8 July 2012

6 minute read

Beef cattle producers spend a significant amount of money on supplements without knowing for certain it provides adequate mineral for their herd. Substantial variation in mineral status can occur due to diet, productivity, location, and environment. The National Research Council (NRC) is the primary source for mineral requirements, defining recommended levels of macrominerals such as calcium (Ca), magnesium (Mg), phosphorus (P), potassium (K), sodium (Na), chlorine (Cl), and sulfur (S). Recommendations also are provided for essential microminerals such as chromium (Cr), cobalt (Co), copper (Cu), iodine (I), iron (Fe), manganese (Mn), molybdenum (Mo), selenium (Se), and zinc (Zn). Macro and micromineral requirements are presented in a “range” to stay within and prevent deficiency or toxicity symptoms, not to maximize production.

The NRC micromineral recommendations are based primarily off of research using inorganic minerals (oxides, sulfates, and salts), with no consideration of mineral bioavailability. Mineral bioavailability is the degree to which the amount of ingested mineral is absorbed and available to the body. This would mean that some forms of mineral would need to be fed above the NRC requirements to meet the animal’s needs. For example, the NRC (2000) states a Cu requirement of a pregnant cow is 10 mg/kg (or ppm). If Cu sulfate or oxide is supplemented, their respective bioavailabilities are 85% and 10% (Kegley and Spears, 1994). Therefore, if you fed 10 mg/kg to each animal in the herd, they would absorb and retain only 8.5 or 1 mg/kg. Most minerals supplemented today are in their inorganic forms (oxides, sulfates, and salts). However, chelation has been used to potentially improve absorption of microminerals. Chelation means “firmly attached”, and in the case of minerals, the inorganic form is attached to an amino acid or other organic component. The process mimics how a mineral would be incorporated in a feed ingredient (grazing forage, grain, etc.). It also allows the mineral to be considered “organic”, following the attachment to an organic substance. Chelation allows the compound to stay together in the digestive tract with a potential increase in absorption. This process is primarily used for microminerals, whereas the macrominerals are more readily absorbed in their inorganic forms.

Magnesium (Mg) bioavailability was similar between inorganic Mg oxide and Mg hydroxide (Davenport et al., 1990). Both sources were effective in preventing deficiency symptoms when fed at the maximum tolerable concentration (Davenport et al., 1990). Kegley and Spears (1994) determined Cu sulfate and Cu lysine had similar bioavailability, but Cu oxide was virtually unavailable. Plasma Cu concentrations and ceruplasmin (a Cu metalloenzyme) activity were used to measure relative Cu bioavailability. This brings up an important point that methodology used to assess mineral status is a significant factor to consider when determining mineral status of an animal. Blood, urine, feces, and liver tissue collection have been the primary sample sources used to approximate mineral status (Kincaid, 1999). Liver concentrations were determined to be the most accurate, and a production response from the animal was determined to be the definitive means of measurement (Kincaid, 1999). Antagonistic relationships between minerals are another contributing factor to mineral status. Primary and secondary deficiencies can occur through cofactors in the diet interfering with mineral absorption. For example, minerals such as Fe, Mo, and sulfur (S) are antagonistic to Cu. Heifers fed Cu deficient diets with or without Fe and Mo produced severely Cu deficient calves (Gengelbach et al., 1994). Ward et al. (1993) reported similar results in finishing steers. Copper sulfate and Cu lysine had similar bioavailability in the presence and absence of Mo and S, and adequate Cu status did not improve steer performance and health (Ward et al., 1993). Research involving one or more mineral, apart from deficiency symptoms and antagonistic relationships, still may not define the mechanistic action and recommendation for maximum production. Also, the mechanistic action of each mineral could compliment the roles of other minerals with synergistic effects.

When mineral status was adequate, both inorganic and organic copper supplementation did not improve pregnancy rates or calf performance compared with unsupplemented cows (Muehlenbein et al., 2001). Neither serum nor placental tissue samples were determined to be appropriate indicators of Cu status. Supplementation of inorganic and organic Cu, Co, Mn, and Zn in excess of requirements had negative effects on reproductive performance (Olson et al., 1999). Organic selenium (selenium yeast) supplementation increased whole blood Se concentrations in cows and their calves compared with sodium selenite (Gunter et al., 2003). Yet, similar cow and calf performance were observed between selenium sources. Research studies in the past, however valuable, have shown the difficulty in defining the exact mineral supplementation to maximize production of the herd. Many variables involved must be considered including the quality of water, forage, and herd genetics. To gain control over these variables is near impossible from a research standpoint. Therefore, each production facility must take into consideration its own circumstances, and apply the proper management techniques.

Mineral status also could affect performance and health in the feedlot setting. Infectious bovine rhinotracheitis virus (IBRV) challenged steers recovered faster and had increased performance when supplemented with Zn methionine (organic) compared with Zn oxide (inorganic; Chirase et al., 1991). Chirase et al. (1994) also concluded that mineral requirements for stressed cattle could be different from non-stressed cattle. Copper lysine (organic), compared with Cu sulfate (inorganic), maintained Cu status during stress induction through ACTH (a stress hormone) administration and feed and water deprivation (Nockels et al., 1993). The authors concluded that the organic form of Cu could be more advantageous in correcting a negative Cu balance in steers due to stress (Nockels et al., 1993). The relationship between minerals and health, especially during times of stress, could affect subsequent feed efficiency and carcass merit. Zinc methionine (organic) supplementation increased carcass quality and fat deposition in finishing steers compared with zinc oxide (inorganic; Greene et al., 1988). A marginal Zn deficiency did not affect muscle mass, but decreased protein turnover in Holstein steers (Engle et al., 1997). Total urinary output also increased, and sodium to potassium ratio tended to increase (Engle et al., 1997)

While mineral status in the feedlot is important, we should focus on the status of the animal through each stage of production. Dam mineral status specifically during conception, gestation, and pre and post parturition is largely forgotten or deemed inconsequential. Abdelrahman and Kincaid (1993) collected fetal liver tissue during various stages of gestation. Concentrations of Cu, Mn, and Zn remained similar, however lower Se concentrations were detected in late gestation. The research also suggested that colostrum should not be the only mineral supply to the suckling calf. The minerals passing the placenta during gestation should help facilitate the mineral status of calves (Aberdelrahman and Kincaid, 1993). These developing fetuses can be a drain on the cow each and every year of their productive lives. By maintaining a consistent nutritional status in the cows (including protein, energy and minerals), the producer has the potential to improve reproductive performance and longevity. These benefits could carry over to the developing calf to be more profitable in later years. Heavier and healthier calves could be weaned to perform in the feedlot, or become successful replacement heifers.

July 2012