While a lot of farmers see great benefits in supplying minerals for their cows, it is worth knowing why they are important and what you are putting your herd at risk of if you forego minerals to your late pregnancy cows. You’ll see that prevention is the only option for quite a few of the problems that develop from deficiency as the internal development of the calf is crucial to their productivity in life and for the welfare of both man and beast.
Historically, Iodine deficiency has been an issue in Ireland and is regularly an addition to water on dairy farms or included in most Lick supplements and rock salts. As a side note, Milk is a great source of Iodine for humans because cows pass it through their milk. Just like in human pregnancy, Iodine is very important to the developing calf, Low dietary iodine intake during pregnancy has been associated with an increased incidence of small and weak calves, increased incidence of goitre, decreased resistance to hypothermia, low immunity and generally low survival. Cows recycle Iodine poorly, which means that Iodine is not stored in the body, leading to shedding into their milk and as such must be supplied in the diet to compensate
Selenium is one of the trace minerals needed in very small amounts. It is one of the minerals which crosses the placenta from the cow to the calf and so Selenium supplementation of pregnant cows has been shown to increase the Selenium reserves in newborn calves. Selenium deficiency causes muscular dystrophy (weakening and wasting of muscle) which can cause issues during birth and higher rates of placenta retention, this is also known as white muscle disease in calves and can present as ‘buckled’ legs (see below). Be careful, as high Selenium areas do exist, and in this case it is dangerous to feed supplementary Selenium due to the potential for Se toxicity. If you are unsure of your animals Selenium status, soil samples or silage testing. Generally, coastal areas tend to be lower in Selenium while shale based soils tend be higher. Selenium and vitamin E are often considered together as they have a similar function.
In contrast to Selenium, the transfer of vitamin E across the placenta from the cow to the calf is low. This means the calf is born with low vitamin E status and is highly dependent on an adequate intake of colostrum, and then milk or milk replacer, to obtain vitamin E during early life. Dry cows with an increased intake of vitamin E during the dry period have colostrum with a significantly elevated vitamin E content. Ensuring the calf receives an adequate supply of vitamin E is important as vitamin E is required for good health and immune function. In cows it help udder health and overall immune response, helpful in the post calving weeks when the cow is more vulnerable to infections
Vitamin A and D
Like vitamin E, vitamins A and D do not cross the placenta in significant amounts and so the calf relies upon ingestion of colostrum for these vitamins. As a result it is extremely important that the colostrum contains adequate amounts of these vitamins. Vitamin A plays an important role in combating infection and it increases disease resistance and stimulates the immune system. Cows that have a deficiency in vitamin A can also produce dead, weak or blind calves because vitamin A is needed for normal growth and development including growth of the foetus. Cows grazing outdoors generally have high levels of vitamin D due to being outdoors and obtain high levels of vitamin A from the pasture. However if housed indoors on winter diets, the concentrations of these vitamins can be variable and in the absence of accurate information on dietary and animal vitamins status, supplementation is often good practice
As every farm is different a good place to start is testing your feed to see what your herd may be lacking and what you need to supplement in your own situation.
All the best,