Importance Of Trace Minerals In The Diet Of Small Ruminants

Small ruminants are mainly dependent on vegetation of unorganized grazing lands (bushes, forbs, shrubs, stubbles of cultivated crops) and tree fodders. Feeding of concentrate mixture and feed additive is only restricted to organized farms and most of the production systems are based on grazing without mineral supplementation. Mineral deficiencies have marked effect on productivity, particularly on growth, reproduction and health of animals. In females, mineral deficiencies negatively impacts reproductive performance in various ways, including delayed estrus, embryonic death, decreased conception, delayed puberty, increased instances of dystocia, silent heat, retained placenta and low birth weight of offsprings. In males, deficiency may lead to delayed puberty, decreased libido, reduced spermatogenesis and reduced semen viability. Essential trace elements include zinc, cobalt, copper, iron, manganese, iodine, selenium and molybdenum. These elements are required in smaller quantities and are important for several biological processes. Inadequate supply of trace elements causes biochemical dysfunction and disturbed physiological functions. Trace minerals are important for enzyme activity, antioxidant status, immune response skin, hair and bone health. Mineral supplementation is always necessary for sheep and goats as they are mostly reared on pasture. There are natural deficiencies or excesses of minerals in soil which is reflected in forages. Some minerals which are found in excess in soil, water and other feedstuffs may bind with other minerals, making them unavailable. For example, excess calcium interferes with the availability of magnesium and excess sulfur and molybdenum interferes with the availability of copper. Furthermore, dietary concentrations are varying depending on season, geographical region and forage species. Commercial mineral mixtures comprising the essential minerals are available for large ruminants and small ruminants have specific mineral requirements which are slightly different from large ruminants. The specific mineral mixture is prepared for small ruminants are based on their mineral requirement, feeding habitat, mineral status of feeds and fodders used in feeding practice. These specific formulations have shown better weight gain, higher immune status and low mortality in sheep and goats.

Trace minerals are mainly supplemented as inorganic forms i.e. sulfate, oxides and chlorides in the ration of animals. However, due to high interaction with other dietary nutrients and low bioavailability of inorganic trace elements, organic trace minerals such as proteinates and chelates are used. Organic forms of trace minerals more closely resemble the natural forms that are present in plants. Recently hydroxy sources of trace minerals are introduced and these are more bioavailable than inorganic and comparable to organic source.

Zinc: It is a key component of more than 200 metalloenzymes such as carbonic anhydrase, alkaline phosphatase, superoxide dismutase, carboxypeptidase A and B, alcohol dehydrogenase, lactic dehydrogenase etc. which are involved in the metabolism of carbohydrates, nucleic acid and fatty acid. Zinc is important for the function of DNA polymerase, thymidine kinase, DNA dependent RNA polymerases involved in the nucleic acid synthesis. Deficiency of Zn in growing animals reduces cellular division, growth and retards puberty. Zinc along with vitamin A is important for the normal functioning of ovary and vision. Zinc regulates phagocytosis by macrophages and neutrophils. It is important for the activity of immune modulators like thymulin which promotes T lymphocyte maturation. It plays an role in embryo implantation, membrane stability of RBC and wound healing. Supplementation of Zn in pasture grazed sheep increases lamb production as compared to non-supplemented sheep. In goat, Zn supplementation increase prolificacy by 14%. Zinc deficient ration in ram’s causes atrophy of seminiferous tubules and complete inhibition of spermatogenesis. In females, Zn is important for uterine involution and tissue repair after parturition. Zinc deficiency in sheep causes stiffness of joints, soft edematous swelling of the fetlock, development of horny overgrowths on mucosa of lips, parakeratosis, rough hair coat, emaciation and alopecia.

Manganese: It is important for bone formation, reproduction, growth and enzyme functioning. It plays an important role in the functioning of corpus luteum. Depressed and delayed estrus, poor conception rate and abortion have been associated with Mn deprivation in goats and ewes. In ram lambs, Mn deficiency restricts testicular growth. Manganese is required for lipid and carbohydrate metabolism as it is involved in the activity of pyruvate carboxylase. It is needed for synthesis of mucopolysaccharides in cartilage through the activation of the glycosyltransferase enzyme. Manganese is commonly supplemented in the ration in the form of MnSO4, MnO and MnCO3.

Cobalt: Cobalt is needed for vitamin B12 synthesis which is essential for energy and protein metabolism in ruminants. It is also assosiated with RBC production. Sheep and goats are more vulnerable to cobalt deficiency than cattle. Cobalt deficiency in sheep leads to anaemia, ill thrift, reduced appetite, poor reproduction, weepy eye with damp matted wool below eyes and wool break. Diet should contain 0.1 mg/kg DMI to prevent deficiency disorders. Availability of pasture cobalt is dependent on soil pH as soil pH rises cobalt availability decreases.

Selenium: It protects the tissue from oxidation and breakdown of cell membrane. It is essential for production of thyroid hormone by activating deiodinase enzyme. It is also essential for the production of prostaglandin. In pregnant ewes efficiency of Se causes white muscle disease in lambs which is known as stiff lamb disease and in male animals deficiency can lead to poor fertility. Excess selenium can be toxic to sheep and lead to colic, diarrhoea and collapse.

Copper: Copper is an essential component of a range of enzymes involved in cell energy metabolism in brain and signalling in the nervous system. It is involved in cellular respiration, bone formation and connective tissue development. Copper deficiency during mid-pregnancy in ewes leads to sway back in newborn lambs characterized by impaired development of spinal cord and cerebellum. In growing lambs copper deficiency leads to poor growth, scouring and poor fleece quality. When goats are exposed to prolonged Cu deficiency they present nymphomaniac reproductive behaviour. Goats are more sensitive to Cu deficiency than sheep. Excess Mo and S lead to Cu deficiency which leads to reproductive disorder in sheep and goats. Recommended level of Cu and Mo ratio in the ration is 3:1 to 6:1. Excess Cu can be toxic to sheep. Recommended level of copper in the diet is 10 ppm however, the maximum permissible level to prevent Cu toxicity is 17 ppm.

Iron: About 60% of Fe is present in the body is in the form of haemoglobin which is required for oxygen transport. It is a component of enzyme i.e. cytochrome oxidase which is involved in oxidative phosphorylation. It is involved in connective tissue development through activation of hydroxylases enzyme. Major deficiency symptom of Fe is anaemia. Milk contains a very low concentration of Fe therefore, kids/ lambs raised on milk alone for a long time can develop anaemia.

Iodine: It is required for the formation of thyroxin hormone which plays an important role in energy metabolism. It is important for normal fetal growth and development. Iodine plays a role in appetite control and adaptation to temperature changes. Along with Se, I2 plays an important role in brown fat metabolism in newborn lamb thus promoting lamb survival in cold climatic conditions. The minimum recommended level of iodine to prevent deficiency disorder in growing animals are 0.2 mg/kg DM whereas, in pregnant and lactating animals it is 0.5 mg/g DM. Care must be taken when animals graze on certain forage crops containing goitrogens which limits thyroid hormone production and results in increased iodine requirement. Iodine deficiency causes goitre, late-term abortion, stillborn, weak lamb and poor survival rate of lamb. However, oversupply of iodine in late pregnancy leads to increased neonatal lamb death due to reduced antibody absorption.

Srobana Sarkar1, Ravi Prakash Pal2, Shilpa Choudhary3, Amit Sharma4, Hujaz Tariq4
1ICAR- Central Sheep and Wool Research Institute, Avikanagar, Rajasthan
2Punjab Agricultural University, Ludhiana, Punjab
3ICAR- Indian Institute of Veterinary Research, Izatnagar, Uttar Pradesh
4Guru Angad Dev University of Veterinary and Animal Sciences, Ludhiana, Punjab