RED DEER – Recommendations for trace minerals in a dairy cow’s diet may not be high enough under certain conditions.
“We know the stage of the life cycle is affecting trace mineral status of the animal,” said nutritionist Mike Socha of Zinpro Performance Minerals at the Western Dairy Seminar in Red Deer March 9.
Twenty-year-old guidelines from the National Research Council had the same recommendations for all types of cows, but those changed in 2001 to better suit the changing weights and milking status of a dairy cow.
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Rations are often formulated under the assumption that environmental conditions are good. However, stress or other outside forces in cows’ lives can affect their retention of trace minerals.
Typically water does not provide many minerals but forages are a good source so feed should be tested and fortified accordingly.
Socha suggested current dairy recommendations for zinc, cobalt and manganese may not be high enough.
However, trace minerals fed in excess of requirements may impede absorption of other minerals and could be toxic. Copper and selenium do not have a wide margin for error.
“Copper is the one trace mineral we can least afford to oversupplement,” he said.
He has seen cases of copper toxicity in the United Kingdom as well as Ontario.
Copper drops in the last stage of pregnancy because it is being transferred to the fetus.
Sufficient manganese improves reproduction and its availability in water and feed is variable. Manganese in blood levels is low before calving so cows should be supplemented. It is a critical mineral for reproductive health, cholesterol synthesis and hormone development of estrogen, progesterone and testosterone. A low balance could result in abnormal sperm production in males and irregular estrus cycles in females.
There are high requirements for zinc to sustain early lactation. During this period cows eat more dry matter so they need more zinc.
Minerals and vitamins work together. High calcium can reduce the availability of zinc. High zinc levels can affect calcium synthesis. A low level of zinc can affect productivity and liver or skin problems may appear.
Vitamin E and zinc in the dry period can improve fertility by reducing the numbers of days cows are open and days to the first estrus.
Socha’s research shows cows could receive more than the requirements for cobalt supplements during early lactation for good milk production. Cows could be in a negative balance after eating high concentrate diets during this period. Cobalt is converted to vitamin B12 in the rumen so dietary factors affect how much is produced. Since B12 is degraded in the rumen, cows may require injections.
Trace mineral use can be reduced if cows eat soil during grazing. They may ingest soil if silage is stored in dirt or earthen bunkers or in hay cut with a discbine. Rain damage can introduce soil to the feed.
Besides minerals, cows need 13 of the 14 known vitamins, said Bill Weiss, a dairy nutritionist of the University of Ohio.
Vitamins are organic compounds needed in trace amounts for health, although it is not known how much is absorbed in the small intestine and into tissue.
Vitamins A and E are essential for dairy health. Cows are immuno-suppressed at calving time so there may be a drop in vitamin E, for instance.
Weiss recommended following the National Research Council guidelines and to remember that more is not necessarily better.
Dairy cattle diets should provide 84,000-100,000 international units of vitamin A. Lactating cows need about 500 IU per day and dry cows at less than 265 days of gestation should get 1,000 IU per day. Those receiving fresh forage or animals that are grazing probably do not need much supplementation.
Biotin at the rate of 20 milligrams per day is useful for hoof health although improvements may take six months.
Many herds feed their cows niacin but Weiss said it offers no particular benefit to the cow’s health.
Choline is destroyed in the rumen so it needs to be provided in a rumen-sensitive package, which is expensive. Between 50-60 grams per day of choline help reduce the risk of ketosis and fatty liver in overconditioned dry cows.
