Minerals and Reproduction
Is There Value?
Reproduction is the most economically important trait for profitability in the cow-calf sector. There are many variables that can have an impact on reproductive performance. Disease, stress, weather, macro nutrition and mineral nutrition can all play a role in reproductive success. We will focus on the role of mineral nutrition in reproductive success, with an emphasis on trace minerals.
In general, most feedstuffs (pasture, hay, grains, etc.) used in ruminant diets are inadequate to meet animal mineral requirements. It is important to use strategic supplementation strategies to balance out the deficiencies commonly seen for both macro and micro minerals. Macro minerals, especially salt, are usually supplemented to balance the diet. In addition to these, copper, zinc, manganese, cobalt and selenium are typically supplemented to ensure adequate trace minerals are available to the animal for its biological functions.
Unfortunately, mineral nutrition is one of the most complicated areas of nutrition. In order to understand the role of minerals in reproduction, we need to first understand mineral requirements and how these minerals are utilized by the animal and why they are important for reproduction.
Copper (Cu) is essential for numerous enzymes, cofactors and reactive proteins. The two main challenges with copper are that basal feedstuffs are generally deficient, and this mineral is prone to dietary antagonists – mainly molybdenum and sulfur – which basically make the copper unavailable for the animal. Copper’s positive role in reproduction is probably direct and indirect. Molybdenum has been proven to have a negative effect on reproduction. Copper’s positive effect on reproduction should be greater if molybdenum dietary levels are high.
Zinc (Zn) is an integral component of more than 300 enzymes that are involved in many biological processes. Like copper, zinc is often deficient in basal feedstuffs and is prone to be antagonized by calcium and phosphorous. Additionally, a common practice is to include additional zinc to help alleviate foot issues (foot rot and hairy heel wart). Caution should be taken when adding additional supplemental zinc. The ideal copper to zinc ratio in the total diet is 1-to-3. If excess zinc is gets above 1-to-3, a subsequent copper deficiency may occur. Zinc is especially important to positive reproduction. Zinc has been proven to improve embryo quality, sperm quality and increased conception rates.
Manganese (Mn) is one of the least researched trace minerals. Like copper and zinc, it is a critical component of numerous enzyme systems and seems to have a role in reproduction. Opposite of copper and zinc, the amount of manganese in basal feedstuffs is quite variable and often exceeds the animal’s requirement. However, the availability of this manganese is poorly understood and may be dependent on forage quality/maturity. Furthermore, manganese can be highly antagonized by iron. This is even more prevalent in fermented feeds like silage and haylage. Recent research increasingly suggests manganese has an important role in embryo quality.
Selenium (Se) is best known because of its deficiency. Selenium deficiency can result in white muscle disease. It functions in selenoenzymes as an antioxidant. Selenium levels can be quite variable in forages. There are parts of the United States that are extremely deficient, and other parts of the United States have forage levels that are quite high and promote toxicity. A good understanding of the basal levels of selenium is critical to determining supplementation of this mineral. Like copper, sulfur can be antagonistic to selenium.
Because these trace minerals are essential for biological functions like reproduction, the goal of trace mineral supplementation should be to provide adequate amounts of a trace mineral in the proper ratios in a form that reaches the small intestine where they can be absorbed and utilized by the animal. The sources we put in the feedbag make a difference and should have low rumen reactivity because the antagonistic reactions generally occur in the rumen.
Generally, sulfate sources are highly soluble and reactive in the rumen and less likely to be fully utilized by the animal. Additionally, there is evidence that sulfate sources can dissociate and form insoluble complexes in the bag, which can also render them unavailable to the animal. Furthermore, before insoluble complexes are formed in the bag, free metals negatively affect fat soluble vitamins like vitamin A and vitamin E. More improved sources like organic and hydroxy trace minerals have more stable chemistry that allows them to have less reactivity in the bag and in the rumen. This allows them to reach the site of absorption more adequately for better animal efficacy.
An extensive review of peer-reviewed publications would indicate that trace mineral supplements formulated with high bioavailable sources fed at the proper rates and not in excess of the animal’s requirements will have a positive impact on reproduction. This positive response is generally seen in animals that are trace-mineral deficient or those in adequate status, and may translate into earlier pregnancies. It has been scientifically proven that more available sources of trace minerals can improve conception rates to artificial insemination and embryo transfer, and bring cows into heat earlier.
You must avoid excessive high amounts. More is not always better, especially when it comes to feeding sulfate sources. Not only do excess amounts of sulfate sources not improve reproduction, but they can also harm reproduction if fed in excess of requirement. Plus, feeding sulfate sources more than the requirement can harm forage/diet utilization because they solubilize and dissociate in the rumen. By nature, copper and zinc sulfate are antimicrobial, so excessive amounts of these minerals in the rumen fermentation vat housing billions of microbes is not a good idea.
Don’t forget, bulls are 50 percent of the genetics in your calf crop, so it is also important to make sure the male part of the reproduction equation is accounted for. Improved sources (non-sulfate) of trace minerals can improve semen quality and quantity. Semen production takes time, so make sure these bulls have a quality mineral that is available every day for at least 60 to 90 days pre-turnout.
Last, make sure the trace mineral source utilized is palatable. Sulfate sources of trace minerals create mineral consumption challenges and inconsistencies that are hard to overcome. A well-balanced mineral formula never helps improve reproduction if it isn’t consumed at a consistent, proper rate.
Mineral supplementation should be based off the need of the animal, the understanding of basal diet, water contribution and level of antagonists. Then put a balanced package of highly available sources in front of the animals to ensure adequate consumption.
Written by: Jeff Heldt, Ph.D., PAS, Beef Technical Lead, Micronutrients, and Chance Farmer, Ph.D., Beef Technical Manager, Micronutrients
Source: Nebraska Cattleman January 2022 Magazine