By Dr. James C. Coomer, Ph.D., P.A.S.
Manganese (Mn) is an important trace mineral (required in very small quantities). It is involved in many aspects of both plant and animal life, primarily as an enzyme activator. One of the most common deficiency symptoms is reduced growth or abnormal growth and development (perosis in chickens). Manganese is involved in activating the enzymes responsible for the production of mucopolysaccharides and glycoproteins which form the organic matrix of bone and cartilage. Therefore a deficiency of Mn may result in shortened or malformed bones, especially in fetuses from cows that have been eating a diet deficient in Mn. Manganese is also a part of Mn-superoxide dismutase, which is involved with limiting the build-up of highly reactive oxide molecules in cells. There is also a metabolic association between Mn and choline which affects fat metabolism in the liver. Manganese is involved in the biosynthesis of choline and thus a deficiency of Mn may result in a deficiency of choline. A choline deficiency limits the liver’s ability to metabolize fats and use them for energy and may result in the build-up of fat in the liver (fatty liver). This situation would be especially important in the early post-partum dairy cow since she is in negative energy balance and is relying on the liver to metabolize body fat to meet her energy needs for milk production. Reproduction in cattle has also been shown to be affected by Mn deficiency, with sterility and reduced conception rates reported in both the US and in Great Britain. The exact reason for this effect has not been determined as yet, but improvements in reproduction were produced when diets low in Mn were supplemented with additional Mn.
About 25% of the total body Mn is found in the skeleton and excess Mn will be reflected in excess concentrations in hair, wool, and feathers. Manganese absorption is generally very poor with most studies reporting 1% or less of the ingested Mn being absorbed from the digestive tract. Manganese competes directly with cobalt (Co) and iron (Fe) for binding sites in the digestive tract. As a result, an excess of Co or Fe may result in lower absorption of Mn and a potential deficiency of Mn. Calcium (Ca) and phosphorus (P) also influence the absorption of Mn. High levels of dietary Ca and/or P also reduce Mn absorption most likely due to lowered solubility of Mn. Manganese is more soluble at a lower pH. With this in mind, plants/crops grown on lower pH soils will have higher levels of Mn than crops grown on soils with a higher pH. Most Mn deficiencies in ruminant animals have been reported in areas where soil pH is higher and forages are lower in Mn content.
As the name trace-mineral implies, the requirement for Mn is very low and is generally expressed as parts per million (ppm) or milligrams/kilogram (mg/kg). Requirements for Mn in chicken diets is the highest of any species with suggested levels of 40-60 ppm in the diet to prevent perosis (slipped tendon). Beef cattle suggested levels in the diet are around 20-40 ppm and dairy cattle at about 40 ppm on a dry matter basis. These requirements may need to be raised if any of the confounding factors (high Ca, P, Co or Fe) that affect Mn absorption are involved in the diet. Manganese supplementation is also more critical in geographical areas where soil pH is higher and therefore crops would have lower levels of Mn. Manganese sulfate has historically been the most common source of Mn used in animal nutrition to supplement the diet. However, in the last 20 years, it has become more and more common to use “organic” forms of Mn to supplement the diets of livestock. The term “organic”, when referring to trace minerals has nothing to do with “Certified Organic” livestock farming. “Organic” trace minerals refer to trace minerals that have been complexed or chelated to an organic molecule such as an amino acid or sugar molecule. This is done to reduce the likelihood of the Mn interacting with or being interfered with by the other confounding factors mentioned earlier and in some cases, it is believed absorption from the digestive tract is increased through the use of a different absorption site associated with the organic molecule. The organic forms of Mn are more expensive to use, but many in the livestock industry, including Agri-King, believe it is worth the expense to supply some of the dietary Mn in the organic form.
It has been shown that glyphosate does in fact complex with Mn as well as Ca and Mg. This appears to be a bigger problem for weed control than for crop or livestock issues. The glyphosate that complexes with one of these minerals, becomes inactive and therefore unable to control weeds in the crop. As for creating a Mn deficiency in the plant, it appears this may only be a problem in areas with very low soil Mn levels and high soil pH.
Manganese toxicity is very unlikely to occur in most species. This is mainly a result of the very low absorption of Mn from the intestine. Any toxicity would likely result from high levels of Mn interfering with the absorption of another mineral (Cu, Fe) and causing a deficiency of that mineral. AK