Effects of volume weight, precision processing and processing index on in vitro ruminal fermentation of dry-rolled barley grain
A study using batch culture technique was conducted to evaluate the effects of volume weight (VW, g/L), precision processing (PP; sieving grains into large versus small kernels and rolling based on kernel size), and processing index (PI; VW after rolling/VW before rolling × 100%) on kinetics of gas production, dry matter degradability (DMD), molar proportions and total short chain fatty acids (SCFA) of dry rolled barley grain. The study was arranged in a 2 × 2 × 2 factorial design. Gas production and DMD were measured at 3, 6, 12 and 24 h of incubation using rumen fluid from 3 fistulated beef heifers fed 70% barley silage and 30% barley grain. We hypothesized that incorporating other factors with PI would help improve prediction of the feeding value of processed barley grain. Barley samples were collected monthly from 10 different feedlots in Southern Alberta for one year. Samples were ranked according to their VW into low (<600 g/L) and high (>600 g/L) which were later subjected to PP (processed vs. control) before dry-rolled with extent of processing expressed as PI 75 or 85% ±3. The dry-rolled samples used in the study were not subjected to further grinding. Precision processing x PI interactions (P < 0.01) were observed for asymptotic cumulative gas volume, rate, lag time and absolute initial gas produced during the first hour. In addition, a PP × VW interaction (P < 0.05) was noted for cumulative gas volume. There were strong interactions (P < 0.01) between PP, VW and PI for the b fraction (insoluble but degradable in the rumen) and effective degradability of the samples. Effective degradability coefficients ranged from 0.18 to 0.26. Greater degradability coefficients were noted for processed samples with lower PI. Only PI had an effect (P < 0.05) on the rate of DMD. Interactions (P < 0.05) between PP, VW and PI were noted for the isobutyric, butyric, isovaleric, valeric and caproic contents of the samples after 6 h of incubation. Total SCFA values ranged from 30.2 to 40.1 mmol/L. Apart from PP and PI interaction (P < 0.05) on C2:C3, no other interaction was observed after 24 h of incubation. Regression results showed that VW and PP was better in predicting rate of DMD than PI and this is consistent with our hypothesis.
Keywords: Barley, Beef cattle, Degradability, Prediction