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Antibiotics as Growth Stimulants for Dairy Cattle: A Review¹

Dairy Section, University of Kentucky, Lexington

ABSTRACT

An attempt has been made to review the available information on the feeding of antibiotics to dairy cattle as completely and in a manner as unbiased as possible. Many reports used in this review are conflicting; nevertheless, the following conclusions seem to be valid.

1. The antibiotics, aureomycin and terramycin, are the only ones which have been studied sufficiently to warrant valid conclusions. Considerably more research needs to be conducted with terramycin before conclusions concerning its use can be accepted with the same degree of confidence as recommendations for aureomycin.
   
2. Seemingly no beneficial effects are derived from the feeding of antibiotics to mature dairy cattle.
   
3. Antibiotics probably improve the growth rate and efficiency of feed utilization of growing dairy animals (over 4 months of age), but unless these animals are to be marketed soon, little economic advantage will result from the feeding of antibiotics.
   
4. Aureomycin and terramycin stimulate the growth rate of calves from 10 to 30% during the first 16 weeks of age. Most of this growth improvement results before the calves are 8 weeks old. In addition to an improvement in growth, antibiotics appear to reduce the incidence of calf scours, increase feed consumption and feed efficiency, and improve the over-all condition and well-being of the animal.
   
5. The inclusion of aureomycin or terramycin in the rations of dairy calves seems to be best justified by the beneficial effects of these antibiotics in reducing calf scours and thus calf mortality. Any growth advantage afforded by these antibiotics during the early life of the calf becomes insignificant in a mature animal.
   
6. Present data indicate that aureomycin should be fed at levels ranging from 15–20 mg. per 100 lb. of body weight daily. There appear to be very few advantages of feeding antibiotics after the calves are 12–16 weeks of age.
   
7. Two fundamental explanations have been presented regarding the possible mode of action of antibiotics in calves. One of these postulates a stimulation of the pituitary gland and increased production of growth hormone. The other postulation states that antibiotics possibly increase the growth of calves through an alteration in energy metabolism probably involving the microflora of the rumen.
   

¹ Orders for reprints of this article at 50 cents each will be accepted by the editor until Dec. 1, 1955.