Genetic and phenotypic parameter estimates between production, feed intake, feed efficiency, body weight and linear type traits in first lactation Holsteins

Production and feed intake data on 36 115 first lactation Holstein cows obt ained from Quebec Dairy Herd Analysis Service were combined with conformati on data From the Holstein Association of Canada to estimate genetic correla tions among production, energy intake, and conformation traits. Traits cons idered were 305-d milk yield, 305-d grain energy and total energy intake, f eed efficiency (fat corrected milk yield/total energy intake), body weight at calving, capacity, size, stature, rump width and final score. Genetic an d phenotypic parameters were estimated using Restricted Maximum Likelihood based on two-trait animal mixed model analyses. The model contained fixed e ffects of herd-year, season of calving, age of calving, sire group and a ra ndom animal genetic effect. Estimates of heritability were within the publi shed range for all traits. Of the conformation tl aits examined, capacity, size and stature had the highest correlations with body weight, with phenot ypic correlations between 0.36 and 0.43, and genetic correlations between 0 .61 and 0.79. Feed efficiency was negatively correlated to all body size me asures, both phenotypically (-0.01 to -0.29) and genetically (-0.31 to -0.5 3), but most significantly with body weight, capacity, size, and stature. F at-corrected milk yield showed negligible phenotypic and low to moderately negative genetic (-0.07 to -0.29) correlations with body weight and related type traits. Total energy intake was positively related to all measures of body size, most notably body weight, while grain energy intake had moderat ely negative genetic correlations (-0.20 to -0.40) with the same body size traits. Because of their detrimental relationships with feed efficiency, ne gative selection emphasis should be placed on body weight and the related t ype traits capacity, size and stature. Capacity, size and stature are of mo derate utility when selecting indirectly for body weight, total energy inta ke and feed efficiency.