The objective of this study was to compute economic values of traits for dairy cattle improvement using an empirical approach. Field recorded data were obtained from the Programme d'Analyse des Troupeaux Laitiers du Quebec (PATLQ) and genetic evaluation data were obtained from the Canadian Dairy Network (CDN). After the editing procedure, the data set consisted of 195,001 lifetime records of Holstein, Ayrshire, Jersey, Brown Swiss and Canadienne cows which calved for the first time between January 1980 and December 1994. / Different profitability measurements were computed and used as the dependent variables in covariance model to compute different sets of economic values. Since the majority of cows produced 5 lactations or less, results obtained by using lifetime profits and profits until the end of the fifth lactation are similar. A kilogram genetic increase in fat production had higher economic values than the same increase in milk production in all breeds. A unit genetic increase in conformation had the highest positive impact on profit while a same increase in capacity had a negative impact on profit. Results obtained by using lifetime profit adjusted for the opportunity cost of postponed replacement showed that this adjustement reduced the influence of type traits on profit. Finally, profits of first lactations were used to study consequences of changes in pricing systems occurred in Quebec in August 1992. Economic values attached to protein production changed drastically. A kilogram genetic increase in protein production had negative economic values in the 80's and positive economic values after August 1992.

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This study, being part of a larger project - "Canadian/New Zealand GxE Interaction Trial" - is comparing Canadian and New Zealand sired heifers for growth traits within Canada, since differences for growth traits were found in the Polish strain comparison (Jasiorowski et al., 1987) and due to selection programs in the two countries. Twenty Canadian Holstein and twenty New Zealand Friesian progeny tested, A.I. bulls were randomly mated to over 1,000 cows in 10 Canadian herds. 3,539 records of weight and wither height from 475 heifers (i.e. 241 Canadian and 234 New Zealand sired) were generated. Subsets of the data for different stages of heifer maturity were analyzed separately. Herd and strain effects least squares means were estimated using analysis of variance. Genetic and phenotypic and correlations and heritability for weight and wither height were estimated by a Derivative-Free Restricted Maximum Likelihood (DFREML) algorithm and an animal model (AM). No differences were found between sire strains for weight except at 15 and 18 months where sib groups of Canadian (CN) sires were heavier than their New Zealand (NZ) contemporaries (393 vs 386 kg and 447 vs 445 kg, respectively). CN sired heifers were taller at all ages except at birth, 3 and 9 months of age. At 24 months CN heifers were 136 cm while NZ heifers were 133 cm. Heritability estimates for weight at birth was 0.62 for the CN strain and 0.59 for the NZ strain. CN estimates (3 to 6 months) and NZ estimates (3 to 9 months) were close to zero. Between 9 to 24 months CN strain estimates ranged from 0.44 to 0.69 while NZ estimates were 0.17 to 0.51. The joint estimates ranged from 0.10 to 0.66. Heritability estimates for wither height for CN strain at birth and between 9 to 21 months were between 0.34 to 0.66 and close to zero between 3 to 6 and at 24 months. The NZ estimates at birth, 18, 21 and 24 months were between 0.36 to 0.93 but close to zero between 3 to 15 months. The joint estimates ranged from 0.32 to 0.75 between 12 to 24 months. Genetic correlations between weight and wither height ranged from 0.62 to 1.0 for CN strain and from -0.04 to 0.91 for NZ strain between 4.5 to 21 months. At six months of age the genetic correlation for CN strain was -0.01 and NZ strain was 0.54. At birth, both sire groups had a genetic correlation of 1.0. At 24 months NZ strain had a genetic correlation of 0.84 while that of the CN strain was 0. Genetic correlations for the joint analysis ranged from 0.61 to 1.0 for all ages except at 6 months (0.18). Phenotypic correlations between weight and wither height were between 0.33 to 0.60 for CN group and 0.33 to 0.62 for NZ group. The joint estimates were 0.36 to 0.61. There were no differences in the phenotypic variances except at 9, 12 and 15 months. Genetic variances were different at all ages except at birth for weight. / Land and Food Systems, Faculty of / Graduate