Chemical and biological treatment of cotton gin trash for fattening Santa Ines lambs

Two experiments were used to evaluate the effects of using cotton gin trash (CGT) treated with urea and exogenous fibrolytic enzymes (EFE) on feed chemical composition, in vitro dry matter digestibility and gas production (Trial 1), and apparent in vivo digestibility, intake and growth performance of feedlot Santa Ines lambs (Trial 2). The Trial 1 used a completely randomized 2 x 4 factorial design with four replications of treating CGT with urea (0 and 6%) and EFE (0, 2, 4, 6 g/kg; 75% cellulase, 25% hemicellulase). The Trial 2 used a complete randomized design with 8 replications to evaluate the use of CGT treated with 6% urea and one of four EFE concentrations (0, 2, 4, 6 g/kg) in 50% concentrate and 50% CGT diets; the control diet contained untreated CGT. In Trial 1, there was interaction between urea and EFE dose for DM, EE, ADF, TN, and fractions A and C of nitrogen (P < 0.001). Urea reduced all cell wall components (P < 0.05) except for hemicellulose (P > 0.05). Increasing EFE resulted in a linear decrease of NDF, ADF, cellulose, hemicellulose, and lignin. Both urea and EFE increased (P < 0.05) IVDMD. There was an interaction (P < 0.001) between urea and EFE for TN and nitrogen fractions A and C. Independently of EFE dose, urea affected all carbohydrate fractions. Increasing EFE linearly increased (P < 0.001) NFC and decreased (P < 0.008) fractions B2 and C. An EFE vs. urea interaction (P < 0.02) affected L, CGP, BIO and TDOM. The CGT pre-treated with urea and 2 g/kg of EFE generated the greatest total gas production but urea without EFE resulted in the least gas production. In Trial 2, increasing EFE linearly increased DM and OM intakes and quadratically NFC intake; as well as linearly increased (P < 0.002) DM, OM and NFC digestibilities. However, fiber apparent digestibility (ADF and FC) was negatively affected by EFE (P < 0.05). Final BW, BW gain and ADG linearly increased with EFE dose (P < 0.02). Combining urea and EFE was efficient in reducing structural cell wall components and improving the in vitro digestibility and gas production of CGT. The EFE improved OM, fiber and NFC digestibility and DM, OM and NFC intake that supported greater growth performance of feedlot sheep.