Thirty crossbreed steer calves were randomly assigned to one of three feedlot treatment groups to evaluate the effectiveness of diatomaceous earth (DE) as an anthelmintic treatment and its effect on subsequent growth performance. Steers were adapted to a cereal-based diet for 15 days on the farm of origin and given an additional 21 days to adjust to the feedlot diet. Calves had not been dewormed prior to starting the study. On day 0 (2 January 1996) the positive control group of steers (CONV; no. = 11) was given 10 mg/kg of albendazole, a second group began receiving (on day 2) 0·3 kg of diatomaceous earth (DE; no. = 9) mixed daily with their food for 46 days and the negative control group (CTRL, no. = 9) received no anthelmintic treatment. Rectal faecal samples were collected upon arrival at the feedlot and the resulting egg counts showed that all steers were positive for nematodes and coccidia. Faecal samples were collected on days 0, 15, 28 and every 28 days thereafter to determine faecal egg counts. The last sample was taken on the day of slaughter. On day 0, the average count for all calves was over 70 eggs per g faeces (epg) for trichostrongyle type eggs; counts for Nematodirus sp., Strongyloides sp., Trichuris sp. and Capillaria sp. were negligible. CTRL and DE steers had higher parasite levels than CONV steers during the 1st (P < 0·01) and 2nd months (P < 0·05) after treatment. Egg counts for CTRL and DE groups decreased in March and none of the groups differed (P > 0·05) significantly for the remainder of the study. Coccidia levels decreased over time similarly for all groups. Offering 20 g DE per kg food intake for 46 days to beef steers on a high cereal -based diet had no effect (P > 0·05) on body weight, average daily gain, dry-matter intake, food conversion or days on food compared with the untreated control steers. Cumulative food conversion during the first 2 months was better for CONV than for DE and CTRL steers (P < 0·01) but did not differ between the latter two groups (P > 0·05). Cumulative food conversion for the rest of the study remained the same for all groups (P > 0·05). CONV calves required fewer days on food than DE calves (P < 0·05) but about the same number as CTRL calves (P > 0·10). Steers in the DE group required a similar number of days on food (230·22 ± 7·86 days) to reach target end points as CTRL steers (218·75 ± 8·34 days; P > 0·05) but more days than CONV calves (201·64 ± 7·11 days; P > 0·05).
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