| Different forages and low (L: 33% of crude protein) or high (H: 43% of crude protein) undegraded intake protein (UIP) in diets to dairy cows were studied in three experiments. Feather meal (3%) or blood meal (1%) were the high UIP sources. Nine early-lactation Holstein cows were assigned to each of 8 treatments for 84 days in the first study. A corn silage (CS) based diet was compared to diets wherein 10% of the dry matter (DM) was replaced with coastal bermudagrass hay (GH), alfalfa hay (AH) or cottonseed hulls (CH) in diets with L or H UIP. Feed intake of cows on high UIP diets was reduced. Cows fed the CH-H diet had lower milk protein percentage and greater milk yield but no difference in DM intake, fat corrected milk or milk fat percentage than cows on the CH-L diet. Cows fed the AH-H diet had lower milk yield than cows on the AH-L diet. The effect of UIP content on milk production was dependent on forage source.;Seventy two mid-lactation Holstein cows received one of 8 diets for 64 d to evaluate varying levels of CH (10, 20 and 30%) in L or H UIP diets with 16% CP and 10% CH with 13% CP. Low protein diets reduced feed intake, but had no effect on yield and composition of milk. Cottonseed hull concentration had a positively linear effect on feed intake, but no effect on milk yield or composition. However, cows fed 20% and 30% CH with H UIP had highest milk yield. Cows fed H UIP had greater milk production but lower feed intake and percentage fat and protein than cows fed L UIP diets.;Four late lactation cows fitted with rumen cannulae were utilized in a 4 x 4 Latin square design (10 d/period) to exam the effects of CS or CH with L or H UIP diets. Bag residues were analyzed for DM, CP NDF and ADF. Ruminal disappearance of CS-L, CS-H, CH-L and CH-H, respectively, were 81.1, 76.4, 66.2, and 65.5% for DM; 94.4, 86.4, 91.2 and 83.1% for CP; 51.8, 39.3, 24.6, 23.4% for NDF; and 45.2, 34.2, 14.7 and 17.2 for ADF. Rate of disappearance h$sp{-1}$ and extent of degradation % of CS-L, CS-H, CH-L and CH-N were 0.021, 0.016, 0.015, 0.013 and 63.85, 61.20, 47.60, 47.62 for DM; 0.023, 0.008, 0.025, 0.011 and 57.2, 36.4, 59.4, 48.1 for CP; 0.005, 0.008, 0.006, 0.006 and 24.5, 25.0,24.7, 22.0 for NDF; and 0.005, 0.003, 0.005, 0.002 and 27.4, 23.8, 27.6 and 27.9 for ADF. |
