Environmental Characteristics and Bacterial Counts in Bedding and Milk Bulk Tank of Low Profile Cross-Ventilated, Naturally Ventilated, and Compost Bedded Pack Dairy Barns

Abstract

Low profile cross-ventilated freestall (CV) and compost bedded pack barns (CB) are two newer housing options for dairy producers in the Upper Midwest. The CV barns are fully enclosed facilities that rely on mechanical ventilation and typically use evaporative cooling for heat abatement during the warmer months. The CB barns are a loose housing system that is generally bedded with dry wood sawdust and tilled twice daily. The objectives of this study were to describe the housing system and assess air quality (aerial ammonia and hydrogen sulfide), air velocity, light intensity, temperature, and relative humidity in CV, CB, and naturally ventilated freestall barns (NV). This cohort study was conducted on 18 commercial dairy farms, 6 of each housing type, in Minnesota and eastern South Dakota. Farms were visited four times, once each season between January and November 2008. Ammonia, hydrogen sulfide, light intensity, and air velocity measurements were taken twice each visit with 10 measurements per sampling time. Aerial ammonia concentrations were significantly higher in CV barns than CB and NV barns (5.2, 3.9, and 3.3 ppm, respectively). Hydrogen sulfide concentrations were 18, 33, and 19 ppb in CB, CV, and NV barns, respectively. There was a trend for higher hydrogen sulfide concentrations in CV barns. Light intensity was significantly lower in CV barns than CB and NV barns (111, 480, and 392 lux, respectively). There were no differences in air velocity among the housing systems. The mechanically ventilated CV barns were warmer in the fall and winter than the CB and NV barns. When outside temperature was above 27C, CV barns were 2.9C and 3.0C cooler than CB and NV barns, respectively. No differences were seen in bedding or bulk tank bacterial counts among the housing systems. Although CV barns had significantly higher aerial ammonia and a trend for higher hydrogen sulfide concentrations than NV and CB barns, ammonia and hydrogen sulfide concentrations were below the threshold that would affect cow performance or human health. In conclusion, the three housing systems assessed had adequate air quality and ventilation to provide a safe environment for workers and animals.