Over a 6 year period, the effects of mating heifers to calve for the first time at 2 or at 3 years of age were studied. Over 3 repetitions of the experiment the average per cent first conception, re-conception and calf mortality (dystocia) of females mated either as yearlings or as two-year-olds was 58,6 vs 84,0, 82,0 vs 94,4 and 7,8 vs 3,6 respectively. When calculations were based on a productive life of 5 years, cows calving for the first time as two-year-olds produced 0,6 more calves than those calving for the first time as three-year-olds. Seven body measurements, viz. heart girt. height at withers, height at rump, depth of chest, length of body, width of thurls and width of hips as well as body mass were recorded at yearly intervals until 6 years of age, for cows that had calved for the first time at 2 or at 3 years of age. Only body mass at 2 years and height of withers at 3 years were significantly affected by early calving. In both these cases the differences had disappeared by the following year. Growth of the cows until 6 years of age was thus not depressed by the early calving. Age at first calving did not affect the mean milk production of three- and four-year-old cows. However, age of the cow significantly affected milk production. The average total milk production for two, three- and four-year-old cows at 1, 3 and 5 months lactation, was 8,49 kg, 11,63 and 15,20 kg. respectively.
Keywords: Two-year-old calving, growth, milk production