Mineral Nutrition in the Cow: Trace Minerals and Managing Interactions
Mineral nutrition is vital to overall cow performance. Without an appropriate balance of minerals, cows may not perform as expected or could exhibit detrimental effects.
About Trace Minerals
Minerals are divided into two groups based on the quantity of the mineral required by the cow: macrominerals and trace minerals (microminerals). The macrominerals are required as a percent of the diet, while the trace minerals are required in ppm (parts per million). This article will discuss trace minerals while a previous article discussed macrominerals.
There are six trace minerals of significant importance in a cow’s diet. These are cobalt (Co), copper (Cu), iodine (I), manganese (Mn), selenium (Se) and zinc (Zn). They each play important roles in the body and can have negative impacts if they are deficient or in excess.
The requirement for Co is 0.10 ppm and is typically adequate in summer range and many silages, but can be deficient in low-quality forage (e.g., winter range, crop residue). Cobalt deficiency is characterized by depressed appetite, listlessness, decreased growth, reduced milk production and a rough hair coat.
Cobalt is necessary for the rumen microbes to produce vitamin B12. Vitamin B12 is then used by the rumen microbes in metabolic processes to produce propionate, which is a volatile fatty acid that provides energy to the cow. The cow does not readily absorb Co, but the rumen microbes use it for vitamin B12 synthesis.
Copper and Molydenum
Copper plays many important roles in the cattle’s systems, including red-blood cell health, collagen development, reproduction, and immunity. Not only does Cu play important roles by itself, but the combination of Cu, S, and Mo creates several important enzymes involved in nucleotide and vitamin metabolism. The challenge is ensuring that the Cu:Mo ratio is correct and will not cause a negative interaction. This ratio needs to be between 2:1 and 4:1. The cow’s requirement for Mo is very small and frequently met by forages in grazing cattle. Depending on soil type, Cu availability may be reduced, specifically in alkaline soils.
Multiple minerals besides Mo and S can also interact and decrease Cu availability. These include zinc (Zn), iron (Fe), selenium (Se) or phosphorus (P). The forage Cu level may be adequate, however secondary deficiencies can occur as a result of increased levels of the minerals listed above, which can tie up Cu and make it unavailable to the cow. Cattle with a Cu deficiency are characterized as having a lighter colored hair or faded hair coat, reduced conception rates, severe diarrhea, brittle bones and reduced immune response.
The requirement for I is very low (0.5 ppm), however deficiencies are more prevalent than toxicities in the northern United States. Iodine plays a key role in maintaining metabolic rate by producing the hormone thyroxin from the thyroid gland. If I levels are low, thyroxin production is reduced and results in lower metabolic rates, that has a snowball effect on decreasing milk production, weaning weights and overall herd health. Cows that are deficient in I while they are pregnant can have calves that are born blind, weak, hairless or stillborn. Another symptom of deficiency is goiter, an enlargement of the thyroid gland.
Manganese plays an important role in growth and reproduction. The requirement for Mn in growing and finishing cattle is 20 ppm, while the requirement in pregnant and lactating cows is 40 ppm. Cattle have a high tolerance level for Mn, up to 1,000 ppm. However Mn interacts with other minerals so deficiency effects could be noticed at lower Mn levels.
If Mn requirements are not met, the primary indicator will be reduced conception rates. Other indicators are poor growth rates, low birth weights and increased abortions.
In the north-central United States producers need to be more concerned about Se toxicity than deficiency. The soil composition drives the Se content of the forages and the arid regions with more Ca in the soil are more likely to have higher selenium levels. Cattle have a small tolerance range for Se, with 0.2 ppm being deficient and 5 ppm being toxic. Selenium toxicity is characterized by “blind staggers”, sloughing of hooves and hair, anorexia and a wide range of birth defects. Depending on the situation, a mineral supplement without added Se may be required.
Zinc plays a role in immune response, enzyme systems and hoof health. The requirement is 30 ppm and forages, grains and proteins are all sources of Zn. Forages average 20 ppm Zn, grains are approximately 35 ppm Zn, and protein sources average between 60 to 70 ppm Zn. Therefore, if cattle are fed forage based diets, additional Zn supplementation may be necessary.
Signs of Zn deficiency are reduced feed intake and weight gain, excessive salivation, rough hair coat and eventually swelling of the feet and legs.
When it comes to supplementing trace minerals, providing a trace mineralized salt that contains Co, I, Cu, Mn and Zn is a good insurance policy for decreasing the occurrence of deficiencies. In certain situations, a trace mineralized salt will be adequate to alleviate mild deficiencies; however there are other situations when an additional mineral supplement will be necessary to overcome interactions or more extreme deficiencies.
Mineral nutrition and balance is key to animal performance and productivity. Take some time to evaluate your mineral program and determine if your mineral supplement is meeting the cattle’s needs. It is often stated that mineral supplements are formulated for the region, but there can be huge variations in mineral content of forages from one side of your ranch to the other. It might be time to sample your forages and water to get a better understanding of what is available to your cows and what they need in the form of a custom-formulated supplement. The final article in this series will address reading the mineral tag and understanding bioavailability of the ingredients in mineral supplements.
Source: Adele Harty, South Dakota State University