Effects of defaunation on digestion and growth, in sheep receiving a mixed diet (fresh Digitaria decumbens grass and concentrate) at four protein to energy ratios

The effects of defaunation on growth and digestion were measured on sheep consuming four mixed diets (D1 to D4) of Digitaria decumbens grass and concentrate, with different protein to energy ratios. The protein digestible in the intestine (protein French feeding system, PDI) to energy (Forage unit, energy French feeding system) levels (P/E) in the diets were 80 (D1), 100 (D2), 120 (D3) and 140 (D4). Conventional and ciliate-free animals were conducted in parallel in 4 × 4 Latin square designs. First, two Latin square designs were conducted with 20 faunated lambs and 20 defaunated lambs to measure the average daily gain. In addition, two other Latin square designs were conducted with 8 conventional mature rams and 8 ciliate-free mature rams to measure digestion parameters. There was no effect of the diet on the average daily gain (ADG) of the lambs. The ADG of faunated lambs was significantly lower (P < 0.05) compared with defaunated lambs with the D2 diet (153.7 vs. 211.6, s.e. = 13.0 g*d-1). The feed conversion ratio was higher with conventional lambs compared with ciliate-free lambs with the D2 diet (7.2 vs. 4.7, s.e. = 1.6 g*g-1, P < 0.05). The same trend was observed with the energy conversion ratio for the D2 diet (6.0 vs. 4.0, s.e. = 0.7 10-3 UFL*g-1, P < 0.05). The differences of ADG between conventional and ciliate-free lambs can be explained by the higher supply of protein in ciliate-free animals when the energy was not the first limiting factor for microbial and animal growth. Duodenal non-ammonia nitrogen (NAN) flow was significantly increased (P < 0.01) by defaunation (144 vs. 172, s.e. = 5.5 g NAN*d-1). However, the differences of NAN flow, observed between faunated and defaunated rams, were only significant (P < 0.01) with the D3 diet. The duodenal microbial N flow was significantly (P < 0.01) higher with ciliate free rams compared with conventional ones, consuming diets D2 and D3. A better microbial synthesis efficiency and a higher nitrogen digestion for the defaunated animals, explain the differences in nitrogen availability between the animals. Les effets de la défaunation sur la digestion de rations mixtes (herbe de Digitaria decumbens et concentré) et la croissance de moutons. Quatre régimes mixtes (D1 à D4) composés de fourrage Digitaria decumbens et de concentré, différenciés par le rapport protéine / énergie dans le régime, ont été constitués. Le niveau de protéines digestibles dans l'intestin (Système PDI français) / énergie (UF, un