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Absence of Phenoxyacid Herbicide Residues in the Milk of Dairy Cows at High Feeding Levels

Departments of Entomology and Dairy Science, Cornell University, Ithaca, N. Y.

ABSTRACT

In earlier feeding studies (3, 4) the herbicides, 2,4-dichlorophenoxyacetic acid (2,4-D) and 4-(2,4-dichlorophenoxy) butyric acid (4-(2,4-DB), were not detectable in the milk when fed to cows at 5 ppm in their daily rations. 4-(2,4-DB) (but not 2,4-D) disappeared rapidly in the rumen of a fistulated Holstein heifer (3). Within the limits of experimental error, 2,4-D and 2-methyl-4-chlorophenoxyacetic acid (MCP) were later found to be eliminated in total in the urine (presumably as the sodium salts) of steers at the 5-ppm level (2, 5). The herbicides, 4-(2,4-DB) and 4-(2-methyl-4-chlorophenoxy) butyric acid (MCPB), underwent partial beta oxidation, respectively, to 2,4-D and MCP, with elimination of the latter compounds [and about an equal amount of intact 4-(2,4-DB) and MCPB] in the urine of steers (2, 5).

Recent studies of the disappearance of these compounds in several forage legumes and grasses showed residues up to 30 ppm persisting 3 wk after application to second-cutting plants.