Effects of rhubarb (Rheum spp.) and frangula (Frangula alnus) on intake, digestibility and ruminal fermentation of different diets and feedstuffs by sheep

Previous in vitro work suggests that rhubarb (Rheum spp.) and frangula (Frangula alnus) potentially modify rumen fermentation, but no in vivo research has confirmed these findings or examined the suitability of these plants in the diet of ruminants. Our objective was to examine effects of these plants on feed intake, digestibility and ruminal fermentation in vivo. Effects on intake were determined in 20 sheep individually housed and fed a TMR ad libitum. Sheep were distributed into 4 experimental groups, which were supplemented with rhubarb (30g/d), frangula (30g/d), monensin (30mg/kg DM) or nothing (control), respectively. The digestibility of the TMR was determined by placing 4 of the sheep of each group into metabolic cages. The impact of these plants on ruminal fermentation was also examined using rumen cannulated grazing sheep. Fifteen sheep were distributed into 3 groups: control, rhubarb (30g/d) and frangula (30g/d); plant material was supplied daily directly into the rumen, and measurements started after 3 wks of supplementation., which consisted in rumen fluid analyses and in vitro and in situ incubations (12 and 24h) of several feedstuffs. In the intake experiment, both rhubarb and frangula groups had an intake comparable to control, while the monensin group had a lower (P<0.05) intake. Effects on intake were similar during the digestibility trial, and the apparent digestibility of dry matter, neutral detergent fibre and crude protein were not affected by any treatment. In the grazing experiment, rumen fluid samples of the rhubarb group had higher concentrations of volatile fatty acids and lower pH. When this rumen fluid was incubated in vitro, the cultures yielded less gas and CH₄, and the gas production curves revealed an overall lower production, but fractional rates similar to control sheep. In situ degradability of several feedstuffs was similar in rhubarb and control sheep. In frangula supplemented sheep there were small effects on some of the parameters described above for the in vitro incubations. Rhubarb changed the fermentation in the rumen of sheep without affecting intake or digestibility of the diet, suggesting a promising role of rhubarb, or its metabolites, as rumen modifiers for ruminants, and suggest more research to elucidate their impacts on productive performance.