Replacement of rice straw with cassava-top silage on rumen ecology, fermentation and nutrient digestibilities in dairy steers

Conserving good source of roughage for dry-season feeding of ruminants is of the utmost importance. Therefore, cassava-top silage (CTS) was prepared and was studied for its feeding level and nutritive value in dairy steers. Four rumen-fistulated dairy steers (75% Holstein Friesian x 25% Thai Native), 3 years old with 209 +/- 50 kg liveweight, were randomly assigned according to a 4 x 4 Latin square design to study the effect of CTS on feed intake, nutrient digestibility and rumen fermentation efficiency. The treatments were four different feeding ratios of CTS to rice straw, as follows: 0:100, 30:70, 60:40 and 100:0 respectively. Increasing the ratio of CTS to rice straw in the feed remarkably reduced the rumen protozoal population (P < 0.01), thus subsequently decreasing rumen methane production (P < 0.01), whereas other rumen microorganisms remained similar among treatments. Correspondingly, rumen propionate production was enhanced (P < 0.01) by increasing the CTS to rice ratio in the feed, and the acetate:propionate ratio decreased (P < 0.01). Furthermore, rumen ammonia nitrogen and blood urea nitrogen increased (P < 0.01) with an increasing proportion of CTS in the feed, whereas nitrogen retention was highest when the proportion of CTS in the feed was 100%. Although the feed DM intakes were similar, apparent digestibilities of DM, organic matter, crude protein as well as neutral detergent fibre and acid detergent fibre were significantly improved by the increase in the percentage of CTS in the feed. It could be concluded that including CTS in the feed at a level of 60-100% improved the rumen fermentation, nitrogen balance and nutrient digestibilities, and is highly recommended for use in the ruminant production in the tropics, as it is a practically simple-to-prepare on-farm feeding intervention.