[Reproductive capacity and milk production in cows of various cattle breeds as related to age at the ist calving].

The course of parturition, the ability to get in-calf, and milk production were studied in 348 first-calved cows, in 162 cows of the Bohemian Spotted breed, 88 cows of the Black-Pied Lowland breed, and 98 crossbreds of these two breeds divided into three categories according to the age at the first calving (from 21 to 23 months, 24 months, and from 25 to 29 months). There were only slight differences in the average calf birth weight between the cows of all the breeds calving for the first time before the age of 24 months and cows calving later (lower by 0.70 kg, 1.15 kg, 0.80 kg, respectively). The frequency of irregular parturitions and the course of early puerperium did not differ considerably in individual categories under study, either. The average time elapsing from parturition to the first insemination was 58, 63, and 53 days, respectively, in the cows of the youngest category, and 56, 57, and 51 days, respectively, in the oldest category. Similarly, insignificant differences were found in the length of the service period (SP = 94, 95, and 85 days compared to 88, 94, and 80 days) and in the value of the insemination index (2.17, 1.91, and 2.02 compared to 1.92, 2.00, and 1.92). Milk production in early-calving cows in the first lactation was significantly lower than in later-calving cows (3155, 3704 and 3267 kg of milk compared to 3788, 3961, and 3515 kg of milk). If the required live weight at calving is reached, no greater complications of parturition and puerperium occur in the cows calving for the first time at an early age. The indices of further fertility and milk production are also favourable. This justifies the view that the reduction of the pre-production period in heifers and the earliness of the first calving can be considered as a generally recommendable method of the intensification of the reproduction process and as a contribution to the improvement of the profitability of cattle breeding.