The objective of the study was to compare calving ease, pelvic structure and pelvic angle in 74 Holstein-Friesian and 45 Jersey heifers. The frequency of difficult calving was 15.2% in Holstein-Friesians, and only 2.2% in Jersey heifers. Compared with Jersey cows, Holstein-Friesians were characterized by a higher calf weight to cow weight ratio, and higher ratios of pelvic area to cow weight and pelvic area to calf weight. The results of the study show that higher frequency of difficult calving recorded in Holstein-Friesians, in comparison with Jersey heifers, could be a consequence of relatively high calf weight and less preferable pelvic structure. Large variation in the internal dimensions of the pelvic heifers HF encouraged reducing the occurrence of dystocia through selection of the dimensions of the pelvic.

Key words: Calving easy, Dairy heifers, Holstein-Friesian, Jersey, Pelvic area