Milk protein synthesis may be limited by amino acid (AA) flow to the duodenum. This can be increased by increasing the flow of microbial AA's or undegraded feed AA's. This experiment was carried out to determine the effect on milk production and nutrient flows at the duodenum of including fishmeal (120g/kg) in the supplement to grass silage at two levels of supplement feeding.

The treatments, arranged in a 2x2 factorial, were 1.) 3.5 kg/day of 0% fishmeal supplement (L-UDP), 2.) 7 kg/day of L-UDP, 3.) 3.5 kg/day of 12% fishmeal supplement (H-UDP), and 4.) 7 kg/day of H-UDP. Supplements were fed to 3 6 Friesian cows in a 4x4 multiple Latin-square trial with three week periods to determine production responses, and to four ruminally and duodenally cannulated cows to determine rumen fermentation and nutrient flows. Flows were determined by the dual marker technique of Faichney (1975) using cobalt-EDTA and ytterbium acetate as liquid and solid phase markers respectively. Purines were used as the bacterial marker (Zinn and Owens, 1986). Degradability of the feeds was measured in 3 other cows using the small bag technique described by De Boer et al. (1987).