The accuracy of intake estimation based on the use of alkane controlled-release capsules and faeces grab sampling in cows

Alkanes are digesta markers for use as a research tool giving the opportuni ty to estimate feed intake and digestibility in vivo. The development of in tra-ruminal controlled-release capsules (CRC) offers a practical method of dosing even-chain alkanes and may give less diurnal variability of marker e xcretion improving the validity of grab-faecal sampling. This was tested in the present study by total faeces collection in four cows for 7 days. Dry matter intake was 10.4 kg forages and 10.4 kg concentrate (diet 1) and 15.1 kg forage (diet 2). The recovery (proportion of dosed or dietary alkane in take found in faeces) of C-31 was lower than that of C-32 and consequently underestimated intake. C-33 and C-32 had similar recoveries giving accurate intake estimates from pooled samples from total daily faecal collections a nd also from grab samples taken at 6.30 a.m. The study confirms that a sing le injection for gas chromatography is sufficient. Alkane CRC are concluded to be an accurate method for estimating forage intake of cows consuming di ets with or without concentrate when spot sampling of faeces is conducted o ver 7 days and only moderately less precise when sampling over 5 days.