Composition and in vitro digestibility of fibrous substrates placed in deep-stacked broiler litter

Effects of mixing urea (0 or 5.4% of broiler litter dry matter) with broiler litter (1.1 m high) on composition and digestibility of various fibrous substrates in dacron bags placed for 3 or 9 weeks at 36 or 72 cm from the surface of deep-stacks open or covered with plastic were determined with a 5 × 2 × 2 × 2 × 2 factorial arrangement of treatments. Urea increased ammonia concentration in broiler litter, but markedly so only when the deep-stack was covered. Overall, urea decreased neutral detergent fiber (NDF) concentration in bermudagrass, wheat straw and rice straw, with small or nonsignificant changes noted for rice hulls and pine shavings. In vitro NDF digestibility at 48 h was increased (P < 0.05) by urea for bermudagrass (58.9% vs. 46.4%) and wheat straw (42.1% vs. 33.3%); greater (P < 0.05) at 9 than at 3 weeks (43.0% vs. 24.2%) for rice straw; and greater (P < 0.05) at 9 than at 3 weeks (10.4% vs. 6.9%) for pine shavings. In summary, covering broiler litter deep-stacked without added urea did not appreciably affect nutritive value of fibrous substrates. Urea increased 48-h in vitro NDF digestibility for bermudagrass and wheat straw regardless of other deep-stack conditions. In conclusion, these results suggest potential to improve nutritive value for ruminants of some fibrous substrates added to broiler litter with urea before deep-stacking.