Importance of palatability in determining the feed intake of sheep offered chopped and pelleted hay

1. In the first of three experiments four sheep received chopped (C) and pelleted (P) hay by mouth (m) or rumen fistula (f) in the four combinations shown below. Feed eaten by mouth was offered ad lib. from 09·15 to 16·00 hours; feed was given by fistula at 09·00 hours in amounts equal to half of total intake (i.e. by mouth and by fistula) on the previous day. Daily dry-matter intake (g/kg metabolic live weight, W0·75) was as follows: treatment CmCf, 51·5; CmPf, 74·5; PmCf, 57·8; PmPf, 85·7. The corresponding dry-matter digestibility coefficients were 0·59, 0·56, 0·57 and 0·53. 2. The intention was that the difference in intake between CmPf and PmCf should provide a measure of palatability, since the animals digested the same composite diet but ate different components of it. For the comparison to be valid the two treatments had to promote equal rates of digestion, but measurements of rumen fill and of rate of passage of digesta suggested that Cf was digested more slowly than Cm. 3. In Expt 2, each form of hay was given entirely by mouth or partly by fistula. Daily dry-matter intake (g/kg W0·75) was as follows: Cm, 45·5; CmCf, 42·4; Pm, 80·4; PmPf, 79·2. In this experiment there was less evidence of Cf being digested more slowly and hence depressing intake. 4. The conclusion drawn from these two experiments is that fistula feeding in its present form is not a suitable technique for measuring the relative palatability of feeds differing considerably in physical structure. However, the technique might be improved if food given by rumen fistula to one animal was previously masticated by, and collected from the oesophageal fistula of, a second animal. 5. In Expt 3, the effects of sudden changes from a composite diet to either C or P, or from C to P or vice versa were measured in sheep receiving food by mouth only. The patterns of intake suggested that total intake might be partially determined by feed palatability.