Investigation of a “fibre appetite” in sheep fed a “long fibre-free” diet

Abstract

Sheep fed a “long fibre-free” diet undergo short spells of pseudorumination (cud regurgitation without cud chewing) and no true rumination. True rumination can be restored by the addition of inert fibre particles directly into the rumen. To assess whether sheep fed a “long fibre-free” diet would actively choose to ingest inert fibre particles, in a series of experiments, 10 sheep were offered a plastic box containing specific amounts of polyethylene fibre, chopped into 10 mm lengths. After 24 h, the remaining fibre was retrieved and weighed. At the same time, jaw movements were recorded for 24 h periods to monitor rumination. Feeding a “long fibre-free” diet for 7 days reduced true rumination to zero. In experiment 1, on offering a plastic box containing 50 g polyethylene fibre, three sheep ingested 34.8 ± 6.8 g of fibre and rumination was significantly ( p < 0.05) increased. In experiment 2, when a plastic box containing 50 g chopped polyethylene fibre was offered daily to 4 fistulated sheep immediately upon switching from hay to the pelleted diet, the sheep commenced eating the fibre within 24 h. In experiment 3, when offered a choice between short-chop (3 mm) and long chop (15 mm) polyethylene fibre, the sheep showed a preference ( p < 0.05) for the 3 mm length fibre, although this was of a length insufficient to evoke adequate rumination. Therefore, the actual choice of fibre consumed may be driven by ease of ingestion rather than which substrate is more ideally suited to induce rumination. In experiment 4, a polyethylene fibre pompom, fixed on a rod, introduced via the rumen cannula and placed so as to brush the reflexogenic areas of the reticulorumen, reduced voluntary polyethylene fibre intake. This suggests that the intake of inert fibre may be a result of the reduction of ruminal sensory input to the brain, normally provided by fibrous reticuloruminal contents.