The Department of Agriculture, Food and the Marine issued its Nematodirus forecast earlier this week.
Peak hatching is likely to have taken place between April 14 and 21 for much of the country, which according to the department is a few days later than what would normally be expected.
However, the south-western coastal fringes are expected to have seen peak egg hatching slightly earlier – before April 10 – which is closer to the normal time of maximum egg hatching in these parts of the country.
What is it?
Nematodirosis is a severe parasitic disease of lambs six to 12 weeks-of-age that become infected by ingesting large numbers of infective larvae from grazing on contaminated pasture.
The life cycle of Nematodirus battus is unlike that of other roundworms in that typically it takes almost a year on pasture before the egg hatches before releasing the infective larva.
After ingestion by lambs, Nematodirus larvae invade the wall of the intestine. Infection is characterised by profuse diarrhoea, dehydration and weight loss.
In outbreak scenarios, lambs can be seen congregating around water troughs due to the severe thirst that develops, while the ewes which are unaffected continue to graze.
This disease is best prevented by keeping the current year’s lambs off pasture that was grazed by lambs or young calves (which can be carriers of infection) in the previous year. Enterprises with high stocking rates are particularly vulnerable.
Twin lambs or single lambs born to ewes of poor milking ability may be at a greater risk of developing the disease, as they begin consuming greater amounts of grass earlier in life. If ‘clean’ pasture is available, preference should be given to moving these lambs first.
When should lambs be treated and with what?
Lambs that are at risk should be treated – approximately – two weeks after the peak of egg hatching.
Therefore, a suitable wormer such as a white drench should be used for lambs in the south-west of the country around this time and for lambs in the rest of the country, they should be targeted with a white drench in the last week in April and the first week in May.
However, consideration should be given to dosing lambs earlier on individual farms where clinical signs consistent with Nematodirus are seen, as the above treatment guidelines are based on the anticipated peak hatch of eggs.