Effects of defaunation on digestion of fresh Digitaria decumbens grass and growth of lambs

Abstract

The effects of defaunation on growth and digestion were measured in sheep fed fresh Digitaria decumbens grass cut at four stages of regrowth 14, 28, 42, and 56 days, and with different protein to energy (P/E) ratios. Two completely randomized designs trials (growth and digestion) were conducted using faunated animals, defaunated rams and protozoa free lambs. The digestion trial: eight faunated and eight defaunated rams fitted with ruminal and duodenal cannulas were fed 4 diets (diets D1 to D4) to measure digestion parameters. The dietary P/E ratios were 120 (D1), 130 (D2), 130 (D3), and 140 (D4) g PDIN/UFL (Protein Digested in the small Intestine supplied by microbial protein from rumen-degraded protein/Feed Unit for Lactation) and the grass stages of regrowth were 56, 42, 28, and 14 days, respectively. Increasing the dietary P/E ratios increased dry matter intake (DMI) and the total tract digestibility of organic matter (OM), NDF and CP. Defaunation decreased DMI, except for rams fed D4 diet. Defaunation also decreased total tract digestibility of OM except for rams fed D1 diet and that of NDF except for rams fed D1 and D4 diets. Increasing the dietary P/E ratios also increased nitrogen intake and ammonia (NH3) concentration in the rumen, whereas defaunation decreased them. The dietary P/E ratio increased non-NH3 nitrogen and microbial nitrogen duodenal flows and microbial efficiency. Defaunation did not affect duodenal flows of neither non-NH3 nitrogen and microbial nitrogen or microbial efficiency. The growth trial: 20 faunated and 20 protozoa free lambs were fed four diets (diets D5 to D8) to measure their average daily gain (ADG). The dietary P/E ratios were 60 (D5), 70 (D6), 80 (D7) and 100 (D8) g PDIN/UFL and the stages of regrowth were 56, 42, 28, and 14 days, respectively. DMI of lambs increased with P/E ratio. Protozoa free lambs had greater DMI than faunated ones when fed D7 diet (80.8 v. 74.9 g/kg LW0.75, respectively). The ADG of the lambs increased with P/E ratio. Fed on the same D5 diet, protozoa free lambs had greater ADG than faunated lambs (29.8 v. 11.6 g/day, respectively). In conclusion, animal response to defaunation was modulated by the P/E ratio of the D. decumbens grass diets. Defaunation increased ADG of lambs fed forage with the lowest P/E ratio, while digestion and nitrogen duodenal flows of rams fed the lowest P/E ratio were not affected.