Effects of Thyroprotein on Excretion of Polychlorinated Biphenyls by Lactating Cows

Abstract

Lactating dairy cows were fed 50mg daily of commercially available polychlorinated biphenyl Aroclor 1254 for 20 days. Upon withdrawal of this from the ration, groups were given 0, 2 g/100kg, or 4 g/100kg body weight of thyroprotein (Protamone) for 57 days. Animals that continued to lactate were studied for an additional 70 days. The average concentration of polychlorinated biphenyls in milk fat on day 20, the last day of dosing, was 6.01±.6ppm. Declines of concentrations in cows not fed thyroprotein were described by a two-component first order equation with half-lives of 5.7 and 68 days. Thyroprotein feeding provided a nearly dose responsive increase in heart and respiration rate and also weight losses among treated animals. Milk and fat production was increased in most animals; however, stage of lactation appeared to influence magnitude of response. Thyroprotein increased clearance of polychlorinated biphenyls during the thyroprotein feeding phase of the study. By day 52 daily excretion by control animals averaged 1.09 mg/day compared to 1.39 and 1.87 for animals receiving 2 or 4 g/100kg body weight of thyroprotein. Withdrawal of thyroprotein resulted in a sharp decline in excretion of polychlorinated biphenyls from thyroprotein treated animals. On experimental day 98, control animals had an average daily excretion of .87mg compared to .67 and .59 for the 2 and 4 g/100kg body weight of thyroprotein groups. These declines ultimately resulted in similar total excretion of polychlorinated biphenyls among all three experimental groups. Thyroprotein was not a practical means to increase rate of excretion of accumulated polychlorinated biphenyls.