The Agri-Food and Biosciences Institute (AFBI) wishes to advise Northern Ireland sheep farmers that we are now approaching the peak risk period for Nematodirus worm infection in young lambs.
Nematodirus infection results from the ingestion of large numbers of infective worm larvae present on contaminated pasture. Lambs grazing the same pasture in the previous year act as the source of this contamination.
For Nematodirus eggs to hatch they must experience a period of cold weather followed by warmer conditions. These conditions are usually achieved during the winter and spring of each year. Nematodirus eggs passed out by lambs in 2018 will generally have remained unhatched on the ground over the winter season. Given suitable conditions of moisture and temperature, egg undergo mass hatching in the spring of 2019, resulting in a high risk of infection for lambs.
Using a forecasting system based on climate data, staff at the Institute have predicted that hatching of Nematodirus eggs has commenced and current meteorological readings indicate that peak hatching will take place during the last week of March and the first week of April.
Nematodirus normally only affects lambs between six and 12 weeks of age and clinical signs usually appear two weeks after ingestion of large numbers of larvae. Affected lambs develop profuse scour and can die rapidly. Although rare, Nematodirus infection can also occasionally cause problems in young calves. Therefore, farmers should be on the alert for signs of scour in lambs (and possibly young calves at grass) from mid-April into May.
Farmers should be aware that Nematodirus infection can be confused with coccidiosis, another disease which causes severe scour in young lambs. As the treatments for Nematodirus infection and coccidiosis are different, accurate diagnosis and treatment recommendation, through your veterinary surgeon, are essential.
Nematodirus disease can be avoided or reduced in lambs by:
Ø not grazing lambs on the same fields as those grazed by lambs of a similar age last year.
Ø using anthelmintic drenches every two to four weeks. The interval between doses depends both on the particular anthelmintic used and the severity of infection. To date, only limited evidence has been found of drug resistance in Nematodirus to any of the available classes of anthelmintic.
Your veterinary surgeon should be consulted at an early stage. He or she is in an ideal position to provide advice on the prevention and/or treatment strategy best suited to your particular circumstances. AFBI’s Veterinary Sciences Division can test faeces samples from sheep or cattle to determine the level of worm eggs present. A minimum of five grams of faeces from each animal is required for this test.