[Conception ability of early mated heifers of Bohemiam spotted and black-pied lowland cattle and their crossbreeds].

The conception rate of heifers was studied in dependence on their age and body weight at the first mating. The trial included 163 heifers of the Bohemian Spotted breed, 72 heifers of the Black-Pied Lowland breed, and 101 crossbreds between these two breeds. The heifers of the Bohemian Spotted breed mated for the first time at the age of 12 months had a lower weight than required by the standard (336 kg -- standard requires 360 kg) and a lower weight than the heifers of the other breeds under study. In the heifers of the youngest age categories (111/2-15 months) the conception rate after the first insemination ranged from 56.5 to 58.8% in the Bohemian Spotted heifers, from 57.5 to 77.7% in the Black-Pied Lowland cattle, and from 52.17 to 66.0% in the crossbreds. There were no greater differences from the heifers of higher age categories (15-18 and more months). These tendencies are proved also by other indices such as the average time from the first insemination to getting in-calf and, in particular, the insemination index. Somewhat better indices of the conception rate of early-mated heifers were found in the Black-Pied Lowland breed. The conception rate of early-mated heifers was only slightly influenced by the season. In the summer months (June to August) the pregnancy percentage was lower but the remaining indices showed no greater differences. On an average, the length of gravidity was longer by five days in the heifers of the Bohemian Spotted breed as compared with the heifers of the Black-Pied Lowland cattle, and longer by two days as compared with the crossbred heifers.