The reproduction performance of about 1,200 beef cows, raised on pasture and given three different mineral supplements, was evaluated during 5 years in Cássia county, Minas Gerais, Brazil. The cows were divided into three groups: For one group (A) a commercial mineral mixture was used in 1997 and 1998; for the second group (B) common salt and dicalcium phosphate 1:1 was offered in 1999; and the third group (C) received only common salt during the same year. In 2000 and 2001, all the cows received exclusively common salt. There was no decrease in reproduction efficiency when only common salt was given; on the contrary, the reproduction performance of the inseminated e pregnant cows, that was respectively 92.5 and 78.2 % (1997) and 92.2 and 80.5 % (1998), increased to 94.5 and 85.7 % (2000) and 96.7 and 89.7 % (2001). The decrease of reproduction performance of the cattle in 1999 was probably due to the severe drought during this year. The authors emphasize the importance of a selective mineral supplementation, i.e. to supplement cattle with mineral mixtures including only the elements which the animals can not obtain from the pasture. Theselective mineral supplementation requires the assistance of professionals with training and experience in clinics, pathology and nutrition of ruminants. These professionals should be able to accompany and evaluate the nutritional condition of a herd when a selective mineral mixture is used. Selective mineral supplementation could represent a two or threefold economy of the total cost of conventional supplementation with ''complete'' mineral mixtures. The authors discuss if the improvement of the reproduction performance of the cattle used in this field experiment was due to a better management of the herd or to possible antagonism between the minerals.
Cattle; mineral deficiencies; mineral supplementation; tropical pastures
