New techniques for studying digestion and absorption of nutrients by ruminants.

Physical constraints on ruminal digestion have received concentrated research attention in the past 10 years. With scanning electron microscopy, microbial attack and digestion of forage components in the rumen have been observed. Limits to passage through the digestive tract have been explored with digesta flow markers and particle-sizing devices. Diet composition analysis has been simplified by near-IR reflectance. NMR procedures, and histological indexing. Rumen microbial function and genetics are being examined by new procedures and genetically altered microbes are being used for production of specific nutrients. Isolated microbial enzymes are being used in feed analysis. The site of digestion in vivo has received detailed attention with new cannula designs, digesta flow markers, and constitutive microbial markers. Ruminants are being maintained by intragastric or i.v. infusion of purified nutrients to quantitate nutrient requirements. Static and dynamic models of digestive function are aiding in the interpretation of research data. Unfortunately, many new procedures have not been critically standardized against traditional methods. The complexity of certain new techniques and models complicates critical review, publication, and comprehension of research results. The most important laboratory tool for increasing research knowledge is still the alert, fertile human imagination.