Whole Cottonseeds Affect Rumen Fill and Passage Rate
Michigan State researchers (Dado and Allen, 1995) noted that, when inert bulk (water-filled rubber container) was placed inside cows' rumens, rumination was increased by about 10%. Because the inert bulk was too big to be regurgitated, the increased bulk apparently stimulated stretch receptors that signaled the brain to spend more time ruminating. Fill of NDF increased over 30% as cottonseed replaced alfalfa silage in a recent OSU metabolism trial (Harvatine, 2000). This was a result of the slower passage rate as well as the slower digestion rate of potentially digestible NDF. When we replaced cottonseed for alfalfa silage, passage rate of marked alfalfa silage decreased. This suggests that whole cottonseeds influence the passage rate of alfalfa, rather than the other way around. Because the hydration and functional specific gravity of ground cottonseed hulls should be optimal to promote a rapid passage rate (Bhatti and Firkins, 1995), the decreased passage rate of potentially digestible NDF with increasing cottonseed substitution for alfalfa silage implicates some physical properties that increase the retention time (decrease passage rate) of cottonseeds. Two likely properties are the linters' role in mat entanglement and the intact seeds being large enough to stimulate rumination. We therefore hypothesized that whole cottonseeds should maintain or even increase milk production when they replaced forage NDF.