The effects of continuous administration of penicillin to successive generations of chicks

For some years antibiotics have been included in the feed of young pigs and poultry to produce faster growth.With this widespread use, it is important to know whether there are any cumulative effects either on the mature treated animals or on successive generations of their progeny.The experiment here described was designed primarily to investigate whether the inclusion of penicillin in the diet of birds throughout life affected the early growth rate and the response to penicillin of their progeny.I n addition, records of egg production, hatchability and mortality were kept and are presented, although these observations must be interpreted with caution in view of the small numbers involved.The mean annual response to penicillin of chicks from a commercial source is given for the last 5 years. EXPERIMENTAL Design of experimentI n 1955 the parental generation was formed from one hatch of about 200 unsexed chicks taken from a single flock of Light Sussex hens.It was divided into two groups of which one was given procaine penicillin continuously in the diet and the other had the same diet without the drug.The response to penicillin was measured by the percentage increase in weight at 4 weeks of the birds receiving the antibiotic over that of the corresponding controls.The pullet chicks were maintained on the two treatments throughout life, and for the next three generations hatches from each flock were tested in the same way for response to penicillin.I n each successive generation sufficient pullet chicks from each of the two groups were treated in the same way as their dams and reared to maturity to give breeding flocks of about thirty-five to fifty hens.The diagram below presents the design of the experiment.