Intra-ruminal concentrations of SF6 from high release rate permeation tubes. (Abstract)

Abstract

17A Intra_ruminal concentrations of SF6 from high release rate permeation tubes J.P. Goopy1, R.S. Hegarty2 and R.T. Woodgate 2 1 2 School of Rural Science and Agriculture, Animal Science, University of New England, Armidale NSW 2351 NSW Agriculture Beef Industry Centre, University of New England, Armidale NSW 2351 jgoopy@pobox.une.edu.au Sulphur hexafluoride (SF6) released from permeation tubes is used as a tracer gas for the estimation of ruminal methane emissions and (e.g. Ulyatt et al. 2002) there is usually a wait of seven days or longer after tube insertion to allow intraruminal SF6 to plateau prior to sampling. Our theoretical calculations, however, suggested that intraruminal SF 6 would plateau within 23 h of permeation tube placement. Because permeation tubes being developed (Hegarty and Woodgate 2003) have release rates ~100 times higher than those used in previous studies they run for shorter periods, and the time available for calibration and achieving plateau is critical. Permeation tubes releasing an average of 170 mg SF6/d (Hegarty and Woodgate 2003) were placed via rumen cannulae into two cows. Rumen gas was regularly sampled (900 ml) through the rumen cannulae over a 5 d period, collected in Tedlar gas sampling bags and immediately analysed for CH4 and SF6 concentrations. No SF6 was detectable in intraruminal gas prior to insertion of the capsules. After insertion, SF6 concentration rose quickly to be close to a plateau value by 2.5 h (Figure 1a). Intraruminal CH4 ranged from 48,000 to 74,500 �l/l in cow V31 and from 3,600 to 49,000 �l/l in cow V14; SF6 was present in the range of 4 to 26 �l/l in V31 and from 0.8 to 19.1 �l/l in V14. The ratio of SF6 to CH4 present was similar between animals. CH4 generally increased postfeeding, whilst SF6 fell contemporaneously (Figure 1b). The results of this trial indicate that intraruminal SF6 rises quickly after capsule placement to peak within 23 h. Thus, delaying measurements for up to a week after placement is not necessary. It may be concluded that despite considerable dif ferences in SF 6 intraruminal concentration between cows, it seems unlikely that it will rise above 40 �l/l at the release rate described. Hegarty, R.S., Woodgate, R. and Clark, D.A. (2003). Performance of highflow permeation tubes releasing SF6. Recent Advances in Animal Nutrition in Australia 14, 19A. Ulyatt, M.J., Lassey, K.R., Shelton, I.D. and Walker, C.F. (2002). Seasonal variation in methane emission from dairy cows and breeding ewes grazing ryegrass/white clover pasture in New Zealand. New Zealand Journal of Agricultural Research 45, 217226. 75 (a) 75 (b) Ga s co n centra tio n Gas co ncentratio n 60 45 30 15 0 0 150 300 450 600 60 45 30 15 0 0 1500 3000 4500 6000 Time ela ps ed (minute s) T ime ela ps ed (minute s) Figure 1 Intra_ruminal concentration of CH4 (ml/l; --) and SF6 (�l/l; ����) in cows V31(t) and V14 () in the first 10 h (a) and over a 5 day period (b) following insertion of permeation tubes (arrows indicate time of feeding). Recent Advances in Animal Nutrition in Australia, Volume 14 (2003)