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ABSTRACT

Roughage is fed in finishing diets to promote ruminal health and decrease digestive upset, but the inclusion rate is limited because of the cost per unit of energy and feed management issues. Rumination behavior of cattle may be a means to standardize roughage in beef cattle finishing diets, and increasing the particle size of roughage could modulate the ruminal environment and aid in maintaining ruminal pH. Therefore, this experiment was conducted to determine the effects of corn stalk (CS) inclusion rate and particle size in finishing diets on digestibility, rumination, and ruminal fermentation characteristics of beef steers. Four ruminally cannulated steers were used in a 4 × 4 Latin square experiment. Treatments were arranged as a 2 × 2 factorial with treatments consisting of 5% inclusion of a short-grind roughage (5SG), 10% inclusion of a short-grind roughage (10SG), 5% inclusion of a long-grind roughage (5LG), and 10% inclusion of a long-grind roughage (10LG). Differences in particle size were obtained by grinding corn stalks once (LG) or twice (SG) using a commercial tub grinder equipped with a 7.6-cm screen and quantified using the Penn State Particle Separator (PSPS) to estimate physically effective NDF (peNDF). Each period included 14 d for adaptation and 4 d for diet, fecal, and ruminal fluid collections. Animals were outfitted with rumination monitoring collars to continuously measure rumination activity. The 10LG treatment had a greater (P < 0.01) percentage of large particles (retained on the top 3 sieves of the PSPS) compared to the other treatments. This resulted in a greater (P < 0.01) percentage of estimated peNDF for the 10LG diet compared to the others. Feeding diets containing 5% roughage tended to increase (P ≤ 0.09) DM, NDF, and starch total tract digestibility compared to diets containing 10% roughage. Cattle consuming LG treatments had greater (P < 0.01) rumination time and greater (P < 0.01) ruminal pH than cattle consuming diets containing SG roughage. Cattle receiving the 5% inclusion rate of roughage tended to have greater (P = 0.09) time (h/d) under a ruminal pH of 5.6 and a larger (P = 0.03) area under the threshold compared to cattle receiving the 10% roughage treatments. Overall, feeding a lower inclusion of roughage with a larger particle size may stimulate rumination and aid in ruminal buffering similar to that of a higher inclusion of roughage with a smaller particle size, without negatively impacting digestibility and fermentation.

INTRODUCTION

Roughages are commonly fed to ruminants to maintain ruminal health; however, they are included at lower levels in finishing diets because of lower energy values and digestibility characteristics (Allen, 1997; Mertens, 1997). Finishing animals receive higher-energy diets for growth efficiency; therefore, it is important to understand the minimum roughage inclusion threshold without negatively affecting rumen function. Previous research has shown that increasing dietary roughage in feedlot diets decreases DM digestibility (Hales et al., 2014; Benton et al., 2015). Mertens (1997) described physically effective NDF (peNDF) as the roughage's ability to stimulate rumination. Increasing the physical effectiveness of the roughage source can aid in maintaining a higher ruminal pH by stimulating salivary buffer secretions via chewing activity (Allen, 1997). Fiber can vary in its effectiveness in stimulating rumination, primarily because of differences in coarseness, digestibility, and particle size (Allen, 1997). Overall, this topic has been more thoroughly researched in dairy cattle than in beef cattle. Limited data exist that investigate whether a higher roughage inclusion can be replaced by a lower roughage inclusion with a larger particle size in finishing diets. The hypothesis was that a longer particle size and lower inclusion rate of a low-quality forage could maintain ruminal pH similarly to a shorter particle size at a higher inclusion rate in steam-flaked corn (SFC) based finishing diets. Therefore, the objectives of this experiment were to determine the effects of roughage inclusion rate and grind size in finishing diets on digestibility characteristics, rumination activity, and ruminal fermentation characteristics of beef steers and determine if roughage of a larger particle size may be included at a lower level compared to a higher level with a smaller particle size in relation to peNDF and rumination behavior.

MATERIALS AND METHODS

All procedures involving live animals were approved by the West Texas A&M University/Cooperative Research, and Education, and Extension Team (CREET) Institutional Animal Care and Use Committee (approval number 01-08-15).

Animals and Treatments

Four ruminally cannulated beef steers (initial BW = 631 ± 19 kg) were used in a 4 × 4 Latin square experiment. Each experimental period lasted 18 d, with 14 d for adaptation and 4 d for sample collection. Dietary treatments were arranged as a 2 × 2 factorial and consisted of roughage inclusion and grind sizes. Roughage inclusion treatments were corn stalks fed at 5% or 10% of diet DM. The grind size treatments were corn stalks that were ground through a commercial tub grinder equipped with a 7.6-cm screen once (long grind, LG) or twice (short grind, SG). The treatment diets (Table 1) were SFC-based finishing diets and included, on a DM basis, 5% SG corn stalks (5SG), 5% LG corn stalks (5LG), 10% SG corn stalks (10SG), or 10% LG corn stalks (10LG). Diets used in this study were similar to those reported by Gentry et al. (2016) with the addition of the 10LG treatment. Steers were housed individually in 2 × 18 m partially covered outdoor pens throughout the study. Animals were weighed at the beginning and end of each 18-d period. Steers were fed to ad libitum intake at 07:00 h each day. Each animal was fitted with a collar (HR Tag, SCR Dairy, Netanya, Israel) that measured rumination minutes continuously via a sensory microphone that detected the passage of a feed bolus as described by Gentry et al. (2016). Initial validation research was reported by Stangaferro et al. (2016). One animal experienced inflammation around the rumen cannula and was removed from the third period to allow time to heal. The animal made a full recovery before the start of the fourth period and was placed back on the experiment. No period effect occurred during the third period by removing the steer.

Table 1.

Ingredient and nutrient composition of treatment diets (DM basis, except DM)

Dietary treatments1
Item 5SG 10SG 5LG 10LG
Ingredient (DM basis), %
    Steam-flaked corn 54.40 57.70 54.58 54.71
    Wet corn gluten feed 29.95 23.38 30.05 25.21
    Short-grind corn stalks2 5.10 9.35 — —
    Long-grind corn stalks2 — — 5.05 9.88
    Supplement3 3.97 3.66 3.99 3.98
    Urea 0.51 0.74 0.51 0.78
    Limestone 2.53 1.77 2.26 1.80
    Corn oil 3.55 3.40 3.56 3.63
Calculated nutrient values, %
    DM 79.8 81.3 79.8 81.4
    OM 93.7 93.5 94.3 93.9
    CP 13.6 13.2 13.4 13.5
    NDF 19.6 20.5 20.4 21.4
    ADF 9.3 10.6 9.1 10.3
    Ether extract 5.9 5.7 6.0 6.3
Dietary treatments1
Item 5SG 10SG 5LG 10LG
Ingredient (DM basis), %
    Steam-flaked corn 54.40 57.70 54.58 54.71
    Wet corn gluten feed 29.95 23.38 30.05 25.21
    Short-grind corn stalks2 5.10 9.35 — —
    Long-grind corn stalks2 — — 5.05 9.88
    Supplement3 3.97 3.66 3.99 3.98
    Urea 0.51 0.74 0.51 0.78
    Limestone 2.53 1.77 2.26 1.80
    Corn oil 3.55 3.40 3.56 3.63
Calculated nutrient values, %
    DM 79.8 81.3 79.8 81.4
    OM 93.7 93.5 94.3 93.9
    CP 13.6 13.2 13.4 13.5
    NDF 19.6 20.5 20.4 21.4
    ADF 9.3 10.6 9.1 10.3
    Ether extract 5.9 5.7 6.0 6.3

1Dietary treatments: 5SG = 5% inclusion of short-grind corn stalks, 10SG = 10% inclusion of short-grind corn stalks, 5LG = 5% inclusion of long-grind corn stalks, 10LG = 10% inclusion of long-grind corn stalks.

2Short-grind corn stalks were passed through a commercial tub grinder twice, and long-grind corn stalks were passed through a commercial tub grinder once. Tub grinder was equipped with a 7.6-cm screen.

3Supplement was formulated to meet or exceed vitamin and mineral requirements established by the NRC (2000) and provided 35.6 mg/kg of monensin and 7.9 mg/kg of tylosin (Elanco Animal Health, Greenfield, IN).

Table 1.

Ingredient and nutrient composition of treatment diets (DM basis, except DM)

Dietary treatments1
Item 5SG 10SG 5LG 10LG
Ingredient (DM basis), %
    Steam-flaked corn 54.40 57.70 54.58 54.71
    Wet corn gluten feed 29.95 23.38 30.05 25.21
    Short-grind corn stalks2 5.10 9.35 — —
    Long-grind corn stalks2 — — 5.05 9.88
    Supplement3 3.97 3.66 3.99 3.98
    Urea 0.51 0.74 0.51 0.78
    Limestone 2.53 1.77 2.26 1.80
    Corn oil 3.55 3.40 3.56 3.63
Calculated nutrient values, %
    DM 79.8 81.3 79.8 81.4
    OM 93.7 93.5 94.3 93.9
    CP 13.6 13.2 13.4 13.5
    NDF 19.6 20.5 20.4 21.4
    ADF 9.3 10.6 9.1 10.3
    Ether extract 5.9 5.7 6.0 6.3
Dietary treatments1
Item 5SG 10SG 5LG 10LG
Ingredient (DM basis), %
    Steam-flaked corn 54.40 57.70 54.58 54.71
    Wet corn gluten feed 29.95 23.38 30.05 25.21
    Short-grind corn stalks2 5.10 9.35 — —
    Long-grind corn stalks2 — — 5.05 9.88
    Supplement3 3.97 3.66 3.99 3.98
    Urea 0.51 0.74 0.51 0.78
    Limestone 2.53 1.77 2.26 1.80
    Corn oil 3.55 3.40 3.56 3.63
Calculated nutrient values, %
    DM 79.8 81.3 79.8 81.4
    OM 93.7 93.5 94.3 93.9
    CP 13.6 13.2 13.4 13.5
    NDF 19.6 20.5 20.4 21.4
    ADF 9.3 10.6 9.1 10.3
    Ether extract 5.9 5.7 6.0 6.3

1Dietary treatments: 5SG = 5% inclusion of short-grind corn stalks, 10SG = 10% inclusion of short-grind corn stalks, 5LG = 5% inclusion of long-grind corn stalks, 10LG = 10% inclusion of long-grind corn stalks.

2Short-grind corn stalks were passed through a commercial tub grinder twice, and long-grind corn stalks were passed through a commercial tub grinder once. Tub grinder was equipped with a 7.6-cm screen.

3Supplement was formulated to meet or exceed vitamin and mineral requirements established by the NRC (2000) and provided 35.6 mg/kg of monensin and 7.9 mg/kg of tylosin (Elanco Animal Health, Greenfield, IN).

Sampling

Estimation of peNDF was adapted from the work by Mertens (1997), in which diets were sieved using a Penn State Particle Separator (PSPS), and peNDF was calculated by multiplying the percentage of particles that were retained on sieves larger than 4 mm by the NDF content. Diet samples and orts were collected, weighed, and subsampled for nutrient analysis on d 14 through 18. Fecal output was estimated by dosing a 5-g bolus of chromic oxide twice daily (07:00 and 19:00 h) via the rumen cannula on d 10 through 18. Fecal samples were collected at 06:00 and 18:00 h on d 15 and 17 and at 12:00 and 24:00 h on d 16 and 18. Fecal samples were wet composited across the entire collection period by animal. Three 250-mL aliquots were prepared from the wet composite and frozen at −4°C. Ruminal fluid samples also were collected on the same schedule and strained through 4 layers of cheese cloth. Ruminal fluid pH was immediately measured using a portable pH meter (VWR symphony, model H10P, Radnor, PA), and three 50-mL aliquots were retained and frozen at −4°C. Sampling was conducted in this manner so that the rumen cannula was opened only twice daily, with 12 h in between, to reduce the amount of oxygen that entered the rumen environment and so that the rumen environment could stabilize between each sampling time point. Diet samples were collected weekly and separated using the PSPS, in which sieves were stacked in the following order: 19.0-mm sieve on top, 8.0-mm sieve second, 4-mm sieve, and then a plastic pan fitted to the bottom of the last sieve. The sieve set was placed on a flat surface, and approximately 400 g of diet sample was spread out on the top sieve. The sieve set was shifted horizontally on the flat surface 5 times, rotated one-fourth turn, and shifted 5 times again. This was repeated until the sieve had been rotated a total of 5 turns as described by Kononoff et al. (2003) and Gentry et al. (2016).

Laboratory Analysis

Diet and ort samples were dried at 55°C for 48 h, and fecal aliquots were lyophilized (Labconco, Kansas City, MO). Diet, ort, and fecal samples were ground using a Wiley mill (model 4, Thomas Scientific, Swedesboro, NJ) to pass through a 1-mm screen, and a subsample of this was ground through a Cyclotec mill (Cyclotec CT 193, Foss, Hoganas, Sweden) to pass through a 0.5-mm screen for starch analysis. Laboratory DM of diet, ort, and fecal samples were determined by drying at 100°C for 24 h, and OM was determined by ashing samples at 500°C for 6 h. Ether extract (EE) of diet and orts was determined using petroleum ether in an automated EE extraction system (Ankom XT15 Extraction System, Ankom Technology, Fairport, NY). Because the EE content was greater than 5%, diet and ort samples were submerged in acetone twice for 10 min before the concentrations of NDF and ADF were determined using an Ankom fiber analyzer (model 200/220, Ankom Technology). Total nitrogen of samples was analyzed at a commercial laboratory (Servi-Tech Laboratories, Amarillo, TX). Starch content was determined using a PowerWave-XS Spectrometer (Bio Tek US, Winooski, VT) after converting starch to glucose with an enzyme kit (Megazyme International Ireland Ltd., Wicklow, Ireland). Chromium concentrations of feces were determined by atomic absorption (AAAnalyst 200, PerkinElmer Inc., Waltham, MA), and fecal output (g/d) was calculated by dividing the amount of chromium dosed by marker concentration in the feces as described by Merchen (1988). Volatile fatty acid concentrations in rumen fluid samples were determined using a Varian 3900 GC (Varian Inc., Palo Alto, CA) according to the procedures of Erwin et al. (1961). Ruminal fluid samples were also analyzed for ammonia concentration using procedures outlined by Broderick and Kang (1980) and quantified using a PowerWave-XS Spectrometer (Bio Tek US) at a wavelength of 550 nm.

Statistical Analysis

Data were analyzed as a Latin square with a factorial arrangement of treatments using the MIXED procedure of SAS (SAS Inst. Inc., Cary, NC). The model included fixed effects of roughage grind, inclusion rate, and grind × inclusion. For VFA, NH3, ruminal pH, and rumination minutes the model statement also included the effect of time, grind × time, inclusion × time, and grind × inclusion × time. Rumination data were analyzed as repeated measures; however, because of staggered sampling times, VFA, NH3, and ruminal pH were not. Animal was included as a random term, and when P ≤ 0.10, the mean separation was performed using the LSMEANS statement with PDIFF option in SAS. Significance was declared at P ≤ 0.05, and trends were declared at P > 0.05 and P ≤ 0.10.

The area below a pH of 5.6 was determined using the MESS package of R (R Core Team, 2014), assuming a cubic spline interpolation and 5.6 as the base pH. The initial and final times (i.e., roots of the spline function) to calculate the area below pH 5.6 were determined using the splinefun procedure of the stats package and the uniroot.all procedure of the rootSolve package of R (R Core Team, 2014). The number of hours below pH 5.6 was the difference between the final and initial times (i.e., roots of the spline function). The area below pH 5.6 and number of hours below pH 5.6 were computed for each animal, period, grind, and inclusion rate combination.

RESULTS AND DISCUSSION

Particle Separation

Particle separation using the PSPS and estimated peNDF results for individual feed ingredients are reported in Gentry et al. (2016). Particle separation and peNDF of treatment diets are represented in Table 2. A grind × inclusion interaction (P = 0.04) was observed for particles that were retained on the 8-mm sieve. The 10LG treatment had a greater (P < 0.01) percentage of particles retained on the 8-mm sieve compared to other treatments. The 10% inclusion treatments had a greater (P < 0.01) percentage of particles larger than 4 mm and a lower (P < 0.01) percentage of particles less than 4 mm compared to the 5% inclusion treatments.

Table 2.

Particle separation and estimated physically effective NDF (peNDF) of dietary treatments

Dietary treatments1 P-value
Item 5SG 10SG 5LG 10LG SEM Grind Inclusion G × I2
No. of samples 10 10 10 10 — — — —
NDF, % DM 19.6 20.5 20.4 21.4 — — — —
Retained/screen, %
    Sieve screen size, mm
    19.0 2.1 3.6 3.3 4.2 0.40 0.02 <0.01 0.39
    8.0 41.6a 43.1a 41.3a 49.4b 1.56 0.07 <0.01 0.04
    4.0 21.5 20.3 21.0 18.5 0.50 0.02 <0.01 0.18
    Particles <4 mm 34.7 33.0 34.5 28.0 1.31 0.06 <0.01 0.08
    Particles >4 mm 65.3 67.0 65.5 72.0 1.31 0.06 <0.01 0.08
Estimated peNDF,3 % DM 12.8a 13.8b 13.3a,b 15.4c 0.27 <0.01 <0.01 0.04
Dietary treatments1 P-value
Item 5SG 10SG 5LG 10LG SEM Grind Inclusion G × I2
No. of samples 10 10 10 10 — — — —
NDF, % DM 19.6 20.5 20.4 21.4 — — — —
Retained/screen, %
    Sieve screen size, mm
    19.0 2.1 3.6 3.3 4.2 0.40 0.02 <0.01 0.39
    8.0 41.6a 43.1a 41.3a 49.4b 1.56 0.07 <0.01 0.04
    4.0 21.5 20.3 21.0 18.5 0.50 0.02 <0.01 0.18
    Particles <4 mm 34.7 33.0 34.5 28.0 1.31 0.06 <0.01 0.08
    Particles >4 mm 65.3 67.0 65.5 72.0 1.31 0.06 <0.01 0.08
Estimated peNDF,3 % DM 12.8a 13.8b 13.3a,b 15.4c 0.27 <0.01 <0.01 0.04

a–cMeans within a row without a common superscript differ (P ≤ 0.05).

1Dietary treatments: 5SG = 5% inclusion of short-grind corn stalks, 10SG = 10% inclusion of short-grind corn stalks, 5LG = 5% inclusion of long-grind corn stalks, 10LG = 10% inclusion of long-grind corn stalks.

2G × I = grind × inclusion.

3Percentage of peNDF was estimated by multiplying the percentage of sample larger than 4 mm in particle size (top 3 sieves) by the percentage of NDF (as a decimal) of the ingredient before separation.

Table 2.

Particle separation and estimated physically effective NDF (peNDF) of dietary treatments

Dietary treatments1 P-value
Item 5SG 10SG 5LG 10LG SEM Grind Inclusion G × I2
No. of samples 10 10 10 10 — — — —
NDF, % DM 19.6 20.5 20.4 21.4 — — — —
Retained/screen, %
    Sieve screen size, mm
    19.0 2.1 3.6 3.3 4.2 0.40 0.02 <0.01 0.39
    8.0 41.6a 43.1a 41.3a 49.4b 1.56 0.07 <0.01 0.04
    4.0 21.5 20.3 21.0 18.5 0.50 0.02 <0.01 0.18
    Particles <4 mm 34.7 33.0 34.5 28.0 1.31 0.06 <0.01 0.08
    Particles >4 mm 65.3 67.0 65.5 72.0 1.31 0.06 <0.01 0.08
Estimated peNDF,3 % DM 12.8a 13.8b 13.3a,b 15.4c 0.27 <0.01 <0.01 0.04
Dietary treatments1 P-value
Item 5SG 10SG 5LG 10LG SEM Grind Inclusion G × I2
No. of samples 10 10 10 10 — — — —
NDF, % DM 19.6 20.5 20.4 21.4 — — — —
Retained/screen, %
    Sieve screen size, mm
    19.0 2.1 3.6 3.3 4.2 0.40 0.02 <0.01 0.39
    8.0 41.6a 43.1a 41.3a 49.4b 1.56 0.07 <0.01 0.04
    4.0 21.5 20.3 21.0 18.5 0.50 0.02 <0.01 0.18
    Particles <4 mm 34.7 33.0 34.5 28.0 1.31 0.06 <0.01 0.08
    Particles >4 mm 65.3 67.0 65.5 72.0 1.31 0.06 <0.01 0.08
Estimated peNDF,3 % DM 12.8a 13.8b 13.3a,b 15.4c 0.27 <0.01 <0.01 0.04

a–cMeans within a row without a common superscript differ (P ≤ 0.05).

1Dietary treatments: 5SG = 5% inclusion of short-grind corn stalks, 10SG = 10% inclusion of short-grind corn stalks, 5LG = 5% inclusion of long-grind corn stalks, 10LG = 10% inclusion of long-grind corn stalks.

2G × I = grind × inclusion.

3Percentage of peNDF was estimated by multiplying the percentage of sample larger than 4 mm in particle size (top 3 sieves) by the percentage of NDF (as a decimal) of the ingredient before separation.

A grind × inclusion interaction (P = 0.04) was observed for estimated peNDF. When evaluating the simple-effect means, the 10LG treatment had a greater (P < 0.01) percentage of estimated peNDF compared to other treatments. The 10SG treatment was intermediate and did not differ (P = 0.30) from the 5LG treatment, whereas the 5LG treatment was not different (P ≥ 0.18) from 5SG and 10SG treatments. The difference in peNDF for the 10LG treatment was due to the increase in particles retained in the top 3 sieves (total of particles remaining on 19.0-, 8.0-, and 4.0-mm sieves). These data suggest that a lower inclusion of roughage with a larger particle size provides peNDF similar to that of a higher inclusion of roughage with a smaller particle size.

Nutrient Intake and Digestibility

Roughage inclusion and grind size had no effect (P > 0.16; Table 3) on DM, OM, starch, or nitrogen intake. Regardless of particle size, diets containing 10% corn stalks had a tendency for greater NDF intake and greater ADF intake compared to 5% corn stalks (P = 0.07 and P = 0.01, respectively), whereas NDF and ADF intake were not different (P ≥ 0.20) because of grind size. Increasing concentrations of roughages in finishing diets typically increases DMI of feedlot cattle, possibly because of the roughage diluting higher-energy feeds (Galyean and Defoor, 2003). In the current trial, the similarities in DMI may be attributed to the replacement of roughage with wet corn gluten feed (WCGF), a high-fiber by-product feed compared to using SFC. Differences in NDF and ADF intake were expected between the 5% and 10% roughage diets as the fiber content in the corn stalks was greater than the WCGF that it replaced.

Table 3.

Effect of roughage grind size and inclusion on intake, fecal output, and apparent total tract digestibility of beef steers

Dietary treatments1 P-value
Item 5SG 10SG 5LG 10LG SEM Grind Inclusion G × I2
No. of observations 4 4 3 4 — — — —
Intake
    DM, kg/d 11.1 11.5 10.7 11.0 0.40 0.16 0.23 0.99
    OM, kg/d 10.4 10.7 10.1 10.4 0.37 0.22 0.28 0.98
    NDF, kg/d 2.2 2.4 2.2 2.4 0.10 0.92 0.07 0.99
    ADF, kg/d 1.0 1.2 0.9 1.1 0.07 0.20 0.01 0.95
    Starch, kg/d 5.3 5.5 4.9 5.2 0.26 0.18 0.35 0.86
    Nitrogen, g/d 241.7 242.6 227.6 238.9 9.56 0.21 0.38 0.44
Fecal output
    DM, kg/d 1.6 2.0 1.5 1.7 0.15 0.18 0.06 0.27
    OM, kg/d 1.1 1.2 1.2 1.3 0.13 0.66 0.11 0.34
    NDF, kg/d 0.6 0.9 0.6 0.8 0.10 0.39 0.04 0.32
    ADF, kg/d 0.5 0.7 0.4 0.5 0.07 0.08 0.03 0.30
    Starch, kg/d 0.03 0.06 0.04 0.05 0.009 0.89 0.05 0.23
    Nitrogen, g/d 41.3 46.3 40.4 41.6 3.35 0.34 0.30 0.52
Apparent TT digestibility,3 %
    DM 85.7 82.5 85.6 84.9 1.28 0.32 0.09 0.26
    OM 89.2 86.9 88.3 87.8 0.97 0.99 0.11 0.25
    NDF 71.1 61.3 71.1 68.5 3.79 0.28 0.08 0.28
    ADF 55.8 41.8 58.4 56.6 7.40 0.20 0.24 0.36
    Starch 99.4 98.9 99.1 99.1 0.18 0.73 0.09 0.22
    Nitrogen 82.9 82.3 80.9 82.6 1.14 0.59 0.38 0.25
Dietary treatments1 P-value
Item 5SG 10SG 5LG 10LG SEM Grind Inclusion G × I2
No. of observations 4 4 3 4 — — — —
Intake
    DM, kg/d 11.1 11.5 10.7 11.0 0.40 0.16 0.23 0.99
    OM, kg/d 10.4 10.7 10.1 10.4 0.37 0.22 0.28 0.98
    NDF, kg/d 2.2 2.4 2.2 2.4 0.10 0.92 0.07 0.99
    ADF, kg/d 1.0 1.2 0.9 1.1 0.07 0.20 0.01 0.95
    Starch, kg/d 5.3 5.5 4.9 5.2 0.26 0.18 0.35 0.86
    Nitrogen, g/d 241.7 242.6 227.6 238.9 9.56 0.21 0.38 0.44
Fecal output
    DM, kg/d 1.6 2.0 1.5 1.7 0.15 0.18 0.06 0.27
    OM, kg/d 1.1 1.2 1.2 1.3 0.13 0.66 0.11 0.34
    NDF, kg/d 0.6 0.9 0.6 0.8 0.10 0.39 0.04 0.32
    ADF, kg/d 0.5 0.7 0.4 0.5 0.07 0.08 0.03 0.30
    Starch, kg/d 0.03 0.06 0.04 0.05 0.009 0.89 0.05 0.23
    Nitrogen, g/d 41.3 46.3 40.4 41.6 3.35 0.34 0.30 0.52
Apparent TT digestibility,3 %
    DM 85.7 82.5 85.6 84.9 1.28 0.32 0.09 0.26
    OM 89.2 86.9 88.3 87.8 0.97 0.99 0.11 0.25
    NDF 71.1 61.3 71.1 68.5 3.79 0.28 0.08 0.28
    ADF 55.8 41.8 58.4 56.6 7.40 0.20 0.24 0.36
    Starch 99.4 98.9 99.1 99.1 0.18 0.73 0.09 0.22
    Nitrogen 82.9 82.3 80.9 82.6 1.14 0.59 0.38 0.25

1Dietary treatments: 5SG = 5% inclusion of short-grind corn stalks, 10SG = 10% inclusion of short-grind corn stalks, 5LG = 5% inclusion of long-grind corn stalks, 10LG = 10% inclusion of long-grind corn stalks.

2G × I = grind × inclusion.

3TT = total tract.

Table 3.

Effect of roughage grind size and inclusion on intake, fecal output, and apparent total tract digestibility of beef steers

Dietary treatments1 P-value
Item 5SG 10SG 5LG 10LG SEM Grind Inclusion G × I2
No. of observations 4 4 3 4 — — — —
Intake
    DM, kg/d 11.1 11.5 10.7 11.0 0.40 0.16 0.23 0.99
    OM, kg/d 10.4 10.7 10.1 10.4 0.37 0.22 0.28 0.98
    NDF, kg/d 2.2 2.4 2.2 2.4 0.10 0.92 0.07 0.99
    ADF, kg/d 1.0 1.2 0.9 1.1 0.07 0.20 0.01 0.95
    Starch, kg/d 5.3 5.5 4.9 5.2 0.26 0.18 0.35 0.86
    Nitrogen, g/d 241.7 242.6 227.6 238.9 9.56 0.21 0.38 0.44
Fecal output
    DM, kg/d 1.6 2.0 1.5 1.7 0.15 0.18 0.06 0.27
    OM, kg/d 1.1 1.2 1.2 1.3 0.13 0.66 0.11 0.34
    NDF, kg/d 0.6 0.9 0.6 0.8 0.10 0.39 0.04 0.32
    ADF, kg/d 0.5 0.7 0.4 0.5 0.07 0.08 0.03 0.30
    Starch, kg/d 0.03 0.06 0.04 0.05 0.009 0.89 0.05 0.23
    Nitrogen, g/d 41.3 46.3 40.4 41.6 3.35 0.34 0.30 0.52
Apparent TT digestibility,3 %
    DM 85.7 82.5 85.6 84.9 1.28 0.32 0.09 0.26
    OM 89.2 86.9 88.3 87.8 0.97 0.99 0.11 0.25
    NDF 71.1 61.3 71.1 68.5 3.79 0.28 0.08 0.28
    ADF 55.8 41.8 58.4 56.6 7.40 0.20 0.24 0.36
    Starch 99.4 98.9 99.1 99.1 0.18 0.73 0.09 0.22
    Nitrogen 82.9 82.3 80.9 82.6 1.14 0.59 0.38 0.25
Dietary treatments1 P-value
Item 5SG 10SG 5LG 10LG SEM Grind Inclusion G × I2
No. of observations 4 4 3 4 — — — —
Intake
    DM, kg/d 11.1 11.5 10.7 11.0 0.40 0.16 0.23 0.99
    OM, kg/d 10.4 10.7 10.1 10.4 0.37 0.22 0.28 0.98
    NDF, kg/d 2.2 2.4 2.2 2.4 0.10 0.92 0.07 0.99
    ADF, kg/d 1.0 1.2 0.9 1.1 0.07 0.20 0.01 0.95
    Starch, kg/d 5.3 5.5 4.9 5.2 0.26 0.18 0.35 0.86
    Nitrogen, g/d 241.7 242.6 227.6 238.9 9.56 0.21 0.38 0.44
Fecal output
    DM, kg/d 1.6 2.0 1.5 1.7 0.15 0.18 0.06 0.27
    OM, kg/d 1.1 1.2 1.2 1.3 0.13 0.66 0.11 0.34
    NDF, kg/d 0.6 0.9 0.6 0.8 0.10 0.39 0.04 0.32
    ADF, kg/d 0.5 0.7 0.4 0.5 0.07 0.08 0.03 0.30
    Starch, kg/d 0.03 0.06 0.04 0.05 0.009 0.89 0.05 0.23
    Nitrogen, g/d 41.3 46.3 40.4 41.6 3.35 0.34 0.30 0.52
Apparent TT digestibility,3 %
    DM 85.7 82.5 85.6 84.9 1.28 0.32 0.09 0.26
    OM 89.2 86.9 88.3 87.8 0.97 0.99 0.11 0.25
    NDF 71.1 61.3 71.1 68.5 3.79 0.28 0.08 0.28
    ADF 55.8 41.8 58.4 56.6 7.40 0.20 0.24 0.36
    Starch 99.4 98.9 99.1 99.1 0.18 0.73 0.09 0.22
    Nitrogen 82.9 82.3 80.9 82.6 1.14 0.59 0.38 0.25

1Dietary treatments: 5SG = 5% inclusion of short-grind corn stalks, 10SG = 10% inclusion of short-grind corn stalks, 5LG = 5% inclusion of long-grind corn stalks, 10LG = 10% inclusion of long-grind corn stalks.

2G × I = grind × inclusion.

3TT = total tract.

Including roughage at 10% of diet DM increased (P ≤ 0.05) fecal output of NDF, ADF, and starch and tended to increase (P = 0.06) fecal output of DM. An effect of grind size was also observed for ADF fecal output, as feeding SG corn stalks tended to have greater (P = 0.08) fecal output of ADF compared to the LG treatments. Diets containing 5% roughage tended to increase (P ≤ 0.09) DM and NDF total tract digestibility. These results agree with those of Hales et al. (2014), who reported DM digestibility decreased linearly with increasing levels of alfalfa up to 14% of diet DM in DRC-based finishing diets, as well as a tendency for a quadratic decrease in NDF digestibility as roughage increased. Likewise, Benton et al. (2015) reported a decrease in DM and NDF digestibility with increasing inclusions of roughage in finishing diets containing a DRC:HMC blend. Furthermore, increasing roughage could increase total manure production and have an effect on the quantity of manure produced and thus negatively affect the cost of pen maintenance and manure removal. In the current experiment, feeding roughage at 5% of diet DM tended to increase (P = 0.09) apparent total tract digestion of starch. This does not agree with the results of Kreikemeier et al. (1990), who reported that a higher inclusion rate (5% vs. 15% DM basis) of alfalfa tended to increase in situ starch digestion of steam-rolled wheat. Kreikemeier et al. (1990) speculated that forage inclusion rate effects on starch digestion were dependent on an increase in microbial growth and turnover, as well as passage rate. Differences in starch digestion reported by Kreikemeier et al. (1990) and the current trial may be due to grain type, roughage quality, or postruminal starch digestion.

Rumination and Fermentation Characteristics

Rumination time increased (P < 0.01; Table 4) in diets containing LG corn stalks compared to diets containing the SG corn stalks. Furthermore, diets containing 10% roughage also had greater (P < 0.01) rumination time compared to the 5% inclusion treatments. These data concur with those of Yang and Beauchemin (2006), who reported a linear increase in rumination time (min/d) with increasing peNDF by increasing chop length of corn silage fed to dairy cows. Park et al. (2015) also reported an increase in total number of chews in relation to increasing peNDF content of the diets in Hanwoo steers. Given that the peNDF content measured in the experimental diets of the current trial increased with roughage inclusion and grind size, an increase in rumination time relative to peNDF was expected because peNDF of a feed is the physical properties of fiber that stimulate chewing activity described by Mertens (2002).

Table 4.

Effect of roughage grind size and inclusion on rumination time and ruminal pH of finishing beef steers

Dietary treatments1 P-value
Item 5SG 10SG 5LG 10LG SEM Grind Inclusion G × I2
No. of observations 4 4 3 4 — — — —
Rumination time, min/d 225 265 283 313 26.20 <0.01 <0.01 0.66
Ruminal pH 5.65 5.83 5.72 5.92 0.06 0.02 <0.01 0.83
Area below pH 5.63 4.18 2.21 2.88 1.87 0.95 0.19 0.03 0.43
Time under pH 5.6, h/d 13.33 9.03 9.07 8.11 1.91 0.09 0.09 0.26
Dietary treatments1 P-value
Item 5SG 10SG 5LG 10LG SEM Grind Inclusion G × I2
No. of observations 4 4 3 4 — — — —
Rumination time, min/d 225 265 283 313 26.20 <0.01 <0.01 0.66
Ruminal pH 5.65 5.83 5.72 5.92 0.06 0.02 <0.01 0.83
Area below pH 5.63 4.18 2.21 2.88 1.87 0.95 0.19 0.03 0.43
Time under pH 5.6, h/d 13.33 9.03 9.07 8.11 1.91 0.09 0.09 0.26

1Dietary treatments: 5SG = 5% inclusion of short-grind corn stalks, 10SG = 10% inclusion of short-grind corn stalks, 5LG = 5% inclusion of long-grind corn stalks, 10LG = 10% inclusion of long-grind corn stalks.

2G × I = grind × inclusion.

3Area = ruminal pH units below 5.6 times hour.

Table 4.

Effect of roughage grind size and inclusion on rumination time and ruminal pH of finishing beef steers

Dietary treatments1 P-value
Item 5SG 10SG 5LG 10LG SEM Grind Inclusion G × I2
No. of observations 4 4 3 4 — — — —
Rumination time, min/d 225 265 283 313 26.20 <0.01 <0.01 0.66
Ruminal pH 5.65 5.83 5.72 5.92 0.06 0.02 <0.01 0.83
Area below pH 5.63 4.18 2.21 2.88 1.87 0.95 0.19 0.03 0.43
Time under pH 5.6, h/d 13.33 9.03 9.07 8.11 1.91 0.09 0.09 0.26
Dietary treatments1 P-value
Item 5SG 10SG 5LG 10LG SEM Grind Inclusion G × I2
No. of observations 4 4 3 4 — — — —
Rumination time, min/d 225 265 283 313 26.20 <0.01 <0.01 0.66
Ruminal pH 5.65 5.83 5.72 5.92 0.06 0.02 <0.01 0.83
Area below pH 5.63 4.18 2.21 2.88 1.87 0.95 0.19 0.03 0.43
Time under pH 5.6, h/d 13.33 9.03 9.07 8.11 1.91 0.09 0.09 0.26

1Dietary treatments: 5SG = 5% inclusion of short-grind corn stalks, 10SG = 10% inclusion of short-grind corn stalks, 5LG = 5% inclusion of long-grind corn stalks, 10LG = 10% inclusion of long-grind corn stalks.

2G × I = grind × inclusion.

3Area = ruminal pH units below 5.6 times hour.

Ruminal pH increased (P = 0.02) for cattle fed the LG corn stalks compared to cattle fed the SG corn stalks. Shain et al. (1999) reported no differences in ruminal pH of finishing steers consuming different grind sizes of either alfalfa or wheat straw as a roughage source. Likewise, Yang and Beauchemin (2006) reported no differences in ruminal pH of dairy cows consuming corn silage with different chop lengths. The similarity in pH between treatments in both trials could be due to forage degradation rates in the rumen. The differences in ruminal pH between grind sizes in the current trial may be related to increasing peNDF in the diet that maintained pH by stimulating salivary buffer secretion via rumination activity (Allen, 1997). Inclusion rate of roughage also increased (P < 0.01) ruminal pH for cattle consuming 10% roughage compared to the 5% roughage treatments. Sindt et al. (2003) reported a linear increase in ruminal pH as roughage level increased from 0% to 6% (DM basis) in SFC-based diets. The increase in ruminal pH with increasing roughage inclusion may be due to increased chewing activity stimulating saliva production or to a reduction in VFA concentration in the rumen. All treatments went below a pH of 5.6, a benchmark for subacute acidosis as described by Owens et al. (1998). Steers receiving the 5% inclusion rate of roughage tended to have greater (P = 0.09) time (h/d) under a ruminal pH of 5.6 and a larger (P = 0.03) area under the threshold (i.e., 5.6) compared to those receiving 10% roughage treatments. These results concur with those of Morine et al. (2014), who fed 4%, 7%, and 10% roughage (DM basis) in a dry-rolled corn-based finishing diet, with cattle fed 10% roughage spending the least amount of time under a pH of 5.6. Rumination minutes and ruminal pH were not different (P ≥ 0.64) over time relative to grind size and inclusion rate (Fig. 1 and 2). Rumination minutes and ruminal pH were observed to peak at similar times relative to feeding. As rumination increased, pH increased, further suggesting that chewing activity aids in buffering of the rumen.

Figure 1.

Effect of roughage grind size and inclusion on rumination in beef cattle. Dietary treatments: 5SG = 5% short-grind corn stalks (line with diamonds),10SG = 10% short-grind corn stalks (line with squares), 5LG = 5% long-grind corn stalks (line with triangles),10LG = 10% long-grind corn stalks (line with circles). The arrow represents feeding time at 07:00 h. N = 4, 4, 3, and 4 for 5SG, 10SG, 5LG, and 10LG, respectively. Grind × time: P = 0.66, SEM = 2.81; inclusion × time: P = 0.20, SEM = 2.81; and grind × inclusion × time: P = 0.77, SEM = 3.56.

Effect of roughage grind size and inclusion on rumination in beef cattle. Dietary treatments: 5SG = 5% short-grind corn stalks (line with diamonds),10SG = 10% short-grind corn stalks (line with squares), 5LG = 5% long-grind corn stalks (line with triangles),10LG = 10% long-grind corn stalks (line with circles). The arrow represents feeding time at 07:00 h. N = 4, 4, 3, and 4 for 5SG, 10SG, 5LG, and 10LG, respectively. Grind × time: P = 0.66, SEM = 2.81; inclusion × time: P = 0.20, SEM = 2.81; and grind × inclusion × time: P = 0.77, SEM = 3.56.

Figure 2.

Effect of roughage grind size and inclusion on rumination in beef cattle. Dietary treatments: 5SG = 5% short-grind corn stalks (line with diamonds),10SG = 10% short-grind corn stalks (line with squares), 5LG = 5% long-grind corn stalks (line with triangles), 10LG = 10% long-grind corn stalks (line with circles). The arrow represents feeding time at 07:00 h. N = 4, 4, 3, and 4 for 5SG, 10SG, 5LG, and 10LG, respectively. The benchmark for subacute acidosis (horizontal double arrow) is below a pH of 5.6 as described by Owens et al. (1998). Grind × time: P = 0.29, SEM = 0.07; inclusion × time: P = 0.63, SEM = 0.07; and grind × inclusion × time: P = 0.64, SEM = 0.08.

Effect of roughage grind size and inclusion on rumination in beef cattle. Dietary treatments: 5SG = 5% short-grind corn stalks (line with diamonds),10SG = 10% short-grind corn stalks (line with squares), 5LG = 5% long-grind corn stalks (line with triangles), 10LG = 10% long-grind corn stalks (line with circles). The arrow represents feeding time at 07:00 h. N = 4, 4, 3, and 4 for 5SG, 10SG, 5LG, and 10LG, respectively. The benchmark for subacute acidosis (horizontal double arrow) is below a pH of 5.6 as described by Owens et al. (1998). Grind × time: P = 0.29, SEM = 0.07; inclusion × time: P = 0.63, SEM = 0.07; and grind × inclusion × time: P = 0.64, SEM = 0.08.

Ruminal ammonia and VFA concentration are reported in Table 5. A corn stalk inclusion rate effect on ruminal NH3 was observed in which diets containing 10% roughage had greater (P = 0.04) ruminal NH3 than the 5% roughage treatments. However, Sindt et al. (2003) reported a quadratic effect of alfalfa inclusion rate on ruminal NH3, which increased for 2% alfalfa and plateaued at 6% alfalfa inclusion (DM basis). This could be explained by the increasing CP and RDP concentration of the diet as alfalfa inclusion rate increased. Since NH3 is the most common base found in the rumen, the increase in NH3 for the 10% inclusion diets in the current study may partially explain the increase in ruminal pH; however, the decrease in VFA concentration is more difficult to interpret. Higher ruminal ammonia concentrations could have come from higher inclusions of urea in the 10% roughage diets, which could increase ruminal pH values as well (Owens et al., 1998).

Table 5.

Effect of roughage grind size and inclusion on ruminal ammonia and VFA concentrations in beef steers

Dietary treatments1 P-value
Item 5SG 10SG 5LG 10LG SEM Grind Inclusion G × I2
No. of observations 4 4 3 4 — — — —
NH3, mg/dL 5.4 6.7 4.8 6.0 1.25 0.29 0.04 0.89
Total VFA, mM 101.8 94.4 103.0 88.6 6.07 0.46 <0.01 0.25
VFA, mol/100 mol
Acetate 40.0 46.9 41.2 49.2 2.07 0.02 <0.01 0.48
Propionate3 45.2 38.9 44.1 38.3 2.02 0.16 <0.01 0.75
Butyrate 11.5 10.4 11.2 10.0 1.18 0.63 0.12 0.97
Valerate 3.4a 3.7a 3.4a 2.5b 0.83 <0.01 0.19 <0.01
A:P3 0.9 1.2 1.0 1.4 1.37 0.01 <0.01 0.39
Dietary treatments1 P-value
Item 5SG 10SG 5LG 10LG SEM Grind Inclusion G × I2
No. of observations 4 4 3 4 — — — —
NH3, mg/dL 5.4 6.7 4.8 6.0 1.25 0.29 0.04 0.89
Total VFA, mM 101.8 94.4 103.0 88.6 6.07 0.46 <0.01 0.25
VFA, mol/100 mol
Acetate 40.0 46.9 41.2 49.2 2.07 0.02 <0.01 0.48
Propionate3 45.2 38.9 44.1 38.3 2.02 0.16 <0.01 0.75
Butyrate 11.5 10.4 11.2 10.0 1.18 0.63 0.12 0.97
Valerate 3.4a 3.7a 3.4a 2.5b 0.83 <0.01 0.19 <0.01
A:P3 0.9 1.2 1.0 1.4 1.37 0.01 <0.01 0.39

a–cMeans within a row without a common superscript differ (P ≤ 0.05).

1Dietary treatments: 5SG = 5% inclusion of short-grind corn stalks, 10SG = 10% inclusion of short-grind corn stalks, 5LG = 5% inclusion of long-grind corn stalks, 10LG = 10% inclusion of long-grind corn stalks.

2G × I = grind × inclusion.

3Effect of inclusion × time (P ≤ 0.05). A:P = acetate:propionate.

Table 5.

Effect of roughage grind size and inclusion on ruminal ammonia and VFA concentrations in beef steers

Dietary treatments1 P-value
Item 5SG 10SG 5LG 10LG SEM Grind Inclusion G × I2
No. of observations 4 4 3 4 — — — —
NH3, mg/dL 5.4 6.7 4.8 6.0 1.25 0.29 0.04 0.89
Total VFA, mM 101.8 94.4 103.0 88.6 6.07 0.46 <0.01 0.25
VFA, mol/100 mol
Acetate 40.0 46.9 41.2 49.2 2.07 0.02 <0.01 0.48
Propionate3 45.2 38.9 44.1 38.3 2.02 0.16 <0.01 0.75
Butyrate 11.5 10.4 11.2 10.0 1.18 0.63 0.12 0.97
Valerate 3.4a 3.7a 3.4a 2.5b 0.83 <0.01 0.19 <0.01
A:P3 0.9 1.2 1.0 1.4 1.37 0.01 <0.01 0.39
Dietary treatments1 P-value
Item 5SG 10SG 5LG 10LG SEM Grind Inclusion G × I2
No. of observations 4 4 3 4 — — — —
NH3, mg/dL 5.4 6.7 4.8 6.0 1.25 0.29 0.04 0.89
Total VFA, mM 101.8 94.4 103.0 88.6 6.07 0.46 <0.01 0.25
VFA, mol/100 mol
Acetate 40.0 46.9 41.2 49.2 2.07 0.02 <0.01 0.48
Propionate3 45.2 38.9 44.1 38.3 2.02 0.16 <0.01 0.75
Butyrate 11.5 10.4 11.2 10.0 1.18 0.63 0.12 0.97
Valerate 3.4a 3.7a 3.4a 2.5b 0.83 <0.01 0.19 <0.01
A:P3 0.9 1.2 1.0 1.4 1.37 0.01 <0.01 0.39

a–cMeans within a row without a common superscript differ (P ≤ 0.05).

1Dietary treatments: 5SG = 5% inclusion of short-grind corn stalks, 10SG = 10% inclusion of short-grind corn stalks, 5LG = 5% inclusion of long-grind corn stalks, 10LG = 10% inclusion of long-grind corn stalks.

2G × I = grind × inclusion.

3Effect of inclusion × time (P ≤ 0.05). A:P = acetate:propionate.

Including higher roughage amounts in ruminant diets often results in a VFA profile shift with an increase in ruminal acetate:propionate (A:P) ratio. Total VFA concentrations were greater (P < 0.01) for the 5% roughage diets than the 10% roughage diets. Molar proportions of acetate were greater (P < 0.01) and molar proportions of propionate were lower (P < 0.01) for diets containing 10% roughage than diets containing 5% roughage. These values resulted in a greater (P < 0.01) A:P for the 10% inclusion treatments compared to the 5% roughage diets. Likewise, Sindt et al. (2003) reported a linear increase in A:P with increasing levels of alfalfa hay fed to finishing cattle. In the current experiment, the LG diets also had greater (P = 0.02) acetate molar proportions than the SG treatments. The A:P were lower (P = 0.01) for the SG diets than the LG diets. In contrast, Shain et al. (1999) observed an increase in acetate with a shorter particle size of alfalfa compared to a longer particle size (2.54 vs. 12.7 mm) of alfalfa but reported no differences of wheat straw particle size on acetate molar proportions. Shain et al. (1999) speculated that animals consuming wheat straw ruminated more, which suggests that roughage quality may have affected VFA concentration but that roughage particle size did not. A grind × inclusion rate interaction (P < 0.01) was observed for valerate molar proportions, where the 10LG treatment had lower (P < 0.01) valerate proportions than the other treatments. An effect of inclusion rate × time (P < 0.02) was observed for both propionate proportions and A:P. Propionate proportions increased after feeding and were maintained until approximately 17 h after feeding in cattle consuming the 5% roughage diets, whereas propionate proportions began to decline approximately 11 h after feeding in cattle consuming 10% roughage diets. These data suggest an increase in rumination time for higher inclusions of roughage may increase salivary buffer flow and make ruminal conditions more favorable for fiber digestion, as described by Allen (1997).

The results of this experiment confirm that the 5LG diet did not differ in peNDF values and rumination time from the 10SG diet. Cattle consuming the LG corn stalks ruminated longer per day than cattle consuming the SG corn stalks, suggesting that particle length increases rumination time regardless of inclusion rate. Feeding roughages with a larger particle size may improve rumen buffering capacity, as we observed an increase in pH by including roughage of a larger particle size. We also observed an increase in DM, NDF, and starch digestion at 5% roughage inclusion compared with 10% roughage inclusion, suggesting a lower inclusion of roughage is optimal for diet digestibility even with a larger particle size. Likewise, VFA profiles were more energetically favorable with 5% inclusion of roughage compared to the 10% inclusion rate, as propionate proportions were greater for 5% roughage diets. These data suggest that feeding roughage in finishing diets at 5% DM basis with a larger particle size may provide the appropriate amount of peNDF and maintain rumination time for cattle consuming SFC-based finishing diets.

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Footnotes

1

This experiment was supported, in part, by a cooperative agreement between the USDA-ARS and Texas AgriLife Research, Amarillo. The mention of trade names or commercial products in this article is solely for the purpose of providing specific information and does not imply recommendation or endorsement by the U.S. Department of Agriculture. The authors thank the Texas A&M University State Initiative for Beef Sustainability and the Texas Cattle Feeders Association for supporting this research.

American Society of Animal Science

© American Society of Animal Science 2017