Eight hundred and ninety-eight records of the interval between calving and conception (service period) of 349 Hariana cows, the progeny of 79 sires, were analysed by fitting constants for the effects of year, month of calving, calving sequence, sex of the calf, weight of the cow at calving and weight of the calf at birth. The average service period was 272·7 days with a coefficient of variability of 50·7%.
The service period was longest after the first calving. Animals calving in the months of February to August had a longer service period than those calving during the months of September to January. Heavier cows tended to have a shorter service period. Sex of the calf, calving sequence and birth weight of the calf did not affect this trait significantly.
Heritability of service period estimated from the paternal half-sib correlation using repeated records was 0·06 ± 0·018 and repeatability was 0·250 ± 0·039. It seems likely therefore that a shortening of the service period may not be possible through direct selection.