Response of lactating dairy cows to various densities of sorghum grain

To examine the effects of various densities of sorghum grain resulting in graded levels of ruminally degradable starch on lactational performance, 32 lactating Holstein cows (90 d in milk [DIM]) were assigned to four treatments for 58 d. Diets contained 37% alfalfa hay, 3% cottonseed hulls, 10% whole cottonseed, 6% soybean meal, 5% of a molasses-mineral-vitamin supplement, and 39% sorghum grain. Treatments were dry-rolled sorghum (DRS) at 643 g/L or stream-flaked sorghum (SF) at 437, 360, and 283 g/L. Dry matter intake was highest for DRS followed by SF360, with the linear (P < .01) and cubic (P < .05) effects significant. The linear decrease in milk (P < .05) and 3.5% fat corrected milk (FCM, P < .025) with decreased density of sorghum was because of large decreases on SF283. Steam-flaking increased total tract digestibilities of DM, OM, CP, starch, and ADF when compared with dry-rolling. Efficiency of conversion of feed DM to FCM and feed CP to milk protein were greater for sorghum flaked at 437 and 360 g/L than for DRS or the 283 g/L flake. The 283 g/L flake decreased DMI, milk yield, and milk fat percentage. Addition of buffer (1% NaHCO3) tended to ameliorate the decrease in DMI. These data show greater efficiency of feed utilization and conversion of feed CP to milk protein in cows fed sorghum grain flaked at 437 and 360 g/L compared with those fed dry-rolled sorghum or that flaked at 283 g/L.