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

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.