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Effect of Stage of Gestation During Contamination on Storage and Excretion of Dieldrin by Dairy Heifers^{1, 2,}

Departments of Dairy and Entomology, Michigan State University, East Lansing 48823

ABSTRACT

Thirty-one pregnant Holstein heifers were contaminated for 60 days with 0.1 mg/kg body weight of dieldrin beginning either 60, 120, or 180 days prepartum. During contamination and decontamination, samples of milk, external body fat, feces, and urine were analyzed for 1,2,3,4,10,10-hexachloro-6,7-epoxy-1,4,4a,5,6,7,8,8a-octa-hydro-1,4-endo-exo-5,8-dimethanonaphthalene (HEOD) to determine storage and excretory pathways.

Greater (P < .005) HEOD storage occurred in body fat when heifers were contaminated early compared to late in gestation. Body fat of the 120- and 180-day groups contained two and three times, respectively (18 and 34 versus 10 mg/kg), more HEOD than the 60-day group. Endocrine changes during late pregnancy might have stimulated metabolism of the pesticide. Very little HEOD was eliminated from pregnant heifers between contamination and parturition. Dietary treatments fed postpartum were: 1) medium energy (three groups), 2) high energy, and 3) high energy-alfalfa pellets (which depressed milk fat). Residue decline in milk fat was similar for all treatments, with levels decreasing to one-half the initial level by three weeks, and to one-third by five weeks. After lactation began, pesticide in shoulder fat declined exponentially at 8.1 to 12.7 per week.

About 2.5% of the daily intake was excreted as unchanged HEOD in the feces during contamination, and traces in urine. The presence of HEOD in feces 30 days after contamination ceased indicates metabolic origin and recycling.

¹ Journal Article no. 4799 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 Science, University of Kentucky, Lexington.

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