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Lactating Holstein cows fitted with ruminal and duodenal T-type cannulae were used in two studies to determine the effect of forage: concentrate ratio and forage particle size on site of nutrient digestion and microbial protein synthesis. In exp. 1, cows were fed alfalfa hay at 24, 38, 58 and 80% of total dry matter intake. Organic matter (OM) digestion in the total tract (OMD) increased with increasing concentrate level but apparent ruminal OM digestion (AROMD) was unaffected by diet. Digestion of acid detergent fiber (ADF) was similar among the higher forage diets, but was depressed at the 24% forage level. Efficiency of microbial protein synthesis (MPS) was depressed by high concentrate diets and was positively correlated (P

Eight lactating Holstein cows fitted with simple cannulae in the rumen and proximal duodenum were used in a 2 × 2 × 2 factorial experiment in a randomized complete block design. The factors studied were: (1) forage length (full bloom alfalfa hay, long or chopped); (2) forage level in the total ration (25 or 75%); and (3) type of grain in the concentrate mixes (barley or corn). Organic matter (OM) intake was not affected by level of forage or grain type but was greater (P

Factors affecting binding of Yb or Ce by forage particles were measured. Retention of markers was low regardless of application procedure (spray or soak). Live incubation media and acidic environment resulted in further marker displacement. The use of Yb or Ce as particulate markers may not be appropriate. Key words: Markers, cerium, ytterbium, rate of passage