M.H. Poore

Mineral supplementation is an important and often expensive part of a good integrated manage ment program for beef cattle. Recent research at NCSU and elsewhere has improved the understand ing of mineral function, and the requirements of different ruminant animals. Despite this, supplemen tation recommendations are difficult because little is understood about levels of minerals present in the forages we produce in North Carolina. Many of our ideas about mineral supplementation come from research conducted in the western states. Supple ments that are designed for use in other areas of the country may not be the best for use in North Caro lina because of the great differences in our forages and feeding practices. To improve our mineral rec ommendations, efforts are underway to evaluate minerals levels in different areas of the state.

This paper describes a study that evaluated winter forages on North Carolina beef farms in the winter of 1992-1993. Because little is known about how fertilization practices influence mineral levels in forages, samples were taken from well managed farms utilizing either conventional fertilization, or fertilization with poultry litter or municipal sludge.

Materials and Methods
During the winter of 1992-1993 (October to February), samples of forages were taken from 29 different sites on 16 farms in 12 different counties, primarily in the Piedmont. Fourteen of the samples were of stockpiled fescue, and 15 were of hay. Sixteen of the samples were produced with commer cial fertilizer (8 stockpiled fescue and 8 hay), and 13 were produced with poultry litter or sludge (6 stock piled fescue and 7 hay). The samples were analyzed by a commercial lab for the minerals of major impor tance including molybdenum (with the exception of selenium.) The mineral levels in the forages were compared to the requirements of an above average lactating cow to determine which minerals were most limiting. The level of each mineral in forages produced by the two different systems were com pared using one-way analysis of variance.

Results and Discussion
Mineral requirements, mineral levels mea sured, and the percentage of samples below the requirement are given in Table 1. The type of for age (hay vs stockpiled fescue) did not influence mineral levels. Considering all the samples, the limiting minerals were sodium, magnesium, zinc, copper, phosphorus and calcium in that order. The other minerals were high enough such that supple mentation should not be needed.

The minerals that were influenced by fertil ization practice were phosphorus, potassium, so dium, zinc, and molybdenum. The differences were great enough to suggest that we may need different recommendations for these two different types of systems. Of the conventionally fertilized samples, 43% were below the phosphorus requirement, while only 8% of those from the waste sites were below the phosphorus requirement. Potassium level was elevated on the waste sites as well, which may be why grass tetany is so prevalent on these sites. A high level of potassium in forages has been shown to be related to a high incidence of this condition.

These data are useful, but additional efforts are underway to further evaluate mineral levels in forages during different seasons and on a wider variety of farms before recommendations are altered.

This study showed that the limiting minerals in the forages sampled were sodium, magnesium, zinc, copper, phosphorus and calcium in descending order. Phosphorus was deficient in many samples from the conventional sites, but not from the waste sites.

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