An analysis of the movement of dairy cattle through 2 large livestock markets in the province of Ontario, Canada.

Data pertaining to the movement of dairy cattle through 2 large livestock markets in the province of Ontario were collected for 1 week per month throughout 2004. Counts and postal codes of sellers and buyers of adult dairy cattle, veal calves, and dairy calves were obtained. Three assumptions were made to represent the level of mixing among animals that could take place at the markets. We estimated the number of livestock holdings that could be exposed to a highly contagious disease agent, should infected animals have been sold through the market in the same week. The estimates ranged from 8 to 20 holdings, when assuming no mixing at the market, to 51 to 171 holdings when assuming complete mixing. These markets are important hubs in the dairy cattle movement network in Ontario and pose the risk of infecting a large number of livestock holdings should animals infected with a highly contagious disease agent pass through them.