SELECTION RESPONSE IN A PUREBRED HEREFORD AND A MULTI-BREED SYNTHETIC POPULATION OF BEEF CATTLE

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Abstract
Phenotypic, environmental and genetic trends were estimated for birth weight, preweaning average daily gain (ADG) and weaning weight in males and females combined; postweaning ADG and yearling weight in males; and 18-mo weight in females in a purebred Hereford and a multi-breed Synthetic population of beef cattle, for the period 1966–1978, from The University of Alberta Ranch at Kinsella. Mean selection differential, heritability, expected genetic response and actual genetic response were estimated for each trait. Methods employed to estimate trends were: (1) deviation from a control population, and (2) best linear unbiased prediction estimates of sire breeding values. Heritabilities, selection differentials and expected gains were higher for traits in the Synthetics than in the Herefords except for the 18-mo weight in females. Realized gains in most of the traits were also higher in Synthetics than in Herefords. Genetic trends obtained by the two methods were variable and deviated from the expected gains. Positive genetic trends for growth traits indicated effectiveness of the selection program in both populations. Key words: Beef cattle, selection response, growth traits