Western Canada study of animal health effects associated with exposure to emissions from oil and natural gas field facilities. Study design and data collection I. Herd performance records and management.

Beef cow-calf herds are the most common livestock operation in Western Canada. Beef cows also have the greatest opportunity for direct contact with their environment through continuous sampling of the air, water, vegetation, and soil. These factors combine to make cow-calf herds a potentially useful sentinel of environmental change. Researchers individually tracked more than 33,000 cows in 205 beef cow-calf herds from spring 2001 to the end of the calving season in 2002 to examine the potential effects of emissions from the oil and gas industry on productivity. This article describes the study design and methodology of the Western Canada Study, with emphasis on herd-selection criteria and study implementation, the collection of herd-production data, and the challenges of tracking individual animals in a large prospective observational study-as the Western Canada Study is the largest on-farm study of its kind in North American cow-calf herds to date. The primary objective of this project was to examine the potential association between reproductive success and cumulative chronic exposure to sulfur dioxide, hydrogen sulfide, and volatile organic compounds in beef herds. Herd-selection criteria included potential exposure to oil and gas facilities, herd size, quality of available records, an established relationship with a local veterinary clinic, and participant interest. With the cooperation of local herd owners and veterinarians, on-farm collection of detailed individual animal data was successful in this group of cow-calf operations. Of the 212 herds initially selected to participate, complete calving season data for 2002 were available for 203 herds (96%). Individual animal records were available for more than 98% of eligible cows for each measurement period throughout the study. Herd-production records were rated as satisfactory or better in 94% of the herds. These process outcomes confirm the practicality of using cow-calf herds as sentinel populations for environmental exposures and support the validity of subsequent research on these animal populations.