(This will make an excellent future topic for the Keeping & Raising Cows Blog. Stay tuned!)
Supplements come in the form of grain such as corn, oats, or barley, by-products such as canola meal or brewer's grains, pelleted feeds such as alfalfa cubes, as well as salt, mineral and vitamin mixes that come in a loose form (crumble, mash, pellets, granulated), or in block form.
Often the answer to this question is yes, a person will often need to feed their cattle supplements. The next question, which is of much greater importance, is what kind of supplements need to be fed.
Typically a mineral-salt block is mandatory for cattle. Cattle cannot get enough salt from their feed alone, and need a source of salt to meet their dietary salt requirements.
The question of what minerals need to be fed depends on what feeds the animals are eating, as well as what the mineral content of the feed is. Macro-minerals such as calcium, magnesium, sulphur and phosphorus are usually found enough in feed, but to what balance? Legumes provide much more calcium and magnesium than grass-type feeds, and grass-based feeds (including grain) fare better in supplying enough phosphorus.
When it comes to micro-minerals however, typically these must be supplied in a loose mineral or block form to meet requirements. Micro-minerals include iron, zinc, selenium, iodine, cobalt, and copper.
Vitamins are not necessary for cattle during summer grazing. However, during the winter, or if feeding cattle stored feed, vitamins are important to add to the diet. Vitamins denature in stored feed and become unusable to the cow. Typically vitamins A, D, and E are supplemented.
Grains and by-products, which are called "concentrates" by most ruminant nutritionists, may be needed if the roughage feeds such as hay, greenfeed, silage, baleage or haylage are not meeting either (or both) protein and energy requirements. Cereal grains are excellent at helping with meeting energy needs, if enough is fed. Legume grains such as peas and faba beans are great for both protein and energy. Byproducts can also assist with meeting protein or energy needs. Canola meal, for example, has a high amount of protein to add to the diet in small quantities. Corn gluten meal and beet pulp are two byproducts that are high in energy that may be useful in ruminant diets.
What supplements you need largely depends on what type of feed you're giving your cows and the nutritional quality that it has been tested to be. It also depends on what type of cattle you're feeding and their bodily requirements. Mineral supplements largely depend on where in the world you live. For example, selenium may be deficient in your area, but not elsewhere.
It is highly recommended to work with a local and reputable ruminant nutritionist to help determine what supplements are needed to give to your animals.
The Bovine Practicum Q&A "blog" is an informative, just-for-fun section where I find a variety of questions that are often (and not-so-often) asked by inquisitive people like you, and answer them to the best of my ability. Much of the questions have come from a wide variety of reaches from the Internet.
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