The effects of dietary pretreatment with fibrolytic enzyme-based cocktail were evaluated in 2 studies: (1) in vitro true digestibility; and (2) intake, digestibility, feeding behavior, and ruminal fermentation of beef steers fed growing diets. For the in vitro assessment, the ruminal inoculum was collected from 2 steers (BW = 543 ± 45 kg; 4-h after feeding; growing diets) and enzymes included or not (Trichoderma reesei fermentation extract; 0.75 µL/g of substrate DM). Within in vitro batches (n = 4), 12 substrates were incubated and in vitro true nutrient digestibility was evaluated. For study 2, 5 ruminally cannulated beef steers (BW = 520 ± 30 kg) were used in a 5 × 4 unbalanced Latin square using a 2 × 2 factorial arrangement of treatments: (a) diet quality (high = HQ; and low = LQ) and (b) enzyme inclusion (0 or 0.75 mL/kg of diet DM). Steers were fed ad libitum during four 21-d periods consisting of 14-d of adaptation and 7-d of collections. An enzyme × substrate was observed (P < 0.01), in which DM, OM, and NDF disappearance of sorghum grain increased with enzymes addition. Addition of enzymes increased (P < 0.01) ADF digestibility for all substrates. No diet quality × enzyme (P ≥ 0.18) was observed for intake variables in study 2. Enzyme-fed steers increased (P ≤ 0.05) intake of DM, digestible DM, NDF, and ADF compared with steers not fed fibrolytic enzymes. Addition of enzyme did not affect (P ≥ 0.28) apparent total tract digestibility of beef steers. Steers fed HQ diets consumed more (P ≤ 0.04) DM, digestible DM and OM, and less (P ≤ 0.03) total and digestible fiber than steers fed LQ diets. Ruminal pH average decreased (P = 0.01) for steers fed HQ or enzyme-fed diets compared with other treatments. A tendency (P = 0.06) toward improved total VFA was observed on enzyme-fed steers with HQ diets, but not for LQ diets. The molar proportion of ruminal propionate increased (P = 0.01) when steers were fed enzyme. Steers fed HQ diets had greater (P < 0.01) propionate and valerate molar proportions, lower (P < 0.01) acetate and acetate:propionate ratio than steers fed LQ diets. In vitro methane and total gas production were not affected (P ≥ 0.50) by dietary treatments. Fibrolytic enzymes positively affected digestion of multiple roughage sources commonly fed to cattle and might have additional benefit when used on unprocessed sorghum grain. Fibrolytic enzymes in beef cattle growing diets stimulated intake and generated positive impacts on ruminal fermentation.

Objectives were to determine interactions between phytase inclusion and dietary P concentration on P utilization by beef cattle fed a starch-based diet. Six ruminally-fistulated steers (BW = 750 ± 61 kg) were allotted to a 6 × 6 Latin square design with a 3 × 2 factorial arrangement of treatments. Factors included phytase inclusion, at 0, 500, or 2,000 phytase units (FTU)/kg of diet DM, and dietary P concentrations, at 0.10% and 0.30% of total diet DM. Feed ingredients, fecal samples, and orts were composited within period, lyophilized and ground. Samples were analyzed for NDF, ADF, CP, fat, ash, total P, and other minerals. Data were analyzed using the MIXED procedure of SAS with animal as the experimental unit. The CORR procedure was used to compare blood and urinary P concentrations. There were no treatment interactions (P ≥ 0.30) for any parameter measured. There were no main effects (P ≥ 0.45) of phytase inclusion on DMI, total fecal output, apparent DM digestibility, water intake, or urinary output. Steers fed 0.10% P had decreased (P &lt; 0.01) DMI and total fecal output, but increased (P &lt; 0.01) apparent DM digestibility compared with steers fed 0.30% P. Although N intake and retention were not affected by treatment, steers fed the 0.10% P diet tended (P = 0.10) to absorb more N compared with steers fed 0.30% P; and, steers fed the 0.10% P diets excreted more N in the urine (P = 0.02) and less N in the feces (P &lt; 0.01) compared with steers fed the 0.30% P diets. Steers fed the 0.10% P diets also consumed 70.1% less (P &lt; 0.01) total P each day, and excreted 51.9% less (P &lt; 0.01) P in feces and 94.6% less P in the urine (P &lt; 0.01) compared with steers fed 0.30% P. Excretion of water-soluble P in the feces was greater (P &lt; 0.01) on a g/d basis for steers fed 0.30% P when compared with steers fed 0.10% P. However, the proportion of total fecal P excreted as water-soluble P increased (P &lt; 0.05) by 23.0% in steers fed 0.10% P compared with steers fed 0.30% P, regardless of phytase inclusion level. There was no effect of dietary phytase concentration on blood or urinary (P ≥ 0.27) P concentrations. Blood P concentration was positively correlated (r = 0.60; P &lt; 0.01) to urinary P concentration when steers were fed 0.10% P; however, when steers were fed 0.30% P, there was no correlation (r = 0.36; P = 0.16) between blood and urine P. Regardless of dietary P concentration, phytase supplementation did not increase calculated P absorption or retention.

The effects of hay type and protein supplementation on intake, feeding behavior, nutrient digestion, and ruminal digestion characteristics were evaluated. Ruminally cannulated Angus beef steers (n = 6; BW = 304 kg ± 11 kg) were randomly assigned within a sequence of treatments using a 4 × 6 unbalanced Latin square design (6 steers; and 4 diets; fed once-daily). A 2 x 2 factorial treatment arrangement was used as follows: 1) ‘WW-B. Dahl’ Old World bluestem [Bothriochloa bladhii (Retz) S.T. Blake; WWBD or Eragrostis tef (Zucc.) Trotter; TEFF); and 2) dried distillers grain (DDGS) at 0 or 0.5% BW. Each period consisted of a 14-d of adaptation and 7-d collection. Steers were observed (5-min intervals, 24 h) for behavioral assessment; while ruminal pH was continuously measured (wireless pH probe), and ruminal fluid collected at 0, 2, 4, 8, and 16 h after-feeding. Steers fed TEFF hay and those fed DDGS (both, P = 0.04) had greater DMI compared to WWBD and not supplemented. Chewing activity did not differ (P ≥ 0.54). Non-supplemented steers spent more time eating hay (P &lt; 0.01) than supplemented steers. Average ruminal pH of TEFF (6.32) was lower (P &gt; 0.01) than WWBD (6.56). Non-supplemented steers produced less in vitro total gas and methane (both, P = 0.02) per g rumen fluid DM. The VFA profile was not affected (P ≥ 0.45) by treatments. Apparent total-tract digestibility and ruminal degradation (P ≤ 0.01) were greater with TEFF fed steers than WWBD. Hemicellulose digestion was reduced by 6.95% (P = 0.03) with DDGS supplementation. An annual hay in place of a conventional perennial hay improved intake, ruminal digestion of nutrients, without affecting feeding behavior, while supplementation with DDGS reduced forage intake time and quantity, without negatively affecting ruminal fiber digestion.

The effect of pre-treatment with fibrolytic enzymes [cellulase/xylanase (Trichoderma ressie)] of growing diets (high quality and low-quality) on ruminal microbiome relative abundance (RA) were evaluated. Ruminally cannulated beef steers (n = 5; BW = 520 ± 30 kg) were used in a 5×4 unbalanced Latin square design using a 2×2 factorial arrangement of treatments: (a) growing diet quality [high (HQ) and low (LQ)] and (b) enzyme inclusion (0 or 0.75 mL/kg of diet DM). Steers were individually fed ad libitum throughout four 21-d periods consisting of 14-d of adaptation and 7-d of collections. Ruminal fluid samples (100 mL) were collected on d-5 of each collection-period, at 6 h post feeding for DNA extraction and determination of microbial RA. Microbiome data were sequenced by Illumnia® NovaSeq™ 6000 (16S rRNA). Regardless of enzyme×diet quality interaction (P ≥ 0.11) or pre-treatment with enzyme (P ≥ 0.12), Domain RA was affected (P ≤ 0.04), in which LQ diets increased RA of Bacteria (93.25 vs. 86.80%) and decreased Archaea (6.75 vs. 13.20%). In Phylum, LQ diets decreased RA (P ≤ 0.04) of Euryarchaeota (6.75 vs. 13.21%), and increased Bacteroidetes (11.22 vs. 2.26%). Within Class, LQ diets decreased RA (P ≤ 0.04) of Clostridia (38.66 vs. 51.40%), Methanobacteria (6.75 vs. 13.21%), and increased Bacteroidia (10.62 and 1.47%). Within Order LQ diets, decreased RA (P ≤ 0.04) of Clostridiales (38.47 vs. 51.29%), Methanobacteriales (6.75 vs. 13.21%), and increased Bacteroidales (10.62 vs. 1.47%). In Family, LQ diets showed decreased RA (P ≤ 0.04) of Methanobacteriaceae (6.75 vs. 13.21%), Ruminococcaceae (6.71 vs. 2.18%), and increased Prevotellaceae (9.83 vs. 1.17%). In Genus, LQ diets showed increased RA (P ≤ 0.03) of Prevotella (9.61 vs. 1.10%). The dietary pre-treatment with fibrolytic enzymes seems to not dramatically affect RA of ruminal microbiome, while growing diet quality greatly influenced ruminal microbiome RA.

Heat stress (HS) has been indicated to increase ruminal temperature, increase digestibility, and reduce ruminal pH of steers fed high concentrate diets. However, it is unclear if this effect is the result of greater fermentation rate, slower passage rate, or a combination. The effect of ruminal incubation temperature on substrate digestibility and rate of fermentation were evaluated. Four cannulated British-crossbreed steers (BW = 520 kg ± 30 kg) consuming an 87% (DM) concentrate diet were utilized as rumen fluid donors in a randomized complete block design with two incubation treatments (CON=39°C and HS=42°C). Within block, duplicate 125 mL serum bottles containing 200 mg of dietary substrate were inoculated with a 2:1 buffer:ruminal fluid mixture and incubated for 24 h to measure total gas production, fermentation rate, fermentation lag, pH, and ammonia-N concentration. In vitro organic matter digestibility (IVOMD) was measured separately in 100 mL centrifuge tubes. Data were analyzed using the MIXED procedure of SAS using the fixed effect of treatment and random effect of rumen fluid donor (block). There was no treatment effect on total gas production (P = 0.92) or fermentation rate (P = 0.11); however, HS began fermenting substrate sooner than CON (P < 0.005). There was a significant effect of treatment on IVOMD where HS was greater compared to CON (79.3 vs. 70.4%; P = 0.05). Final pH and relative pH change were not different (P ≥ 0.25) likely due to buffering capacity of the in vitro technique Ammonia-N concentration was greater for HS than CON (7.92 vs. 5.33 mM; P < 0.05) and may indicate a temperature effect on ruminal nitrogen availability.In conclusion, it does not appear that incubating at a greater temperature affected the fermentation rate but likely induced a change in fermentation kinetics, which may have contributed to the greater overall IVOMD