1 September 2009

4 minute read

Ttace minerals are so named because the amount required in the diet per day by animals is small, typically less than 100 mg/kg (parts per million; Miller et al., 1988). The role of trace minerals in animal production is an area of great interest as they have a wide range of activities and functions within the body. .

These include, but are not limited to, vitamin synthesis, hormone production, enzyme activity, collagen formation, tissue synthesis, oxygen transport, and other physiological processes related to growth, reproduction and health (Paterson et al., 1999).

The requirement for trace minerals by a dairy cow is affected by many factors including genetics, age, maintenance, growth, reproduction and lactation. This article will highlight why trace mineral supplementation during the dry period of a dairy cow is important, and the effects it can have on the newborn calf and subsequent lactation performance.

The transition period for a dairy cow begins two to three weeks prepartum and continues until two to three weeks postpartum. During this four- to six-week period, the cow undergoes considerable stress as she prepares for and recovers from parturition.

Previous research has indicated that trace minerals play a critical role in minimising the negative effects of stress and it is important the cow has good reserves of trace minerals to help her through this period. Nockels et al. (1993) suggested stress can potentially reduce an animal's ability to retain trace minerals. Thus, it is important that cows have adequate trace mineral status during gestation and particularly during the dry period immediately before parturition to avoid sub-clinical problems leading to decreased lactation performance or reproduction in the subsequent lactation.

Adequate mineral status is also needed during gestation to provide the foetus with sufficient trace minerals for development and/or tissue accretion. The storage of minerals in foetal tissue reflects both foetal demand for growth and the ability of the dam to transfer minerals to the foetus to meet requirements (Abdelrahman and Kincaid, 1993). If trace mineral levels are sub-optimal in a transition cow, although she may not exhibit signs of deficiency, the transfer of these minerals to the calf may be affected.

Therefore, supplementation of the pregnant cow with adequate trace minerals is essential. As Hidiroglou and Knipfel (1981) stated, the foetus relies entirely on the dam for a sufficient supply of trace minerals and other nutrients needed for growth and development. As the trace mineral status in the calf declines, immunity and enzyme functions are compromised first; this is followed by a reduction in maximum growth; and finally normal growth decreases prior to clinical deficiency (Wikse, 1992).

Newborn calves depend not only on mineral reserves acquired from the dam but also those acquired from colostrum. Colostrum is the main source of minerals for the calf and mineral content of colostrum is largely affected by mineral supplementation to the cow during the transition period. Therefore, supplemental trace minerals should be fed to the dam during the prepartum transition period to increase the trace mineral content of colostrum as well as in foetal tissues to enhance immunity in the calf.

The following table describes the important function of seven trace minerals for the dry cow and foetus along with a recommended supplementation level. Current practice in industry is to supplement trace minerals in the diet to requirement levels, independent of those amounts supplied by basal feedstuffs. This is commonly done to be sure adequate amounts of trace minerals are fed.