Effect of heifer size at mating and calving on milk production during first lactation

Abstract

Liveweight and skeletal size at mating and first calving, and milk production in the first lactation of 193 heifers from 16 farms in West Gippsland, Vic., were compared with the productions of mature cows in each herd (mean mature cow production, 136-270 kg milkfat/cow). Mean minimum target liveweights ( ± s.e.) for successful conception were calculated to be 219 ± 3 and 319 ± 7 kg for Jerseys and Friesians, respectively. These weights were related by regression to skeletal sizes to aid in the management of feeding heifers. Within the range of heifer sizes considered in this study (mean liveweight [±s.e.] after calving of 279 ± 28 kg and 383 ± 40 kg for Jerseys and Friesians, respectively), we conclude that, provided heifers are sufficiently grown to conceive, their milk production in first lactation will not be substantially affected by size at mating and calving.