Health & Husbandry
Solving the mystery of preweaning mortality.
January 17, 2026
It was Colonel Mustard in the ballroom with the candlestick! You don’t want to submit that as your final guess in Clue® unless you are sure of your answer.
Preweaning mortality can feel just as puzzling, but good records and investigation can turn the mystery into targeted health management. Solving this mystery involves clearly defining the problem, evaluating disease risks by timing and using findings to adjust preventative health practices.
Defining the problem
Preweaning calf death is a source of frustration and economic loss. Hoping for zero death loss is unrealistic, but managing the herd to minimize preventable deaths requires a good understanding of the causes of mortality.
Preweaning calf mortality varies among cow-calf ranches, with overall industry averages around 3%-3.5%, according to the National Animal Health Monitoring Systems (NAHMS) 2017 Cow-Calf Survey.
Data in this survey represent all herd types, and magnitude of losses is influenced by a variety of management practices. The national average makes a good upper bound. If herd preweaning mortality is consistently at or above this level, an intervention may be necessary.
Common mortality causes differ by calf age. In the 2017 NAHMS study, the most common infectious causes of calf death were digestive disease among calves younger than 3 weeks of age and bovine respiratory disease (BRD) among calves older than 3 weeks of age. Yet, neither was the most common cause of death. That distinction belongs to the notorious “unknown,” which is the most frequent cause of preweaning death.
There are times when calves go missing and the cause of death cannot be determined. However, the survey showed that 35%-45% of deaths were attributed to unknown causes. Preventing “unknown” is nearly impossible, because health management efforts cannot be focused in a specific direction. One of the first battles we face to curb calfhood death loss is putting the effort into determining and logging mortality causes.
Recording when and where calves died can be helpful. These numbers can be augmented by having your veterinarian perform a necropsy to determine the cause of death. We may assume cause of death, but this could be misleading.
Tracking mortality timing and causes over time can help build a valuable database to help identify changes in disease patterns or trends.
Timing of disease
Scours occurs early in life, but this is not the only disease affecting young calves. Based on the NAHMS 2017 survey, 14% of mortalities were associated with scours, 12% to BRD and 35% were birth-related. These are aggregate national numbers. However, within individual farms, the predominant challenge is likely associated with one of these areas.
Each component cause requires different solutions. Scours result from environmental challenges, pathogen exposure influences BRD early in life, and precalving/calving management practices influence birth-related mortalities. Formulating a long-term solution requires understanding of which disease is predominant.
After 3 weeks of age, BRD is more common; however, scours and other causes of sudden death may still occur. Mortality during this phase may be sporadic, but investigating each mortality is important because a single death may be due to an oddity or may be a signal for a bigger problem. Good records and identifying cause of death can help distinguish signals from noise in the production system.
Three-legged stool
Understanding mortality causes can be used to define the most appropriate preventative health programs. Principles of disease prevention are like three legs of a stool: animal, environment and pathogen.
Animals must have adequate immunity and the ability to respond to each disease challenge. Environmental management includes reducing pathogen burden, and specific pathogens may require additional disease-control techniques.
All three legs must be adequate to hold up the stool. When one area is the weakest, focusing resources in this area is most productive. Mortality records can provide insight into specific areas to focus the health management program.
Conclusions
Preweaning mortality doesn’t have to remain a mystery. Careful recordkeeping, timely necropsies and attention to age-specific disease patterns can turn guesswork into informed management. Each investigated death provides another piece of the preweaning mortality puzzle, and solving this mystery can lead to healthier calves.
Editor’s note: Author Brad White is the E.J. Frick Chair at Kansas State University College of Veterinary Medicine and serves as director of the Beef Cattle Institute. The Beef Cattle Institute has two weekly podcasts focused on a variety of cattle topics: Cattle Chat and Bovine Science with BCI. Learn more at www.ksubci.org.
Angus Beef Bulletin EXTRA, Vol. 18, 1-B
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