This study was conducted on 300 mares kept under one of the two managemental conditions: field (individual management) and farm (organizational management). Mares were categorized as estrual, fertile, subfertile or pregnant. Any possible relationship between fertility and serum levels of sodium, magnesium, phosphorus, potassium and calcium was investigated. The serum sodium level differed significantly (P<0.05) among all groups of mares at both conditions, with pregnant mares having the highest and subfertile the lowest levels. Also, independent of the condition, the pregnant mares had significantly higher (P<0.05) serum potassium levels compared with subfertile ones. Serum calcium levels were significantly higher in estrual mares when compared with those of pregnant mares under farm management or subfertile mares under field conditions. In each group, mares kept under farm management had significantly higher serum magnesium levels but significantly lower serum calcium levels than those of mares kept under field. In estrual group, mares raised under field condition had significantly higher serum phosphorus levels. These results sufficiently provide the foundation for more rigorous and controlled studies to establish a firm basis for fertility versus serum-mineral-profile relationship. Moreover, due to marginally adequate serum mineral levels in mares kept under both managements, supplementation with mineral mixture was recommended for optimum fertility.

Key words: Fertile, Macro minerals, Mare, Serum, Subfertile, Pregnant