The trace mineral status of our cows and calves is a significant challenge for western Canadian producers and veterinarians.
I have written several times about Canadian studies documenting the importance of copper, selenium and other trace minerals, and their impact on health and reproduction. Although clinical disease can occur with severe deficiencies of these microminerals, many of the effects of deficiencies are not clinically obvious and may just result in lower productivity.
Two areas often affected are cow fertility and the ability to mount an adequate immune response.
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A recent study published in The Bovine Practitioner adds some more information on this important topic. The study was conducted at the California Animal Health and Food Safety Laboratory and used its database from 2012 to 2021. Researchers downloaded 857 beef cattle and 638 dairy cattle cases that included both a liver trace minerals test and a post-mortem diagnosis.
This study differs from others I have written about because the animals examined had died. This is a very different population than sampling healthy cows within a herd.
The populations also included a wide range of ages, from calves to cows. The study focused on three important trace minerals: copper, selenium and manganese.
One of the most striking results is the drastic difference between beef and dairy cattle. Copper deficiency in the liver was found in 33 per cent of the beef cattle and five per cent in dairy cattle. Selenium deficiency was evident in 45 per cent of beef cattle and five per cent in dairy cattle. Manganese deficiency was the only one more common in dairy cattle, at 32 per cent compared to 17 per cent in beef cattle. Overall, 73 per cent of the beef cattle in the sample had at least one trace mineral deficiency, compared to 45 per cent of dairy cattle.
Manganese deficiency was more common in dairy cattle, but less is understood about this mineral, including the difficulty in establishing normal levels in cattle.
This observation was somewhat expected because beef cattle often rely on free-choice minerals throughout much of the year, while dairy cattle are typically fed a total mixed ration that includes a trace mineral package. The authors noted many dairy cattle may have been over-supplemented with trace minerals, as many cows were above normal levels in copper and selenium.
Trace mineral deficiencies linked to illness
The second objective of this study was to evaluate associations between the cause of death determined by the pathologist and trace mineral status.
Results showed beef cattle that died of bovine respiratory disease were more likely to be copper deficient. This could mean copper deficiency is affecting the immune system of these animals, but the study cannot claim it “causes” bovine respiratory disease. Respiratory disease is infectious, but the authors established a relationship between the two factors in this population.
The study reinforces previous work showing beef cattle herds are more prone to trace mineral deficiencies. This may be due to a reliance on free-choice mineral intake or to complex interactions with elements such as sulphates or molybdenum, which can cause secondary deficiencies that beef cattle are more exposed to.
Trace mineral deficiencies are complex, and their impact is not always obvious.
As cattle come off pasture this fall and winter feeding begins, it may be a good opportunity to work with your veterinarian and nutritionist to evaluate your herd’s trace mineral status. This may involve taking liver biopsies or serum samples from a sample of cows and submitting them to a diagnostic laboratory for trace mineral levels. Feed and water testing may also be necessary when planning your winter feeding program.
