Salt, Trace Minerals and Fertility in Beef and Dairy Cattle

by Larry L. Berger, Ph.D.
Professor, Animal Sciences
University of Illinois

Introduction

Trace minerals have been shown in numerous studies to be essential to maintaining high fertility in beef and dairy herds. For the cow-calf producer, fertility is 10 times more important in determining profitability than production traits (size, growth rate, and feed efficiency) and 20 times more important than carcass traits (quality and yield grade). Similarly, dairy producers lose $2 to $5 per day per cow for every day a cow is open after 100 days post-calving. However, some producers may still doubt the economic impact trace minerals can have through influencing fertility.

Doyle et al (1988) recently demonstrated that supplementing range cows with zinc, copper and manganese can pay handsome returns with small changes in fertility. The four treatments compared were: (1) no supplementation, (2) 2.2 lbs of a grain-urea mix, (3) grain mix plus 15 grams phosphorus, and (4) grain mix plus phosphorus plus trace minerals. All cows were fed salt free-choice and there were no signs of mineral deficiency. The effect on fertility was demonstrated by the fact that the average days from the start of the breeding season to conception was 42, 35, 29, and 22 days (P <0.05) for the four nutritional treatments, respectively.

Economic response to trace mineral supplementation can be calculated based on the following assumptions. Assume the beef producer calved 100 cows and increased the average age at weaning 7 days because the calves were conceived 7 days earlier by feeding the trace minerals compared to the grain plus phosphorus treatment. Those calves should be approximately 14 pounds heavier at weaning (7 days X 2 lbs per day) and if sold for 80 cents per lb would generate an additional $1,120.00 (100 calves X 14 lbs X 80 cents per lb = $1,120.00). Since it would cost approximately $33.00 per year to provide the zinc, copper and manganese (33 cents per head X 100 cows), there would be a 33.9 fold return on investment ($1,120.00/$33.00 = 33.9). This calculation does not take into account the fact that cows which conceive early in the breeding season are more likely to breed again the following year and thus could further increase the return on investment.

Because of its economic importance and recent research which more clearly defines the role of individual trace elements in reproduction, the goal of this article is to review for the nutrition professional our current understanding of how trace elements affect fertility.

Zinc

Zinc is required throughout the body to activate enzymes and to from metalloenzymes. The enzymes required for nucleic acid metabolism and protein synthesis are most critical to achieving maximum fertility. Zinc deficiency is most obvious in the male but also affects the female. Research by Pitts et al (1966) showed that Holstein bulls fed zinc deficient diets had reduced testicular development compared to bulls fed a zinc adequate diet. Underwood (1981) reported that growth retardation and delayed onset of puberty were common in zinc deficient bull calves. This is due, in part, to decreased appetite and impaired protein synthesis.

In the female, low conception rates and abnormal estrus behavior are the most common symptoms associated with zinc deficiency. Underwood (1981) states that all phase of the reproductive process from estrus to parturition to lactation may be affected.

Diagnosis of a zinc deficiency should be based on clinical signs, diet analysis, serum zinc concentrations and treatment response. The National Research Council (NRC) suggest 30 ppm to be adequate, but Puls (1988) suggest that 60-100 ppm may be better for optimum health and fertility. Serum zinc concentrations less than 0.4 micrograms per milliliter of serum or below 20-40 ppm in the liver are considered deficient (Maas, 1987). Feeding a trace mineralized salt mix containing 0.5% to 2.0% zinc is recommended for treating a suspected zinc deficiency (Underwood, 1981). Zinc toxicity is very rare in ruminants. Cattle have been fed diets containing 1,000 ppm zinc for extended periods with no toxic effects (NRC 1984).

Copper

Only in recent years have we begun to appreciate the role of copper in bovine fertility. With the possible exception of phosphorus, copper is the mineral most likely to be deficient in grazing cattle. The exact mechanism by which copper deficiency causes infertility is not clear, but is probably related to one or more of the enzyme systems requiring copper.

Herd (1994) identified delayed or suppressed estrus and embryo death, often between day 30-50 of gestation, to be common symptoms of copper deficiency in beef cattle. Louisiana researchers (Kappel et al., 1984) reported that dairy cows with higher serum copper concentrations had significantly low days to first service (56 v. 70), fewer services per conception (1.1 v. 4.4), and fewer days from calving to conception (58 v. 183) compared to cows with low serum copper levels.

Infertility due to copper deficiency is becoming a more wide-spread problem in beef cattle because of the change in genetic makeup of the cow herd. Simmental and Charolais have been documented to have higher copper requirements than Angus (Herd, 1994). Practical experience suggest that Limousin and the other exotic breeds also have higher copper requirements than the British breeds. In fact, Herd (1994) suggests that the Exotic breeds perform best when their copper intake is about 50% greater than the NRC requirement of 10 ppm.

Identifying a copper deficiency requires the integration of animal observations, copper intakes from the feed, blood and liver copper concentrations and response to treatment. Herd (1994) recommends that the first step involve visual evaluation of the hair. Cows that have a marginal copper deficiency often have depigmentation of the hair around the eyes and ears, especially the peripheral hairs of the ears. In black cattle the hair around the edge of the ears will turn reddish-brown or mouse-colored. In cattle with red hair coats, the hair around the ears will often turn a yellowish-dun color. Often the hair will appear dry, kinky, lack luster, and be slow to shed in the spring. Although these symptoms can occur with other diseases, copper deficiency should be considered when they appear.

Blood copper levels of less than 0.5 mg/ml or liver tissue concentrations below 25 ppm on a dry matter basis are considered deficient (Smart et al., 1981). The beef NRC (1984) and dairy NRC (1989) recommendation is 10 ppm in the diet. However, if the diet is high in molybdenum and/or sulfur, 10 ppm may be marginal. Many researchers believe that copper requirements for maximum fertility are greater than those required for immune function and growth. Consequently, blood and liver copper concentrations above the "deficient" level may be necessary for high fertility.

The most common method of treating a copper deficiency is to feed a supplemental copper source with high bioavailability. Copper sulfate or copper chloride have been proven to be excellent sources while copper oxide is not recommended due to low availability. Free-choice feeding of a salt or mineral mix with 0.2% to 0.5% copper from copper sulfate has been very effective (MacPherson, 1983). In severe deficiencies, injections of copper glycinate or copper EDTA can be used. However, side effects such as injection site abscesses and hepatic necrosis are potential problems with this method of treatment.

Selenium

The role of selenium in maintaining high fertility has only recently been revealed. Selenium functions through glutathione peroxidase, which reduces hydrogen peroxide and other organic peroxides to less damaging endproducts. Glutathione peroxidase is active in the cytosol while another antioxidant, vitamin E, performs a similar role in the cell membrane.

Reproductive problems associated with selenium deficiency included retained placenta, abortions, birth of premature, weak, or dead calves, cystic ovaries, metritis, erratic or silent heats, and poor fertilizations (Corah and Ives, 1991). Ohio researchers (Julien and Conrad, 1976) reported that supplemental selenium reduced the incidence of retained placenta from 38% to 0% in deficient dairy cows with plasma selenium concentrations below 0.025 ppm. Feeding 0.92 mg selenium as selenite for the last 60 days of the dry period was 100% effective in this trial.

Because selenium and vitamin E play very similar roles in the body, both are often supplemented simultaneously. Kappel et al., (1984) reported that injecting selenium and vitamin E increased the number of fertilized ova from superovulated cows compared to control cows not receiving the injection. However, when the selenium status of the cows was adequate, no response to injectable selenium and vitamin E were observed.

Liver tissue is the best indicator of selenium status with 0.25 to 0.50 ppm wet weight considered adequate and concentrations below 0.20 ppm considered deficient (Puls, 1988). Blood selenium concentrations are more difficult to interpret. Generally, blood selenium concentrations < 0.5 ppm are considered deficient, 0.5 to 0.8 ppm are considered marginal, and concentrations > 0.8 ppm are adequate. The NRC beef cattle publication (1984) recommends 0.20 ppm selenium in the diet.

Selenium toxicity can be a problem in certain parts of the United States. Herbage grown on seleniferous soils often contain 5 to 20 ppm of selenium and can be toxic if consumed for extended periods. Toxicity symptoms included loss of appetite, sloughing of hooves, loss of tail and death.

Manganese

Manganese levels are often above NRC requirements in forage based diets, but may be poorly absorbed, especially if the diet is high in calcium. Hignett (1950) found that with cows fed low levels of manganese, fertility was adequate when calcium and phosphorus were in balance, but fertility was depressed when either calcium or phosphorus was high and the other was low.

Manganese is required for the enzyme needed to synthesize the mucopolysaccharide in cartilage and bone. In addition, manganese plays a key role in activating enzyme required for carbohydrate and lipid metabolism. It also may affect fertility directly because of its involvement with steroid hormone synthesis.

When Wilson (1966) compared 11 beef herds grazing low-manganese pastures, first service conception rates were improved from 51% to 63% by feeding 4 grams of manganese sulfate for 9 weeks beginning 3 weeks before the first service. In a study involving manganese, copper and zinc supplementation, DiCostanzo (1986) saw a trend toward increase ovarian activity and conception rates with manganese supplementation. Bentley and Phillips (1951) concluded that manganese deficiency delays the onset of puberty, reduces conception rate and increases the number of calves born with weak legs and pasterns. Manganese is nontoxic for ruminants and should not be a problem in a normal production environment.

Iodine

Iodine deficiency affects reproduction primarily as a result of hypothyroidism. Iodine is required for thyroxine production, the major hormone controlling basal metabolic rate. In the female, silent heat, early embryonic mortality, abortion, weak calves, retained placenta, and decreased conception rates have been observed with iodine deficiency (Corah and Ives, 1991). Bulls show a decreased libido, lower sperm count and lower semen quality.

The NRC recommends 0.5 ppm of iodine in the diet. Deficient soils or the presences of feed containing goitrogens are the most common factors causing an iodine deficiency. Plants such as cabbage, canola, kale, soybean meal or feeds high in nitrates are goitrogenic. Iodize salt is the best means of insuring the appropriate iodine intake. Infertility, as a result of iodine deficiency, is rare due to the widespread use of iodized salt for cattle. Iodine toxicity is almost never a problem in cattle. Diets contain 50 ppm will slow growth, but 200 ppm to 400 ppm are required to cause permanent damage or death.

Cobalt

Cobalt is required by the rumen microflora to synthesize vitamin B12. Vitamin B12 is required for normal protein, carbohydrate and mineral metabolism. Infertility resulting from a cobalt deficiency is associated with the wasting away of the animal. The most common symptoms are low conception rates, abortion and weak calves. Cobalt supplementation will normally correct these symptoms rapidly.

Vitamin B12 levels in the blood are the most common method of diagnosing a cobalt deficiency and should be above 0.5 nanograms per milliliter to be considered adequate (Puls, 1988). Free choice salt containing 120 grams of cobalt sulfate per ton has been effective in treating cobalt deficiency. Cobalt toxicity is not a problem with cattle because the toxic level is over 300 times the requirement.

In many production environments, trace minerals may be just as important as energy, protein and phosphorus nutrition to maintain optimal fertility in beef and dairy herds. The economic advantage is that the trace minerals can be supplied for less than a dollar per head per year. Providing a well-fortified trace mineralized salt should be at the foundation of any reproductive management program.

Literature Cited

Bentley, O.G., and P.H. Phillips. 1951. The effect of low manganese rations upon dairy cattle. J. Dairy Sci. 34:396.

Corah, L.R., and S. Ives. 1991. The effect of essential trace minerals on reproduction in beef cattle. Vet. Clinics of North America: Food Animal Practice. vol 7, No. 1 pp. 41.

Doyle, J.C., J.E. Huston, and D.W. Spiller. 1988. Influence of phosphorus and trace mineral supplementation on reproductive performance of beef cattle under range conditions. J. Anim. Sci. 66(Suppl. 1):462.

DiCostanzo, A., J.C. Meiske, and S.D. Plegge. 1986. Influence of manganese, copper and zinc on reproductive performance of beef cows. Nutr. Rep. Int'l. 34:287.

Herd, D.B. 1994. Identifying copper deficiencies under field conditions. Proc. Florida Ruminant Nutr. Symp. p. 76.

Hignett, S.L. 1950. Factors influencing herd fertility in cattle. Vet. Rec. 46:654.

Julien, W.E., and H.R. Conrad. 1976. Selenium and vitamin E and incidence of retained placenta in parturient dairy cows. J. Dairy Sci. 59:1954.

Kappel, L.C., and R.H. Ingraham and E.B. Morgan. 1984. Plasma copper concentration and packed ALI volume and their relationships to fertility and milk production in Holstein cows. Am. J. Vet. Res. 45:346.

Kappel, L.C. and R.H. Ingraham, and E.B. Morgan. 1984. Selenium concentrations in feed and effects of treating Holstein cows with selenium and vitamin E on blood selenium values and reproductive performance. Am. J. Vet. Res. 45:691.

Maas, J. 1987. Relationship between nutrition and reproduction in beef cattle. Vet. Clinic North America: Food Animal Practice 3:633.

MacPherson, A. 1983. Oral treatment of trace element deficiencies in ruminant livestock. Br. Soc. Anim. Prod. 7:93.

NRC. 1984. Nutrient Requirements of Beef Cattle. National Academy Press. Washington, D.C.

NRC. 1989. Nutrient Requirements of Dairy Cattle. National Academy Press. Washington, D.C.

Pitts, W.J., W.J. Millers and O.T. Fosgat. 1966. Effects of zinc deficiencies and restricted feeding from two to five months of age on reproduction in Holstein bulls. J. Dairy Sci. 49:995.

Puls, R. 1988. Mineral Levels in Animal Health. Sherpa International.

Smart, M.E., J. Gudmundson, and D.A. Christensen. 1981. Trace mineral deficiencies in cattle: A review. Can. Vet. J. 22:372.

Underwood, E.J. 1981. The Mineral Nutrition of Livestock. Commonwealth Agricultural Bureaux.

Ward, D. 1978. Molybdenum toxicity and hypocuprosis in ruminants: A review. J. Anim. Sci. 46:1078.

Wilson, T.G. 1966. Bovine functional infertility in Devon and Cornwall:Response to manganese therapy. Vet. Rec. 79:562.

© Salt Institute, 1994

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