EFFECT OF INCREASING DEGRADABLE INTAKE PROTEIN ON INTAKE AND DIGESTION OF LOW-QUALITY, TALLGRASS-PRAIRIE FORAGE BY BEEF-COWS

Five ruminally and duodenally fistulated Angus x Hereford cows were us ed in a 5 x 5 Latin square to monitor intake, ruminal fermentation res ponses, and site and extent of digestion associated with providing inc reasing amounts of supplemental degradable intake protein (DIP). Cows had ad libitum access to low-quality, tallgrass-prairie forage (1.9% C P, 77% NDF) that was fed twice daily. The supplemental DIP (sodium cas einate; 90% CP) was infused intraruminally at 0630 and 1830 immediatel y before feeding forage. Levels of DIP were 0, 180, 360, 540, and 720 g/d. Each period consisted of 14 d of adaptation and 6 d of sampling. Forage OM intake increased quadratically (P < .01) with increasing sup plemental DIP, reaching a peak at the 540 g/d level. True ruminal OM a nd NDF digestion increased with the addition of 180 g/d supplemental D IP, but exhibited only moderate and somewhat variable responses when g reater amounts of supplemental DIP were infused (cubic, P < .03). Micr obial N flow and efficiency increased linearly (P < .01) with increasi ng supplemental DIP. However, a quadratic effect (P < .01) was observe d for total duodenal N flow, which was maximized at 540 g/d supplement al DIP. A linear (P = .02) treatment effect was observed for ruminal f luid dilution rate. Total ruminal VFA and ammonia concentrations incre ased (P < .01) in response to DIP supplementation. In conclusion, incr easing supplemental DIP generally improved forage utilization; intake of digestible OM was maximized when it contained approximately 11% DIP .