Skibiel, A. L., B. Dado-Senn, T. F. Fabris, G. E. Dahl, and J. Laporta. 2018. In utero exposure to thermal stress has longterm effects on mammary gland microstructure and function in dairy cattle. J. Dairy Sci. 57:1055-1060.

Tao, S. and G. E. Dahl. 2013. Invited review: Heat stress effects during late gestation on dry cows and their calves. J. Dairy Sci. 96:4079-4093.

Tao, S., A. P. A. Monteiro, I. M. Thompson, M. J. Hayen, and G. E. Dahl. 2012. Effect of late-gestation maternal heat stress on growth and immune function of dairy calves. J. Dairy Sci. 95:7128-7136.