CO2 and 100 mL of a 20% rumen luid 80% buffer solution was added to begin the 72 h incubation period. Rumen luid was collected from a single Holstein cow, receiving a common dairy TMR. During Exp. 1, the CONV and NAT diets with and without Fibrozyme at 0, 0.6, and 1.2 mg/mL of inoculum were compared. Fibrozyme was then applied to the NAT diet at 0, 0.6, 1.2, and 1.8 mg/mL of inoculum in Exp. 2. Enzyme by diet interactions occurred (P < 0.05) for true DM (TDMD) and NDF digestibility (NDFD) in Exp. 1. Fibrozyme increased TDMD (87.4, 88.7, and 89.1%) and NDFD (26.1, 33.7, and 36.1%) linearly (P < 0.05) in the CONV diet but only the highest dose increased TDMD (86.0 vs. 87.0%) and NDFD (30.3 vs. 35.4%) in the NAT diet. After elevating the dose further in the NAT diet (Exp. 2), the increases in TDMD (86.0 vs. 89.0 and 89.1%) and NDFD (25.8 vs. 41.8 and 42.3%) were similar for 1.2 and 1.8 mg/mL of supplemental Fibrozyme inclusion. In addition, 1.8 mg/mL of supplemental Fibrozyme increased (P < 0.05) inal culture pH (6.51 vs. 6.56) and reduced butyrate molar proportions (0.183 vs. 0.173). Fibrozyme inclusion also tended (P = 0.06) to increase the fractional rate of degradation linearly (0.065, 0.073, 0.077, and 0.079 h-1). These results are consistent with our hypothesis that Fibrozyme will increase digestibility in inishing feedlot diets with a lower effective dose of Fibrozyme in the presence of monensin. Key Words: ibrolytic enzyme, digestibility, inishing diet M371 Inluence of condensed tannin supplementation on protein eficiency, microbial protein yield, nitrogen balance and ruminal fermentation characteristics in beef steers fed high concentrate diet. R. Mezzomo*1, P. V. R. Paulino1, M. S. Duarte1, L. S. Moura1, L. H. P. Silva1, E. San Vito1, L. D. A. Ruino1, C. Cabral2, D. Grandini3, and S. C. Valadares Filho1, 1Universidade Federal de Viçosa, Viçosa, MG, Brazil, 2Silva Team, Buenos Aires, Argentina, 3Nutron, Itapira, SP, Brazil. This trial was conducted to evaluate the effects of condensed tannin (TN) associated or not with a true protein source on protein eficiency, microbial protein yield, nitrogen balance and ruminal fermentation characteristics (RFC) in beef steers fed high concentrate diet (87% of DM). Four crossbred steers (407 kg BW) itted with rumen cannula were assigned to a 4x4 latin square design, arranged in a 2x2 factorial arrangement. Steers were fed a basal diet based on cracked corn, whole cottonseed, sugar-cane bagasse, mineral mixture and one out of 4 supplements: soybean meal with condensed tannin; soybean meal without condensed tannin; condensed tannin without soybean meal and a treatment without both soybean meal and condensed tannin. Quebracho extract were used as tannin source, included to provide 4 g of TN/100 g of diet DM and the diets were formulated to be isonitrogenous. The nitrogen balance indicated that the use of TN improved the eficiency of nitrogen utilization (P < 0.10), however, no differences were observed when soybean meal was added to the diet (P > 0.10). There was an interaction (P < 0.10) between condensed tannin and soybean mean supplementation on the lux of rumen undegradable protein (RUP), metabolizable protein (MP) and on the ratio MP:CP. In the presence of soybean meal the addition of TN increased the lux of RUP (302.24 to 416.02 g/d), MP (540.23 to 671.03 g/d) and improved the ratio MP:CP (58.69 to 46.54). Microbial protein yield and microbial eficiency did not differ among treatments (P > 0.10). There was no effect of TN supplementation (P > 0.10) on ruminal pH, VFA and ammonia (N-NH3) concentration. N-NH3 increased and ruminal pH decreased with the inclusion of soybean meal (P < 0.10) in the diet. The utilization of condensed tannin as an additive in cattle fed high concentrate diet using soybean meal as true protein source implies in positive effects on eficiency of N utilization, increasing the lux of metabolizable protein. M372 Effects of supplementing an exogenous proteolytic enzyme on growth performance in growing beef steers. J. M. Vera1, C. T. Noviandi*1, Arief2, J.-S. Eun1, and D. R. ZoBell1, 1Department of Animal, Dairy, and Veterinary Sciences, Utah State University, Logan, 2Faculty of Animal Science, Andalas University, Padang, West Sumatra, Indonesia. An exogenous proteolytic enzyme (EPE) has been previously found to increase in vitro NDF degradability of dried distillers grains with solubles (DDGS). To further investigate the effects of EPE, 48 Angus crossbred growing beef steers (292 ± 25.2 kg BW) were used to assess the growth performance when fed a DDGS-based TMR diet without or with an EPE supplementation in a completely randomized design. The growing TMR diet consisted of 13.6% alfalfa hay, 50.3% corn silage, 30.7% DDGS, and 5.4% feedlot supplement (DM basis). The EPE contained 38,622 U/g protease activity with negligible ibrolytic activities. The EPE was diluted with water and added at a rate of 0.52 g/kg DM TMR as it was mixing for the group of EPE treatment. Four animals were placed in each pen, and 6 pens allocated to each treatment. All steers were adapted to the TMR diet for a 2-week period before start of the trial. Feed was offered for ad libitum consumption once daily at 0800 h with free access to water. Feed intake was measured weekly, and individual BW of steers was recorded on 2 consecutive days at the beginning of trial and wk 4 and 8. The experiment lasted 56 d, and data were analyzed using the MIXED procedure of SAS. There were no signiicant differences (P > 0.10) for inal BW (398 vs. 401 kg), BW gain (107 vs. 108 kg), and ADG (1.90 vs. 1.93 kg/d) between control and EPE treatment, respectively. Furthermore, EPE supplementation did not affect DM intake (10.5 vs. 10.0 kg/d) and gain to feed ratio (0.191 vs. 0.199). Therefore, supplementation of an EPE product at the dose rate used in this study did not alter growth performance of growing beef steers fed a DDGS-based TMR diet. Key Words: exogenous proteolytic enzyme, growing beef steers, growth performance M373 Effects of zinc and chlortetracycline supplements on growth performance, blood metabolites, carcass characteristics, and claw health in young Holstein bulls. H. Fagari-Nobijari1, H. Amanlou1, M. Dehghan-Banadaky*2, and M. H. Shahir1, 1University of Zanjan, Zanjan, Iran, 2University of Tehran, Karaj, Tehran, Iran. This study conducted to evaluate the effects of supplementing inishing diet with zinc and/or chlortetracycline on growth performance and claw health of calves. Holstein bulls (n = 212; initial BW = 375.5 ± 18.4 kg) were randomly allocated to one of 4 treatments in a completely randomized design as a 2 × 2 factorial experiment for 56 d. Dietary treatments include: 1) the basal diet (control); 2) basal diet plus 150 mg of Zn/kg of DM as ZnSO4; 3) basal diet plus chlortetracycline (200 mg/animal/d; CTC); and 4) basal diet plus 150 mg of Zn/kg of DM + CTC (200 mg/animal/d). Animals received fresh total mixed ration for ad libitum. DMI was measured daily. BWs were recorded and blood samples were collected on d 0, 28, and 56. Liver samples were taken on d 56. Ultrasound measurements of backfat thickness (UFAT), rump fat thickness (URPFAT), and longissimus muscle area (ULMA) were made on d 56. All claws of animals were examined every 2 weeks to identify claw lesions. Data were statistically analyzed using the repeated measures option in Proc Mixed of SAS. Zn supplement decreased ADG, G:F, and apparent DM digestibility (P < 0.01); however, DMI was not inluenced. Dietary CTC improved G:F on d 28 to 56 and decreased DM digestibility, but it did not affect ADG and DMI. Dietary CTC increased plasma total protein and urea nitrogen. Zinc supplementation decreased ULMA. The supplementation of CTC decreased UFAT and URPFAT. Key Words: Quebracho extract, feedlot, RUP 140 J. Anim. Sci. Vol. 88, E-Suppl. 2/J. Dairy Sci. Vol. 93, E-Suppl. 1/Poult. Sci. Vol. 89, E-Suppl. 1