Revisiting Total Weaning Weight as a Selection Criteria

K.L. Bunter and D.J. Brown - Animal Genetics and Breeding Unit, University of New England, Armidale

Type: Research Paper
Knowledge level: Advanced

Farm Table says:

This paper aims to investigate the potential implications of using a complex selection criterion such as lamb weaning weight. This is not easy as trait values for total weaning weight combines many sources of variation, many of which are non-genetic.

What is the problem?

Total lamb weight weaned per ewe joined has been proposed as a simple selection criterion for increasing reproduction and ewe productivity in dual purpose sheep.

However, lamb weaning weights are also influenced by genes of the lamb (the direct genetic effect), half of which
were received from the sire.

Individual lamb weaning weights are also significantly influenced by a number of non-genetic factors, such as season, age of dam, birth and rear type, lamb gender, and weaning age.

Therefore, trait values for total weight weaned combine many sources of variation, several of which are non-genetic in origin.

In this study they estimated parameters for weaning weight traits defined as traits of the ewe in a prolific Merino population, particularly with respect to illustrating the effect of using alternative trait definitions and correction for non-genetic effects, to investigate potential implications of using a complex selection criterion such as total lamb weight weaned.

What did the research involve?

  • data was obtained from a prolific (high fertility, high litter size) Merino population recorded over 10 years for reproductive performance
  • ewes with reproductive records  were daughters of 308 sires and 3540 dams
  • a subset of individual lamb weaning weights was obtained over eight years
  • lambs recorded with weaning weights were progeny of 4197 ewes and 136 service sires

What were the key findings?

Selection for total weaning weight is simple at face value, but the response to selection for contributing traits will vary depending on

  • population characteristics
  • the trait definition used
  • the corrections for non-genetic effects applied
  • and therefore underlying genetic parameters

Final comment

They conclude that selection on an index which combines breeding values for reproductive performance, and both direct and maternal contributions to weaning weight traits, should be considered to improve ewe productivity in a more predictable manner under dual purpose breeding goals.


2015 - Australia - K.L. Bunter and D.J. Brown - Animal Genetics and Breeding Unit, University of New England, Armidale
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