With current economic trends in the dairy industry, the producer needs to ensure efficiency in all aspects of milk production. Controlling diseases, such as mastitis, and reproductive performance are both key areas that contribute to overall profitability. Using nutrition to increase a cow’s defense against infections and improve reproduction has recently been an important area of research.
Minerals, such as selenium (Se), copper (Cu) and zinc (Zn), when properly supplemented, can enhance immunity against diseases by increasing resistance to and decreasing severity of infections when they occur. Additionally, proper mineral supplementation can reduce the incidence of retained placenta and fertility disorders in the cow and white muscle disease in calves or weak or stillborn calves.
Cow requirements for minerals are influenced by several factors including age, stage of pregnancy and stage of lactation. For some nutrients, the requirement for optimum immune response is greater than for growth and reproduction. Cattle can have sufficient mineral intake for adequate growth and reproductive performance but not have optimal immune performance. By the time clinical signs of deficiency become apparent, immunity, growth, and fertility have already been compromised.
Role of selenium, copper and zinc
Increased susceptibility to infectious disease because of malnutrition in livestock has been recognized for many years. The potential to influence immune function by nutritional supplementation has gained interest, especially because of the desire to decrease antibiotic use to ease consumer concerns.
Selenium and vitamin E have a critical role in protection of the body from infection. Vitamin E is important in protecting membranes of cells from oxidative damage by free radicals and selenium is a component in glutathione peroxidase. Glutathione peroxidase is an enzyme within cells that limits internal oxidative damage by free radicals. Deficiencies of these nutrients can decrease the phagocytic ability of cells in the mammary gland, which is needed to destroy ingested bacteria and reduce mastitis incidence and severity.
Copper has an important role in the immune system where its compounds are involved in reducing infections and diseases. Deficiencies of copper have also been associated with retained placenta, embryonic death and decreased conception rates. Inadequate Cu status may be related to an increased incidence of infections at calving, increased severity of infections and a higher SCC than that seen in Cu-adequate cattle. Copper is also a component of enzymes, such as cytochrome oxidase, necessary for electron transport during aerobic respiration, lysyl oxidase for strong bone and connective tissues, ceruloplasmin which is essential for hemoglobin synthesis, and superoxide dismutase which protects cells from the toxic effects of oxygen metabolites.
Zinc is an integral part of immunity as a key element of superoxide dismutase. It is also important in other enzyme systems that affect the metabolism of carbohydrates, proteins, lipids and nucleic acids. Zinc is essential in wound healing, epithelial tissue repair and maintenance of cellular integrity. Keratin, the substance that lines the inside of the teat duct and helps protect against pathogens by functioning as a physical and chemical barrier against pathogens, requires zinc for its formation. Zinc deficiencies delay sexual maturity, can cause fetal abnormalities and alter prostaglandin synthesis.
In the last decade the form of minerals supplied in feed has been the focus of much research. Concerns regarding pollution and animal production have led to the development of minerals chelated with an organic ligand. This makes them similar to the forms found in animal and plant material and allows for improved absorption and utilization when supplied in feed compared to inorganic mineral sources.
Mineral proteinates have been developed as a source of organic zinc, copper, manganese and cobalt. Proteinated minerals are a blend of single amino acid chelates and short chain peptide chelates. Certain minerals cannot be chelated due to their electrochemical properties. One such example is selenium. In order to produce an organic form of selenium it is necessary to supply it as a substrate for yeast fermentation. The mineral is metabolized into seleno-amino acids within the yeast.
Boland et al. (1996) conducted three trials in which organic minerals were supplemented in dairy diets. The control diets had similar mineral concentrations as the organic mineral treatments but without mineral proteinates. Supplemental organic minerals provided 100 mg organic Cu, 300 organic mg Zn and 2 mg organic Se per cow per day. Blood mineral status between treatment groups was similar, suggesting mineral status was adequate and unaffected by treatments. Cows supplemented with proteinated minerals in the three trials showed 52 percent, 45 percent and 35 percent reductions respectively in SCC when compared to controls. In the third trial, SCC was reduced by 52 percent during the final four weeks of the study. Boland also observed decreased days to first service (68.8 versus 75.4 days) and improved conception to first service (65.2 percent versus 57.7 percent) for cows supplemented with organic trace minerals.
Harmon (1998) supplemented heifers at 120 days prepartum with 10 ppm Cu (Cu sulfate or Cu proteinate) in a basal diet containing 6 to 7 ppm copper. Heifers supplemented with Cu proteinate had a higher proportion of quarters confirmed uninfected (67.5 percent) compared to control (47.5 percent) or Cu sulfate- (45.5 percent) fed cows. Fewer quarters were infected with staphylococci in cows supplemented with organic Cu (7.5 percent) compared to control (27.5 percent) and Cu sulfate- (31.8 percent) fed cows.
Scaletti et al. (2003) supplemented heifers beginning 60 days prepartum with 10 ppm Cu sulfate or Cu proteinate providing about 110 mg supplemental Cu daily prepartum and 200 mg daily postpartum. One quarter from each cow was infused with E. coli as an intramammary challenge to induce mastitis. Following challenge, Cu proteinate cows had higher white blood cell counts, lower E. coli in the milk and greater milk production compared to the control and Cu sulfate-fed cows.
In a more recent study (Silvestre et al., 2006), close-up cows 23 days prior to calving were fed diets containing selenium in the form of selenium yeast or inorganic selenium (sodium selenite). It was shown that feeding selenium yeast reduced the occurrence of fever in multiparous cows during the 10-day postpartum period, improved uterine health status within 10 days postpartum, improved second-service conception rates and increased milk production.
Selenium, copper and zinc in diets are important for optimizing health and reproduction of dairy cows. Adequate trace mineral status may protect the cow from adverse effects of acute inflammation caused by mastitis organisms. Further, supplementation with Cu and Zn proteinates and organic Se has improved udder health and reduced SCC. Reducing mastitis and lowering SCC will result in economic benefits and improved health and welfare of dairy cattle. Improving reproductive performance with Cu and Zn proteinates and organic Se will also have an economic impact on the farming operation, as this dictates daily milk production, number of replacements available and selective culling opportunities within the herd. Nutritional approaches for improving immunity and reproduction must be implemented along with proper mastitis management practices that reduce exposure of cattle to pathogens and proper reproductive management procedures. PD