Dairy cows selectively consume their rations, generally sorting longer particles in favor of finer particles. Feed sorting decreases fiber intake while increasing the consumption of grains and co-products. It also creates instances where cows eat different rations throughout the day.
In 2010, researchers from University of Minnesota evaluated ration change over time in 50 Minnesota freestall barns. At each farm, samples were collected from rations fed to high-producing cows. One sample was collected immediately after the TMR was delivered, three additional samples were collected every two to three hours after feed delivery, and the last sample was taken from the accumulated weigh-backs.
Researchers evaluated particle size in the TMR samples using a threesieve Penn State Particle Separator. On average, the researchers found a noticeable change in the percentage of material retained in the top screen from the initial TMR to the weigh-backs showing cows were selecting against long particle size. In addition, fiber content—percent of neutral detergent fiber (NDF)— of the TMR increased throughout the day.
Similar results were obtained in a Canadian survey including 22 free stall herds. On average, the refused ration was higher in the percentage of long particles recovered in the top screen (19.8% versus 33.1%) and physically effective NDF (17% versus 24.5% dry matter) than the average offered ration.
Continue reading this article published in Dairy Herd Management.
