DOES GENETICS INFLUENCE A CALF’S SUSCEPTIBILITY TO DISEASE?

It is well known that the largest contributors to morbidity and mortality in preweaning calves are digestive issues and pneumonia (Urie et al., 2018; NAHMS, 2014). High levels of disease have substantial economic consequences in dairy heifer rearing systems, as the cost of raising a dairy replacement heifer to the close-up period is approximately $2,619 in 2026 USD (Overton and Dhuyvetter, 2020; inflation-adjusted). Treating digestive issues and pneumonia during the preweaning phase increases this cost, with the cost per calf for treating digestive issues $27.50 (Cangiano, 2023; inflation-adjusted) and respiratory disease $43.99 (Dubrovsky, 2020; Elmore et al., 2023; inflation-adjusted). In our current market, the value of a replacement heifer is high, increasing the need to improve the health of these animals to support long-term productivity. Both digestive issues and pneumonia are influenced by various environmental and management factors on the farm (McGuirk, 2008).

The Council on Dairy Breeding announced the incorporation of two new health traits, which will be introduced in August 2026. These traits will include Resistance to Diarrhea (DIA) and Resistance to Respiratory Problems (RSP) and will be reported as predicted transmitting ability (PTA) for both Holsteins and Jerseys. This leads me to the important question of whether some calves are born with a greater disease susceptibility. Axford et al. (2024) reported a low genetic variance of heritability of diarrhea, and Lynch et al. (2024) reported a low heritability for both diarrhea and respiratory disease. Although diarrhea and respiratory disease had a moderate correlation, suggesting that these diseases are primarily influenced by the environment and management of calves. The same study compared a sire’s estimated breeding value with the rate of disease incidence in their daughters. Calves born to the bottom 10% of sires were 1.8 times more likely to develop respiratory disease and 1.9 times more likely to develop diarrhea. In addition to sire effects, maternal health may also influence calf disease risk. Aufmhof et al. (2025) reported that calves born to dams affected by mastitis or claw disorders were more likely to develop diarrhea or pneumonia. However, could these observed associations be partially confounded by management practices? For example, producers may provide more intensive monitoring or care to calves from genetically superior or otherwise high-value animals, potentially influencing disease detection or treatment rates. Furthermore, environmental and management factors remain major determinants of calf health and should be considered when interpreting these associations.

Nutrition, stress, toxicants, maternal care, pair interactions, housing conditions, etc., all impact the health of the calf and its non-genetic inherited factors. These factors include the microbiota, which reside in and on the body of the animal. The intergenerational transmission of microbiota may increase the inheritance of disease susceptibility. The microbiota is dynamic and can be modulated throughout the animal’s lifetime. The future of breeding could incorporate these non-genetic inherited factors, although there is very little known about how to implement this (David et al., 2019). Modulation includes appropriate colostrum management and the use of direct-fed microbials, which are beneficial for the development of the gastrointestinal tract in the calf (Davies et al., 2022). Supplementation with Saccharomyces cerevisiae fermentation-derived products (SCFP) in calves increased average daily gain and reduced the incidence of diarrhea. However, when fed to close-up cows, there were inconclusive results on the impact on the calf. Replication of maternal supplementation of direct-fed microbials and their impact on the calf is needed (Li et al., 2026). The microbiota is vertically transmitted through the dam to the calf, from maternal sources such as colostrum, feces, and vaginal secretions. The environment that a calf lives in has a strong influence on the development of the gut microbiota later in the neonatal period (Gomes et al., 2024). Together, these findings emphasize that disease susceptibility is shaped by a complex interaction between inherited and environmental influences, with management practices playing a central role in determining calf health.

Overall, calf susceptibility to disease during the preweaning period is determined by the complex interaction among genetics, the microbiome, management, and the environment. Caution should be exercised when considering genetics as a major influence, given the low heritability of disease. As we continue to collect more data and improve record-keeping systems, these new health traits may become more reliable. Above all, good calf husbandry should take precedence.

— Victoria Blaney

vblaney@whminer.com