Submitted to: Journal of Dairy Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: March 21, 2006
Publication Date: August 1, 2006
Citation: Bannerman, D.D., Paape, M.J., Baldwin, R.L., Rice, C., Bialek Kalinski, K.M., Capuco, A.V. 2006. Effect of mastitis on milk perchlorate concentrations in dairy cows. Journal of Dairy Science. 89(8):3011-3019.
Interpretive Summary: Perchlorate is a natural compound and environmental contaminant that has recently been detected in forages and commercial milk supplies. Milk perchlorate concentrations correlate with perchlorate intake, however, clinically healthy dairy cows may act as a biological filter by reducing the transfer of ingested perchlorate to milk, urine, and feces. The current study establishes that perchlorate levels in milk decrease during mastitis and that the mechanism for this decrease is through the breakdown of the blood-milk barrier and the corresponding elimination of an established perchlorate concentration gradient.
Recent surveys have identified the presence of perchlorate, a natural compound and environmental contaminant, in forages and dairy milk. The ingestion of perchlorate is of concern due to its ability to competitively inhibit iodide uptake by the thyroid and to impair synthesis of thyroid hormones. A recent study established that milk perchlorate concentrations in cattle highly correlate with perchlorate intake. However, there is evidence that up to 80% of dietary perchlorate is metabolized in clinically healthy cows, thereby restricting the available transfer of ingested perchlorate into milk. The influence of mastitis on milk perchlorate levels, where there is an increase in mammary vascular permeability and an influx of blood-derived components into milk, remains unknown. The present study examined the effect of experimentally-induced mastitis on milk perchlorate levels in cows receiving normal and perchlorate-supplemented diets. Over a 12 day period, cows were ruminally infused with 1 L per day of water or water containing 8 mg of perchlorate. Five days after the initiation of rumen infusions, experimental mastitis was induced by the intramammary infusion of 100 'g of bacterial lipopolysaccharide (LPS). Contralateral quarters infused with phosphate-buffered saline served as controls. A significant reduction in milk perchlorate concentration was observed in the LPS-challenged glands of animals ruminally infused with either water or perchlorate. In control glands, milk perchlorate concentrations remained constant throughout the study. A strong negative correlation between mammary vascular permeability and milk perchlorate concentrations in LPS-infused glands was identified. These findings, in the context of a recently published study, suggest that an active transport process is operative in the establishment of a perchlorate concentration gradient across the blood-mammary gland interface, and that increases in mammary epithelial and vascular endothelial permeability lead to a net outflow of milk perchlorate. The overall finding that mastitis results in lower milk perchlorate concentrations suggests that changes in udder health do not necessitate increased screening of milk for perchlorate.