Zinc is one of about a dozen trace minerals essential to the good life and productivity of dairy cattle. Yet unlike some of the other essential trace minerals, zinc is not easily forgotten in a well-balanced dairy diet because it performs so many different functions in dairy cows, and in so many different ways.
Much of this attention upon dietary zinc is because it has been studied so extensively over the last 100 years. In 1922 it was first discovered to play a vital role in the growth of mice. Since then, zinc has been scientifically proven to be part of over 300 mammalian enzyme systems (specialized proteins that trigger biochemical reactions in the body) involved in cellular energy metabolism, protein synthesis and the reproductive process, as well as genetics and immune function in cattle.
A bit of trial and error
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The National Research Council (NRC) says dairy cattle require about 40 mg/kg zinc in their diet to adequately perform these functions. Being a dairy nutritionist, I have balanced several lactating, dry and young stock dairy diets with these NRC amounts and even more fortified levels, and from many different zinc sources. Here are some of the “hit or miss” dairy examples that come from my experience:
- Hit. About 10 years ago, I developed the dry cow and lactation diets for a southern Manitoba 100-cow dairy herd. The herd had a high incidence of foot rot and white-line sole separation. I suggested we feed zinc-methionine (a specific chelated-zinc) at four grams per head daily. After six months, most of these hoof issues were almost non-existent. The hoof trimmer even commented that the cow herd’s hoof horn became much harder during trimmings.
- Miss. In a similar way, I instructed a 300-cow dairy to add four grams per head per day of zinc methionine to his lactation dairy premix, which in turn was added to his daily milking TMR. At the time, he had a string of cows that became lame due to hairy warts. I thought extra dietary chelated-zinc would help reduce its incidence. After two weeks, my suggestion was sidelined in favour of running cows biweekly through a clean acidified copper or acidified footbath, and more strict use of medicated footwraps.
- Hit. Zinc methionine has been proven to stimulate cellular keratin production in cows’ teat ends, tissue that forms a protective covering over the teat opening and helps prevent mastitis. So at the producer’s request, about five years ago I added zinc methionine at five grams per head daily to a lactation TMR diet fed to a 150-cow dairy. His herd SCC dropped from 260,000/ml to about 190,000/ml in about three weeks. About a week later, he culled a few cows with SCC of over 1.5 million/ml, which dropped herd SCC even further.
- Miss. Elevated zinc levels have been used as a growth promotant in baby pigs. I elevated the zinc level by formulating more zinc oxide in a dairy calf starter from 40 ppm to 60 ppm. Neither growth rate, feed efficiency or health were noticeably improved in pre-weaned calves raised in dairies that fed my zinc-fortified calf starter.
Enzymatic functions
Much of my “hit” experience on zinc for dairy cattle is most likely due to heightened enzymatic functions. In contrast, there is a growing body of studies that are examining the more physical/direct non-enzymatic and antibacterial activities of dietary zinc in dairy cattle.
For example, zinc oxide nanoparticles (ZnO-NP) have been recently developed, with a microscopic particle size of one to 100 nm. At this ultra-small size, researchers in India (2020) demonstrated 650 and 850 ug/ml ZnO-NP significantly lowered the level of mastitis organisms and in contaminated milk samples collected from a local lactation dairy herd. Similar laboratory in-vitro studies of ZnO-NP improved the growth rate of rumen micro-organisms by improving their rumen fermentation of added dietary nutrients as well as improved rumen microbial proteins synthesis.
While there has been plenty of research, study of zinc technology is still in its infancy. More research is necessary before nano-zinc like common-grade zinc oxide can be added to practical dairy diets. Regardless of this current timeline, it still shows that dietary zinc has a timeless vitality in dairy nutrition and has a promising future as a vital essential nutrient for dairy cattle.
