1. The supplementation of diets rich in soluble polysaccharides with microbial cellulases
and hemicellulases decreases digesta viscosity and promotes broiler performance.
2. In contrast, recent experiments suggest that polysaccharidases are ineffective for improving the
nutritive value of pasture biomass used by free-range broilers. However, the feasibility of using cellulases
and hemicellulases to improve the utilisation of cereal-based feeds by pastured poultry remains to be
established.
3. A study was undertaken to investigate the capacity of a recombinant cellulase from Clostridium
thermocellum to improve the nutritive value of a barley-based feed for free-range pastured broilers of the
RedBro Cou Nu RedBro M genotype.
4. The results show that supplementation of a barley-based diet with a recombinant -glucanase had
no effect on the performance of free-range broilers, foraging in legume-based diets from d 28 to 56.
In addition, the results confirm that the lack of effect of the recombinant enzyme in improving the
nutritive value of the barley-based feed does not result from enzyme proteolysis or inhibition in the
gastrointestinal tract.
5. Significantly, -glucanase activity was identified in the crop of non-supplemented animals. The data
suggest that endogenous cellulases originated both from the barley-based feed and from the crop
microflora.
6. The results presented here suggest that in older birds of slow-growing genotypes associated with
free-range production systems, previously unknown sources of -glucanases, such as the feed and
microbial symbiotic microflora, can affect the effectiveness of exogenous enzymes added to the feed
