Effects of main protein, non-forage fibre and forage source on digestibility, N balance and energy value of sheep rations

Two in vivo digestion trials were conducted, by using a latin square 4 x 4 experimental design with castrated rams, to evaluate the effects of main protein source, non-forage fibre source (NFFS) and forage source on nutrient digestibility, N balance and energy value of sheep rations. In each trial, rams were fed at maintenance level four isocaloric-isonitrogenous and isofibrous rations, differing in the main protein and/or NFFS. At the first trial, alfalfa hay was used as a forage source whilst in the second trial, corn silage was used as a forage source. At both the trials, the 1st ration contained soybean meal (SBM) and wheat bran (WB), the 2nd SBM and corn gluten feed (CGF), the 3rd corn gluten meal (CGM) and WB and the 4th CGM and CGF. Data of both the trials were analyzed in common as 2 x 2 x 2 factorial experimental design. Main protein source (SBM versus CGM) did not affect nutrient digestibility, energy value and N balance of diets, except an increase in crude fibre (CF) digestibility of diets containing SBM. Those results suggest that an increase in rumen undegradable protein (RUP) content does not negatively affect digestibility or nutritive value of the diets if adequate fermentable metabolizable energy (FME) is provided. CGF significantly elevated CF, NDF and ADF digestibility in comparison with WB, but NFFS did not affect other nutrients' digestibility or N balance or energy value (ME) of the diets. Rations containing alfalfa hay had higher digestibility of crude protein (CP), organic matter (OM) and gross energy (GE) in comparison with those containing corn silage; the opposite was true for NDF and ADF digestibilities. The combination of CGM and CGF (16% of concentrate mixture each) did not have a negative effect on nutrient digestibility, N balance and energy value of sheep rations when isonitrogenous replaced SBM and WB (22% of concentrate mixture each), respectively. Probably, CGF had positive effect on digestibility of the fibre fraction of the ration regardless of the main protein and forage source used. There were no significant interactions between forage x protein, forage x NFFS and protein x NFFS, for any parameter studied.