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Breech-strike on mulesed, clipped and unmulesed Merino ewes and hoggets in south-eastern Australia
L D Tyrell1, J W A Larsen, N Anderson
1The Mackinnon Project, University of Melbourne, 250 Princes Hwy, Werribee, Victoria, 3030, Australia. j.larsen@unimelb.edu.au.
Objective:
Compare breech-strike on Merino ewes and hoggets that were mulesed, had breech and tail clips applied ('clipped') or left unmulesed and treated strategically with long-acting insecticide.
Design:
A cohort study on two farms in southern Victoria.
Methods:
Three treatment groups were established at lamb marking in 2008 and 2009 on each farm. The unmulesed group was treated with a long-acting insecticide in early spring. The prevalence of breech-strike and key risk factors, including presence of dag, urine stain and breech wrinkle, were compared between groups.
Results:
Breech-strike was detected from October to December on 1.9% and 7.2% of mulesed, and on 14.8% and 12.5% of clipped ewes, respectively, on each farm. Thus, clipped ewes had a relative risk of breech-strike 7.8- and 1.7-fold that of mulesed ewes. Unmulesed ewes treated with insecticide had similar or less breech-strike compared with mulesed ewes (3.4% and 1.4%), but significantly more dag, stain and breech wrinkle. From January, breech-strike on unprotected unmulesed ewes was 8.5% and 2.8%, compared with 3.5% and 0% on mulesed ewes.
Conclusion:
Early-season treatment of unmulesed sheep prevented most breech-strikes during spring and early summer on both hoggets and breeding ewes, confirming it as a short- to medium-term option for the control of breech-strike. Some benefits were associated with the use of clips but, to control breech-strike, clipped sheep should be treated the same as unmulesed sheep. Genetic selection to reduce the prevalence of dag will be required for future strategies to control breech-strike on Merino sheep in south-eastern Australia.