CATTLE REPRODUCTIVE-PERFORMANCE IN THE PA IAGUAS SUBREGION OF THE BRAZILIAN PANTANAL .4. EFFECT OF CALF WEANING AGE ON BREEDING COWS

Effects of weaning age on reproductive performance of breeding cows we re studied from 1979 to 1984 in the Brazilian Pantanal. Three hundred cows were randomly assigned to a 3 x 3 factorial. Treatments were thre e calf weaning ages (6,8 and 10 months) and three mineral supplements. Cows were first assigned to mineral supplementation, then, at calving , animals within each group were randomized to calf weaning age. Each group comprised 100 cows and 10 bulls. Groups were kept in three nativ e pasture areas where groups were rotated monthly. Data were analyzed by Stepwise Multiple Regression. Calving interval was regressed on wea ning age, mineral suplement, year of parturition, weight at conception , linear and quadratic effect of month of parturition and cow weight a t weaning. Average calving interval was 599 +/- 120 days. All variable s influenced (P < 0,01) calving interval, except mineral supplement. C alving rates were 62%, 61% and 55%, for weaning at 6, 8 and 10 months, respectively.