Feeding value of tree leaves (hybrid poplar and black locust) evaluated with sheep, goats and rabbits

Abstract

Feeding trials were conducted with rabbits, sheep and goats to evaluate black locust ( Robinia pseudoacacia) and hybrid poplar ( Populus spp.) leaves as animal feed. The crude protein (CP), neutral detergent fiber (NDF), and acid detergent fiber (ADF) values for black locust (BL) foliage used in the feeding trials were: CP, 17.8%; NDF, 48.1%; ADF, 29.8%. The hybrid poplar (HP) foliage used in Experiment 1 (rabbit trial) contained CP, 14.77%; NDF, 42.09%; ADF, 29.26%. In Experiment 2 (sheep trial), the HP contained: CP, 11.40%; NDF, 36.39%; ADF, 29.45%. In Experiment 1, 10 New Zealand White (NZW) weanling rabbits per treatment were fed diets with 40% alfalfa meal (AM), and 10, 20 and 40% dried HP leaves substituted for AM. Digestibilities for AM diet and the average of all HP diet treatments were: crude protein (CP): 78.8 vs. 63.9% ( P < 0.05); ADF: 26.3 vs. 18.1%; NDF: 36.9 vs. 26.3% ( P < 0.05); dry matter (DM): 64.4 vs. 58.3%; ash: 60.6 vs. 49.8% ( P < 0.05). Average daily gain (ADG) and DM intake were 35.5 g vs. 37.7 g and 106 g vs. 121 g ( P < 0.05) for AM and HP. In Experiment 2, 10 mature crossbred ewes were fed diets with 50% AM or 50% HP for 14 days. Nutrient digestibilities for AM and HP diets were: DM: 75.5 vs. 67.0; CP: 84.3 vs. 55.4; ADF: 51.7 vs. 24.8; NDF: 54.1 vs. 41.1; ash: 62.6 vs. 51.0. All values were lower ( P < 0.05) for HP. In Experiment 3, BL leaf meal and AM were fed each at 25% of the diet to 10 NZW weanling rabbits per treatment, with 50% AM in the control diet. BL treatments were BL alone, BL + 1% polyethylene glycol (PEG), BL + 1% phytase and BL + 0.3% DL methionine + 0.3% choline chloride. PEG binds tannins; phytase may increase P availability and methyl donors are needed for metabolism of phenolic acids. A 20 day trial was conducted. The % digestibility for AM vs. all BL treatments were: CP: 77.1 vs. 60.7; ADF: 15.8 vs. 6.7; NDF: 25.8 vs. 18.6; DM: 68.8 vs. 63.2; ash, 75.3 vs. 67.8; Ca: 84.5 vs. 74.8; P: 70.3 vs. 62.1. All BL values were lower than for AM ( P < 0.05). ADG was 37.0 g vs. 31.9 g ( P < 0.05) for AM and all BL treatments. Addition of PEG increased ( P < 0.05) CP digestibility compared to the unsupplemented BL diet (55.8 vs. 66.3%). The other supplements had no effect on BL digestibility and ADG. In Experiment 4, 4 mature ewes and 4 mature female Angora goats were fed diets of 100% BL or AM in a digestibility trial. Within diet, there were no differences between sheep and goats. With both species combined, digestibilities for AM vs. BL were: DM: 61.9 vs. 44.5; CP: 78.8 vs. 40.1; ADF: 30.4 vs. −21.8; NDF: 28.9 vs. 2.9; ash: 50.4 vs. 33.1. All values for BL were lower ( P < 0.05) than for AM. The negative ADF digestibility is probably due to formation of CP-tannin complexes in the gut. Daily kg DM intake kg −1 BW for AM and BL were 0.0341 vs. 0.0180. Both HP and BL leaves have lower feeding value than AM, probably due to adverse effects of tannins.