INFLUENCE OF LEVEL OF FEED INTAKE ON DIGESTION AND BACTERIAL YIELD IN THE FORESTOMACHS OF DAIRY CATTLE

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Abstract
Four dairy cows fitted with duodenal T-type cannulae were fed a diet containing 65% forage to determine effects of diet intake level on digestion and bacterial yield in the forestomachs. Intake ranged from 5.99 to 17.40 kg organic matter (OM) per day. Apparent digestion of OM and neutral and acid detergent fiber was depressed disproportionally more than the increase in intake (60.2–41.8%, 63.1–49.8%, and 59.0–46.2%, respectively), and that observed for OM was most pronounced. However, if OM digestion was expressed as feed OM truly digested in the rumen, then the depression in OM digestion was less pronounced (71–57%) than for fiber, suggesting that non-fiber dietary components may be less susceptible than fiber to depressions in digestibility at higher intake levels. Non-ammonia and bacterial nitrogen (N) flow at the duodenum increased proportionally more than intake (97.4–402.8 g/day and 64.0–271.0 g/day, respectively). Bacterial N yield increased at an increasing rate as intake level increased (17.4–38.2 g bacterial N/kg OM apparently digested) suggesting that a constant value for bacterial yield may be inappropriate for all levels of intake. Key words: Rumen digestion, bacterial yield, dairy cattle, feed intake, forestomach