Four trials were conducted in separate geographic regions in New Zealand, using a total of 483 cattle to compare different treatment regimes with topical ivermectin in weaned beef calves. Trial cattle received topical ivermectin at 500ug/kg liveweight once (control group), four times (4x) or six times (6x) at six-weekly intervals commencing at weaning (March/April) and continuing into early or late summer (November/February). Cattle were weighed at intervals of approximately six weeks, and at each weighing faeces were collected from approximately 50 per cent of the cattle in each study, the same animals being sampled on each occasion. In each study, pooled faecal samples from each treatment group were cultured for identification of parasitic nematode larvae. Geometric mean faecal egg counts in control groups were generally low throughout the study, reaching a peak mean count of 703 eggs per gram on Day 123. Three control cattle in one study and one in another study were salvage treated with ivermectin to avoid development of overt parasitic gastroenteritis. With the exception of these four cattle, the controls in all studies maintained a healthy appearance, suggestive of a low parasite challenge. Larval differentiation demonstrated that Cooperia and Trichostrongylus were the predominant parasite species throughout the trial period, regardless of region. In contrast Ostertagia was present in each trial but at low prevalence and generally in only the latter period of the trials. Average daily weight gains in 6x groups ranged from 355 to 655 grams, in the 4x groups from 323 to 636 grams and in control groups (1x) from 211 to 538 grams. In all trials the 4 and 6x treated groups gained significantly more weight than the control animals (p<0.05). In all trials the 6x group gained weight at a greater rate than the 4x group. In one study the weight gain benefit of the 6x group was significantly better than that of the 4x group (p<0.05) and in the other three studies it was greater, but the difference was not significant. In each study, the 6x groups had a higher mean valuation than the other groups. Overall, dollar valuations per head ranged lowest to highest from the control to the 6x treated group. The valuations emphasise the significant impact parasitism can have on beef weaners in New Zealand in their first year of life and demonstrate the substantial economic impact of subclinical parasitism. In these trials, the treatment of beef weaners with ivermectin topical solution at 6-weekly intervals, from weaning through to mid-spring, was beneficial for improving weight gains, animal values and parasite control.

MC, Webster, WB McPherson, JY Bowie, WG Ryan, and SJ Gross

Proceedings of the New Zealand Society of Animal Production, Volume 57, , 199-203, 1997
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