Forages and pastures symposium: an update on in vitro and in situ experimental techniques for approximation of ruminal fiber degradation

Abstract

Static quantification measures of chemical components are commonly used to make certain assumptions about forage or feed nutritive value and quality. In order for modern nutrient requirement models to estimate intake and digestibility more accurately, kinetic measures of ruminal fiber degradation are necessary. Compared to in vivo experiments, in vitro (IV) and in situ (IS) experimental techniques are relatively simple and inexpensive methods to determine the extent and rate of ruminal fiber degradation. This paper summarizes limitations of these techniques and statistical analyses of the resulting data, highlights key updates to these techniques in the last 30 yr, and presents opportunities for further improvements to these techniques regarding ruminal fiber degradation. The principle biological component of these techniques, ruminal fluid, is still highly variable because it is influenced by ruminally fistulated animal diet type and timing of feeding, and in the case of the IV technique by collection and transport procedures. Commercialization has contributed to the standardization, mechanization, and automation of the IV true digestibility technique, for example, the well-known DaisyII Incubator. There has been limited commercialization of supplies for the IS technique and several review papers focused on standardization in the last 30 yr; however, the IS experimental technique is not standardized and there remains variation within and among laboratories. Regardless of improved precision resulting from enhancements of these techniques, the accuracy and precision of determining the indigestible fraction are fundamental to modeling digestion kinetics and the use of these estimates in more complex dynamic nutritional modeling. Opportunities for focused research and development are additional commercialization and standardization, methods to improve the precision and accuracy of indigestible fiber fraction, data science applications, and statistical analyses of results, especially for IS data. In situ data is typically fitted to one of a few first-order kinetic models, and parameters are estimated without determining if the selected model has the best fit. Animal experimentation will be fundamental to the future of ruminant nutrition and IV and IS techniques will remain vital to bring together nutritive value with forage quality. It is feasible and important to focus efforts on improving the precision and accuracy of IV and IS results.

Rumen Content from Slaughterhouse as an Alternative Inoculum Source for In Vitro Analysis of Feeds: A Multivariate Approach

“…Using univariate analysis methods, Alba et al [20] concluded that the rumen inoculum of cattle in slaughterhouses with unknown data, such as feeding, management, sex, breed, and others, can be used as a potential substitute for rumen inoculum obtained from cannulated cattle. However, the authors found some differences, as did other authors who used other sources of ruminal inoculum [36]. Therefore, we believe that multivariate analysis can help us find what is or are the factors that must be taken into account when using this source of rumen inoculum.…”

“…Furthermore, the amount and digestibility of NDF are directly responsible for the increase or decrease in acetate production [39,40]. In an extensive review, Foster et al [36] observed that even if all the variables of the animals used as a source of ruminal inoculum were controlled, the cell wall components of the feed are the main components that could affect the digestibility of dry matter or organic matter in in vitro studies. When equine feces were used as an alternative inoculum source in in vitro trials, significant differences between ruminal inoculum sources were observed for IVDMD and IVNDFD [41].…”

Ruminal inocula with distinct fermentation profiles differentially affect the in vitro fermentation pattern of a commercial algal blend

“…In vitro rumen batch culture is a technique widely used for predicting the degradability and nutritive value of feed sources ( 23 , 24 ). It is also used to screen the potential of non-conventional additives and feeds, such as biochars, microalgae, and seaweeds ( 6 , 25 , 26 ), to modulate ruminal fermentation and, in particular, to reduce methane production.…”