Animal Nutrition begins with energy which is probably the best definite requirement of farm animals and is expensive. Animals derive most of the energy they need from breaking down the fibre contained in the forages. The remaining amount needed comes from burning concentrated starches and fats. The feed industry usually measures energy in 2 different ways.
The first and more used method is the Total Digestible Nutrients (TDN). The TDN consists of the sum of the digestible carbohydrates, protein, and fats (multiplied by 2.25 since fats contain much more energy than protein or carbohydrates). This system considers energy that is lost in the faeces, urine, gases, and the work of digestion. A more refined version of this system accounts for varying energy utilization needs for body maintenance, weight gain, and milk production.
Gross energy is the total energy in feed, determined by the complete oxidation (burning) of the feedstuff and measuring the heat produced. The energy value is expressed in calories. Common feedstuffs are similar in gross energy content but differ in feeding value because of differences in digestibility.
A total digestible nutrient (TDN) is another method of expressing the energy content of feeds or the energy requirements of cattle. TDN is comparable to digestible energy. It has been used longer than the net energy system, and more values are available for feedstuffs.
TDN = Digestible nitrogen-free extract (carbohydrate) + digestible crude fibre + digestible protein + (digestible ether extract x 2.25)
Carbohydrates are the major source of energy in diets for dairy cattle. Between 50 and 80% of the DM (dry matter) in forages and grains is carbohydrate. Three major categories of carbohydrates exist in feeds:
- simple sugars (glucose)
- storage carbohydrates (starch)
- structural carbohydrates or fibre (cellulose and hemicellulose). Sugars are found in the cells of growing plants and such feeds as molasses. Starch is the main component of grains.
The fineness at which forages are chopped during harvesting can alter the effectiveness of fibre for maintaining chewing activity. Hay crop silages should be chopped at a minimum of 3/8 inch theoretical cut length to provide 15 to 20% (weight basis) of the particles greater than two inches long. Chopping at 1/4 inch provides only about 10% of the forage particles greater than two inches long. Maize silage should be chopped at 1/4 to 3/8 inches.
The energy content of fat is about 2.25 times the energy in carbohydrates. Diets for baby calves that include large quantities of milk or milk replacer may contain 10 to 35% fat in the DM consumed. Fat may be added to the diets of adult ruminants to increase energy density and reduce feed dustiness. Normally diets contain no more than 4% fat in the DM. Total fat and oil should be limited to less than 7% of the DM in lactating cow rations. Too much fat decreases feed intake, may depress the fat and protein content of milk, and may cause scouring. Commonly fed sources of fat include whole cottonseeds, fat soybeans, sunflower seeds and various rumen-inert fat products.
Protein is essential for maintenance, growth, and milk production. The protein requirement of dairy cattle is a requirement for amino acids by the animal tissues. Amino acids are supplied by the digestion of microbial protein and by feed protein that escapes microbial breakdown in the rumen. Protein is the only nutrient that contains nitrogen. Rumen microorganisms manufacture their own body protein, consisting of all the necessary amino acids, which are later digested by the host animal. Protein makes up the basic animal tissue of the body and is vital for growth, milk production, disease resistance, reproduction, and general maintenance. The body has very little if any excess protein. Mostly, the nitrogen is eliminated by the kidneys, and the rest is burned as energy. Since protein is generally the most expensive part of the ration, feeding more than needed is costly. Protein requirements vary between 12 and 16% of the ration dry matter, which is needed for high milk production.
The microorganisms of the rumen for the production of a protein can utilize urea and other non-protein nitrogen products. They are not generally recommended for goats because they are very selective in their diets.
The optimal diet fed to dairy cattle will
- Meet the nitrogen requirement of rumen microorganisms for maximum synthesis of microorganism protein
- Allow for maximum escape or bypass of high-quality feed protein for digestion in the small intestine. Protein synthesis by rumen microbes will depend on feed intake, organic matter digestibility, feed type, protein level, and feeding system.
Vitamins are organic compounds needed in small amounts for life support. They contribute no measurable amount of protein or energy to the animal but function in chemical reactions involving other nutrients. If a vitamin deficiency occurs, definite symptoms appear and become more severe unless corrected.
The vitamins can be classified into two broad groups:
- Water soluble vitamins,
- Fat-soluble vitamins.
Water soluble vitamins include the B vitamins: thiamine or B1, riboflavin or B2, niacin, Pantothenic acid, pyridoxine or B6, vitamin B12, biotin, and folic acid. Choline is often included in the B complex group. Under normal dietary conditions, B vitamins are synthesized in sufficient amounts in the rumen to meet the animal’s needs. Supplemental B vitamins may be required during diseased conditions, periods of stress, or for very young animals. Vitamins are needed by the body in small amounts. Since all the B vitamins and vitamin K are produced in the rumen and vitamin C is manufactured in the body tissues, the only vitamins of concern in ruminant nutrition are vitamins A, D, and E. During the good season, with rains and a warm climate, the animals can get all they need from green pastures and plenty of sunshine. It is a good idea to add these vitamins at the rate of 6 million units of vitamin A and 3 million units of vitamin D to each ton of grain mix when supplementing animal feeds as an added precaution since they are relatively inexpensive.
Supplementing 6 grams of niacin from 2 weeks before calving (prepartum) to 8 to 12 weeks after calf down (postpartum) can reduce ketosis and minimize fatty liver formation in high-producing cows. Another water-soluble vitamin, vitamin C (ascorbic acid), is not required by dairy cattle because they can synthesize it within their tissues.
Vitamin A or its precursor, carotene, is needed for normal vision and for the avoidance of reproductive problems and respiratory disturbances. Carotene is found in green forages and yellow maize. Synthetic forms of vitamin A are available. One milligram of beta carotene provides 400 international units (IU) of vitamin A.
Vitamin D, the sunshine vitamin, is needed for bone growth and development and the absorption and metabolism of calcium and phosphorus. Vitamin D supplementation is essential when animals are confined without direct sunlight and receive silage forages and grains primarily.
Vitamin E is an antioxidant, reducing off-flavours in milk (1000 IU per cow per day), preventing white muscle disease in calves, lessening the severity and duration of subclinical mastitis, improving reproductive performance, and stimulating the immune system. One milligram of alpha-tocopherol equals 1 IU of vitamin E.
Vitamin K normally is synthesized in adequate amounts in the rumen and intestine to meet the animal’s needs. Vitamins are most commonly supplemented in the diet but are available in injectable forms. The recommended minimum and maximum vitamin content in diets for dairy cattle are listed.
Minerals have both structural and regulatory functions. They are needed for bone and teeth formation, hormone actions, enzyme activation, and water balance. They are a structural part of hormones and haemoglobin (iron). The minerals needed in the largest amounts (macrominerals) by the dairy cow include calcium, phosphorus, magnesium, sodium, chlorine, sulphur, and potassium. Sodium and chlorine usually are provided in the form of salt. Minerals required in small amounts (trace minerals) include iron, copper, manganese, zinc, iodine, cobalt, and selenium. Other minerals may be required in very minute amounts, including molybdenum and fluorine. Many minerals are required by animals can be obtained from good forage and a regular concentrate mixture. The major minerals of concern are calcium, phosphorus, and salt, which are usually added to the ration either in the grain mix or by free-choice feeding.
Trace mineralized salt is a common source of salt and trace minerals. The adequacy of trace mineralized salt to meet the requirements of an animal will depend on the potency of trace minerals in the salt and the productivity level of the animal. Trace mineralized salt does not contain appreciable amounts of magnesium, sulphur, or potassium. In many diets, these minerals are in adequate amounts and do not require supplementation. However, if they are needed, proper supplements will have to be provided. Magnesium oxide is a common source of magnesium. Sulphur can come from elemental sulphur, sodium sulphate, magnesium sulphate, or potassium sulphate. Potassium is available in potassium salts such as potassium chloride or potassium sulphate. Many commercially formulated feeds contain trace mineral information on the feed tag.
Mineral excesses should be avoided because of interaction with other minerals and possible toxicity. For example, even though copper is needed in small amounts, it can be toxic. Lead causes toxicity and can be a problem when stalls are painted with lead-based paint. Such paint should be avoided in painting paddock equipment and other items to which cattle have chewing access.
Water is the nutrient required in the largest amount by dairy cattle. This is the cheapest feed ingredient (compared to the rest). Nevertheless, it is essential since a deficiency can affect milk production more quickly than the lack of another nutrient. Water is the largest single constituent of nearly all living plant and animal tissue; it is also essential during digestion, excretion of waste products, assimilation of nutrients, control of body temperature, and milk production. Ready access to water is important. Milk animals with water constantly available produce more milk than those watered 2 times per day and over 10% more than those watered only once per day, based on research findings.
Advisably, 3 litres of water for every litre of milk produced should be given to a dairy milking animal. Keep the drinking place clean by putting up a concrete area where cattle can stand as they drink or a small wall to prevent them from entering the water. The water can also be deviated from a stream using a furrow and channelled into a cattle trough. Another source of clean water is wells which should be constructed close to the farm yard or main grazing area. The amounts of water (litres per day) cattle need for growth, maintenance, pregnancy, and milk production are estimated. An equation can also be used to estimate the water intake of lactating dairy cows.
Water intake (litres/day) = 4.22
+ (0.19 x Dry Matter intake)
+ (0.049 x kg of milk)
+ (10.6 x grams of sodium)
+ (0.02 x minimum daily temperature in ºC)
Eg. A lactating cow consuming 18 kg of Dry matter and 85 grams of sodium, producing 29 kg of milk and experiencing an average minimum temperature for the week of 14 ºC should
Consume a minimum of 56 litres of water per day. Water supplies contaminated with bacteria or high in nitrates and sulphates may cause health problems and reduce animal performance. Fresh water should always be available for cattle.
Find more information in the Books of the Author: Success in Agribusiness
Farm Animal (Cattle) Nutrition