Theme Diet formulation

By Dr D. J. Tomlinson, M. T. Socha and J. M. DeFrain, Zinpro Corporation, USA

Trace minerals play critical roles in the development and function of the immune system. It is, therefore, imperative that trace mineral status be maintained to insure sufficient stores are available for optimal animal performance or when animals become diseased or stressed.

Zinc for better skin
Zinc has a critical role in maintaining the health and integrity of skin due to its role in cellular repair and replacement, all keys to the natural defence mechanisms of the mammary gland. The type of zinc is also important. Cornell University research indicated that cows challenged with Streptococcus agalactiae recovered faster when supplemented with complexed (bioavalable)  zinc versus ordinary zinc sources as indicated by lower somatic cell counts. Research conducted in Germany showed cows fed complexed zinc during the dry period and into early lactation had numerically lower SCC and lower lactate dehydrogenase activity (a measure for mastitis) than cows similarly supplemented with only inorganic zinc. A study conducted in 2004 showed that feeding a combination of complexed and inorganic zinc reduced SCC by an average of 33%

 

 

 

 

 

 

 

 

(98,000 cells/mL) while increasing milk production 1.3 kg/d (Figure 1). An additional mode of action for zinc in improving mammary health is related to its role in keratin formation (Moynahan, 1981). Keratin is a wax-like substance secreted into the teat-end orifice or opening. The keratin lining of the teat canal entraps bacteria and prevents their upward movement into the mammary gland through its bactericidal properties.

Strong effects of copper
Like zinc, copper is considered to have strong effects on the immune system. Copper is active in neutrophil production and affects phagocyte killing ability. Copper is required for antibody development and lymphocyte replication. Copper, in combination with zinc, plays a role in superoxide dismutase activity and the removal of oxygen free radicals. It is therefore a key component in the protective mechanism of cellular membranes against superoxide free radical damage. In addition to superoxide dismutase, the copper containing enzyme, ceruloplasmin has been shown to exhibit anti-inflammatory activity, which may prove beneficial when mastitis occurs. Cattle suffering from a marginal copper deficiency will have reduced growth rates and reduced feed efficiencies. They will also have reduced fertility (male and female) and increased incidences of retained placentas. Workers at the University of Kentucky reported heifers supplemented with 20 ppm copper from copper sulphate had lower bacterial counts, SCC and peak rectal temperatures following exposure to an E. coli challenge than control

animals supplemented with 6 to 7 ppm copper. Research at Texas A&M showed severely copper-deficient late gestation beef cows supplemented with complex copper responded with lower colostrum SCC than non-supplemented cows (Figure 2).

Limited knowledge on manganese
Similar to zinc and copper, manganese plays an important role in removing superoxide radicals (free radicals) from the body. However, evidence that manganese plays a major role in immunological function is limited. Increasing manganese has been shown to
enhance the killing ability of macrophages via increased enzymatic activity within non-specific immunity.

Iodine and metabolism
Iodine is required for the synthesis of the thyroid hormone, thyroxin, which regulates the rate of  metabolism (NRC, 2001). Among the signs of subclinical iodine deficiency is a suppressed immune system resulting in increased incidences of foot rot and respiratory diseases. There have been several studies conducted that show a benefit of feeding iodine in the form of ethylenediamine dihydriodide (EDDI) in excess of the nutritional requirement to prevent foot rot. Only 8.3% of calves on pasture fed a salt mixture containing EDDI had foot rot, while 20.8% of calves receiving a salt mixture without EDDI had foot rot. When cattle were inoculated intradermally in the interdigital space with a mixture of Fusobacterium necrophorum and Bacteriodes melaningenicus to induce acute foot rot, cattle receiving 12.5-200 mg/head/ day of EDDI had less lameness than control cattle.

Role of iron
Iron is a necessary component of hemoglobin and myoglobin for oxygen transport and cellular use. Iron also has a role in energy metabolism as it facilitates transfer of electrons in the electron
transport chain for the formation of ATP. Iron supplementation is usually not needed in ruminant diets due to the high iron content of many feedstuffs and soil contamination of many feedstuffs that are ingested by cattle. Recent changes in meat and bone meal and phosphorus supplementation have greatly reduced the amount of background iron normally provided in dairy diets. However, field reports are beginning to indicate increased incidences of dairy cows suffering from anaemia around calving.

Antioxidant properties of selenium
The interaction of selenium and immune function focuses around the selenoprotein, glutathione peroxidase. Glutothione peroxidase inactivates oxygen radicals such as hydrogen peroxide and prevents them from causing cellular damage. Research by Reffett et al. (1988) indicated that selenium deficiënt calves had lower serum IgM (an antibody produced by B cells) concentrations and anti-IBRV titers when challenged with infectious bovine rhinotrachetis virus than selenium adequate calves. Weiss reported that supplementing dairy cattle with adequate levels of selenium (0.3 ppm of dry matter) reduced the prevalence, severity and duration of mastitis as well
as SCC (2005). In addition, this report suggested organic forms of selenium have little benefit over inorganic sources, but warrant further investigation.

Chromium boosts growth
Chromium promotes insulin action, resulting in increased uptake of glucose and amino acids by cells in the body. Signs of a chromium deficiency include reduced growth rate, reduced feed efficiency and reduced immune function. A chromium deficiency in cattle may result in increased incidences of ketosis, decreased milk production, decreased feed efficiency and suppressed immune response. Research has shown that chromium supplementation may help alleviate the effect of stress on the animal. Feeding 200 to 1000 ppb of supplemental chromium from
organic sources to newly arrived beef cattle in the feedlot reduced serum blood cortisol levels by 40 to 60%. Chromium supplementation during the calving period may help improve the immune function, reducing the incidence of disease and metabolic disorders that accompany immune suppression.

Assessing trace mineral status
Trace mineral status is not static, fluctuating throughout the lifecycle of an animal. Research at the University of Minnesota indicates that zinc, manganese and copper status, as measured by concentration in the liver, are lowest in late gestation and early lactation. In order to gain a better understanding of trace mineral status, body tissues (i.e. blood, liver, etc.) may be sampled. However, trace mineral content of some tissues may not be reflective of trace mineral status of the animal and may result in erroneous conclusions. While blood is a suitable tissue to sample and to assess iodine, iron (saturation of iron binding proteins, non-heme iron) and selenium status in cattle, it is an inappropriate tissue to sample and to assess copper, zinc, and manganese status. Liver is a better indicator of manganese, copper and selenium status than blood. Liver cobalt can be used to indirectly assess an animal’s vitamin B12 status, yet results must be interpreted with caution. Zinc and copper concentration in liver are a better indicator of the mineral status than serum or plasma zinc or copper concentration.

Trace mineral recommendations
For nutritionists balancing trace mineral levels in livestock rations, the following steps are suggested:
1) Identify specific mineral needs of the animals. Theactual mineral requirement will depend upon stage of growth, production rate, metabolism and mineral concentration in the ration. 2) Determine a realistic requirement for each trace mineral, taking into consideration the presence of antagonists in the diet. 3) Because trace mineral bioavailabilities vary with different chemical forms and diets, evaluate available research and determine what is the most consistent and predictable product on the market that suits the animals’ needs and the producer’s performance expectations. Table 1 lists the current recommendations from Zinpro Corporation.

Conclusion
Balancing rations for today’s high performance dairy cattle require that we not only deliver proper amounts of amino acids, energy, carbohydrates and fat, but that we also balance rations to deliver the proper amounts of trace minerals in forms that an animal can utilise. Trace minerals are key components in the normal functionality of the immune system and are therefore critical to maintenance of immune competence for optimal animal performance.

• This article has been edited from its original form, presented at the latest AFMA congress in South Africa.

Source: Feed Tech magazine. Volume 11. No. 10