Effect of Thyroprotein and a Low-energy Ration on Removal of DDT from Lactating Dairy Cows

Abstract

Rates at which 1,1,1-trichloro-2,2-bis(p-chlorophenyl) ethane (DDT) levels in milk fat of Holstein cows declined under four different feeding conditions were determined. Each experimental cow was contaminated with 600mg per day of crystalline DDT for 30 days.Prepartum DDT-contaminated cows, upon parturition, produced milk containing 7 to 12ppm of the insecticide residue on a milk fat basis. This level declined at a fairly rapid rate for 35 days, until approximately 4ppm was reached. Thereafter, rate of decline was slower. These cows required an average of 189 days from parturition to reach 1.25ppm. There was no appreciable difference between cows that received normal rations and those receiving thyroprotein. However, cows on a low-energy ration showed an appreciable increase in rate of decline. Their milk reached 1.25ppm DDT in an average of 114 days from parturition.Postpartum DDT-contaminated cows reached a maximum insecticide level in milk fat of 5 to 7ppm. Upon cessation of DDT intake, rate of decline in insecticide levels was more rapid than in prepartum contaminated cows. The DDT level of 1.25ppm was reached in an average of 35 days.