2012 Annual Report 1a.Objectives (from AD-416): The objective of this cooperative research project is to evaluate the effects of breed of dam on hornfly infestation in beef cattle; the relationships of hornfly infestation to milk production and quality, serum cortisol, and serum prolactin; and the relationship of the promoter region of the prolactin gene to variables measured in this study. 1b.Approach (from AD-416): The project will consist of 48 crossbred cows sired by Bonsmara, Brangus, Charolais, Gelbvieh, Hereford, and Romosinuano sires with approximately 8 cows per sire breed. Cows will be managed on tallgrass native prairie throughout lactation. Fly counts will be done on pasture prior to milking and fly control treatment every 28 days starting in late May and continuing for 6 milkings or early October. Two native pastures will be used in this research, with cows and pastures located at the USDA Grazinglands Research Laboratory at El Reno, OK, and will be stocked at the rate of 6 acres per animal. Fly control will be done every 28 days prior to milking. Cows will be milked using single cow milking machines, and blood samples will be taken at each milking via jugular venipuncture. Data will be analyzed as a repeated measures design with the main unit breed of cow and subunit time of lactation. 3.Progress Report: Data collection phase on fly counts, cow behavior, and milk production has been complete. Genotyping the cows and statistical analyses of the data are in progress.