The Effect of Estradiol, Progesterone, Terephthalic Acid and Low Calcium upon Oxytetracycline Utilization

Addition of terephthalic acid to the diet (Peterson, 1958) or reducing the calcium content of the diet to 0.18% (Price and Zolli, 1959) has been shown to increase the antibiotic content of blood serum three to fourfold. Harms and Waldroup (1961) found that it was only necessary to reduce the calcium content slightly below the chick’s requirement to get maximum antibiotic blood level. Waldroup and Harms (1961) found only a small increase in serum content of oxytetracycline (OTC) by using low levels of calcium in laying hen diets. It was later found (Harms and Waldroup, 1962) that the OTC content of the serum increased as the egg shell was being calcified and dropped shortly thereafter. Injecting hens with progesterone, a hormone shown by Dunham and Riddle (1942) to inhibit egg shell formation, resulted in a drastic drop in OTC content of the serum. These studies were conducted to determine the…