Sheep - don’t get caught out by Worms this Winter
Think again if you consider worms to be just a summer problem. In
both 2014 and 2015 SAC’s veterinary laboratories made double the
number of diagnoses of parasitic gastroenteritis (worms) in the October
- December period compared to June - August. Sheep become
infected by eating worm larvae along with the grass. These larvae
happily survive through the winter and are not killed by frosts or snow. The mild
temperatures will have allowed worm eggs passed in dung to continue to hatch and
the larvae to develop. Fields stocked with lambs since the spring could have high
numbers of worm larvae on the pasture. Fields grazed by cattle during this time will
be lower risk for sheep.
The type of worms that infect sheep can change with the season. The best known
example of this is nematodirus which usually causes problems in the spring. During
autumn and winter the black scour worm (Trichostrongylus sp.) is often the most
common worm living in the gut. Does this matter? Yes - if you are relying on long
acting wormers to control worms at this time of year. Most people know that
wormers containing moxidectin are long acting and prevent re-infection with worms
for a period of time. What you might not realise is that the length of persistence
varies depending on worm type and the product used. The table below summarises
the differences. More information can be found on the product data sheets.
Product
Brown Stomach Worm
(Teladorsagia sp.)
Summer/Autumn
Persistence
Black Scour Worm
(Trichostrongylus sp.)
Autumn/Winter
Persistence
Meat
Withdrawal
Moxidectin
0.1% Drench
5 weeks
0
14 days
Moxidectin 1%
Injection
5 weeks
2 weeks
70 days
Moxidectin 2%
LA 20mg/kg
14 weeks
6 weeks
104 days
If you have ill thriven or scouring hoggs don’t assume it can’t be worms because you
have treated them with a long acting wormer. Also remember that worms can
become resistant to moxidectin as identified on 21% of Welsh farms screened in
autumn/winter 2014. (See www.hccmpw.org.uk and search WAARD for more
details.) Talk to your vet/advisor and investigate any problems. At this time of year
worm infection and cobalt deficiency often go hand in hand so it can be worth
checking for both. This is a good time of year to monitor groups of hoggs by
collecting ten dung samples for a pooled worm egg count in order to decide whether
treatment is required or not.
English and Welsh clients please contact: SAC Consulting Veterinary
Services, Allan Watt Building, Bush Estate, Penicuik, EH26 0QE
Tel: 01315353130 Email:[email protected] www.sac.co.uk
Scottish clients please contact your local disease surveillance centre
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Author: HStevenson122015