The data on 635 Karan Fries cattle up to 4th lactation spread over a period of 16 years (1980–95) were considered for studying the effect of postpartum breeding interval (PPBI) on milk production and reproductive efficiency traits. The effect of PPBI classes (based on 10 and 5 class interval) on lactation length, total lactation milk yield, service period and calving interval was highly significant. The effect of various PPBI classes on 305-day milk yield was not significant (based on 5 day class interval) but significant based on 10 day class interval. The effect of various PPBI classes (based on 10 and 5 class interval) on dry period and milk production efficiency trait i.e. total milk yield per day of calving interval (TMY/Cl) was not significant. Nevertheless, up to 65 day PPBI classes, the highest milk yield per day of calving interval (9.72±0.43 kg) was observed in 61–65 day PPBI class. Further, when the data were partitioned into <60 and >60 day PPBI classes the milk yield per day of calving interval (9.31 kg) was higher than >45 day PPBI class (9.20 kg), >50 day PPBI class (9.19 kg) and >55 day PPBI class (9.27 kg). Therefore, it can be inferred that a minimum period of 60 days should be taken as postpartum breeding interval for better reproductive efficiency and higher milk production.
