Producers often wonder about the cause of death when a cow dies.
A post mortem can be performed and an exact cause identified, but due to cost and inconvenience, few producers ask their veterinarian to do one. More often, they ask the veterinarian to make a guess without the benefit of an examination.
To help veterinarians, researchers set out in 2002 to find out how many cows die and why.
The study included production units with more than 50 cows in Alberta, Saskatchewan and northeastern British Columbia. In all, 34,665 adult cows and replacement heifers were studied in 203 herds.
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Average herd size at the start of the study was 171 cows and replacement heifers. At the end of the study, before replacement heifers were added for the next breeding season, it was 145.
In all, 6,338 animals were removed because of culling, sale, mortality or disappearance.
The researchers calculated the risk of cows leaving the herd as a rate per 100 cow years. Loss from inventory for any reason was 19.8 per 100 cow years, which means about 20 percent of animals are lost in a year. Culling amounted to 14.3 percent, being sold four percent, mortality 1.1 percent and disappearance 0.4 percent.
In the one-year study, 355 breeding female cattle were reported as having died or been euthanized on 151 farms. Of these, 209 had a post mortem, which is excessively high because of the producers’ participation in the study.
Significant causes of death (10 or more animals per cause) included:
The rest of the deaths included such causes as heart failure, orthopedic issues, kidney infections and toxemia. Only two died from clostridial disease and only one died from nitrate poisoning.
The study discovered that the mortality causes we are familiar with, which are based on studies done at slaughter plants primarily in the United States, are not valid. Those studies suggest high incidences of lameness, cancer eye and lumpy jaw.
In contrast, death on the Canadian farms studied in 2002 is attributed more to acute conditions that don’t allow salvage because of condemnation.
With this information, veterinarians can now have valid discussions with producers about reasons for culling and death losses. Also, benchmarks have now been identified so producers will know if their losses are too high.
The other advantage is that we also know we can affect death loss rates. Factors linked to nutrition and feeding management were the most common contributors to death loss – 25 percent of all causes. By making feeding changes, we can help avoid hardware disease, bloat, nitrate poisoning, encephalomalacia, atypical interstitial pneumonia and myopathy, which is linked to vitamin E or selenium deficiency.
Most deaths occurred between March and May, which was partly because of calving season. However, myopathy occurred because feed’s vitamin E content becomes depleted by this time of year. Calving and early lactation are times of high vitamin E requirement because of exertion and high oxidative stress. Supplementing with vitamin E can avoid this.
Ensuring there is no metal in the feed prevents hardware disease. Modifying ration formulation can help avoid bloat and AIP.
Published in the 2009 Canadian Veterinary Journal, this data provides an insight into the percentage of animals lost from the herd inventory.
Because the study was done in 2001-02, we may find that culling practices have changed because of economic pressures caused by BSE.
However, the incidence of the different diseases would not have changed substantially.
