THE EFFECT OF DEWORMING NATURALLY INFECTED HEIFERS ON LIVEWEIGHT GAIN, REPRODUCTIVE-PERFORMANCE AND FECAL EGG COUNTS

Twenty-six of 52 heifers with an average liveweight of 318 kg were dew ormed by intraruminal injection of oxfendazole and placed in drylot on 31 January. The other 26 animals served as controls. All heifers were pastured starting on 14 June and the treatment heifers were dewormed in the same manner as at the start of the experiment (31 January) on 1 July and 31 July. The groups started out with similar total worm eggs per gram of fecal sample, but the dewormed heifers had fewer counts e ach month thereafter. The drylot average daily gain of the treated hei fers was higher (P = 0.01) and less variable (P = 0.12) and by 29 May these animals were heavier by 11.7 kg (P = 0.10). The treated animals did not gain as fast on pasture (P = 0.20), but the gain continued to be less variable (P = 0.09). Age at puberty was not different. Number of open heifers in the treated group was 4 vs. 15 % for the control gr oup (P = 0. 18). Deworming by intraruminal injection resulted in faste r feedlot gains, more uniform gains during both drylot and pasture, re duced parasites and no abscess at injection sites.