A clinical study was designed to record the gestation length in bitches after mating at different intervals after the onset of peak vaginal cornification. All the bitches which were subjected to pregnancy diagnosis at 30 to 35 days after mating by abdominal palpation or ultrasonography examination. Animals which were found pregnant were selected for the study and were kept under observation till completion of pregnancy and duration of gestation was calculated as the interval from the day of first mating to the onset of whelping. Blood samples for estimation of serum progesterone concentration were obtained on the first day of peak vaginal cornification and on which they were recommended to be mated. The serum progesterone concentration was also very low on the first day of peak vaginal cornification and serum progesterone concentration on day three was also suggestive of LH surge. However, on day five, the serum progesterone concentration was also very high and was indicative of post ovulatory phase. Gestation period is not significant in those animals which were bred on day one and three (66.80 ± 0.70) and on day three and five (65.80 ± 0.27a) but there is a significant difference between group I and II with group III (62.25 ±1.27b) it appears that the LH surge is likely to occur between days two and four after the onset of peak vaginal cornification.