Submitted to: Journal of Dairy Science
Publication Type: Abstract Only
Publication Acceptance Date: 6/30/1998
Publication Date: N/A
Citation: Interpretive Summary:
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 completed the 11-wk trial. Animals were individually fed once daily in a open free-stall barn equipped with electronically controlled feeders. Milk yields were similar for diets equal in NDF (28.0 kg/d for AS and OS, P>0.9). The diet (ROS) containing more dietary NDF reduced milk yield (26.9 kg/d, P=0.11) compared to the AS and OS diets. Dry matter intake was similar for diets equal in NDF (20.9 kg/d and 20.3 kg/d for AS and OS, respectively, P>0.3), and the ROS diet resulted in intakes that were less (19.2 kg/d, P<0.02) than intakes for the two diets similar in NDF. The reduction in milk yields and intakes suggest that less energy was available for milk production when more fiber was consumed per day. Production efficiency was greater (P<0.07) for the orchardgrass silage diets (1.46 and 1.43 kg of milk/kg of DMI for OS and ROS, respectively) compared to the alfalfa silage diet (1.26 kg of milk/kg of DMI). Grass silages can be used in dairy diets when dietary NDF levels are applicable for cows in mid lactation.