Multiple-Trait Selection for Maternal Productivity
A comprehensive measure of maternal productivity should consider inputs as well as outputs.

AgCanada's Denny Crews presented concepts in using multi-trait selection indexes to improve maternal productivity during Thursday morning's session.

BILLINGS, MONTANA (July 7, 2005) — Evaluation of productivity in a beef production enterprise generally refers to the measurement of outputs. Sire selection usually requires the consideration of traits that influence outputs. Multiple-trait selection for maternal productivity requires a different kind of thinking, said geneticist Denny Crews of Agriculture and Agri-Food Canada Research Centre, Lethbridge, Alberta.

According to Crews, a comprehensive measure of maternal productivity should also consider inputs or costs. It is a composite trait influenced by several cost components, and some are hard to measure.

Reproductive rate, for example, is influenced by age at puberty, heifer pregnancy rate, calving ease, the rebreeding rate of 3-year-olds and stayability. Reproductive rate is difficult to evaluate, as are cow maintenance requirements influenced by mature weight and feed intake.

Genetic evaluation and prediction of maternal productivity are difficult because properly designed research data is lacking, Crews said. However, Agriculture and Agri-Food Canada Research Centre has used historical data to develop a maternal productivity index (MPI) in collaboration with the Canadian Hereford Association. The objective was to create a tool for genetic selection of cattle with the ability to consistently wean heavy calves, during a sustained period of time, while maintaining input costs.

Component traits of the MPI include weaning weight, maternal effects on weaning weight (milk), weight of the cow at weaning time, as well as stayability to account for reproductive consistency. The emphasis or economic weighing of each component trait was based on its relative contribution to maternal productivity.

“The Maternal Productivity Index represents a combination of EPDs (expected progeny difference values) with relative economic values,” Crews explains. “There was a definite emphasis on maternal characteristics and stayability, rather than growth.”

Application of this selection tool is expected to result in a positive genetic change for all component traits. It could be used in varying production environments, with economic weighing of component traits adjusted accordingly. However, the MPI requires further validation to build confidence in its value as a selection tool, he said.

— by Troy Smith, field editor, Angus Productions Inc._© Copyright 2005 Angus Productions Inc.

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