Ventilation Rate Measurements and Gas Emissions from a Naturally Ventilated Barn for Dairy Cows

Abstract

<abstract> <bold>Abstract.</bold> This study was aimed at evaluating the CO₂ and H₂O balance methods for estimating the ventilation rate in a naturally ventilated barn for dairy cows during the spring transitional season. Animal activity measured using the DeLaval activity meter system was also studied and the emission factors of CH₄, N₂O and NH₃ were generated. Measurements were carried out in a free-stall dairy barn with cubicles. The main barn had a solid concrete floor which was mechanically scraped six times in a day. The activity of the cows showed a distinct diurnal pattern with peaks between 7 and 9 a.m. and also between 6 and 8 p.m. The lowest activity measured at about 5 a.m. was 275% lower than the peak activities. Variations in animal activity were similar to reported patterns suggesting that the DeLaval meter system might provide a high resolution measurement of animal activity and hence ventilation rates based on the CO₂ balance method since all cows are considered. The average ventilation rates were fairly similar (p = 0.08) with means of 502 ± 248 m³ LU^-1 h^-1 and 575 ± 258 m³ LU^-1 h^-1 for the CO₂ and H₂O methods respectively (1 LU = 500 kg animal mass). The H₂O method can provide a reasonable alternative for estimating ventilation rates in dairy cow barns when CO₂ concentration is not measured. The mean emission factors were 12.4 g CH₄ LU^-1 h^-1, 0.60 g NH₃ LU^-1 h^-1 and 40.3 mg N₂O LU^-1 h^-1.