The influence of liveweight at calving on milk production in Friesian heifers

Abstract

SummaryRecords of 81 heifers, daughters of 6 bulls, were examined to determine the regressions of milk yield, corrected for lactation length, on initial liveweight and age at calving.Age was found to have no significant effect and was discarded in the final analysis.The regression equations were similar for the different groups of half-sibs, except for one group whose members had not been fed according to milk yield. After removal of this group, a highly significant positive relationship between lactation yield and liveweight at calving was found ‘within bull groups’. The mean values of groups of halfsibs did not show this relationship, and significant differences in milk yield still persisted between groups after adjustment for liveweight differences.It was concluded that herd improvement by choosing heifers solely on the basis of liveweight shortly after calving appears unlikely to be effective unless the sire's potential is known and the feeding during lactation takes into account the greater maintenance requirements of heavier animals.