Breeding for Flystrike Resistance

A multi-faceted approach is recommended to achieve effective flystrike control. This includes breeding for flystrike resistance, appropriate timing of shearing and crutching and strategic use of chemical treatment. Breech modifications can also be used, but can gradually be eliminated with the combination of other strategies.

Breeding is the only practice to create permanent change in your flock and can provide useful improvements relatively quickly—even in the first generation—if wrinkle-free rams are selected.

The 3 key breeding strategies involve reducing skin wrinkle, decreasing breech cover and reducing dag.

Firstly, consider whether your flock is already very plain or still has many sheep with wrinkle, be it on the breech, body or neck.

For more wrinkled flocks the priority is to decrease the amount of skin wrinkle


1. Use rams with low breech wrinkle (it is strongly related to body and neck wrinkle)

  • Choose lower (more negative) Early Breech Wrinkle Australian Sheep Breeding Values (EBWR ASBV), or if not available from your stud, low breech wrinkle score (or lower neck wrinkle if the breech wrinkles have been removed).

2. Select less wrinkled ewes

  • Select replacement ewes with low wrinkle score

3. Mating Strategy — mate selected rams with selected ewes

  • Breed Merino replacements with less wrinkled ewes (wrinkle-free, scores 1 or 2)
  • Breed sale animals, either Merino or crossbred from the ewes that you retain that are more susceptible to flystrike (score 3 and 4).
  • Particularly wrinkled ewes, score 5, should not be used for breeding where possible.

For less wrinkled flocks decrease the breech cover (wool cover around the anus and vulva) and the amount of dag.

  • Use the same strategies as for breech wrinkle shown above, but focus on breech cover (BCOV ASBV) and dag (DAG ASBV).

Also take into account ASBVs for other traits important to you to ensure that you achieve a balanced selection.

You can find the Wrinkle Scores in the Sheep Visual Scores publication on the Sheep Genetics website.


More information can be found on the ParaBoss website

Practical Wisdom Notes / Fact Sheets

PW1.4 Parasite control in sheep

PW4.1 New Opportunities in Genetics and Genomics

Products & Training Resources

ASBV Pocket Guide

Australian Sheep Breeding Values - A guide for ram buyers

Marketing your sheep with genetic data

Reports, Articles and Presentations

Getting Started with Sheep Genetics

Sheep CRC Genomics Breakfast Workshop - LambEx 2012

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