Reproduction And Mineral Nutrition

by Associate Professor & Extension Beef Cattle Specialist Jason Banta, PhD., PAS

Is mineral nutrition the magic bullet for reproductive success in your beef operation? The number of mineral products for sale may give the impression that the answer is yes. However, in reality, mineral nutrition is just a part of a good nutrition and management plan. First, protein and energy requirements must be met. A good mineral program can’t make up for a lack of protein and energy and low body condition scores in the herd. Once protein and energy requirements have been met, then a complete mineral supplementation program is next. The mineral supplement should be formulated to match regional forage and water resources. While it is important to develop mineral supplements based on regional needs, it is generally not beneficial to develop a custom mineral supplement for each ranch.

Minerals can be categorized into two groups, macro and micro. Macro minerals include calcium, phosphorus, potassium, magnesium, sodium, and sulfur. These minerals are measured in terms of percentage contained in the supplement. For example, a mineral may contain 16 percent calcium and 5 percent phosphorus. Micro minerals, or trace minerals, include copper, zinc, manganese, selenium, iodine, cobalt, and iron.  These minerals are measured in ppm; for example, 7,500 ppm zinc or 27 ppm selenium. Sulfur and iron are not normally added to well-formulated mineral supplements.

Throughout history, several minerals, such as phosphorus, copper, zinc, manganese, and selenium, have been touted to improve reproductive performance. However, some of these claims may not be well supported by research or the response to supplementation may not be the same as it once was.

Some of the first published work with phosphorus supplementation occurred in the 1920s. In the 1930s and 1940s, research in South Texas at the King Ranch demonstrated an increase in pregnancy rates and weaning weights for cattle grazing native range supplemented with phosphorus. An important observation from this work is that the results were similar for cattle supplemented with phosphorus or those that grazed pastures fertilized with phosphorus. Also important, is that these cattle did not receive any protein or energy supplements.

Although this early research was positive, we do not see the same results today from phosphorus supplementation. The reason for the lack of results is due to the differences in the way cattle are supplemented and managed today, compared to 80 or 100 years ago. This is important to keep in mind when choosing mineral supplements because higher levels of phosphorus will reduce mineral intake and increase the cost of the mineral. Once animal requirements have been meet, extra phosphorus will not improve herd performance.

Copper is one of the most talked about trace minerals and it is important for many metabolic functions. However, based on the available research, copper supplementation does not have a direct positive impact on reproductive performance.

Zinc, selenium and manganese do appear to have important roles in reproductive performance. Adequate amounts of zinc are important for testicular development in young bulls and appear to be important for proper ovarian function in cows and heifers. Selenium appears to be important for uterine involution, which would impact the post-partum interval and pregnancy rates in cows. Additionally, available data would suggest that manganese may be important for proper estrous cycles in cows.

The key to mineral supplementation is providing the right amounts. Too much mineral can be as much of a problem as not providing enough. Excess supply of certain minerals has reduced pregnancy rates and herd performance in some studies. For some minerals, cattle excrete excess supplies in urine and feces. However, for other minerals, excretion is limited and excess mineral amounts can increase to levels that are detrimental to performance, toxic, and, in some cases, even fatal.

The margin of safety is pretty big for most minerals, but problems with excess mineral levels appear to be on the rise over the last several years. Problems with excess mineral levels usually occur when cattle receive supplemental mineral from multiple sources. For example, if cattle are provided a traditional loose mineral supplement, a molasses tub with added minerals, and a liquid feed with added minerals they can consume too much of certain minerals overtime.  Another situation where this can be a problem is if cattle are provided a loose mineral supplement and, also, given multiple mineral injections, drenches or boluses. In certain parts of the country, some forages can contain high levels of selenium; in these areas, using the wrong mineral supplement along with mineral injections is concerning.

Ideally, a good, complete mineral supplement (loose or tub) would be provided year-round. A complete mineral supplement would provide salt, macro minerals, trace minerals, and potentially vitamins A, D and E. When feeding a good, complete mineral supplement, don’t provide salt blocks as this will reduce the consumption of the mineral. As with any feeding strategy there are exceptions to this general recommendation, so consult a beef cattle nutritionist for appropriate recommendations if non-typical situations exist.

If a complete mineral supplement is not provided year-round, then the most critical times to provide a complete mineral supplement are the last three months of gestation and the first three months of lactation. A white salt block should be provided the rest of the time. Don’t use a sulfur block as it will reduce the absorption of certain trace minerals.

Mineral tags can be complicated, and the label amounts of each mineral don’t always tell the whole story. This is because two mineral supplements may contain similar levels of a trace mineral, but the sources of the mineral can differ significantly in their bioavailability to the animal. Additionally, some products with lower values may be better options than products with higher levels because of differences in mineral source.  Whenever possible, visit with a beef cattle nutritionist about selecting a good mineral supplement for your operation.

Additionally, here are few brief tips and questions to keep in mind:

• Choose the best formulation for your region and cattle needs.
• Look for a company that has a research program and is continually striving to improve their product.
• Does the product have good weatherization so it doesn’t turn into a concrete block if it gets wet?
• Do cattle consume the targeted amount?
• Look for the best value, which may not be the cheapest.

Although mineral supplements are not the magic bullet some hope for, they can be an important part of a good nutrition and management plan. Remember, the goal is to make up for any deficiencies in the animal’s diet. Providing minerals in excess of animal requirements will not improve performance.