Effects of supplemental degradable intake protein on utilization of medium- to low-quality forages

Three independent experiments were conducted each using 16 ruminally fistul ated beef steers fed bermudagrass (8.2% CP, 71% NDF; Exp. 1), bromegrass (5 .9% CP, 65% NDF; Exp. 2), or forage sorghum (4.3% CP, 60% NDF; Exp. 3) hays to evaluate the effects of increasing level of supplemental degradable int ake protein (DIP) on forage utilization. In each experiment, steers were bl ocked by weight and assigned to one of four treatments, and hay was offered to each steer at 130% of average voluntary intake for the preceding 5-d pe riod. Supplemental DIP (sodium caseinate) was placed in the rumen at 0700, immediately before feeding forage. Levels of DTP supplementation were .041, .082, and .124% BW; the control received no supplemental DIP Following a 1 0-d adaptation, intake and total fecal output were measured for 7 d. In Exp . 1, neither forage OM intake (FOMI) nor fiber(NDF) digestion were influenc ed (P greater than or equal to .20) by increasing level of DIP supplementat ion. The DIP supplied by the bermudagrass hay was estimated to be 8.2% of t he total digestible OM intake (TDOMI) for control steers. In Exp. 2, increa sing level of supplemental DIP did not affect (P greater than or equal to . 26) FOMI but tended to increase total OM intake linearly (TOMI; P = .10). T he tendency for a rise in TOMI coupled with a slight numeric increase in di gestion resulted in an increase (linear; P = .06) in TDOMI. In the treatmen t group in which the maximum TDOMI was observed (supplemental DIP treatment of .082% BW), total DIP intake constituted approximately 9.8% of the TDOMI . In Exp. 3, FOMI, TOMI, organic matter digestion (OMD), and TDOMI were imp roved (P < .01) by increasing amounts of supplemental DIP. Although there w as some evidence of a tendency for a decrease in the magnitude of change in TDOMI in response to increasing DIP supplementation, a clear plateau was n ot achieved with the levels of supplement provided. When the highest level of supplemental DIP was fed, DIP constituted approximately 12.8% of the TDO MI. In conclusion, significant variation was observed among forage in the a mount of DIP needed to maximize intake and digestion when expressed in rela tionship to the digestible OM.