Health Events in Dairy Cattle: Prevent Them All for Optimal Repro!

Health events are undesirable events in dairy farms, and in my opinion, are one of the biggest challenges the dairy industry has been facing. Although the incidence of some specific diseases, such as milk fever or clinical ketosis, has decreased in the last 20 years or so, the overall percentage of animals experiencing one or more diseases in the first 60 days after calving hasn't changed.

 If we start from the basis, a sick animal has impaired welfare since optimal health is a key component of animal welfare. Furthermore, diseases require costly interventions to treat affected animals and represent an important economic loss for the farm. Nevertheless, the biggest economic loss associated with animal diseases is not the cost of treatment, but the loss in animal performance and the higher chance of being culled.

Diseases can be defined as a deviation from an animal's tissues or cells' normal functions or structure that can be caused by a pathogen or metabolic disturbances, among others, and that is often associated with clinical signs or subclinical findings. This definition matches common dairy cattle diseases such as mastitis, lameness, and hypocalcemia. However, in dairy cattle, we have a broader term to refer to health issues, which is health events.  A health event is slightly different from a disease since the term includes animal losses, such as stillbirth, short-length events, such as dystocia, and undesirable events that have been associated with poor performance, such as twin births.

Regardless of the definition we used, these undesirable events have been associated with poor animal performance and lower longevity. Considering that 35-40% of dairy cows in the U.S. develop a health event in the first 60 days in milk, the latter is very relevant, and preventing disease should be the focus of any animal management program. The initial loss in performance is usually seen in milk yield since one of the primary signs of clinical disease in dairy cattle is a drop in dry matter intake and milk yield. On top of this, the veterinary treatment bill adds to the overall short-term loss of the disease. It has been estimated that common diseases such as clinical ketosis and lameness cost the farm between $145 and $400 per case.

However, the most significant loss in profit arises from the long-term effects of disease. Animals that experience a disease during the first 60 days in milk have decreased milk yield, decreased fertility, and an increased risk of being culled. A recent study reported the global cost of diseases in dairy cattle by loss category (i.e., yearly milk losses, calving interval increase, and culling rate), estimating a wide range of losses depending on the disease. For instance, in clinical ketosis, yearly milk loss was estimated to be 1.5% while in clinical metritis, it was 5.6%. Similarly, for other loss categories, such as culling rate, they reported a large range on the disease impact, suggesting a 1.1% increase in culling rate for cows with clinical metritis, while cows with clinical hypocalcemia were found to have a 3% increase.

In the past, there was the belief that diseases that affect the reproductive tract would have more severe effects on the animal’s reproductive performance. This belief has some scientific evidence, and in cases of severe reproductive diseases that can cause scarring of the reproductive tract, this still may hold true. Early studies assessing the effects of uterine diseases on reproductive performance reported strong associations between metritis and endometritis and a lower conception rate. A recent review by Dr. Leblanc, at the University of Guelph, summarized the literature in this area, reflecting on clear associations between metritis, purulent vaginal discharge, and endometritis and decreased reproductive performance, commenting on a broad range of negative effects such as decreased progesterone concentration and cyclicity.

In the global economic disease loss study mentioned above, it was reported that cows that had clinical metritis had the highest increase in calving interval compared to other common diseases. Similarly, research from Dr. Santos’s lab at the University of Florida that looked at 5,719 cows reported that calving-related diseases had a more severe negative effect on resumption to cyclicity at 60 days in milk compared to others. However, when looking at other reproductive parameters such as pregnancy at first service and pregnancy loss, it appears that no matter the health event the animal had, these parameters would be negatively impacted to the same magnitude. The latter was supported by more recent data published by Dr. Santos’s lab, where authors reported reproductive outcomes of cows categorized as having uterine diseases (retained placenta and clinical metritis) or non-uterine diseases (lameness, Mastitis, respiratory and digestive problems). In this study, the authors reported that both disease categories negatively affected reproductive outcomes to the same magnitude and suggested a synergistic effect between disease categories, where cows affected by both types of diseases would suffer a more profound negative effect in their reproductive performance.

I always reflect back on my veterinary school years when we used to be taught to cure diseased animals. Although this is still critical nowadays, because there will always be sick animals, the veterinary field priorities have shifted in the last 15 years or so to preventing diseases through proactive management instead of curing sick animals. This is even more important in production animal veterinary medicine, where the focus is on maintaining a healthy population of animals instead of individual animal care. With this being said, the key to optimal reproduction performance in dairy cattle is having excellent management focused on optimal animal welfare and health. Best management practices (e.g., excellent nutrition, low stocking density, clean and comfortable facilities) during times of challenge, such as the transition period, must be high up on the priority list to prevent diseases.

Although preventing disease is the ideal scenario in the path to optimizing reproductive performance, this may be a long-term process in some farms requiring high upfront costs (e.g., building a new barn). In this scenario, targeted reproductive management is required for animals that have had a health event in the first 60 days in milk. As mentioned before, an animal that has a health event early in lactation will have impaired fertility.  Proactive reproductive management, such as early evaluation of uterine soundness and cyclicity and proper intervention (e.g., hormonal treatment to restart cyclicity), may be beneficial in this group of animals. Similarly, if the cow fails to conceive in the first service, an aggressive re-breeding approach should be implemented with monitoring of ovary structures and a re-synchronization program accordingly. Another aspect to consider is that when choosing animals for breeding with high-cost semen, sex semen, or other more costly reproductive strategies, such as in vitro fertilization, these animals should be excluded from the breeding pool when possible.

Previously Published in Progressive Dairy, 07/11/25