In situ and Other Methods to Estimate Ruminal Protein and Energy Digestibility: A Review

Abstract

Methods to estimate ruminal protein and carbohydrate availability were reviewed. Solubility of carbohydrate and protein is dependent on the chemical characteristics of the buffer. Protein solubility is highly correlated to shortterm (1 to 3 h) ruminal digestion of protein, however, not to extent of ruminal digestion. Enzymatic digestion techniques for both protein and carbohydrate offer precision in ranking feeds; however, absolute values may be questioned. Combining several enzymes may offer more accurate estimates. Continuous culture techniques offer enhanced simulation of the ruminal environment compared with batch culture and is more applicable to examination of total rations than individual feedstuffs. Several variables associated with in situ experimentation were evaluated and recommended guidelines were proposed. This methodology offers a better way to simulate the rumen environment within a given feeding regimen. However, its usefulness will be dependent on the standardization of inherent variables associated with its conduct (i.e., bag porosity, sample size, feed particle size). Although in vivo methodologies (postruminal cannulation) are usually the standards by which other techniques are compared, they are plagued with variation associated with microbial and particulate or liquid flow markers and animal variation.