Effects of extrusion of grain and feeding frequency on rumen fermentation,nutrient digestibility, and milk yield and composition in dairy cows

The effect of corn extrusion and feeding frequency on ruminal and postrumin al digestibility and milk yield was studied in cows fed a high concentrate diet. Four Israeli Holstein cows fitted with rumen and abomasal cannulas we re used. The experiment was arranged as a 2 x 2 factorial design, with two diets and two feeding frequencies (two or four meals per day). One diet con tained 40% ground corn. In the second diet, half of the ground corn was rep laced with extruded corn. Feeding cows the extruded versus ground corn diet decreased ruminal ammonia N and plasma urea N concentrations, increased po struminal digestibility of nonstructural carbohydrates, reduced dry matter intake, decreased yield of milk and milk components, and increased efficien cy of milk energy and milk protein synthesis. The inclusion of extruded cor n in the diet did not affect ruminal volatile fatty acid. Increasing the fe eding frequency reduced the diurnal variation in ruminal pH, ruminal ammoni a, and plasma urea, and increased dry matter intake-considerably more in th e cows fed ground versus extruded corn-and improved postruminal organic mat ter, nonstructural carbohydrate, and crude protein digestibility. Total tra ct digestibility of organic matter and crude protein and milk yield and com position were also increased when cows were fed four versus two meals. Conc urrent with the feeding frequency and grain processing effect, an increase in rumen-undegradable protein flow was related to increased digestion of no nstructural carbohydrate postruminally (r = 0.54). We concluded that for co ws fed high-starch diets more frequent meals are useful for improving postr uminal digestibility and milk yield and composition.