Interpretive Summary: In vitro and in situ techniques yield different estimates of ruminal disappearance of barley
By: Anne Wallace
Barely (Hordeum vulgare) is a good energy source in commercial animal feed, however processing of the hull is required in order to optimize feed efficiency, which adds additional cost.
This study, published in the January 2020 issue of Translational Animal Science, studied three kinds of barley – unprocessed traditional barley with hulls, rolled (processed) traditional barely, and hulless (unprocessed) barely. The goal was to evaluate and compare the ruminal degradation of these three barely types both in vitro and in situ. The authors hypothesized that the hulless variety would have a greater disappearance of dry matter (DM), neutral detergent fiber (NDF) and starch, when compared to traditional processed or rolled varieties. Hulless barely has a decreased fiber content and therefore should have increased digestibility.
The in vitro samples were incubated for 72 hours in ruminal fluid collected from two steers. Residual contents were analyzed for the disappearance of DM, NDF, and starch at multiple time intervals. For the in situ portion of this study, after going through a process of artificial mastication, fistulated steers were incubated with the three barely types for 72 hours.
Results indicated that rolled barely (in situ) had the most significant disappearance of DM and starch. Hulless barely had the greatest disappearance of DM (in vitro), and the greatest disappearance of NDF both in vitro and in situ. The authors noted a great deal of variation between their in vitro and in situ study results, which they attributed to differences in techniques, including processing of the barley prior to incubation. The authors therefore stressed that different techniques to estimate digestibility may end up with notable variation in results. Overall, the results of this study suggest that comparison studies are useful but less established methods should be validated against more established methods to ensure they are reliable.