Growth of Holstein dairy heifers in the United States.

Data were collected on the heart girth (n = 8,565; a measure of body weight) and height at withers (n = 8,568) of Holstein dairy heifers from 659 dairy farms as part of the National Dairy Heifer Evaluation Project during 1991 and 1992. Means and standard deviations for weight and height were determined for ages .5 to 23.5 mo. Third-order polynomial regression equations were derived to study the relationship of weight and height to age. Stepwise mixed-model regression, using REML estimation, was used to identify factors associated with Holstein heifer growth and to build a multivariate model describing Holstein heifer growth across the United States. Holstein heifers on the sample of dairy farms in this study were heavier and taller at the withers than standards published 30 to 50 yr ago. Increased rolling herd average milk production was associated with a greater rate of growth in Holstein heifers. Holstein heifers in the West and Midwest were larger at a given age than those in the Northeast and Southeast.