12 January 2009

4 minute read

Feeding a free-choice mineral product at the high end of the cost scale can result in an annual mineral cost that may represent 10% of the value of a calf. The obvious question is whether decreasing mineral costs will have significant effects on production or health.

The choices for mineral supplementation fit into the following major categories, in order of increasing cost:

1. Plain salt which supplements only sodium and chloride
   
   
2. Salt with added trace or micro-minerals (micro-minerals are needed by cattle in only milligram amounts) such as copper, zinc, cobalt and iodine. A newer one of these products contains enough selenium (90 parts per million) to meet the government maximum for supplementation.
   
   
3. A wide variety of salt/ mineral mixes that contain salt (to promote consumption of the product), micro-minerals and macro-minerals as well. The major macro minerals (needed by cattle in gram amounts). Most products contain calcium, phosphorous and magnesium.

Phosphorous is one of the components of salt mineral mix which has dramatically increased in price. The question then becomes, “How great are supplemental phosphorous needs for Virginia cows?”

Table 1 shows the needs for an Angus cow from the National Research Council. Also in the table are some projected amounts of calcium and phosphorus that would be obtained by typical intakes of average quality fescue hay or pasture.

Note from Table 1 that average quality hay will fail to meet cows needs for calcium and phosphorous early in the nursing period (through month four after calving), but will the rest of the nursing period. Pasture only fails to meet the phosphorous requirement during the first three months after calving, but meets the calcium requirement at all times. Of course, these are only averages and requirements, intakes and analysis of feeds can vary significantly. For example, hays and pastures with clover or alfalfa will have significantly more.

Magnesium requirements are also higher in early lactation. It is also likely to be low in pastures at times of the year when grass is very lush or highly fertilized.

Selenium is a micro-mineral that has frequently been reported to be lacking in Virginia forages. Routine supplementation has frequently been recommended. Periodically copper and zinc has been suspected of being deficient in Virginia forages.

It should also be noted that calving is a crucial time for mineral needs in beef cows. Winter tetany, grass tetany and milk fever can all occur when cows’ mineral nutrition is not proper in the period before and after calving. Cows should generally be consuming a high magnesium complete mineral for three weeks before calving and for a few weeks after calving.

All of the above suggests that some savings can be made in mineral costs by using high selenium trace mineral salt during part of the beef cow cycle. High selenium salt is only about one dollar per 50 pounds more expensive than regular trace mineral salt. Cows will also eat considerably less trace mineral salt than salt/ mineral mix.

In summary, mineral cost can be lowered by judicious use of high selenium trace mineral salt in the late nursing and pre-calving period. A salt/ mineral mix with higher levels of magnesium as well as calcium and phosphorus should usually be supplemented free choice during the late dry period and for the first few months of nursing. Magnesium supplementation is especially important during the early spring when grass is lush for recently calved cows.

December 2008