Aldrin, heptachlor and beta -hexachlorocyclohexane to dairy cows at three oral dosages. II. Residues post partum in milk and body fat of cows fed on pesticides in the dry period.

Abstract

The 9 cows used in the preceding trial [see DSA 39, 2470] were allocated during the dry period (approx. 8 wk) to 3 levels of aldrin, heptachlor and beta -hexachlorocyclohexane ( beta -BHC) mixed with the concentrate ration. The daily dosages/cow were (i) 0.5, (ii) 1 or (iii) 2 mg of each pesticide. Because the date of parturition could only be predicted roughly, the dry period/cow varied resulting in large differences in total doses for cows within a group; mean total dose of each pesticide was (i) 26, (ii) 56 and (iii) 87 mg/cow. The pesticide levels in milk fat after parturition did not only represent the effect during the dry period because the cows had also been dosed with pesticides late in the preceding lactation. Aldrin and heptachlor residues in milk fat were below the detection limit of 0.01 mg/kg and content of beta -heptachlor epoxide was <0.1 mg/kg immediately post partum in all groups. Levels of beta -BHC and dieldrin in milk fat immediately after calving (adjusted for carry-over effects from the preceding trial) averaged resp. (i) 0.19 and 0.10, (ii) 0.67 and 0.39, and (iii) 1.38 and 0.87 mg/kg. Content of beta -BHC in milk fat was reduced by 50% after 2 wk in (ii) and (iii) and 4 wk in (i). The rate of decline of dieldrin in milk fat was slower: contents were halved after 3 wk in (ii) and (iii) and after 5 wk in (i). Max. tolerable content of the pesticides in the daily ration during the dry period were estimated from accumulation and transfer coeff. (Abstract retrieved from CAB Abstracts by CABI’s permission)