Water Soluble Vitamins
B-vitamins are abundant in milk and other feeds. B-vitamins are synthesized by rumen microorganisms, beginning soon after a young animal begins feeding. As a result, B-vitamin deficiency is limited to situations where an antagonist is present or the rumen lacks the precursors to make the vitamin or impaired rumen microbial activity.
Vitamin B12
Vitamin B12 is the generic descriptor for a group of compounds having vitamin B12 activity. One feature of vitamin B12 is it contains 4.5 % cobalt. The naturally occurring forms of vitamin B12 are adenosylcobalamin and methyl cobalamin. These are found in both plant and animal tissues. The primary functions of vitamin B 12 involve
metabolism of nucleic acids, proteins, fats and carbohydrates. Vitamin B12 is of special interest in ruminant nutrition because of its role in propionate metabolism, as well as the practical incidence of vitamin B12 deficiency as a secondary result of cobalt deficiency. Primarily, cobalt content of the diet is the limiting factor for ruminal microorganisms synthesising vitamin B12. A vitamin B12 deficiency is difficult to distinguish from a cobalt deficiency. The signs of deficiency may not be specific and can include poor appetite, retarded growth and poor condition. In severe deficiencies, muscular weakness and demyelination of peripheral nerves occurs. In young ruminant animals, vitamin B12 deficiency can occur when rumen microbial flora have not reached adequate populations or are depleted due to stress.
Thiamin
Thiamin functions in all cells as a coenzyme cocarboxylase. Thiamin is the coenzyme responsible for all enzymatic carboxylations of keto-acids in the tricarboxylic acid cycle, which provides energy to the body. Thiamin also plays a key role in glucose metabolism. Synthesis of thiamin by rumen microflora makes it difficult to establish a ruminant requirement. Generally, animals with a functional rumen can synthesize adequate amounts of thiamin. In all species, a thiamin deficiency results in central nervous system disorders, because thiamin is an important component of the biochemical reactions that break down the glucose supplying energy to the brain. Other signs of thiamin deficiency include weakness, retracted head and cardiac arrhythmia. As with other water-soluble vitamins, deficiencies can result in slowed growth, anorexia and diarrhea.
Niacin
Niacin functions in carbohydrate, protein and lipid metabolism as a component of the coenzyme forms of nicotinamide, nicotinamide adenine dinucleotide (NAD) and nicotinamide adenine dinucleotide phosphate (NADP). Niacin is particularly important in ruminants because it is required for liver detoxification of portal blood NH3 to urea
and liver metabolism of ketone in ketosis. Niacin is supplied to the ruminant by three primary sources: dietary niacin, conversion of tryptophan to niacin and ruminal synthesis. Although adequate quantities of niacin are normally synthesized in the rumen, several factors can influence ruminant niacin requirements, including protein (amino acid) balance, dietary energy supply, dietary rancidity and niacin availability in feeds. Young ruminants are most susceptible to niacin deficiency and a dietary source of niacin or tryptophan is required until the rumen fully develops. In most species, the first signs of niacin deficiency are loss of appetite, reduced growth, general muscular weakness, digestive disorders and diarrhea. The skin may also be affected with a scaly dermatitis. These signs are often followed by a microcytic anemia.
Choline
Choline is essential for building and maintaining cell structure and for the formation of acetylcholine, the compound responsible for transmission of nerve impulses. While all naturally occurring fats contain choline, little information is available on the biological availability of choline in feeds. Unlike most vitamins, choline can be synthesized by most animal species. However, it is recommended that milk-fed calves receive supplementation of 0.26 % choline in milk replacers. Calves fed a synthetic milk diet containing 15 % casein exhibited signs of choline deficiency. Within a week, calves developed extreme weakness, labored breathing and were unable to stand. Supplementation with 260 mg choline/L milk replacer alleviated the signs of choline deficiency.
Conclusions
Minerals play a significant role in production and reproduction either singly or in combination. Overcoming the deficiency or imbalance of the trace minerals improves the productive efficiency of livestock to great extent. Hence minerals are to be considered in tropical feeding system not in isolation but as a part of total nutrient management system. In India, where land availability for grazing or fodder cultivation is less and type of cultivar (grains, legumes, oil seeds) is designed mostly for human consumption, only the by-products become available to animals. Hence the emphasis should be on ways of mineral supplementation cost-effectively based on prevailing livestock farming system and available resources. Three forms of mineral supplements can be practically adopted. 1. General purpose, productivity supporting, inorganic mineral compounds 2. Special purpose (high phosphorus, high calcium, high zinc), which are area specific formulated depending upon valid area survey results. 3. Organic ligand bound specific supplements (chelates, proteinates, amino acid complexes) for feeding under stressful / deficient conditions.