Potentiation of Terramycin II. Evaluation of Low Dietary Calcium in Laying Hen Diets

ERTAIN alterations of the diet have been shown to increase the effectiveness of tetracycline antibiotics. Peterson4 reported that the inclusion of terephthalic acid (TPA) in broiler feeds increased the antibiotic content of the blood serum by three- to fourfold. Later, Price and Zolli5 reported that a similar increase in the serum antibiotic content could be obtained by reducing the calcium content of the diet to 0.18%. Harms and Waldroup3 reported that decreasing the calcium content of the feed slightly below the level required by the chick gave maximum potentiation benefits as measured by the antibiotic content of the blood serum. These experiments were made to evaluate with the laying hen the use of low-calcium diets for the potentiation of Terramycin, and to determine the effect of feeding low levels of calcium upon subsequent rate of egg production and egg shell thickness. EXPERIMENTAL PROCEDURE Pullets of commercial egg-production type, maintained in individual.wire cages, were used in these studies. The pullets in experiment 1 had been in production for four months, and those in experiment 2 had been in production for eleven months.