Methoxychlor residues in milk of cattle treated with Marlate 50 insecticide as a dermal spray.

Lactating Holstein cattle were treated twice at an interval of 14 days with methoxychlor (Marlate 50 insecticide) as a 0, .25, or .50% dermal spray, with 2 quarts of spray mix applied to each animal. Residues of methoxychlor in whole milk were highest on the 1st or 2nd day after treatment and, when expressed as part per million equivalent in milk fat, were as high as 2.0 and 3.0 ppm in samples from the low and high dosage sprays. Residues in milk dropped rapidly after residues were at most only slightly above the sensitivity limit (.005 ppm in whole milk) of the analytical method. Applicative specifications for Marlate 50 insecticide use on lactating dairy cattle might result in violative methoxychlor residues in milk during the first 1 to 3 days after treatment.