Precaecal digestibility of crude protein and amino acids from alfalfa (Medicago sativa) and red clover (Trifolium pratense) leaves and silages in broilers

The aim of the present study was to determine the precaecal (pc) digestibility of crude protein and amino acids from organically produced alfalfa and red clover leaves and whole plant silages by a linear regression approach in slow-growing male Hubbard JA-757-broilers. Dried alfalfa leaves (AL; 219 g crude protein/kg dry matter (DM)), dried red clover leaves (RCL; 262 g crude protein/ kg DM), alfalfa silage (AS; 240 g crude protein/kg DM) and red clover silage (RCS; 190 g crude protein/kg DM) were included in the diets at the levels of 100, 150 and 200 g/kg respectively at the expense of maize starch. Titanium dioxide was used as an indigestible marker for digestibility estimation. On day 41/42, digesta was sampled pen-wise from the terminal two thirds of the intestine section between Meckel’s diverticulum up to 2 cm anterior to the ileocaeca-colonic junction. Feed intake did not differsignificantly between feeding groups. All broilers grew during the experimental phase of digestibility estimation (day 30-41/42). The pc crude protein and amino acid digestibility of alfalfa and red clover leaves was lower than of alfalfa and red clover silages. Methionine was less digestible in AL (0.61) and RCL (0.73) than in AS (0.84) and RCS (0.99). This tendency was also observed for lysine (AL 0.49, RCL 0.61, AS 1.00, RCS 0.88) as well as for other amino acids. Anti-nutritional factors, e.g. saponins, were suspected of being responsible for the lower pc digestibility of the leaf products. The saponin analysis showed a higher content of medicagenic acid glycosides in AS than in AL, whereas a higher content of a zanhic acid glycoside was found in AL than in AS. Differences in saponin contents suggest that certain individual saponins, e.g. zanhic acid glycosides, might have a more negative effect on crude protein and amino acid digestibility than other saponins.