Energy partitioning and substrate oxidation by Guirra ewes fed soy hulls and corn gluten feed blend as a replacement for barley grain

The aim of this experiment was to study the effect of substituting barley grain by soy hulls and corn gluten feed blend on energy partitioning, substrate oxidation, carbon and nitrogen balance in sheep. The experiment was conducted in a crossover design with 12 dry and non-pregnant adult Guirra ewes (57.5 ± 1.9 kg of BW) in each group, and sheep were fed two dairy treatments in two 27 d periods. The ewes were fed with two different mixed diets; one group was fed a mixed diet with 365 g/kg of dry matter (DM) of barley grain (BRL diet) and the other diet (SHGF diet) replaced barley with soy hulls (271 g/kg DM) and gluten feed (93 g/kg DM). Six sheep per group were used to determine apparent total tract digestibility (10 d adaptation plus 5 digestibility and balance of nutrients), gas exchange (12 d), oxidation of nutrients and carbon and nitrogen balance. The average values of metabolisable energy (ME) intake, heat production (HP) and retention of energy (RE) were 498, 436 and 62 kJ/kg 0.75 of body weight (BW), respectively, with no differences between diets. The estimated value of ME for maintenance was 391 kJ/kg 0.75 BW. The efficiency of use of ME for maintenance (km) was 0.64 and the nutritive value of the diets was 7.6 MJ of net energy/kg DM, on average. Most of the HP derived from oxidation of fat (0.48) for the fibrous diet, and from oxidation of carbohydrates (0.63) for the starchy diet, with no differences in total tissue energy recovered (67 kJ/kg 0.75 BW). This fibrous by-product was utilised by the ewes with no detrimental effect on energy metabolism and resulted in a similar positive energy balance to that of a traditional cereal based diet. The economic advantages and sustainability of this choice should be evaluated.