The Agri-Food and Biosciences Institute (AFBI) Veterinary Sciences Division wishes to advise sheep farmers of the likely risk of Nematodirus worm infection in young lambs occurring at this time of year.
Nematodirus infection results from the ingestion of large numbers of infective worm larvae present on contaminated pasture. Lambs grazing the same pasture last year act as the source of this infection. 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 2015 generally remained unhatched on the ground throughout the winter season. Given suitable conditions of moisture and temperature, they will undergo mass hatching in the spring of 2016, resulting in a high risk of infection for lambs. Affected lambs develop profuse scour and can die rapidly.
Hatching of Nematodirus eggs has already commenced and current meteorological readings indicate that peak hatching will take place during the first and second weeks of April.
Nematodirus normally only affects lambs between 6 and 12 weeks of age and clinical signs usually appear two weeks after ingestion of large numbers of larvae. Although rare, Nematodirus infection can 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 cause similar clinical signs and might be confused with coccidiosis, another disease which can cause 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:
l not grazing lambs on the same fields as those grazed by lambs of a similar age last year.
l 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. As part of the Animal Disease Surveillance and Investigation service offered by AFBI’s Veterinary Sciences Division, faeces samples from sheep or cattle can be tested to determine the level of worm eggs present. Samples should be submitted through your veterinary surgeon, with a minimum of five grams of faeces from each animal required for this test.