MULTISTAGE SELECTION FOR MAXIMUM ECONOMIC RETURN WITH AN APPLICATION TO BEEF-CATTLE BREEDING

Methodology for selection index updating was developed to allow multis tage selection. The program determines truncation points for each stag e of selection that will maximize either profit or the ratio of aggreg ate economic gain to cost (R = Delta H/C). Either maximum profit or R may be attained by reducing the cost of performance testing in later s tages of a multistage program. In order to eliminate the need for mult iple integration and assure convergence, a piecewise algorithm was dev eloped. Examples of beef bull selection compared single-stage selectio n at 1 yr of age, two-stage selection at birth and 1 yr, two-stage sel ection at 205 d and 1 yr, and three-stage selection at birth, 205 d, a nd 1 yr. Selection based on three traits (birth weight, gain birth to 205 d, and gain 205 to 365 d) was compared with selection based on fou r traits (the above three plus ultrasound fat depth) and selection bas ed on five traits (the above four plus feed:gain ratio). Five scenario s were used that allowed variation in proportion of candidates selecte d for breeding, number of progeny per selected bull, and proportion of profit returned to the nucleus herd. General conclusions based on the examples were 1) multistage selection reduced aggregate economic gain relative to that attained by single-stage selection, 2) inclusion of feed conversion in the index of traits resulted in reduced profit and aggregate economic gain, 3) measurement of feed conversion could be ju stified when selected bulls produced a large number of progeny, and 4) three-trait selection produced greater profit in all five scenarios t han did four- or five-trait selection. Use of the selection updating p rogram described here provides a new source of information that can be used in developing economically sound performance testing and selecti on programs.