The effect on cattle of long-continued cutaneous applications of DDT.

Abstract

An experiment was carried out near Brisbane and another near Melbourne to determine the hazard of long-continued cutaneous applications of DDT to cattle. In Queensland, steers were used. They were treated weekly for three years with 22.5 g DDT in peanut oil, and some were autopsied at the end of each year. In Victoria the experiment was commenced with heifers, and the same dosage of DDT in peanut or substitute oils was applied. They bore up to three calves, which they suckled for 5-6 months, and were autopsied 3½ years after the commencement of the experiment. Signs of toxicosis were never observed in adults or calves and except for a brief period during the second year of the Queensland experiment, there was no significant difference between the growth rates of treated and untreated animals. At autopsy UDT was found in tissues, particularly fatty tissues, in amounts up to 425 parts per million, and lower concentrations were found in similar tissues of untreated animals pashred with those treated. In no case was histological evidence of toxic effects upon tissues found. Milk samples taken during the first lactation of the Victorian heifers 20 months after treatment began contained 3-4 parts per million DDT. Since the intensity of application exceeded that of any treatment conceivable under field conditions, it is concluded that any likely rate of dipping in aqueous suspensions of 0.5 per cent. pp'-DDT for tick control would be quite harmless to cattle.