OPTIMUM BODY-SIZE OF HOLSTEIN REPLACEMENT HEIFERS

Criteria that define optimum body size of replacement heifers are requ ired by commercial dairy producers to evaluate replacement heifer mana gement programs. Historically recommended body size criteria have been based on live BW measurements. Numerous research studies have observe d a positive relationship between BW at first calving and first lactat ion milk yield, which has served as the impetus for using live BW to d efine body size of replacement heifers. Live BW is, however, not the o nly available measurement to define body size. Skeletal measurements s uch as wither height, length, and pelvic area have been demonstrated t o be related to first lactation performance and(or) dystocia. Live BW measurements also do not define differences in body composition. Diffe rences in body composition of replacement heifers at first calving are also related to key performance variables. An updated research data b ase is available for the modern Holstein genotype to incorporate measu res of skeletal growth and body composition with BW when defining body size. These research projects also lend insight into the relative imp ortance of measurements that define body size of replacement heifers. Incorporation of these measurements from current research into present BW recommendations should aid commercial dairy producers to better de fine replacement heifer growth and management practices. This article proposes enhancements in defining optimum body size and growth charact eristics of Holstein replacement heifers.