Nematodirusbattus in lambs UPDATE
The Nematodirusdisease risk in lambs this spring is forecast to be average.
Incidence is generally high when spring is late, as the hatch of larvae is delayed until main-crop lambs are
consuming significant amounts of grass. The forecast peak of pasture larval infectivity in northeast England is around the 12-15th April.The high-risk period is often assumed to be the 6-8 weeks following this, although cool and damp May and June weather may extend this risk period by extending the period of larval survival on the pasture and/or allowing hatching to continue for longer.
Lambs are usually considered most at risk between 6 to12 weeks old, although younger lambs can be at risk as soon as they start grazing when pasture infectivity is high.
The best control method is to avoid grazing lambs on pasture used for pre-weaning lambs the previous year,or ideally the previous two years.If this is not possible, a risk assessment should be carried out based on farm and pasture history,forecasts, and the age of the lambs during the risk period. Three-weekly prophylactic treatments can then be given as required, aiming to cover the period when the high-risk age range and the high-risk time period overlap. In spring born lambs this may result in a single treatment in low-risk years, and up to three in high-risk years.
For example, this year lambs born at the beginning of April over much of the country may be treated in mid-May and early June. A change to cooler weather or a prolonged dry spell may mean a third dose is required in late June, particularly in northern regions. Theprophylactic treatment approach is always at risk of breaking down due to the sudden appearance of larvae on the pasture, so the safe grazing approach is to be preferred.
Parasitic Gastroenteritis – PGE (Gut Worms)
In the spring, significant numbers of overwintered larvae will migrate onto herbage and infect lactating ewes, andif pastures are heavily contaminated, may also cause spring/early summer disease in grazing lambs. Eggs deposited by the lactating ewes and lambs will develop slowly initially, but will begin to develop more quickly as the weather warms up.
The development of strategiesto keep pasture larval contamination down to a level that allows acceptable lamb performance, while also allowing the deposition of some anthelminticsusceptible worm eggs on the pasture to dilute any resistant parasites present, requires veterinary input on an individual farm level.
However, if BZanthelmintics (White wormers) are to be used for treatment in outbreaks of nematodirosis, the faecal egg count of several lambs should be checked to indicate whether significant PGE infestation is present or not.