1. a National Farm Medicine Center, Marshfield Clinic Research Institute, Marshfield, WI, USA
2. b Current address: USDA-ARS, U.S. Dairy Forage Research Center, Environmentally Integrated Dairy Management Research Unit, Marshfield, WI, USA
3. c Center for Clinical Epidemiology and Population Health, Marshfield Clinic Research Institute, Marshfield, WI, USA
4. d Department of Civil and Environmental Engineering, University of California, Davis, CA, USA
5. e Current address: Global Alliance for Improved Nutrition, Washington, DC, USA
6. f U.S. Dairy Forage Research Center, U.S. Department of Agriculture – Agricultural Research Service, Marshfield, WI, USA