Diets based on restrictively fermented grass silage do not provide sufficient gluconeogenic precursors in high-yielding dairy cows (Huhtanen 1998). In principle, manipulating the glucose supply of cows may be done either by increasing the proportion of propionate in rumen volatile fatty acids or by increasing glucose supply to the intestines. The objective of this experiment was to compare casein, glucose, propionic acid, and starch as glucose sources in dairy cows fed diets based on restrictively fermented grass silage.

Four rumen cannulated Finnish Ayrshire cows 15-16 weeks into their 4. or 5. lactation were used in an experiment designed as a 4 x 5 incomplete Latin square with 14-d periods. The five treatmens allocated to four animals were continuous infusions of 1) water (Control), 2) casein 300 g/d (Cas), 3) glucose 300 g/d (G), 4) propionic acid 247 g/d (P) and 5) barley starch 270 g/d (S). Substrates dissolved in water were infused either into the rumen (P) or the abomasum (other substrates).