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Excretion and Storage of Dieldrin in Dairy Cows Fed Thyroprotein and Different Levels of Energy^{1, 2,}

Departments of Dairy and Entomology, Michigan State University, East Lansing

ABSTRACT

Two trials investigated the effect of dietary energy and thyroprotein on retention and excretion of dieldrin fed to lactating cows and pregnant heifers. Sixteen Holstein cows (Trial I) and 18 heifers (Trial II) were contaminated for 56 to 60 days with about 0.1 mg/kilogram body weight of dieldrin.

In Trial I, treatments during decontamination furnished 75, 100, and 150% of the recommended allowance for total digestible nutrients. A fourth treatment included the highest nutrient level and 22 mg thyroprotein/kilogram body weight. In Trial II, heifers were contaminated starting 60 days prepartum. Postpartum treatments were: 1) medium energy, 2) high energy, and 3) high energy plus alfalfa pellets.

Varying dietary energy did not alter the rate of dieldrin decontamination, but thyroprotein decreased the time for residue in milk fat to reach 1.0 ppm (12 compared to 16 weeks). In both trials, concentrations dropped to one-half their initial levels after four weeks of decontamination and to one-third after six weeks. Dieldrin in whole milk did not change when milk fat was decreased by pelleted hay. Adipose in cows fed thyroprotein contained higher levels of dieldrin than the controls. The data suggest that the hormone mobilized body fat without stimulating release of a proportional amount of dieldrin.

¹ Journal Article no. 4516 from the Michigan Agricultural Experiment Station. Work supported in part by USDA Contract no. 12-14-100-8165(44).

² Data taken from dissertation by the senior author in partial fulfillment of the requirements for the Ph.D. degree. Michigan State University, January, 1968.

³ Present address: Department of Animal Sciences, University of Kentucky, Lexington.

⁴ Present address: Department of Agriculture, Western Kentucky University, Bowling Green.