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

Three independent experiments were conducted each using 16 ruminally fistulated 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 intake protein (DIP) on forage utilization. In each experiment, steers were blocked 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 period. Supplemental DIP (sodium caseinate) was placed in the rumen at 0700, immediately before feeding forage. Levels of DIP supplementation were .041, .082, and .124% BW; the control received no supplemental DIP. Following a 10-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 influenced (P > or = .20) by increasing level of DIP supplementation. The DIP supplied by the bermudagrass hay was estimated to be 8.2% of the total digestible OM intake (TDOMI) for control steers. In Exp. 2, increasing level of supplemental DIP did not affect (P > or = .26) FOMI but tended to increase total OM intake linearly (TOMI; P = .10). The tendency for a rise in TOMI coupled with a slight numeric increase in digestion resulted in an increase (linear; P = .06) in TDOMI. In the treatment 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 improved (P < .01) by increasing amounts of supplemental DIP. Although there was 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 not achieved with the levels of supplement provided. When the highest level of supplemental DIP was fed, DIP constituted approximately 12.8% of the TDOMI. In conclusion, significant variation was observed among forage in the amount of DIP needed to maximize intake and digestion when expressed in relationship to the digestible OM.

Degradability of forage proteins by in situ and in vitro enzymatic methods.

The overall objective of these two studies was to evaluate the efficacy of using the proteolytic enzyme from Streptomyces griseus to estimate concentrations of ruminally degradable protein (RDP) in a wide array of forages. In the first study, alfalfa and prairie hays that previously had been evaluated in vivo for RDP were incubated in a replicated 3 x 3 factorial combination of enzyme concentrations (6.6, 0.66, and 0.066 activity units/ml of incubation medium) and incubation times (2, 4, and 48 h). Two treatment combinations (6.6 activity units for 4 h and 0.066 activity units for 48 h) yielded respective RDP estimates for alfalfa and prairie hay that were close to the known in vivo values. In the second study, 20 diverse forages were evaluated for RDP by using the in situ technique. These forages also were evaluated for RDP with the two enzyme concentrations identified in the first study, but incubation times were expanded to include 1, 2, 3, 4, and 5 h at the high concentration and 24, 30, 36, 42, 48, and 54 h at the low concentration. At the high enzyme concentration, r2 statistics from linear regressions of enzymatic estimates of RDP on corresponding estimates obtained by the in situ procedure were high (r2 > or = 0.898) at all incubation times; in addition, slopes (range = 0.88 to 1.00) and intercepts (range = -9.4 to 3.5%) approached unity and 0, respectively. At the lower enzyme concentration, r2 statistics were still good (> 0.81), but slopes (0.59 to 0.67) and intercepts (18.5 to 21.9%) for all incubation times did not meet the respective goals of unity and 0.

Ruminal availabilities of protein and starch: effects on growth and ruminal and plasma metabolites of dairy calves.

Newborn Holstein calves (n = 75) were blocked by date of birth and sex and assigned randomly to one of eight isonitrogenous starters that contained protein and starch sources of different ruminal availabilities. Soybean meal or soybeans roasted to an exit temperature of 146 degrees C, raw or conglomerated corn, and urea at 1% of DM or no urea were used in a 2 x 2 x 2 factorial arrangement. The conglomeration process consisted of grinding the grain, adding water, pelleting the mixture, and roasting, which increased the degree of starch gelatinization fivefold. Starters were fed for ad libitum intake from 0.5 to 8 wk. Urea supplementation of conglomerated corn starters depressed performance, but the depression was greater when conglomerated corn was used with soybean meal than when it was used with roasted soybeans. Ruminal NH3 and plasma urea increased with increased RDP in starters, but the response varied according to corn type and soy protein source. Urea supplementation depressed plasma Lys, doubled plasma Cit with soybean meal and conglomerated corn starters, but depressed plasma Cit with roasted soybeans and conglomerated corn starters. Conglomerated corn depressed plasma Val and Gly, and roasted soybeans increased plasma Phe. Performance was similar when calves consumed starters containing ruminally synchronous or asynchronous CP and starch sources.