Long term breeding for flystrike resistance
For producers who have decided to phase out mulesing, the long term goal is to breed a flock that has increased resistance to flystrike.
The fastest way to achieve this goal is to:
- Select sires with favourable breeding values (ASBV) for wrinkle or have low visual wrinkle scores.
- Score ewe flocks for wrinkle and segment them based on flystrike risk. Apply culling and breeding approaches that will rapidly reduce the proportion of high wrinkle score sheep in your flock.
- Apply other annual management procedures that will assist in reducing the risk of flystrike, particularly in the early stages of a breeding program.
Selecting the right rams for genetic change
Breech wrinkle is the most important factor in determining susceptibility to breechstrike in the flock. Sheep with breech wrinkle scores of 1 or 2 have a substantially reduced risk of breechstrike compared to sheep with breech wrinkle scores of 3 and greater. Visual Scores Guide .
Breeding flystrike resistant sheep requires a reduction in the proportion of high wrinkle score sheep in the flock. Secondary traits that will also have an impact are dags, breech cover, tail cover and wool colour.
Breech wrinkle and body wrinkle are closely related and highly heritable (as heritable as body weight, staple strength and staple length). Dags, breech cover, and wool colour are also moderately to highly heritable. This means that there are substantial opportunities for producers to breed more flystrike resistant sheep and phase out the practice of mulesing.
There is a slightly negative relationship between wrinkle score and fleece weight but it is less than the negative relationship between fibre diameter and fleece weight. Data from Sheep Genetics shows that there are also ample animals with low wrinkle, high fleece weight and good staple length to ensure that breeders can select for low breech wrinkle and still make progress on fleece weight and other important production traits.
Research to date also suggests a positive impact on fertility, survival and fitness from breeding plainer, flystrike resistant sheep.
Sheep Genetics has now released Australian Sheep Breeding Values (ASBV) for Early Breech Wrinkle that assist with the selection of rams to producer plainer progeny. It is important that ram breeders and producers use these ASBVs to select low breech wrinkle rams as they provide scores, information and pedigrees that are not obvious through visual assessment of the animal at the time of selection or purchase. There are some significant effects of sex, birth type, dam and age that are accounted for in the ASBV, which could bias selection if not handled effectively.
This new ASBV is the result of 10 years of information and research funded by the Sheep CRC and partner organisations Australian Wool Innovation, Meat and Livestock Australia, Australian Merino Sire Evaluation Association and the state departments.
Early Breech Wrinkle ASBVs are now available for more than 300 industry sires. Identifying sires that have low wrinkle and high production for other important traits (such as growth rate, fertility, fleece weight and fibre diameter) speeds up the rate of genetic gain that can be made in your breeding program.
Within flock selection and segmentation to manage breechstrike risk
For rapid genetic progress in breeding breechstrike resistance into a flock, ewes must be assessed. Every flock will have a range of breech scores within it. The aim should be to remove high wrinkle score ewes from the breeding flock and reduce the average breech wrinkle score to 1 or 2 as soon as possible.
Breech and body wrinkle are very closely related. Because ewes have most probably been mulesed as lambs, you can use the body scoring system in the
Visual Scores Guide to rapidly identify the range of scores within a ewe flock. Having done this, animals need to be tagged to identify the different wrinkle score groups.
There is a range of ways that selection pressure within the flock can be increased to remove high wrinkle score animals and lower the average wrinkle:
- Rather than cull ewes based on age, cull high wrinkle score ewes from all age groups so that these ewes are not contributing undesirable genes to the future flock.
- Mate ewes with high wrinkle score to terminal sires rather than Merino sires.
- Mate low wrinkle score ewes to sires with a favourable ASBV for wrinkle to breed the replacements for a flystrike resistant flock.
There are also a range of management actions that can be considered to immediately reduce the numbers of sheep on your property that are mulesed. With current management techniques and chemicals there will be certain groups that probably don’t require mulesing for effective flystrike control:
- Crossbred ewes and Merino wethers for slaughter at an early age can be managed with crutching and jetting applications.
- Breech wrinkle score at lamb marking and tag each lamb accordingly. Lambs with low breech wrinkle score could be left un-mulesed and run as a different management group. This would enable the wool to be declared non-mulesed at sale time and also provide for a different management and monitoring regime for these sheep eg clips, additional crutch or jet.
The sections below provide some ideas, scenarios and case studies on:
How do I get started?
Still under development.
Scenarios for segmentation and ram selection
A range of scenarios for decreasing wrinkle by ram selection and segmentation of the ewe flock are currently under development for this page. The scenarios will be developed in the next few weeks and posted on the website.
The starting assumptions for these scenarios will be;
The flock has:
- 19um average fibre diameter
- 3.5 kg clean average fleece weight
- 50 kg mature body weight
- An average wrinkle score of 3.5
The target, is to end up with ewe flock with an average wrinkle score 1 or 2.
Changes in response to breeding and selection will be predicted for each generation and "translated" into proportions of each score using a wrinkle calculator.
Scenario 1 - 'Control'
- Continue to purchase ‘average’ rams from same source.
- The ram source is attempting to breed for plainer bodied sheep using within-stud selection.
Scenario 2 – ‘Best rams’
- Purchase rams with low Early Breech Wrinkle ASBVs using Sheep Genetics data base.
- ASBVs for traits other than wrinkle should have neutral or positive effect on base flock characteristics.
- Continue to cull on same ‘traditional’ basis.
Scenario 3 – ‘Best rams + Ewe selection’
- Purchase rams with low Early Breech Wrinkle ASBVs using Sheep Genetics data base.
- Cull ewes from flock as heavily as possible, based on wrinkle score, whilst maintaining a stable flock.
Scenario 4 – ‘Best rams + Segmentation’
- Purchase rams with low Early Breech Wrinkle ASBVs using Sheep Genetics data base.
- ASBVs for traits other than wrinkle should have neutral or positive effect on base flock characteristics.
- Segment the ewe flock based on wrinkle score and mate the high wrinkle score ewes to terminal sires or high growth/muscling Merino sires and sell all of these progeny.
- Breed merino flock replacements from the low wrinkle score segment of the ewe flock.
Case studies of breeders
Andrew Burgess and Carol Watson at Ruby Hills Merino Stud are using breech scoring and the ASBV for breech wrinkle to breed a plainer and more flystrike resistance fine wool flock at Walcha in the New England district of NSW.
Read about their experiences to date.
To read the press release 'Unmulesed sheep manageable' download the article below.
Development of FlyBoss
The Sheep CRC is currently developing an important new tool to assist with the management of flystrike in the Australian sheep flock. FlyBoss will be launched in early 2010.
This site will provide the most up to date information on managing flystrike risk and breeding flystrike resistant sheep and will replace this Managing Flystrike site once it is launched.
CJ Hawkins Homestead, University of New England, Armidale NSW 2351