Intensive beef production. 8. The effect of chlortetracycline on growth, feed utilisation and incidence of liver abscesses in barley beef cattle

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Abstract
An experiment was conducted on 13 commercial barley beef units in Scotland, using a total of 301 early-weaned Friesian male calves. On each unit the trial batch of calves was divided into two groups, which were then allocated to a control diet (85% barley + 15% protein supplement) or the same diet supplemented with 20 mg. chlortetracycline per kg. of feed. The experiment was conducted over the live-weight range 115 to 360 kg.The chlortetracycline significantly (P<0·01) improved live-weight gain ( + 4·9%) and feed utilisation ( + 4·8%). This overall effect was largely due to a high response during the first 12 weeks. From 13 to 28 weeks the chlortetracycline had only a marginal effect, which was not significant. There was no significant difference in the feed intakes of the two groups. There was a significant (P<0·01) negative correlation between the effect of the chlortetracycline on live-weight gain at each unit and the growth rate of the control animals at that unit; the response was greatest on farms with poor hygiene. The animals given chlortetracycline showed a significantly (P<0·05) lower incidence of liver abscesses (11·8%) than the controls (28·2%). Macroscopic examination of the rumens showed that rumenitis is common among intensively fed cattle, but no correlation could be found between incidence of liver abscesses and rumen lesions.