SIRE X NUTRITION INTERACTIONS AND GENETIC-PARAMETERS FOR ENERGY-INTAKE, PRODUCTION AND EFFICIENCY OF NUTRIENT UTILIZATION IN YOUNG BULLS, HEIFERS AND LACTATING COWS

Sons of 19 Red Danish, 19 Danish Friesian, 2 Danish Red and White and 16 Danish Jersey bulls were reared from 6 weeks to 11 months of age on a high concentrate (C) or high roughage (R) diet. Daughters of the same sires were reared on diets formulated to promote low (L), medium (M) or high (H) daily gain from 6 weeks of age to puberty. Heifers then were managed similarly through 250 days of their first lactation. Sire x diet interactions were significant for traits measured in bulls; genetic correlations between the same traits expressed in C-versus R-feeding systems were -0.10 for daily energy intake (DEI), 0.16 for average daily gain (ADG), and 0.18 for efficiency of nutrient utilization (EFF), Heritabilities of these traits were higher when expressed in the R-feeding system than in the C-feeding system (1.09 versus 0.29 for DEI, 0.58 versus 0.28 for ADG, and 0.82 versus 0.34 for EFF), whereas phenotypic variances of the traits were larger under C-feeding. Sire x rearing intensity interactions were not significant for most traits of growing or lactating females. Heritability estimates of DEI, ADG and EFF in females ranged between 0.22 and 0.27; and heritabilities of weight at calving, energy corrected milk yield (ECM), and DEI and EFF during lactation were 0.35, 0.50, 0.16 and 0.69, respectively. Weight change patterns related to post-partum energy balance were lowly heritable (0.14 to 0.23). Genetic correlations of ECM were -0.67 with post-partum weight loss, 0.60 with number of days of lactation when minimum body weight was reached, 0.50 with DEI during lactation, and 0.91 with lactation EFF.