In vitro and in situ techniques were used in the present study to evaluate the potential of enzymes to improve dry matter digestibility (DMD) of corn modified distillers grains (MDG) in feedlot diets. Eight exogenous enzymes (alpha-amylase, cellulase, mannanase, protease, xylanase, Aspergillus niger extract, Aspergillus oryzae extract, and a combination of A. oryzae and A. niger extract) were evaluated in the present study at 5 levels of inclusion (2, 4, 6, 8 and 10 g/hd/d) using the in vitro batch culture technique. In vitro dry matter digestibility (IVDMD) was measured at 6, 12 and 24 h of incubation using rumen fluid from 3 cannulated beef steers fed a high concentrate diet. It was hypothesized that inclusion of enzymes would improve digestibility of a MDG based feedlot diet. There was no interaction (P>0.05) between enzyme treatment and level of inclusion for IVDMD. Additionally, inclusion level had no effect (P=0.916) on IVDMD. Dry matter digestibility was highest (P=0.036) for the protease treatment which resulted in an increase of 9.3% IVDMD compared with the control (no enzyme). Based on the in vitro batch culture results, cellulase, protease and Aspergillus oryzae extract (increased IVDMD of 7.7, 9.3 and 6.0% respectively compared to control) were selected for further evaluation using the in situ technique. For the in situ study, these 3 enzymes were compared with a control treatment (no enzyme) and incubated for 6, 12 and 24 h in the rumen of 3 cannulated steers. Compared with the control, all the enzyme treatments had higher (Pin vitro batch culture result, protease inclusion resulted in an increase of 9.9% ruminal DMD (versus 9.3% for IVDMD). Overall, these two techniques were utilized to identify an exogenous enzyme (protease) that can potentially increase dry matter and fiber digestibility of MDG in feedlot cattle. Key Words:

A 64-d receiving study was conducted to evaluate the effects of 3 feed additives on rate of bovine respiratory disease (BRD), fecal E. coli O157:H7 shedding, and performance of newly received steer calves. One hundred and forty-two crossbred steer calves (initial BW 295 ± 23 kg) from multiple sources (n=22) were utilized in this study. On d 0, steers were blocked by initial BW and assigned to 1 of 16 pens. Treatments consisted of basal diet with 114 g/hd/d of (1) placebo (Control), (2) direct-fed microbial blend, (3) direct-fed microbial/yeast extract blend, or (4) prebiotic/probiotic blend. No differences (P>0.05) in BRD incidence were observed in this study. A tendency (P=0.08) for a day by treatment interaction was observed for fecal E. coli O157:H7 prevalence with cattle consuming treatment 4 having less fecal E. coli O157:H7 on d 28 and d 56 relative to cattle on the control treatment. Dry matter intake, BW, ADG, and G:F were similar (P>0.10) among treatments. However, variability was reduced for steers on treatments 3 and 4 relative to steers on treatments 1 and 2 for d 64 DMI (SD = 2.8, 2.3, 1.2, and 1.8 kg for treatments 1, 2, 3, and 4 respectively) and BW (SD = 41.6, 38.7, 25.9, and 25.0 for treatments 1, 2, 3, and 4 respectively) and for ADG on d 28 (SD = 0.15, 0.15, 0.08, and 0.08 for treatments 1, 2, 3, and 4 respectively) and d 64 (SD = 0.30, 0.30, 0.08, and 0.09 for treatments 1, 2, 3, and 4 respectively). Results indicate that the cattle in this trial were not high risk for BRD. Although the feed additives used in this trial did not impact steer performance, 2 of the 3 additives reduced variability in steer performance, and 1 additive reduced fecal E. coli O157:H7 shedding.

Greenhouse gas (GHG) emissions from concentrated animal feeding operations vary by stage of production and management practices. The objective of this research was to study the effect of two dietary crude protein levels (12 and 16%) fed to beef steers in pens with or without corn stover bedding. Manure characteristics and GHG emissions were measured from feedlot pen surfaces. Sixteen equal-sized feedlot pens (19 × 23 m) were used. Eight were bedded approximately twice a week with corn stover and the remaining eight feedlot pens were not bedded. Angus steers (n = 138) were blocked by live weights (lighter and heavier) with 7 to 10 animals per pen. The trial was a 2 × 2 factorial design with factors of two protein levels and two bedding types (bedding vs. non bedding), with four replicates. The study was conducted from June through September and consisted of four ˜28-day periods. Manure from each pen was scrapped once every 28 days and composite manure samples from each pen were collected. Air samples from pen surfaces were sampled in Tedlar bags using a Vac-U-Chamber coupled with a portable wind tunnel and analyzed with a greenhouse gas gas chromatograph within 24 hr of sampling. The manure samples were analyzed for crude protein (CP), total nitrogen (TN), ammonia (NH3), total volatile fatty acid (TVFA), total carbon (TC), total phosphorus (TP), and potassium (K). The air samples were analyzed for methane (CH4), carbon dioxide (CO2), and nitrous oxide (N2O) concentrations. The concentration of TN was significantly higher (p < 0.05) in manure from pens with cattle fed the high protein diets. The volatile fatty acids (VFAs) such as acetic, propionic, isobutyric, butyric, isovaleric, and valeric acids concentrations were similar across both treatments. There were no significant differences in pen surface GHG emissions across manure management and dietary crude protein levels. Implications: Livestock manure produces odor and emits GHGs (CO2, CH4, and N2O) at different stages of production and management practices that have significant environmental concerns. Thus, it is important to measure GHG contributions from different sources and develop appropriate mitigation strategies for minimizing GHG contribution from livestock production facilities. Two dietary protein levels (12 and 16%) fed to beef steers in pens with or without corn stover bedding were studied. The results indicated that dietary protein levels and bedding vs. no bedding had very little effect on GHG emissions and manure composition under open feedlot conditions in North Dakota climatic conditions and management practices.