Associations between total sulfation, hydrogen sulfide deposition, and beef-cattle breeding outcomes in western Canada.

Beef cows sometimes are pastured close to oil- and gas-production and processing facilities. We measured the health and productivity of cow-calf herds with differing exposure to sour-natural-gas processing facilities in western Canada. In seven cow-calf herds, the numbers of eligible mature females included in the study for the breeding seasons beginning in 1993, 1994, and 1995 were 1177, 1251, and 1236, respectively. Outcomes included pregnancy status, calving interval, and the occurrence of twins, abortions, stillbirths, and neonatal mortality. Information also was collected on other risk factors known to influence beef-herd health and productivity. Monthly measurements from a network of passive air-monitoring devices were used to estimate exposure. Total sulfation and H2S deposition were used as markers for the complex mixture of compounds found in emissions from sour-gas processing plants and sour flares. Most herds were managed in multiple pasture groups. Cumulative exposure assessments were made from records of individual-animal movements between pastures. Generalized estimating equations were used to evaluate the association between exposure and outcome and to adjust for potential confounders and clustering of binomial outcomes within herd. No consistent associations were found between either total sulfation or H2S deposition and productivity parameters across the cow-calf production cycles. There were, however, five examples of significant associations between increasing cumulative exposure to total sulfation and decreased productivity in the 18 models examined.