Abstract:
21A Recovery in faeces of alkanes from a controlled release device R.M. Herd, R.S. Hegarty, R.T. Woodgate and S. Sinclair The Cooperative Research Centre for Cattle and Beef Quality, NSW Agriculture Beef Industry Centre, University of New England, Armidale NSW 2351 robert.herd@agric.nsw.gov.au Knowledge of the nalkanes found in pasture species combined with a known daily dose of synthetic alkanes and measurement of alkanes in faeces can be used to calculate intake of pasture. The extent of recovery in faeces of the different carbon chainlength alkanes needs to be known to make these calculations. Dosing of the synthetic alkanes C32 and C36 by intraruminal controlledrelease device (CRD) is convenient and reduces disruption to grazing. This experiment was to determine the extent of recovery in faeces of C32 and C36 in ground alkane CRD matrix fed to cattle. Eight Angus steers (ca. 300 kg; 10 months old) were individually penned and fed a ration of 60% rolledbarley, 32% chopped sorghum hay and 8% additives. After they were accustomed to the ration and to wearing a faecal collection bag they were fed a known weight (ca. 10 g) of ground CRD matrix mixed into feed, and then all faeces were collected over the next seven days. The ground matrix was prepared by grinding tablets from the core of two CRD (Captec Ltd, Auckland, NZ) to the consistency of table sugar. Total faeces for each animal each day was mixed and sub sampled. Duplicate samples of dried (70oC) ground feed, feed spiked with known amount of CRD matrix, and faeces were analysed for their alkane contents using previously described methods (Herd et al. 2002). The concentrations of C32 and C36 in the ground CRD matrix were equal, being 210 and 214 ppm dry matter (DM) when determined from the spiked feed samples, and 214 ppm for both when measured in ground matrix. Large amounts of C32 and C36 appeared in faeces over the first two days after dosing; their concentrations thereafter quickly approached background levels (Figure 1). Despite ingesting similar amounts of C32 and C36, considerably less C36 than C32 was excreted. Recoveries for different chainlength alkanes are shown in Figure 2. Recoveries for C32 were 87 � 19% (SD) and C36 were 63 � 14%. Whether these recoveries for ground, pulsed dosed alkane apply in the field where CRD alkane matrix is slowly eroded over time remains to be determined. Recoveries of C36 lower than for C32 from similar CRD reported by Herd et al. (2002) would, without compensation, lead to erroneous calculation of feed intake. This report confirms the need to validate recoveries under the conditions of each experiment. Herd, R.M., Hegarty, R.S., Dicker, R.W., Archer, J.A. and Arthur, P.F. (2002). Selection for residual feed intakes improves feed efficiency in steers on pasture. Animal Production in Australia 24, 8588. Faecal alkanes (ppm DM) 500 400 300 200 100 0 1 2 3 4 5 6 7 Days after dosing on day 1 C C C C 31 100 80 32 33 36 Recovery ( %) 60 40 20 0 C27 C29 C31 C32 C33 C36 Alkane Figure 1 Faecal alkane concentrations. Figure 2 Mean recoveries of alkanes in faeces. Recent Advances in Animal Nutrition in Australia, Volume 14 (2003)