Roles of Minerals in Reproduction of Dairy Animals

Introduction

Reproductive efficiency of the animal is an important factor for the success of any dairy farm. Among other nutrients minerals play very important role in maintaining reproductive health of a dairy herd. The minerals of prime importance are classified into macro elements (Ca, P, K, NaCl, and Mg) and trace elements (Cu, Co, Se, Mn, I, Zn, Fe Mo and Cr) depending upon the quantities (NRC, 1989). Trace elements are also important for reproductive health (Chester-Jones et al., 2013). Adequate concentration of trace minerals helps in achieving higher conception rates. Trace minerals helps in improving the reproductive performance of cattle (Kumar et al., 2011; Grace and Knowles, 2012). Reports suggest that mineral deficiency greatly influence the ovarian activity in ruminants (Boland, 2003). Minerals are also involved in the synthesis of hormone essential for reproduction. Their deficiency will affect the production of both steroidal (Boland, 2003) and thyroid hormone (Abdollahi et al., 2011). The normal cellular functions of the body is unaffected if the required physiological concentrations of the mineral in present in the body (Ceylan et al., 2008). In India, the main factor behind low production and suboptimal reproductive efficiency of our livestock is due to inadequate nutrition and that too particularly because of minerals deficiencies. Because of their role in follicular dynamics, ovarian activity and fertility, minerals are the integral component of production animal’s diet (Ansotegui et al., 1999, Boland, 2003, Corah and Ives, 1991). Reproductive failure may be induced by deficiencies of single or combined minerals or by their imbalances. This review will focus on the mechanism by which various minerals act and their daily requirements by the dairy cattle.

Macro Minerals

1. Calcium:

Calcium is the most abundant mineral present in the body as most of the body skeletal part is formed from it. Major function of calcium in reproduction is assisting in parturition, muscle contractibility, maintaining the muscle tone of the uterus and uterine involution. Low blood calcium levels will lead to delay in involution, increase the chances of retained placenta, dystocia and higher incidence of uterine prolapse (Morrow, 1980). If calcium deficiency occurs, it causes decreased in muscle contraction which in turn leads to less feed intake as rumen function decreases and hence leading to severe Negative Energy Balance (NEB). As a result mobilization of fat increases which in turn causes fatty liver syndrome and ketosis (Boland et al., 2001). This will lead to decrease in milk production and will impair fertility. Hence, the chances of retained placenta increase in the fresh calving and also it delays the uterine involution. Postpartum anestrous is enhanced leading to economic loss to owner. Excess of calcium can also affect the reproductive performance by causing secondary deficiency of various minerals like phosphorus, magnesium, zinc and copper by inhibiting their absorption from intestine. Increased calcium concentration can also cause a decline in the conception rate among cow by causing the secondary deficiency of P, Mg, Zn, Cu, and other trace elements, by inhibiting their absorption in the intestine (Saba et al., 1987). The ration for dairy cow should preferably contain 0.75 to 0.80 per cent calcium on dry matter basis.

2. Phosphorus:

Phosphorus is an important bone mineral and plays a major role in various biochemical reactions in body. Phosphorus is present in the ATP which is the energy source of majority of metabolic processes. It is also a component of cell wall in the form of phospholipids. A deficiency of phosphorus is frequently associated with anorexia, retarded growth, decreased milk production and reproductive insufficiency. It is mainly involved in altering or disturbing the estrous cycle (Cromwell, 1997). In a study, heifers were fed with 70-80% of required phosphorus, and then the number of services per conception was high approx. 3.7 this number reduced to 1.3 when adequate phosphorus supplementation was done (Bindari et al., 2013). Its deficiency can also lead decreased ovarian activity, irregular or anestrous and lower conception rates. It has been reported that animals with reproductive disturbances are deficient in phosphorus. Therefore it is recommended that adequate supply of phosphorus must be made to the cattle to avoid fertility related problems. The ration should contain a minimum of 0.45-0.50 % of phosphorus on dry matter basis.

3. Potassium (K):

Toxicity of potassium may lead to delay in onset of puberty, delayed ovulation, poor quality of corpus luteum and high rate of anestrous in heifers. Smith and Chase reports lower fertility in cows fed with high levels of potassium or diets in which the potassium-sodium ratio was too wide.

4. Salt (NaCl):

Salt contains Sodium (Na) and Chloride (Cl) and is often supplemented as a free lick to animals. Sodium is essential in maintaining the osmotic balance, helps in cellular uptake of glucose and in amino acid transport (NRC, 1989). Salt deficiency can lead to problems of digestive systems and hence indirectly affects the reproductive health. The daily requirement of dairy cattle can easily be met by adding 1 % salt to the grains and offering additional salt as free lick.

5. Magnesium:

Magnesium plays an important role in maintaining normal bone growth, various enzyme systems and nervous system. It helps in degradation of fiber in rumen. High magnesium levels are required during early lactation to maintain the normal milk output. Magnesium antagonizes with calcium and hence can have an indirect effect on reproductive health and also any change in Ca-P-Mg hemostasis will lead initiate the reproductive problems. In heifers, udder edema can be prevented by feeding of 18 mg magnesium oxide 5-6 weeks prior to parturition. Decreased reproductive efficiency can occur due to magnesium deficiency following general loss of appetite (Kumar, 2003). In a 500-kg cow, there is about 0.7 g of magnesium in the blood, 2.5 g of magnesium in all extracellular fluids, 70 g of magnesium inside cells, and 170 g of magnesium within bone mineral. In pregnant animals, the fetalplacental requirement for magnesium is about 0.181 g/day in Holsteins from day 190 until the end of pregnancy (House and Bell, 1993). Grace (1983), however, estimated the requirement of the fetoplacental unit in late gestation was 0.33 g/day.

Trace Elements

1. Copper:

Copper exerts its role as a cofactor in the activity of various enzymes and reactive proteins ceruloplasmin (Suttle, 2010).When the level of Cu is below physiological needs problems like early embryonic deaths, fetal resorption, necrosis and increased chances of retention of placenta develops. In dairy cows they may show delayed or suppressed oestrous, impaired ovarian function and infertility. Adequate serum copper level of dairy cow have positive effect on reproductive health leading to less days to first service, fewer services per conception and fewer days to open. Deficiency of copper along with cobalt is having deleterious effect on the reproductive performance leading to delay in onset of puberty, low conception rate, early embryonic death and higher chances of retention of placenta. Copper is essential for the absorption and transport of iron necessary for haemoglobin synthesis, hence needed for erythrocyte production. It is also necessary for melanin synthesis and interaction of copper and oestrogen are also observed.

2. Cobalt (Co):

Cobalt plays its role in the synthesis Vitamin B12. Levels of Vitamin B12 are high in milk and colostrum which is required for the conversion of propionate into glucose and folic acid metabolism. Cobalt deficiency leads to reduce fertility and poor conditioning of the developing fetus. In dairy animal deficiency leads to prolonged uterine involution, irregular estrous cycle, lower conception rates and early calf mortality (Kumar, 2003). Deficiency of cobalt will in turn lead to Vitamin B12 deficiency. Manganese, zinc and iodine may reduce cobalt deficiency (Patterson et al., 2003). The dietary requirement of cobalt for dairy cattle is 0.11ppm (Miller et al., 1998).

3. Selenium:

Selenium along with vitamin E acts as protective and anti-oxidant in the body by deleting the free radicals formed during per oxidation. In pregnant animal marginal deficiency of selenium leads to abortion, birth of weak calves that are unable to stand. Research indicates that selenium supplementation reduces the incidence of retained placentas, cystic ovaries, mastitis and metritis (Patterson et al., 2003). Being having direct link to the uterine involution selenium is important dietary mineral. Chronic selenium toxicity leads to hoof problems mainly sore feet, lameness, deformed claws, and rocket shaped hoofs (Patterson et al., 2003). In herds where selenium levels are extremely low, injections are often required to rapidly return blood selenium levels to normal. After injection, feed supplements may provide enough selenium to maintain adequate blood levels in the cow. Among dairy animals, where subclinical selenium deficiency is there, reproductive performance may get retarded with delayed ovulation, increased services per conception and high incidence of mastitis. Selenium helps in enhancing the reproductive efficiency by increasing the activity of glutathione peroxidase in blood and tissues. Selenium easily crosses placenta whether fed as inorganic or organic food. It has been reported that selenium supplementation leads to improved conception rate at first service. In herds, supplementation of feed resources with selenium injection is helpful in maintaining the recommended blood level within normal range i.e. 8-10 mg/100 ml. Selenium injections prior to parturition helps in reducing the incidence of retained placenta in deficient animals. On dry matter basis the ration should contain 0.1 ppm selenium for ruminants (Miller et al., 1998).

4. Manganese (Mn):

Manganese acts as activator of many enzyme systems that take part in metabolism of carbohydrate, fats, protein and nucleic acids (Patterson et al., 2003). It is required for the synthesis of cholesterol which is responsible for steroidal hormone synthesis like estrogen, progesterone and testosterone. Decreased production of these steroid hormones will have effect on the reproductive performance by delaying the ovulation and disturbing the cyclicity of estrous. The corpus luteum, which is essential for maintaining the level of progesterone during pregnancy, has high level of manganese. Manganese acts as a co factor in the reaction for synthesizing cholesterol which acts as a precursor for estrogen, progesterone and other steroidal hormone. Concentration of vaginal manganese in cyclic animal is higher than in non-cycling animal (Dutta et al., 2001). Manganese deficiency will lead to infertility, congenital limb defects in newborn, retarded fetal growth, cystic ovaries, poor follicular growth, delayed ovulation, increased embryonic mortality and lower conception rates. Supplementation of manganese in feed helps in early postpartum estrous and higher conception rate in dairy animals.

5. Zinc:

Zinc act as cofactor and coenzyme of many enzymes and various reproductive hormones. Zinc plays an essential role in the maintenance and repair of uterine lining after calving, helps in early involution. Abnormal levels of zinc is associated with decreased conception rate, abnormal estrous and abortion. Zinc as coenzyme, is involved in the formation of prostaglandins form arachidonic acid suggesting its profound effect on reproductive cycles and maintenance of pregnancy (Kumar et al., 2011). Zinc also increases the plasma beta carotene level that has been directly correlated to higher conception rate and embryonic development. Delayed puberty and low conception rates, failure of implantation and reduction of the litter size are also found in association with the zinc deficiency in feed. The recommended dietary requirement of zinc for dairy cattle lies between 18-73 ppm (Patterson et al., 2003) depending upon the stage of the lifecycle and dry matter intake, whereas according to the feeding standards the requirement is 40 ppm (NRC, 2001). Apart from this, various other minerals like copper, cadmium, calcium and iron reduce zinc absorption and interfere with its metabolism (Patterson et al., 2003).

6. Iron:

Iron is essential for the synthesis of hemoglobin and myoglobin and various other enzymes that help in formation of ATP through electron transport chain. It helps in transport of oxygen to tissues, maintenance of various oxidative enzyme systems (Khillare et al., 2007). Deficiency is rare in adult animals due to its abundance in feed stuffs. But in cases where deficiencies are there, reproductive health is deteriorated due anemia, reduced appetite and poor body condition. Chances are there that deficient animal will become a repeat breeder and will require increased number of services per conception and may abort occasionally (Kumar et al., 2011).

7. Iodine:

Iodine due to its action on thyroid gland affects the reproduction. Iodine is regarded as essential for the developing fetus and maintaining the basal metabolic rate. Iodine through its effect on thyroid gland helps in secretion of gonadotropin by stimulating the anterior pituitary gland, thereby affects the estrous cycle (Khillare et al., 2007). Deficiency of iodine affects the fertility and increases the abortion rate, the incidence of retained placenta and post-partum uterine infections, respectively. Conception rate and ovarian activity is reduced with the impaired thyroid functions. Thus iodine affects the reproduction in many ways and a recommended dose of 15-20 mg of iodine each day is necessary for a cow to have good reproduction status. Excess of iodine also have deleterious effect on reproductive health by inducing premature births of weak calves, abortions and lowers the immunity status of animal (Kumar et al., 2011). Subclinical iodine deficiency is characterized by increased stillbirths, suppressed oestrous, increased chances of retained placentas and prolonged gestation periods. Normal plasma level of inorganic iodine in cows should be maintained between 100- 300 ng/ml.

8. Chromium:

Chromium is essential for carbohydrate metabolism. It is present in nuclear protein in higher amount thus has a role in gametogenesis and for healthy fetal growth. It is also an integral part of the pregnancy specific protein that is secreted by uterine endometrium which helps in preventing the early embryonic mortality (Kumar et al., 2011). It is having a crucial role in maturation of follicle thus maintaining the oestrous cycle and also in LH release which triggers the ovulation. Deficiency of chromium will lead to irregular oestrous cycle, delayed ovulation, early embryonic mortality and retarded fetal growth. In lactating animals it may predispose the animal to ketosis and decreased milk production.

9. Molybdenum:

Molybdenum deficiency in animals delays the onset of puberty, decreases conception rate and causes anestrus (Kumar, 2003). Molybdenum and copper are interlinked with each other as deficiency of one occurs in the presence of toxic levels of other. Therefore a proper balance in feeding the copper and molybdenum must be followed to avoid the reproductive problems.

Conclusion

Mineral are help in maintaining growth, health, production and reproduction in animals. The reproduction of animal is greatly influenced by minerals present in diet of animal. Mineral whether in deficiency or in toxicity have been shown to affect the reproduction on animals. Minerals have a beneficial role in resuming the follicular activity and fertility in dairy cattle. Hence in order to avoid the chances of reproductive failure and other reproductive disorders we have to supplement adequate quantities of mineral required by the animal.

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