Studies on reproductive performance of beef cattle in a subtropical environment. 1. Conception rate, length of oestrous cycle and length of gestation

Data from 198 cow matings and 209 heifer matings were provided by animals equally distributed between 9-wk mating periods in either spring, summer or autumn during 1961-65 at " Brian Pastures " in south-eastern Queensland. First service and over-all C.R.s showed no effect from the influence of season of mating, year, class of animal or lactational status. Calving rate was similarly unaffected. Recorded services per conception were higher for the spring-mating than for the autumn group. There was a positive association between live-weight change during the 1st mth of mating and 1st-service C.R. Length of oestrous period was 20.5 0.96 days for cows and 20.9 0.96 days for heifers. Gestation length was 278.6 1 .00 days for cows and 278.7 1.00 days for heifers. Oestrous period and gestation length were not affected by any of the factors considered.-A.S