EFFECTS OF TREATMENT WITH TOPICAL IVERMECTIN 3 AND 8 WEEKS AFTER TURNOUT ON NEMATODE CONTROL AND THE PERFORMANCE OF 2ND-SEASON BEEF SUCKLERCATTLE

Two groups of yearling suckled beef calves born between January and Ma y of the preceding year and another two groups of lighter and slightly younger calves born between the previous March and July were grazed d uring their second year on four separate paddocks known to be contamin ated with infective larvae of gastrointestinal nematodes. One of the h eavier and one of the lighter groups were treated with a topical formu lation of ivermectin three weeks and eight weeks after turnout. The tr eatment of the heavier group had only relatively minor parasitological effects and no effect on weight gains, whereas the treatment of the l ighter cattle resulted in increased weight gains due to effective nema tode control. The paper highlights that small differences in previous performances, age and exposure to parasites can have a substantial imp act on the benefits accrued from anthelmintic treatment.