131I CONVERSION RATIO IN DOMESTIC BIRDS

The 131I conversion ratio (CR) in chickens at 24, 48, 72, and 96 hours following injection of 131I was increased by TSH administration. In radiothyroidectomized chickens and in birds with hereditary hypothyroidism, 24-hour and 48-hour CR's were below normal; but 72-hour and 96-hour values were normal or above normal. A possible explanation for this seemingly anomalous situation is presented. Experiments with chickens and turkeys showed that the following are important sources of variation in CR: (1) genotype (species, strain), (2) sex, (3) age, (4) time elapsed between 131I injection and drawing of blood, and (5) interactions among the foregoing. In chickens, significant strain differences in cR agreed well with other indicators of thyroid state. Limited data indicate that the CR in Japanese quail is lower than that in chickens. Data on Pekin ducklings show that the CR reaches a maximum at least as high as that in the chicken. The avian CR appears usually to reach a plateau by 48-72 hours following 131I injection, instead of continually rising, as might be expected from theoretical considerations. In chickens, the maximum mean value is usually no greater than 75-80%, and in many cases is less than that. © 1968.