Sawdust represents a locally available lignocellulosic resource that may complement ruminant diets during periods of forage shortage. This study evaluated the feeding value of birch (Betula pendula) sawdust subjected to physical and chemical processing using a stepwise experimental approach. Steam-exploded and fresh sawdust were treated with 0, 4% ammonia, or 4% sodium hydroxide in a 2 × 3 factorial design and initially evaluated by in vitro gas production, dry matter digestibility, and fermentation pH. Based on these results, selected materials were further assessed for rumen dry matter and fiber degradation using the in sacco technique in cannulated dairy cows, with untreated and ammonia-treated wheat straw included for comparison. In addition, steam-exploded sawdust was compared with wheat straw and grass silage for in vivo digestibility in sheep. A pilot study also tested aspen (Populus tremula) sawdust in lactating cow diets. Steam explosion substantially reduced fiber fractions, particularly hemicellulose, and increased residual carbohydrates, resulting in higher gas production and in vitro digestibility compared with fresh sawdust (p < 0.05). Ammonia treatment markedly increased crude protein content, whereas sodium hydroxide primarily increased ash concentration. In sacco, steam-exploded birch showed similar or higher ruminal dry matter and neutral detergent fiber degradation compared with ammonia-treated wheat straw, while untreated fresh birch remained largely undegraded. In vivo, steam-exploded sawdust exhibited greater organic matter digestibility and net energy than untreated wheat straw but remained less digestible than grass silage (p < 0.0001). A pilot feeding test with lactating dairy cows demonstrated good acceptance of untreated aspen sawdust as a partial roughage substitute under non-standardized conditions. Overall, the results indicate that steam-exploded sawdust has potential as a complementary roughage source for ruminants when conventional forages are limited.
Yimam et al. (Fri,) studied this question.