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      PCDD and PCDF depletion in milk from dairy cows according to the herd metabolic scenario.

      Animal Feed, Animals, Benzofurans, chemistry, metabolism, Cattle, Dairying, Food Contamination, Linear Models, Milk, Tetrachlorodibenzodioxin, analogs & derivatives, Time Factors

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          High level of PCDD+PCDF contamination in bulk milk (9.7 pg WHO-TE g(-1) fat) from 1604 Holstein Fresian lactacting cows was observed just four weeks after the beginning of their exposure to a feed supplement contaminated at 10.4 ng WHO-TE kg(-1) dry matter. In-farm produced hay and silage showed levels not exceeding 0.2 ng WHO-TE kg(-1) dry matter. After the supplement withdrawal, it was possible to monitor the depletion phase for a following 75-day period in milk, until the levels dropped well below 3.0 pg WHO-TE g(-1) fat, the EU regulatory Maximum Residue Level for PCDD+PCDF. During this phase, the half-life was calculated as 17+/-3 days, on WHO-TEQ basis. The full availability of farm data on both cow nutrition and milk production allowed the calculation of the carry-over rate (COR) (PCDD+PCDF milk excretion vs. feed), which was 46% at the end of the exposure. This COR value is justified from the main TE contribution of Penta-CDD and -CDF congeners (63%), and the half-life is among the shortest of all those described in the literature both for experimental and naturally-exposed dairy cows. A fugacity-based model predicts a bulk milk contamination of 5 pg WHO-TE g(-1) fat, compared to the 10 pg WHO-TE g(-1) fat level observed. Such findings are discussed in light of the lactation and metabolic status of the herd for which the transition period, characterised by a negative metabolic energy balance and a consequent adipose tissue mobilization, could play a relevant role.

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          Animal Feed,Animals,Benzofurans,chemistry,metabolism,Cattle,Dairying,Food Contamination,Linear Models,Milk,Tetrachlorodibenzodioxin,analogs & derivatives,Time Factors


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