Submitted to: Journal Dairy Science Supplement
Publication Type: Abstract Only
Publication Acceptance Date: July 31, 1998
Publication Date: N/A
Technical Abstract: Forages differ in their concentration of fiber thus altering the energy density of a diet when direct substitutions are made among forage sources. The objective of this study was to determine lactating cow responses when orchardgrass silage replaced alfalfa silage either at equal levels of dietary NDF or at equal dietary percentage in a TMR. Alfalfa silage (AS) and orchardgrass silage (OS) diets were formulated to contain 30% dietary NDF. Orchardgrass silage was directly substituted for alfalfa silage to obtain a third treatment (ROS) that contained about 35% dietary NDF. All diets were formulated to meet NRC recommendations using finely ground high moisture corn and a protein-vitamin-mineral supplement. Thirty-two mid to late lactation cows were individually fed once daily for 11 wk using electronically controlled feeders. Milk yields were similar for diets equal in NDF (28.0 kg/d for AS and OS), but ROS containing more dietary NDF resulted in less milk yield (26.9 kg/d). Dry matter intake was similar for diets equal in NDF (20.9 kg/d and 20.3 kg/d for AS and OS), and ROS resulted in intakes that were less (19.2 kg/d). Production efficiency was greater for the orchardgrass silage diets (1.46 and 1.43 kg of milk/kg of DMI for OS and ROS) compared to the alfalfa silage diet (1.26 kg of milk/kg of DMI). Body condition score and animal weights were not significantly different among treatments throughout this study. Cows fed the OS diet gained the most body weight and cows fed the ROS diet gained the least body weight during the study (38.8 kg, 48.5 kg, and 29.8 kg for AS, OS, and ROS, respectively). Grass silages can be used in dairy diets when dietary NDF levels are applicable for cows in mid lactation.