Control of roundworm in lambs

Waimarino Bulletin, Volume 1, Issue 27, 6 December 1983, Page 12

Control of roundworm in lambs

Sound management, good nutrition and pastures with low larvae numbers help prevent worm burdens in lambs. Drenching programmes to control parasites are based on either: preventive drenching commencing at weaning to reduce the autumn build up of pasture larvae; or Autumn drenching to prevent the clinical or sub-clinical effects of parasitism. The observable effects of parasitism, i.e. scouring, illthrift, anaemia and dull, poor quality wool are well recognised. Less recognised are the losses due to non apparent parasitism where growth rates are depressed despite good feeding. The well nourished lamb has a greater resistance to the effects of parasites than the poorer fed lamb. A grazing management system which provides a constant supply of high quality pasture aids control. Rotational grazing systems can provide this assurance. Weaning is a traditional drenching time on most properties. In order to achieve maximum benefit the weaning drench should be part of a 'preventative drenching programme.' The 'preventive drenching programme' begins at weaning and entails three drenches with a broad spectrum drench at 21-day intervals followed by two drenches with a 28-day interval. For this programme to be successful the 21-28 day drenching intervals must not be exceeded. This ensures that most of the worms picked up by the

sheep do not reach matunty and thus contamination of pastures is minimal. All lambs must be drenched notjust'tailenders'. If the preferred 'preventive drenching programme' is used, drenching in the autumn should normally not be necessary. However in the absence of this programme, 'autumn drenching', entailing three drenches at 28-day intervals, should be given commencing in early March. For effective parasite control: animals should be grazed on those pastures, which have been free, for the longest periods, of grazing by young animals. Such pastures should have the lowest numbers of larvae, so the worm burden in the animals will increase only slowly; the young animal is the multiplier of worms and will contaminate pasture to a greater degree than older animals. Hence, a mob^^ lambs should not follow^B earlier mob of lambs in your grazing system; high quality pasture provides the best diet for lambs, and should be used as such to aid parasite control; drenching programmes should aim to reduce the number of worm larvae on pasture and to prevent the cumulation of a worm burden in the lamb; a 'preventive drenching programme' is more effective than drenching limited to the treatment of obviously parasite burderied animals. If you have any doubt about the effectiveness of your drenching programme, veterinary advice should be sought. Ministry of AgricuUm^ and