Estimation of total intake
In the crate sheep, mean DM intake estimated using the C31/C32 alkane pair under-estimated known intake
by 2% (706 v. 720 g/day; Table 3). The estimate of DM intake based on the C32/C33 alkane pair was only
0.8% different from the known mean intake (726 v. 720 g/day). In the 16 pen sheep, total DM intake
estimated using C31/C32 was very close to known intake, but the mean intake estimated using C32/C33 was
44 g/day (5.8%) higher than known intake (766 v. 722 g/day). The standard errors associated with the
estimated intakes in pen sheep were higher than those found with crate sheep.
Faecal DM output estimated using C36 alkane was 5% less than known faecal output (269 v. 282 g/day)
despite the almost complete faecal recovery of this alkane. As a result, whole-diet digestibility was slightly
over-estimated (63.0 and 61.9% v. 60.8%). In pen sheep, true faecal outputs and digestibilities were by
definition unknown, but estimates of faecal output based on faecal grab samples taken only in the morning,
were similar to those found with the crate sheep.