Abstract:
18A In vitro ruminal VFA production is unaffected by the presence of sulphur hexafluoride J.P. Goopy1, S.H. Bir d1, R.S. Hegarty2 and J.V. Nolan1 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 Since first proposed by Johnson et al. (1994), the sulphur hexafluoride (SF6) tracer technique has been used to quantify ruminal methane emissions from both cattle and sheep. To make the SF6 technique more robust, permeation tubes with higher release rates have been developed (Hegarty and Woodgate 2003). Although SF6 is thought to be an inert and nontoxic marker gas, the higher release rates from the new capsules could invalidate this method of determining methane production if there is any effect on microbial metabolism. The intraruminal concentration of SF6 after inserting capsules releasing 100200 mg/d was from 135 �l/l (Goopy et al. 2003). A study was made to determine whether SF6 had any effect on microbial VFA production in the range of 1100 �l/l. A rumen liquor sample (2 litres) was obtained from an Angus heifer fitted with a rumen cannula and the contents were strained and used in a 3 h in vitro fermentation based on that of Bird et al. (1999). Six levels of SF6 (0, 0.5, 1, 10, 20 and 100 �l/l) were established in the head space of the fermentation flasks. Total VFA production did not differ (P>0.05) between any of the treatments (Table 1), and all treatments produced similar percentages of acetate, propionate and butyrate in the total VFA. The results of this trial indicate that concentrations of SF6 up to 100 �l/l in the headspace gas do not have detectable effects on rumen microbial metabolism. It can be concluded that intraruminal permeation tubes releasing up to 200mg SF6/d will not adversely affect rumen microbial function. Bird, S.H., Rowe, J.B., Choct, M., Stachiw, S., Tyler, P. and Thompson, R.D. (1999). In vitro fermentation of grain and enzymatic digestion of cereal starch. Recent Advances in Animal Nutrition in Australia 12, 5359. Goopy, J.P., Hegarty, R.S. and Woodgate R. (2003). Intra ruminal concentration of SF6 from high release rate permeation tubes. Recent Advances in Animal Nutrition in Australia 14, 17A. Hegarty, R.S., Woodgate, R. and Clark, D.A. (2003). Performance of highflow permeation releasing SF6. Recent Advances in Animal Nutrition in Australia 14, 19A. Johnson, K., Huyler, M., Westberg, H., Lamb, B. and Zimmerman, P. (1994). Measurement of methane emissions from ruminant livestock using a SF6 tracer technique. Environmental Science and Technology 28, 35962. Table 1 VFA production in vitro in the presence of increasing concentrations of SF SF6 �l/l 0 0.5 1 10 20 100 Mean S.D. Acetic acid % 62.8 62.5 62.1 61.9 62.3 62.5 62.4 Propionic Acid % 22.4 22.7 22.5 22.6 22.6 22.6 22.6 6 . Total VFA (mM/l) 47.8 48.7 47.0 46.1 47.5 47.6 47.4 Butyric Acid % 13.6 13.7 14.1 14.2 13.9 13.9 13.9 0.364 0.239 0.336 1.692 Recent Advances in Animal Nutrition in Australia, Volume 14 (2003)