A study of subclinical worm infestation in sheep: I. The effect of level of infestation on the growth of the lamb

The experiment described confirmed earlier findings that a folding management across wormfree pasture was capable of preventing infection of the lamb by all species except Strongyloides papillosus. 2. The growth and productivity of lambs infected at five different levels were compared with those of ‘worm-free’ controls grazing with them. 3. Live-weight gain of the total infected group was significantly depressed; within the infected group only level 5 differed significantly from the control group. 4. Loss of productivity was, in this experiment, associated with egg counts between 30 and 57 e.p.g. 5. The problem of definig a ‘tolerance’ level below which no appreciable damage occurs is discussed in relation to the results obtained.