GENETIC EFFECTS ON POSTWEANING GROWTH OF THREE-WAY CROSS BEEF CATTLE
Genetic effects on postweaning growth traits were evaluated for 3592 crossbred steers and heifers fed at two locations, Brandon, Manitoba and Lacombe, Alberta during a 6-yr period (1973–1978). The calves were sired by Chianina (Chi), Charolais (C), Limousin (L) and Simmental (S) bulls mated to 10 F1 dam-crosses representing the Hereford × Angus (HA) and nine dam-cross combinations produced by mating C, S and L sires with H, A and Shorthorn (N) females. Progeny rankings by terminal sire breed for weight on-test were C = Chi = S > L. For the trait 140-d postweaning average daily gain, progeny rankings were C > Chi = S, C = Chi > L and Chi > S > L. The progeny from the majority of "exotic" cross-dams were heavier on-test, and had higher postweaning average daily gain than progeny from HA dams. Ranking of dam-crosses according to their breed of sire (DS) for the trait weight on-test were S > C > L. The DS comparisons for postweaning average daily gain were C > S > L. The ranking of dam-crosses by breed of dam's dam, for on-test weight and postweaning average daily gain were N > H = A. Genetic interactions (terminal sire by breed cross of dam) were absent. Genotype environment interactions involving breed of terminal sire with year, sex and location were found for weight on-test and postweaning average daily gain. All resulted from changes in the magnitude of breed of sire differences, not from changes in sire rankings. Key words: Cattle, breeds, cross breeding, growth