Groups were placed in separate four acre pastures of Roselawn St. August-
inegrass and fed four pounds of a concentrate mixture per head daily for 98
day test periods. Pastures appeared to be equal in amount and quality of
forage present and abundant forage was available throughout the trials. The
concentrate mixture consisted of two parts of ground snapped corn, two parts
of citrus pulp, 6ne part of cottonseed meal and a salt-mineral mixture. Threc
of the groups received either, aureomycin, terramycin or oleandomycin in the
concentrate mixture while the fourth group was not supplemented with an anti-
biotic. The antibiotics were incorporated in the mixture at rates to provide
an average of 75 mg. of aureomycin, 75 mg. of terramycin and 25 mg. of olean-
domycin per calf daily in the respective groups.

 Calves were individually weighed at 28 day intervals but the major crit-
erion for evaluating differences between antibiotic treatments was the gains
for the entire test period. The statistical significance of difference in
gains among the treatment groups and sexes were determined by an analysis of
variance. Market grades given to the calves at the beginning and termination
of the trial were also compared.


Results and Discussion

 One male calf died during the 1st trial (1959) from unknown causes and
three calves were removed during the conduct of the second trial (1960). The
largest gains by each group, in both years, occurred during the first 28 days
of the experiments. This might be expected as calves recover the weight lost
during the immediate post-weaning period rather quickly. Poorest gains were
recorded during the last 14 days of the test periods by every group in each
year. This was probably caused by the heavy rainfall which occurred during
the final part of these test periods. Losses in weight actually occurred in
the second trial during this period when the rainfall was excessive. In-
dividual gains, during the 98 day test periods, ranged from 25 to 140 pounds.

 In the first trial, calves receiving aureomycin made the best gains and
those being supplemented with oleandomycin the poorest gains. However, olean-
domycin caused the highest gains in the second trial. Gains of the control
and terramycin supplemented groups in the first study were almost identical.
The same situation resulted for the control, aureomycin and terramycin sup-
plemented groups in the second study.

 The steer calves gained slightly better than heifer calves, in each trial,
and in most cases within each antibiotic treatment. These differences were
usually rather small. The average gain for all steer calves in the first and
second trial was the same but heifer calves in the first trial gained better
than heifer calves in the second trial. The combined data by years showed
that the average gain of all calves in the first trial was almost 0.9 pounds
a day compared to slightly over 0.8 pound for all calves in the second trial.
Since one pound of gain per day is considered satisfactory during the post-
weaning period for calves not being fattened, the gains of these calves may
be considered sufficient. The average daily gains by treatment, sex and year
are illustrated in Table 1.