Effects of body measurements and weight on calf size and calving difficulty of Holsteins.

Body measurements (heart and paunch girths, wither height, chest depth, pelvic length and width, and body length), body weight, and calving evaluation data (calf birth weight, calf sex, calf presentation, and calving assistance needed) were collected from 1974 parities of 762 Holstein cows between 1968 and 1986. Degree of calving assistance was scored continuously from 1 (no assistance) to 10 (hard mechanical assistance). Phenotypic correlations of dam body traits with calf birth weight were all significantly positive when combined for all parities and ranged from .23 for paunch girth to .27 for body weight and heart girth. Correlations of dam body traits with calving assistance scores were all significantly negative across parities and ranged from -.24 to -.30. Correlations of calf birth weight with calving assistance were higher for first parity (.37) than for all parities (.20). Least squares analysis showed that cows with shorter wither height and shorter pelvises tended to require more calving assistance. Heavier calves, winter calvings, and earlier parity all were related to increased dystocia. Male calves were heavier than female calves and also were associated with greater calving difficulty.