Relationship between external body measurements and calving difficulties in Canadian Holstein-Friesian cattle.

Thirteen body measurements per cow were collected from 1980 to 1981 on 3,193 Canadian Holstein-Friesian cows by 576 sires in 100 herds. These data were analyzed to test effects of herd, age of cow, stage of lactation, and generation group; to predict sire proofs; to estimate heritabilities and genetic and phenotypic correlations among body measures; and to estimate correlations between sire proofs for body measures and sire (maternal grandsire of calf) proofs for calving ease. Herd and age of cow were important sources of variation for all external body measures. Stage of lactation was an important source of variation for heart girth, and for slopes from hip to pin and from thurl to pin. Effects of generation group were not significant for any body measures. Heritabilities were moderate to high (.21 to .45). Genetic correlations among all height characteristics were large and positive (.68 to .99). Daughters that were large with wide pins, long sloping rumps, and little slope from thurl to pin bone seemed to be favored for easy calving.