Bulls are prone to digging up paddocks and are subject to contamination by ingestion of soil. Castration has been used to decrease masculine behaviour and assist animals to fatten and dilute the level of OC residues but the best option is to keep them away from contaminated areas entirely. Production of bull beef on contaminated land is not re-commended. There is no easy method of decontaminating bulls, so they must be managed to prevent contamination. Breeding Cows Cows with suckling calves rapidly decline in pesticide residue level on clean feed.
Lactation lowers residue levels markedly because OCs are excreted in the milk with the milk fat.
Cows producing milk lose OCs from their fat and become less contaminated. OCs are also passed into the foetus of pregnant cows if they are contaminated or grazing contaminated paddocks. By removing cows with calves at foot from affected land in early lactation, it is possible on late winter, spring and early summer pasture, to reduce the cows' pesticide levels to less than one tenth of their initial levels. The calves' levels can be reduced to less than one third of their initial levels by weaning at about six to nine months of age. Purebred beef type cows would probably decline slower than this because they give less milk.