The age of cattle also affects nutrient requirements. Higher amounts of all nutrients are needed during growth as compared to adult maintenance needs. Another fact is that the rumen does not begin to function until a calf is about 6 to 8 weeks old. Before this time, therefore, the calf requires a diet similar to that of non-ruminant animals, one which contains all the energy, protein, vitamins, etc., in a readily digestible form.
Whole milk, of course, is the best food for the young calf, but many milk replacer products are also available for this purpose.
After the rumen begins to function, dairy calves must be fed rations that contain all nutrients at levels high enough to support growth. With beef cattle, however, the growth period is most important since this is the time during which the meat (muscle) is formed. Therefore, the diet must be designed to promote rapid growth and formation of the right combination of muscle and fat to produce quality meat.
Growing and finishing (being readied for market) beef cattle require slightly higher protein and considerably higher energy levels than do growing dairy cattle. High levels of concentrate feeding are most often used with just enough forage included to keep the rumen functioning normally.
Another technique that promotes weight gain in beef cattle is the use of growth stimulants. These are substances that increase the efficiency of conversion of food to muscle (meat).
For example, some antibiotics when mixed in small amounts with the feed will alter the microbial population of the rumen and intestine, resulting in improved growth and feed efficiency. Also, certain chemicals and hormones stimulate growth by altering chemical reactions in the body. These substances can be formed into pellets and placed under the skin (implanted) in growing beef cattle. The active chemicals then are slowly dissolved into the blood over several months, resulting in long term stimulation of growth.
When formulating rations (deciding upon the mixture of various feeds) of dairy or beef cattle for various functions such as growth and production, be sure the ration is balanced that is, contains all the necessary nutrients at appropriate concentrations. This requires a knowledge of those requirements. Such information is available in several textbooks and government publications.
One must also know what basic feeds and supplements are available for use and at what cost. Availability and cost of ingredients differ in various parts of the United States.
On dairy farms, the roughages such as corn silage or hay often are grown on the farm and hence are used as the basis of the ration. Many farmers have these forages analyzed in order to be sure of the nutrient content. The amounts to be fed daily to each animal will depend upon the number of animals, the total amount of feed available, and the number of days during which the feed will be used.
Information on nutrient content of the forages as well as how much will be fed per animal each day can then be combined to determine how much of each essential nutrient (protein, energy, minerals) is supplied by the forages to be used.
Comparing this information with the nutrient requirements allows a calculation of how much of each essential nutrient must be provided by the concentrate, protein and mineral supplements, etc. This procedure is known as ration balancing. This can be done by hand; however, today many computer programs can also be used for this purpose.
Frequently, in feedlot situations where finishing cattle are fed, purchase of all feeds is necessary. In this case a "least cost" approach often is used in balancing rations. That requires considering costs of the available feeds as well as their nutrient content.
While least cost ration balancing is complex, computer programs are available which can be used to formulate a balanced ration by using the most economical combination of the feeds and supplements available. The least cost technique also can be used to balance rations for dairy cattle and other animals.
When, for any number of reasons, balanced rations in adequate amounts are not fed, nutritional disease results. Both underfeeding and overfeeding of any or all essential nutrients can result in disease problems.
Failure to provide adequate amounts of nutrients in general results in various degrees of starvation syndrome. In animals that are mildly underfed, a slightly decreased growth rate may be the only sign in growing cattle, with decreased production seen in adults.
Moderate underfeeding will result in a significant decrease in size compared to age in young animals, and decreased production and weight loss in adults. Severe underfeeding results in weight loss and eventual death in both young and adult animals.
Overfeeding of a balanced ration results in overconditioned cattle which can also result in disease problems, particularly at and shortly after calving.
Individual nutrient deficiencies can result in specific diseases in both beef and dairy cattle. For example, a frequent problem in beef cattle on pasture in the winter is hypomagnesemic tetany or winter tetany.
This disease is the result Of low blood magnesium levels caused by too little magnesium in the diet, and is most common in beef cows with nursing calves. Signs of the disease include nervousness and a stiff gait progressing to falling down, paddling, and convulsions. Death occurs within a few hours of the onset of convulsions. Sometimes cows are just found dead in the pasture.
Treatment of affected animals must be accomplished quickly by intravenous administration of magnesium and calcium.
A similar disease known as grass tetany can occur in beef or dairy cattle on lush grass pastures in the spring. The disease can be prevented by insuring adequate intake of magnesium.
Overfeeding of specific dietary ingredients can cause serious disease problems. Grain overload is a common disease of this type in feedlot beef cattle. Micro-organisms of the rumen in cattle fed forage are adapted to breaking down fiber. Feedlot cattle must be slowly changed to a high concentrate ration which contains high levels of starch and sugar. When too much grain is fed to unadapted cattle, the starch and sugar is broken down to acids.
The consequences of this are many, including overdistention of the rumen with fluid, dehydration of the animal, death of the rumen wall, founder, severe metabolic changes, and death of the animal. A similar problem can occur in dairy cattle if they suddenly consume large amounts of grain. This disease can be prevented by slowly increasing the concentrate intake so that micro-organisms in the rumen can adapt to breaking down starch and sugar rather than fiber.