Compared with carbohydrate and protein metabolism, mineral metabolism in cattle is much less understood. The lack of knowledge about the mineral metabolism has led to an idea among cattlemen that there is something special about certain minerals. Based on what we do know about mineral absorption, the key is to use mineral forms with high absorption. Generally, chloride and sulfate forms (e.g. copper chloride or copper sulfate) have greater absorption than oxide forms (e.g. copper oxide), although this is not always the case (e.g. magnesium oxide ~ magnesium chloride).
Another major issue with mineral absorption is antagonists. Antagonists bind the mineral in the rumen making it unavailable for absorption in the intestine. A common example of antagonism is high levels of sulfur and molybdenum bind with copper creating thiomolybdates rendering copper unavailable for absorption.
Mineral content of feeds can be highly variable affected by the plant species, mineral content of the soil, and mineral availability in the soil where the plants were grown. In many cases, cattlemen have little information on the mineral content of the forage and feed because testing is expensive and rarely performed.
In this uncertainty, the development of organic trace minerals have gained interest as they generally have greater absorption than their inorganic counterparts. In forages and feeds, the minerals are generally in an organic form and thus organic minerals are more similar to the natural minerals in feeds consumed by cattle. However, in feeds, the mineral element is released from its organic form during digestion allowing for absorption.
Organic forms of minerals have generally been reported to be beneficial during times of stress, but results have been inconsistent. A recent meta-analysis of the published studies summarized the results comparing organic and inorganic trace mineral supplementation to feedlot receiving cattle. Overall, organic trace mineral supplementation improved average daily gain 0.13 lb/day but there were some caveats (Figure 1). Average daily gain was improved by organic trace mineral supplementation in cattle classified as low risk (increase in ADG = 0.15 lb/day) for bovine respiratory disease, but not in cattle classified as high risk. In studies with a receiving period longer than 30 days, ADG was increased 0.13 lb/day by organic trace mineral supplementation, but not in studies with a receiving period less than 30 days. Average daily gain was increased 0.13 lb/day when antibiotics (monensin and tylosin) were not used in the feed, but was ADG was not increased when antibiotics were used in the feed.
In regard to bovine respiratory disease morbidity, organic trace mineral supplementation had no effect overall. The effect of organic trace mineral supplementation on morbidity was not affected by BRD risk classification, length of the receiving period, or use of in-feed antibiotics.
In conclusion, supplementation of organic trace minerals can be beneficial in some situations, particularly when antagonisms are impacting absorption of inorganic trace minerals. However, using organic trace minerals in place of inorganic trace minerals will not always result in improved animal performance and health outcomes.
