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

摘要

This study was aimed at evaluating the C0_2 and H20 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, N_20 and NH_3 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 reportedpatterns suggesting that the DeLaval meter system might provide a high resolution measurement of animal activity and hence ventilation rates based on the C0_2 balance method since all cows are considered. The average ventilation rates were fairly similar (p = 0.08) with means of 502 ± 248 m3 Llf1 h'1 and 575 ± 258 rr? LLT1 h'1 for the C0_2 and H20 methods respectively (1 LU = 500 kg animal mass). The H20 method can provide a reasonable alternative for estimating ventilation rates in dairy cow barns when C0_2 concentration is not measured. The mean emission factors were 12.4 g CH4 LLT1 h' 0.60 g NH_3 LLT1 h'1 and 40.3 mg N_20 LU~1 h~(-1)