Progress on alternatives to mulesing
Although breeding strategies offer a long-term and permanent benefit, many wool producers continue to have their sheep mulesed in the interim to manage the risk of flystrike; this risk depends on local conditions and the particular type of sheep. Surveys on the use of the topical pain relief product TriSolfen® indicate that 60–70% of mulesed lambs receive pain relief. At the same time, initiatives have continued to further improve sheep welfare during mulesing, and to develop practical, effective measures to alter breech conformation without the need for the surgery of mulesing. This article provides an update on progress with these developments and other new technologies.
The main intradermal approach under active development is the Skintraction™ technology. This involves needleless injection of the chemical sodium lauryl sulfate into the skin layer of the breech. The chemical breaks down protein within the skin, causing a scab to form that then leads to an increase in bareness and skin stretching. Animal studies by CSIRO have shown that the Skintraction™ approach does not cause significant stress to sheep and results in only minor change in normal behaviours. Other results indicate that the sodium lauryl sulfate injection can achieve changes in breech conformation that are comparable to mulesing. A notable aspect of the Skintraction™ approach is that it is only suitable for use on older sheep that have a bodyweight of more than 30 kg.
The developers of Skintraction™ are currently negotiating registration of their product with the Australian Pesticides and Veterinary Medicines Authority. Although the outcome of these processes cannot be assumed, the developers of Skintraction™ have put in place plans for the roll-out of the technology by QA-accredited livestock contractors, should registration be successful. The stated target price for Skintraction™ is equivalent to the price of mulesing with pain relief, plus crutching.
Preventive insecticides have been around for a long time in one form or other. Two factors are relevant to this article:
- The duration of protection offered by modern products is much greater than was once the case—up to 4 months in the case of dicyclanil.
- We need to consider the risk of resistance developing to these critical tools in the armory.
The New South Wales Department of Primary Industries has recently studied the extent of fly larval resistance to the two key chemicals used: cryomazine (e.g. Vetrazin®) and dicyclanil (e.g. Clik®). Larval resistance to cryomazine was present in 62% of samples tested. Fortunately, this was classified as low-level resistance, in that it was related to larvae experiencing a lower level of the chemical, rather than being absolutely resistant. Cryomazine resistance varied with region, although every New South Wales sample tested had some degree of resistance. Only 15% of samples submitted from Victoria showed resistance.
Resistance to dicyclanil was less frequent, at 22%, all in samples from New South Wales. Again, this was classified as low-level resistance—it was not so severe that it would cause failure of control.
The main concern with these findings is that the current low-level resistance will progress to full resistance at some point in the future. Where insecticides are used, avoiding underdosing can help delay the development of resistance.
Targeting the blowfly genome
The development of new insecticides or other ways to control the sheep blowfly (Lucilia cuprina), such as vaccine development, may be assisted by a greater knowledge of the genes of this insect. Genomic sequencing and analysis may reveal areas of weakness that can be targeted via chemical control, or proteins that can serve as vaccination targets. So far, 14 466 different genes have been identified in the Australian sheep blowfly, of which 2950 appear to be unique to this species.
Targeting the genome of the blowfly may be described as high-risk research, but with high return. Although there are no guarantees of breakthrough and it is a medium- to long-term process, the pay-off could be significant if a completely new control strategy is identified and developed.
Targeting the sheep genome
The use of genomic selection tools represents the third generation of animal breeding technology. At its most basic, first-generation animal breeding for desired traits involves selecting animals that express those traits (phenotype), and breeding from these individuals in preference to others that do not have the desired phenotype. Use of the visual scoring system, such as for breech cover and wrinkle, developed by Australian Wool Innovation is an example of this type of breeding.
The second generation involves calculating estimated breeding values. Australian Sheep Breeding Values have been available since 2011 for traits such as breech wrinkle and cover, to help wool producers select their ram purchases. Now, research and development is focusing on analysis of the sheep genome, in conjunction with data on breech characteristics and flystrike incidence. This analysis should identify genomic selection tools for improving flystrike resistance in merinos, which would improve the accuracy of selection and lead to faster genetic gain.
This project has only recently begun as DNA chip technology has become more available, and so it is likely to be several years before new selection tools are available.
The use of clips as an alternative to mulesing is no longer in development. A number of other approaches are in the early stages of proof of concept for replacing mulesing:
- Liquid nitrogen, which is used in human medicine to remove warts and small skin tumours, is being investigated for its potential as a mulesing alternative. Nitrogen is liquid at –196 ºC. Application of liquid nitrogen damages skin cells through the freezing and thawing action. The theory is that this skin damage and subsequent healing will provide an increase in bare area and reduction in wrinkle. Initial work suggests that the application of liquid nitrogen has the potential to reduce breech wrinkle by 1.4 scores, 4 months after application. Preliminary studies by CSIRO have shown that, although the application of liquid nitrogen appears to cause some initial discomfort in sheep, the overall effect is very mild. Further development work is progressing, aimed at improving the infrastructure for application and the rate of throughput.
- The use of lasers to alter breech skin has been investigated in proof-of-concept studies. In humans, lasers are used to achieve permanent hair loss, among other applications. Although the behavioural responses of lambs to laser application were minimal, the current generation of lasers did not appear to prevent wool regrowth unless an excessive dose was used. Developments in laser technology are being reviewed to determine whether this approach can be revisited in the future.
Is there a price incentive for not mulesing?
Analysis by Australian Wool Innovation and the University of Sydney of the price paid for wool of varying mulesing status indicates that, overall, a small premium is paid for wool from sheep that have not been mulesed, where this is feasible. Across all fleece types, 2012–13 prices showed a 0.9% premium for lines declaring 'ceased mulesing' status on the National Wool Declaration, and a 1.5% premium for those identified as 'not mulesed'. It should be noted that these premiums alone would not outweigh the costs of a premature decision to cease mulesing. Any decision to stop mulesing on a property should be planned well in advance, based on the type of sheep, the year-to-year variation in flystrike risk, and the capacity of the operation to rebalance the suite of anti-breech strike measures available.
Andrew Fisher, Professor of Cattle and Sheep Production Medicine, University of Melbourne, Werribee
Editor's note. This is a modified version of an article that first appeared in the Mackinnon Newsletter in September 2014.