The effects of variety and roasting on physical characteristics and ruminal degradability of barley grain

Barley grain is one of the major feedstuff in ruminant animal’s nutrition due to its high energy density and lower price than grains such as corn. Rate of barley starch digestion in the rumen is critical issue in high-grain fed ruminants because it is associated with higher performance of animal. Feeding high amount of barley in ruminant animal rations can cause an increase in the incidence of digestive disorders including reduced feed intake, off-feed, acidosis, and liver abscesses. Processing methods such heat treatment can affect physical characteristics and ruminal fermentation of grain. Moreover, barley grains from diverse cultivars are different in their chemical composition and fermentation characteristics due to geographical, environmental and genetic variations as well as their interactions. This experiment was conducted to investigate the effects of variety and heat treatment duration on physical characteristics and ruminal disappearance of barley grain. Two varieties of endemic barley grain (i.e. Sahand and Makoei) were prepared from Seed and Plant Improvement Institute, Karaj, Iran. The grains were roasted in three time duration (5, 10 or 15 min at 120o C) in a cast iron container. The experiment was conducted using a 2*3 factorial design. The samples were dried in 60° oven for 48 hours. Chemical composition was determined according to prescribed procedures of AOAC (2002). Neutral detergent finer (NDF) and acid detergent fiber (ADF) were measured by method of Van-Soest et al. (1991). Bulk density of sample was determined using the method described by Montgomery and Baumgardt (1965). Water holding capacity (WHC) determined by filtration method (Robertson and Eastwood, 1981). Dry matter solubility and ash solubility of samples were determind by method of Giger-Reverdin (2000). Dry matter degradability was measured by in situ technique using two fistulated Ghezel sheep (fed 60% forage + 40% concentrate). Samples were put in the polyester bags and incubated in the rumen for 2, 4, 8, 12, 16, 24, 36, and hours. After the specific incubation periods, bags were washed under running tap water until the effluent was clear and then dried at 55◦C for 48 h. Bags and contents were weighed to estimate DM disappearance (DMD). Kinetic parameters of DM degradation was estimated by the nonlinear regression procedure of SAS (SAS Inst. Inc., Cary, NC) using the model of McDonald (1981) y = a + b (1 − e−c(t−lag)). Data were subjected to analysis as a factorial in a completely randomized design using the General Linear Model (GLM) procedure of SAS. Roasting increased dry matter (DM) content of both barley varieties (P<0.05). An increase in ADF and NDF content of roasted grain was due to decrease in water content of grain. Sahand variety showed higher degradability than Makoei (P<0.05). Dry matter degradability of both barley varieties decreased during 16 to 48 h of incubation due to roasting process (P<0.05); however, these varieties showed different kinetics of degradation during early period of incubation. Roasting increased DM degradability of the Sahand variety during initial 6 h of incubation; however, it showed different pattern in the Makoie variety. The rapid and slow degradable fractions (ie; a and b) decreased by roasting duration in both varieties (P<0.05). Also heat processing of barley grain resulted in a lower effective degradability of dry matter (P<0.01). Effective degradability of Sahand variety was higher than Makoie in all passage rates and all duration of heat processing (P<0.05). Fractional rate of degradability did not change by heat treatment. Makoei variety had higher water holding capacity (WHC), bulk density (BD), dry matter solubility (DS), and ash solubility (AS) than Sahand (P<0.05). Roasting increased WHC and decreased BD in both varieties (P<0.05) but had no effect on DS and AS. There were positive correlations between BD100 and Ether Extract (EE), NDF and ADF content of barley grain, which were 0.53, 0.40, and 0.35, respectively. Also, water holding capacity showed high positive correlation with NDF and ADF content (r =0.84 and r =0.71 respectively) and as expected conversely correlated with EE content (r = -0.61) of barley grain. Both of DMS and AS conversely correlated with EE content of barley grain (r = -0.24 and r = -0.49 respectively). The results of the current study demonstrated that it is possible to decrease ruminal degradability of barley grain by using the right roasting treatment and choosing the proper variety. Makoei variety showed more decrease in fractional rate of digestion, which should be considered in the ration formulation