The Professional Animal Scientist 29 (2013):124–132
©2013 American Registry of Professional Animal Scientists
Effects of hay supplementation in corn-based and dried
distillers grains with solubles– based diets on performance and ruminal metabolism in feedlot cattle1 L. A. Morrow,* T. L. Felix,† PAS, F. L. Fluharty,* PAS, K. M. Daniels,* and S. C. Loerch,*2 PAS *Department of Animal Sciences, The Ohio State University, Wooster 44691; and †Department of Animal Sciences, University of Illinois, Urbana 61801
ABSTRACT Sulfuric acid in dried distillers grains with solubles (DDGS) decreases ruminal pH, potentially inhibits fiber digestion, and may increase the risk of polioencephalomalacia. At high dietary inclusions of DDGS, increased forage may be needed to attenuate negative effects of low ruminal pH. The objectives of this research were to determine the effects of hay inclusion (7 or 14% of dietary DM), energy source (corn or DDGS), and their interactions on performance and ruminal metabolism in feedlot cattle. In Exp. 1, Angus-cross steers (n = 47) and heifers (n = 24; BW = 253 ± 3 kg) were evenly allotted to treatments by sex, blocked by
1 Salaries and research support provided by state and federal funds appropriated to the Ohio Agricultural Research and Development Center, The Ohio State University. 2 Corresponding author:
[email protected]
BW, and allotted in a 2 × 2 factorial arrangement of treatments to 12 pens. Dietary treatments were 1) 7% hay and cracked corn, 2) 14% hay and cracked corn, 3) 7% hay and DDGS, and 4) 14% hay and DDGS. Increasing hay did not affect (P > 0.12) DMI, ADG, G:F, or final BW. Cattle fed DDGS had 5.8% lower DMI (P = 0.01), 2.7% decreased final BW (P = 0.05), and tended to have decreased (P = 0.06) ADG compared with those fed corn. In Exp. 2, ruminally fistulated heifers (n = 8; BW = 645 ± 14 kg) were used in a replicated 4 × 4 Latin square design and fed the diets used in Exp. 1. Increasing dietary hay concentration tended to increase (P ≤ 0.08) ruminal pH from 0 to 3 h postfeeding but did not affect (P ≥ 0.15) pH thereafter. In situ DM disappearance of soy hulls was 35% greater (P = 0.01) for heifers fed DDGS than for those fed corn and tended (P = 0.09) to be greater with 14% hay. Heifers fed DDGS had less (P = 0.01) total VFA and greater (P = 0.01) ratio of acetate to propionate
than those fed corn. Increasing hay from 7 to 14% of the diet did not increase performance of cattle fed corn or DDGSbased diets. However, increasing dietary percentage of hay tended to increase ruminal pH and in situ DM digestion. Key words: dried distillers grains, feedlot cattle, sulfur
INTRODUCTION High corn prices provide economic incentive to use distillers grains as an energy source for finishing cattle. However, increasing dietary inclusion of distillers grains increases dietary S content (Klopfenstein et al., 2008) and reduces ruminal pH in cattle (Felix and Loerch, 2011). Excessive S intake has been associated with polioencephalomalacia (PEM; Gould et al., 1991). The predominant mechanism behind S-induced PEM involves the bacterial reduction of sulfate to sulfide (S2−) and subsequent proton-
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ation to hydrogen sulfide gas (H2S; Beauchamp et al., 1984). The presence of H2S in the ruminal gas cap is concerning because ruminants inhale a large portion of the gasses they eructate (Dougherty and Cook, 1964). When inhaled, H2S directly enters circulation and bypasses liver detoxification. In cells, H2S blocks the enzyme cytochrome c-oxidase, which results in an energy deficiency and cerebrocortical necrosis (Beauchamp et al., 1984). Low ruminal pH values cause increased free hydrogen ions to be available to form H2S. Adding forage to high-S diets may increase ruminal pH and decrease H2S formation (Felix and Loerch, 2011), thereby reducing the risk of PEM. Low ruminal pH reduces feed intake (Owens et al., 1998) and reduces fiber digestibility by inhibiting the fiber fermenting capacity of cellulolytic bacteria (Mould et al., 1983). Adding forage attenuates low ruminal pH by increasing salivary buffering (Owens et al., 1998). Thus, adding forage to high-distillers-grains diets may be an effective strategy to maximize fiber digestibility and G:F. We hypothesized that increasing ruminal pH, through added hay, would have minimal effects on the performance of corn-fed cattle and would improve performance in cattle fed dried distillers grains with solubles (DDGS) via increased fiber digestion and reduced ruminal H2S. The objectives of this research were to determine the interactions of hay inclusion (7 vs. 14%) and energy source (corn or DDGS) on 1) ADG and DMI of feedlot cattle and 2) ruminal pH, H2S, S2−, short-chain fatty acid (SCFA) concentrations, and in situ DM disappearance of soy hulls.
MATERIALS AND METHODS All animal procedures were approved by the Agricultural Animal Care and Use Committee of The Ohio State University. All animal procedures followed guidelines recommended in the Guide for the Care and Use of Agricultural Animals in Agricultural Research and Teaching (FASS, 2010).
Exp. 1 Animals and Diets. Seventy-one Angus-cross steers and heifers (n = 47 and 24, respectively; initial BW = 253 ± 3 kg) were fed at the Eastern Ohio Agricultural Research and Development Center from March to August of 2011. Cattle were weighed on 2 consecutive days to determine initial BW and blocked by BW into 3 blocks (small, medium, and large). Cattle were then allotted within block to a total of 12 pens (5–6 animals/ pen) with an even allotment of steers (3 or 4) and heifers (2) in each pen. Pens (7.3 × 37 m) were constructed in an open-sided barn and provided 70 cm of bunk space per head. Treatments were arranged in a 2 × 2 factorial with hay (7 or 14%) and energy source (corn or DDGS) as main effects. Pens within block were randomly allotted to 1 of 4 dietary treatments: 1) 7% hay and cracked corn, 2) 14% hay and cracked corn, 3) 7% hay and DDGS, or 4) 14% hay and DDGS. The diet also contained 15% supplement (DM basis), and the balance was from the energy source as described in the treatment (Table 1). The aforementioned diets were offered ad libitum until cattle within a block were deemed by visual appraisal to possess 1.2 cm of back fat, at which point the experiment was terminated for that block. Therefore, average days on feed was the same for all treatments (154 d). Feed was delivered daily at 1100 h. Feed samples were collected every 28 d and were composited during the experiment for later nutrient analysis. The DDGS used in the experiment was obtained from a single source. The DDGS averaged 0.65% S. The pH of DDGS was evaluated by combining 20 g of DDGS with 80 mL of distilled water and mixing for 30 s, and the pH was then recorded (Accumet excel XL25 dualchannel pH/ion meter; Fisher Scientific, Pittsburg, PA). The average pH of DDGS was 4.3. The hay was a first-cutting, mixed-grass, squarebaled hay composed predominately of orchardgrass. The hay contained 9.0% protein, 61.8% NDF, and 41.6% ADF.
The hay was fed as long-stemmed hay (without processing). Steers were implanted with Synovex S and heifers with Synovex H (Fort Dodge Animal Health, Overland Park, KS) at the start of the trial (d 0) and were reimplanted on d 112. Cattle were weighed every 28 d during the experiment and then were weighed on 2 consecutive days at the end of the experiment to determine final BW. Sampling and Analysis. Composited feed samples were dried for 3 d at 55°C then ground using a Wiley mill (1-mm screen; Arthur H. Thomas, Philadelphia, PA). All samples were analyzed for DM (24 h at 100°C). All samples were subjected to perchloric acid digestion and inductively coupled plasma atomic emission spectroscopy analysis of complete minerals (AOAC, 1988; Method 975.03). Feed samples were analyzed for ADF and NDF (Ankom Technology Method 5 and 6, respectively; Ankom200 Fiber Analyzer, Ankom Technology, Fairport, NY), CP (macro Kjeldahl N × 6.25), and fat (ether extract method; Ankom Technology). One animal was removed from the study for reasons unrelated to treatment. Statistical Analysis. The experimental design for this study was a randomized complete block design with a 2 × 2 factorial arrangement of treatments. Data were analyzed using the MIXED procedure of SAS (SAS Institute Inc., Cary, NC). The model used for the performance data considered block as a random effect. Hay level and energy source were considered as fixed effects. Pen was the experimental unit. Significance was set at P < 0.05, and trends were discussed at P < 0.10.
Exp. 2 Animals and Diets. Eight Anguscross, ruminally fistulated heifers (initial BW = 644 ± 14 kg) were used in a metabolism experiment starting on June 20, 2011, at The Ohio Agricultural Research and Development feedlot in Wooster. Heifers were randomly allotted to the 4 dietary treatments from Exp. 1 (Table 1).
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Table 1. Composition (% DM basis) of diets fed in Exp. 1 and 2 Corn Item
71
DDGS Cracked corn Orchardgrass hay Supplement Ground corn Soybean meal Urea Dicalcium phosphate Limestone Trace mineral salt3 Vitamin A, 30,000 IU/g Vitamin D, 3,000 IU/g Vitamin E, 44 IU/g Selenium,4 201 mg of Se/g Monensin5 Tylosin5 Animal–vegetable fat Analyzed composition Exp. 1 NDF, % ADF, % CP, % Ether extract, % S, % Calculated NEm, Mcal/kg Calculated NEg, Mcal/kg Exp. 2 NDF, % ADF, % CP, % Ether extract, % S, % 2
78.00 7.00 15.00 4.13 6.40 0.85 1.00 1.50 0.38 0.01 0.01 0.02 0.04 0.02 0.04 0.60 14.34 6.17 13.65 3.24 0.13 1.87 1.28 16.27 6.39 13.82 3.15 0.12
DDGS 141
71.00 14.00 15.00 4.13 6.40 0.85 1.00 1.50 0.38 0.01 0.01 0.02 0.04 0.02 0.04 0.60 17.85 8.85 13.76 3.08 0.13 1.79 1.22 20.67 9.24 13.81 3.04 0.13
7
14
60.00 18.00 7.00 15.00 11.58 0.00 0.00 0.00 2.30 0.38 0.01 0.01 0.02 0.04 0.02 0.04 0.60 23.21 10.23 19.93 7.25 0.43 1.84 1.25 25.12 9.96 20.29 8.11 0.44
60.00 11.00 14.00 15.00 11.58 0.00 0.00 0.00 2.30 0.38 0.01 0.01 0.02 0.04 0.02 0.04 0.60 26.72 12.92 20.04 7.08 0.43 1.76 1.19 29.37 12.80 20.28 8.00 0.45
DM basis: 7 or 14% hay. Dried distillers grains with solubles: 26.60% NDF, 10.21% ADF, 28.11% CP, 10.44% ether extract, and 0.65% S (DM basis). 3 Contained 95% NaCl, 0.35% Zn, 0.28% Mn, 0.175% Fe, 0.040% Cu, and 0.007% I. 4 Sodium selenite. 5 Rumensin (200 g/kg) and Tylan 10 (22 g/kg) from Elanco (Greenfield, IN). 1 2
Diets were offered ad libitum in a replicated 4 × 4 Latin square design. Dietary treatment sequences were assigned randomly according to procedures described by Patterson and Lucas (1962). Heifers were housed in individual pens (2.4 × 3.0 m) on slatted concrete floors and were fed daily at 0800 h. Dietary ingredient samples were collected at the beginning of each period to determine DM adjustments. Diet and orts samples were collected and
weighed on the day before collecting the ruminal samples. A sample of orts and 0.45 kg of each diet component were saved for later analysis of NDF, ADF, CP, ether extract, and minerals, as described in Exp. 1. The DDGS in the experiment was obtained from the same source as described above and was obtained at the same time. The hay was a first-cutting, mixedgrass, square-baled hay composed predominately of orchardgrass. The hay contained 9.1% protein, 73.6%
NDF, and 44.8% ADF. The hay was fed as long-stemmed hay (without processing). Each period consisted of a 16-d feeding phase followed by 1 d of rumen sample collections [for hydrogen sulfide gas (H2S), liquid sulfide (S2−), and pH determination] and 2 d for determining in situ soy hull disappearance (after 24 and 48 h of incubation). Sampling and Analysis. Samples of ruminal gas were obtained through the cannula cap via puncture with a 10-gauge needle at 0, 1.5, 3, 6, 9, and 12 h after feeding. The concentration of H2S in the ruminal gas cap was measured using H2S precision gas detector tubes (No. 120SF, Sensidyne, St. Petersburg, FL) attached to a calibrated gas detection pump (Model AP-20S, Sensidyne). The concentration of H2S was read from the tube by the same individual for each sampling as described by Gould et al. (1997). Ruminal fluid samples were strained through 2 layers of cheesecloth and analyzed for pH, S2−, and SCFA measurements. Measurements of pH and liquid S2− were taken at 0, 1.5, 3, 6, 9, and 12 h postfeeding. A dualelectrode meter was used to measure pH and S2− (Accumet Excel XL25 dual-channel pH/ion meter; Fisher Scientific) and samples were measured within 2 min of collection. To measure pH, the electrode (Accumet pH/ ATC polypropylene body liquid-filled combination electrode with Ag/AgCl reference with BNC mini connector; Fisher Scientific) was submersed in strained ruminal fluid. To measure liquid S2−, 25 mL of strained ruminal liquid was mixed with 25 mL of sulfide antioxidant buffer (SAOB, Fisher Scientific) to stabilize the S ions. The samples were shaken vigorously, and then S2− was measured via sulfide electrode (Accumet silver/sulfide combination electrode; Fisher Scientific). Samples for SCFA were taken at 0, 3, and 6 h postfeeding to measure SCFA concentration before feeding and at peak fermentation. Samples were initially prepared by mixing 10 mL of 10 N H3PO4 with 50 mL of ruminal fluid; 40 mL of water was then added to generate a 50% rumi-
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nal fluid solution. This mixture was placed in the refrigerator for 2 d and mixed several times daily by shaking. On the third day, samples were removed from the refrigerator, and ~40 mL of sample was poured into centrifuge tubes and spun at 12,000 × g at 4°C for 20 min. The supernatant was filtered through a 0.45-μm filter. Then, 1.0 mL of the filtered sample was pipetted in to a 3-mL gas chromatography vial with 0.1 mL of internal 2 ethyl-butyrate standard. The gas chromatography vials were stored at −20°C until analysis by gas chromatography (Model 5890A, Hewlett Packard, Palo Alto, CA) for VFA according to the protocol validated by Supelco (1975). Lactic acid was analyzed using filtered ruminal fluid that was deproteinized by 2:1 mixture of 8% phosphoric acid:ruminal fluid. The deproteinized sample was then analyzed using a colorimetric method (Boehringer Mannheim Test-Combination D/L-Lactic acid; R-Biopharm AG, Darmstadt, Germany) on a plate reader spectrophotometer (Multiskan MCC, Thermo Electron Corporation, Fisher Scientific). Ruminal fiber degradation was estimated by the in situ DM disappearance of soy hulls. A sample size of approximately 10 g of soy hulls was weighed into in situ bags (Ankom Technology, 10 × 20 cm Forage Bags). Bags were tied off with nylon string and then placed in larger mesh sacs containing steel weights. These larger mesh bags, one per animal, were placed in the rumen before feeding at 0800 h on the second day of ruminal collections. Four replicate bags were removed after 24 and 48 h of incubation. After incubation, in situ bags were rinsed on the rinse and spin cycle of a washing machine 6 times and then stored frozen. Later, the frozen in situ bags were then dried in a 100°C oven for 24 h and allowed to cool in desiccators. Weights of the dried bags were recorded. Additionally, substrate wash-out was estimated by subjecting 4 in situ bags (containing 10 g of soy hulls) that were never incubated in the rumen to the same rinsing, freezing, and drying procedures as the incubated bags. In situ
DM disappearance for all samples was corrected for wash-out. The soy hulls used for substrate were analyzed as 49.9% ADF and 66.6% NDF. Statistical Analysis. The experimental design was a replicated 4 × 4 Latin square design with a 2 × 2 factorial arrangement of treatments. Repeated measures were used to analyze ruminal H2S, liquid S2−, pH, and SCFA because these data represent a single animal on a given day. Statistical data were analyzed using the MIXED procedure of SAS (SAS Institute Inc.). The Bayesian information criterion was used to select the AR(1) covariance structure. The model used included the fixed effect of square, the random effect of heifer nested within square, the random effect of period, the fixed effect of hay inclusion, the fixed effect of energy source, the fixed effect of the interaction of hay and energy source, and the fixed effect of repeated time of collection; all interactions were considered to be fixed effects. When an interaction of time and treatment main effect occurred (P < 0.05), the SLICE option (SAS Institute, 2004) was used to compare treatments at each time point. Animal was the experimental unit. Significance for main effects was set at P < 0.05, and trends were discussed at P < 0.10.
RESULTS AND DISCUSSION Exp. 1 There were no interactions (P > 0.31) of hay inclusion and energy source on cattle performance; therefore, only the main effects will be discussed (Table 2). Cattle consuming DDGS-based diets had reduced (P ≤ 0.05) DMI and final BW and tended (P = 0.06) to have reduced ADG compared with cattle fed cornbased diets; G:F was not affected (P = 0.41). Contrary to our hypothesis, increasing hay from 7 to 14% did not affect (P > 0.12) cattle ADG, DMI, or G:F. In previous reports, performance was maximized in cattle and sheep when DDGS inclusion was between 20 and 30% (Buckner et
al., 2007; Felix et al., 2012b). However, inclusion up to 60% DDGS had no effect on ADG or G:F in lambs when DDGS replaced barley in diets containing 12.5% alfalfa hay as the source of roughage (Schauer et al., 2008). Felix and Loerch (2011) reported a 19% increase in DMI and a 9% increase in ADG when 10% haylage replaced corn in diets containing 60% DDGS + 10% corn silage. In the present experiment, forage consisted of long-stemmed grass hay; it is not known if lack of forage processing was the reason for the lack of a performance response when hay was increased from 7 to 14% of the diet. In a meta-analysis of by-product feeding experiments, Vanness et al. (2009) reported the incidence of PEM was 0.14% when diets contained less than 0.46% S; however, the incidence increased to 6.06% when dietary S exceeded 0.56%. The data from one experiment out of the 4,143 analyzed in this meta-analysis were removed because of a high incidence of PEM associated with diets that were 0.47% S but did not contain dietary roughage. This suggests that forage plays a role in preventing PEM (Vanness et al., 2009). The DDGS used in the present experiment was from a single source and was analyzed to be 0.65% S. Zinn et al. (1997) reported reduced DMI, ADG, and feed efficiency when the diet exceeded 0.2% S. In the present experiment, total dietary S was calculated to be 0.43 and 0.13% (DM basis) for DDGS and corn-based diets, respectively (Table 1). There were no cases of PEM in the current study.
Exp. 2 Fistulated heifers fed corn-based diets had greater (P = 0.01) DMI compared with those fed DDGS-based diets, and hay inclusion did not affect (P = 0.67) DMI (Table 3). This was similar to the responses observed in Exp. 1. Hay inclusion did not affect (P = 0.83) S intake; however, heifers consuming DDGS-based diets had increased (P = 0.01) S intake due to the relative abundance of S in DDGS (Table 3).
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Table 2. Main effect means of corn-based versus dried distillers grains with solubles (DDGS)–based diets and 7 versus 14% hay inclusion on cattle performance in Exp. 1 ES1 Item n, animal (pen) Initial BW, kg Final BW, kg ADG, kg DMI, kg/d G:F 1 2
H2
Corn
DDGS
35 (6) 253.4 491.3 1.60 8.6 0.180
36 (6) 252.9 477.8 1.46 8.1 0.174
P-value
7
14
SE
H
ES
H × ES
35 (5–6) 252.7 486.4 1.57 8.3 0.182
36 (6) 253.6 482.7 1.49 8.3 0.172
— 15.4 17.3 0.04 0.27 0.005
— 0.46 0.51 0.21 0.59 0.12
— 0.68 0.05 0.06 0.01 0.41
— 0.77 0.84 0.32 0.99 0.31
Energy source: effects of corn versus DDGS. Hay: effects of 7 versus 14% hay, DM basis.
Felix and Loerch (2011) reported that ruminal pH in steers consuming 60% DDGS diets decreased approximately 1 pH unit during this first 1.5 h postfeeding. They speculated that sulfuric acid used in the production of ethanol contributed to this decrease in ruminal pH. Felix and Loerch (2011) reported that pH continued to fall 12 h postfeeding to near or below 5.0 in animals consuming 60% DDGS diets. We hypothesized that buffering of ruminal acid by adding hay to the diet may be more beneficial in alleviating low ruminal pH for ruminants consuming DDGS-based diets compared with corn-based diets. There was a hay × time interaction (P = 0.04) for ruminal pH (Table 4). Additional hay increased ruminal pH in cattle from 0 to 3 h postfeeding regardless of energy
source. The 60% DDGS diets in the current experiment did not reduce ruminal pH to the degree reported when a 60% DDGS diet was fed by Felix and Loerch (2011). This may be due to the variability of sulfuric acid content in the DDGS or the source of additional dietary fiber. The current experiment used long-stem hay whereas Felix and Loerch (2011) used 10% corn silage and 10% haylage. Acidic conditions in the rumen inhibit cellulolytic organisms (Mould et al., 1983). Ruminal pH below 6.0 reduces fiber fermentation (Owens et al., 1998). Felix and Loerch (2011) reported that ruminal pH in steers fed 60% DDGS diets dropped below 5.0 from 1.5 to 12 h postfeeding. The NRC (2000) reports the mean NDF content of DDGS to be approximately
46%. Acidic ruminal conditions when feeding DDGS-based diets could inhibit fermentation of a significant amount of potentially digestible fiber. We hypothesized that mitigating low ruminal pH with effective fiber from long-stemmed hay (Mertens, 1997) would be more effective at increasing in situ DM disappearance of soy hulls in heifers fed DDGS-based diets than in heifers fed corn-based diets. However, no hay × energy source interaction was detected (P = 0.72) for in situ DM disappearance of soy hulls (Table 4). Soy hulls contained 66.6% NDF, and they were used in this experiment as an indicator of ruminal fiber fermentation capabilities. A tendency for an energy source × time interaction of in situ DM digestion was suggested (P = 0.07), but the interaction
Table 3. Treatment means for DMI and S intake of heifers fed corn-based or dried distillers grains with solubles (DDGS)–based diets with 7 or 14% hay in Exp. 2 Corn Item1 DMI, kg/d S, g/d 5
DDGS
72
142
10.7 12.9
11.6 15.0
n = 8 animals per treatment. DM basis: 7 or 14% hay. 3 Hay: effects of 7 versus 14% hay, DM basis. 4 Energy source: effects of corn versus DDGS. 5 Intake was measured on the day before sampling. 1 2
P-value
7
14
SE
H3
ES4
ES × H
8.8 39.5
8.4 28.2
0.64 2.07
0.67 0.83
0.01 0.01
0.17 0.33
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Table 4. Mean ruminal variables for heifers fed corn-based or dried distillers grains with solubles (DDGS)– based diets with 7 or 14% hay in Exp. 2 Corn Item1 pH (SE = 0.12) 06 1.5 3 6 9 12 S2− fluid, mg/L (SE = 1.10) 0 1.5 3 6 9 12 H2S gas, mg/L (SE = 360) 0 1.5 3 6 9 12 ISDMD7 (SE = 4.43) 24 48
72 6.09 6.05 5.75 5.83 5.58 5.40 2.65 2.76 2.56 2.43 2.22 2.42 190 274 241 313 169 261 23.3 41.1
DDGS 142
7
6.48 6.26 5.79 5.57 5.51 5.31
2.34 2.70 1.97 1.84 2.02 2.02
139 261 191 173 247 154 29.6 45.8
6.39 6.05 5.84 5.74 5.54 5.31 10.72 7.87 9.19 10.86 14.41 14.94 1,730 2,284 3,001 3,041 4,343 4,568 33.4 52.9
P-value 14
6.86 6.59 6.19 5.90 5.85 5.72 8.78 6.81 7.72 9.53 13.16 16.12 643 1,979 2,961 3,151 4,040 4,803 37.8 64.7
H3
ES4
0.01 0.01 0.01 0.08 0.68 0.26 0.15 0.16 — — — — — — 0.57 — — — — — — 0.09 — —
0.01 — — — — — — 0.01 0.01 0.01 0.01 0.01 0.01 0.01 0.01 0.01 0.01 0.01 0.01 0.01 0.01 0.01 0.02 0.01
ES × H
0.03
0.55
0.69
0.72
H × T5
0.04
0.72
0.74
0.29
ES × T5
0.34
0.01
0.01
0.07
n = 8 animals per treatment. DM basis: 7 or 14% hay. 3 Hay: effects of 7 versus 14% hay, DM basis. 4 Energy source: effects of corn versus DDGS. 5 Time effect was detected (P < 0.05) for all measures. The P-values in the row with the item name are from the repeated-measures model of SAS. When an interaction of time × main effect was suggested (P < 0.10), the SLICE option (SAS Institute, 2004) was used to determine probability of the main effect at each time period. The SE shown is associated with the time × main effect cell means. 6 Hours postfeeding. 7 Percentage of in situ DM disappearance of soy hulls. 1 2
was due to the magnitude of increase of in situ DM digestion in heifers fed DDGS- versus corn-based diets (9 vs. 15 percentage unit increases at 24 and 48 h, respectively) and hay tended (P < 0.09) to increase in situ DM digestion of soy hulls for both corn- and DDGS-based diets. Sulfate-reducing bacteria use sulfate as a final electron acceptor in the metabolism of a variety of electrondonating substrates and produce S2− as the end product (Huisingh et al., 1974). Then, by a pH-dependent step, S2− present in the ruminal liquid
is protonated (pKa1 = 11.94 and pKa2 = 7.04) to HS− and then to H2S gas (Beauchamp at al., 1984). Using the dissociation constants, Bray and Till (1975) determined that at a ruminal pH of 5.2, the percentage of H2S versus HS− is 97.2 and 2.8, whereas at a pH of 6.8 the percentage of H2S versus HS− is 46.8 and 50.4, respectively. We hypothesized that mitigating low ruminal pH with added effective fiber (Mertens, 1997; Owens et al., 1998) would reduce H2S gas concentrations in the ruminal gas cap and increase concentrations of sulfide in the rumen
liquor. Reducing H2S gas concentrations would reduce risk of S-induced PEM, and absorption of S would allow detoxification by the blood (Evans, 1967) and liver (Anderson, 1956). The S content of DDGS-based diets in Exp. 2 averaged 0.45% S whereas the corn-based diets averaged 0.13% S (Table 1). Increasing hay from 7 to 14% of diet DM did not affect (P = 0.16) ruminal liquid S2− concentrations, and no hay × energy source interaction (P = 0.55) was detected. A time × energy source interaction was detected (P = 0.01) for ruminal
130 liquid S2− concentrations. Rumen liquid S− concentration did not differ greatly over time in cattle fed cornbased diets; however, S2− increased between 3 to 12 h postfeeding in cattle consuming DDGS-based diets. Vanness et al. (2009) reported that at 8 h postfeeding, H2S decreased and ruminal pH increased linearly when grass hay was added at 0, 7.5, and 15% of DM to wet distillers grains– and wet corn gluten feed–based diets. Felix and Loerch (2011) reported that 10% alfalfa haylage did not reduce H2S concentrations in cattle fed 10% corn silage and 60% DDGS. In the current experiment, increasing hay from 7 to 14% of DM did not affect (P = 0.57) H2S concentrations, and no hay × energy source interaction (P = 0.69) was detected. A time × energy source interaction was detected (P = 0.01) for H2S concentrations. Whereas, H2S concentrations in heifers fed corn-based diets remained low throughout the day, in heifers fed DDGS-based diets, the H2S concentrations increased from 0 to 12 h postfeeding, and peak H2S concentrations were over 4,500 mg/L. Gould (1998) suggested that concentrations of H2S above 2,000 mg/L typically preceded observed cases of PEM. The pattern of response in the current experiment followed our hypothesis: lowest ruminal pH and greatest H2S values occurred at 12 h postfeeding, indicating maximum availability of hydrogen ions to form H2S. These data suggest that measurement of H2S concentrations at a single time point (as is often done when using rumenocentesis; Vanness et al., 2009, Neville et al., 2010) may not be an adequate to accurately characterize diet effects on ruminal S metabolism. The concentrations (mM) of common SCFA are presented in (Table 5). There was no interaction (P > 0.13) of hay × energy source on acetate or total VFA concentration. Time × energy source and time × hay interactions were detected (P < 0.05) for these variables. Acetate and total VFA were greater (P < 0.01) for corn-fed heifers than for DDGSfed heifers at 0, 3, and 6 h postfeed-
Morrow et al.
ing, whereas the magnitude of this increase was less at 0 h postfeeding. Increased dietary hay reduced (P < 0.01) acetate and total VFA concentration at 0 h but not at 3 and 6 h postfeeding (P > 0.14). This response was unexpected because generally, ruminal acetate concentrations are greater with increased fiber fermentation and a ruminal environment that is more favorable to fiber fermentation (Zinn et al., 1994). However, Felix and Loerch (2011) also reported that added alfalfa haylage did not increase ruminal acetate concentrations. Felix and Loerch (2011) reported that 60% DDGS reduced acetate and propionate at 0 h, but not at 3 and 6 h postfeeding, compared with a corn-based diet without DDGS. In the present experiment, there were no effects of hay (P = 0.40) or hay × energy source interactions (P = 0.75) on propionate concentration. However, a main effect of energy source was detected; heifers that were fed DDGS-based diets had reduced (P = 0.01) propionate concentrations compared with heifers corn fed corn-based diets. These responses influenced the acetate to propionate ratio (A:P). There was no effect of hay (P = 0.79) or hay × energy source interaction (P = 0.37) on A:P. A time × energy source interaction was detected (P = 0.01). The A:P was greater (P = 0.01) for DDGS-fed heifers than for corn-fed heifers at 0 h postfeeding but not at 3 and 6 h postfeeding (P > 0.17). Some studies have reported a decrease in A:P when dietary S is increased (Zinn et al., 1997). The NDF content of the DDGS-based diets was at least 40% greater than that of the corn-based diets in the current experiment. Increased dietary fiber typically results in increased acetate fermentation (Zinn et al., 1994). Felix and Loerch (2011) reported an increase in A:P when 10% haylage was added to a 60% DDGS diet. However, in the present experiment, VFA concentrations were lower for cattle fed the DDGS-based diets than for those fed the corn-based diets. This suggests overall ruminal function may be suppressed when diets high in DDGS are
fed. Adding hay to corn-based diets had little effect on butyrate, whereas adding hay to DDGS-based diets tended to decrease butyrate (interaction; P = 0.06). The pKa of lactate (3.9) is considerably lower than the pKa for VFA (~4.9; Swenson and Reece, 1993). Wilson et al. (1975) found that the mean ruminal lactic acid concentration in normal healthy cattle was 1.33 mM and was 3.67 mM in cattle diagnosed with sudden death from lactic acidosis. Huntington et al. (1981) reported that wethers consuming 85%-concentrate diets had total lactic acid concentrations between 6.85 and 11.29 mM. Based on previous experiments where lactic acid concentrations in the ruminal fluid of cattle fed high inclusions of DDGS were very low (Felix et al., 2012a), we hypothesized that sulfuric acid and not lactic acid was a primary cause of low ruminal pH in cattle fed 60% DDGS. In the present experiment, cattle fed DDGS-based diets had greater ruminal lactic acid concentrations than did those fed corn-based diets at all times measured. However, this effect was lessened when diets contained more hay (interaction P = 0.01). Lactic acid values were within the range for healthy cattle and would not have likely had a large effect on ruminal pH.
IMPLICATIONS Compared with corn-based diets, DDGS included in cattle diets at 60% of diet DM did not affect feed efficiency; however, ADG tended to be decreased. Supplementing DDGS-based diets with additional hay tended to increase ruminal pH and measures of ruminal fiber fermentation. Under our experimental conditions, the shift in ruminal pH with added hay was not sufficient to alter S metabolism in the rumen. More direct strategies to alleviate acid load from DDGS may be needed to alter S metabolism and mitigate risk of S-induced PEM as a result of excessive ruminal H2S concentrations.
131
Dietary hay and distillers grains for cattle
Table 5. Short-chain fatty acid profiles of heifers consuming corn-based and dried distillers grains with solubles (DDGS)–based diets with 7 or 14% long-stemmed hay in Exp. 2 Corn Item1 Acetate, mM (SE = 2.34) 06 3 6 Propionate, mM (SE = 2.83) 0 3 6 Butyrate, mM (SE = 1.13) 0 3 6 Total VFA, mM (SE = 4.49) 0 3 6 A:P7 (SE = 0.16) 0 3 6 Total lactate, mM (SE = 0.11) 0 3 6
72
DDGS 142
P-value
7
14
45.49 53.58 50.08
40.52 54.10 54.25
35.90 42.76 45.81
28.44 37.32 44.45
28.75 33.60 32.36
21.98 31.01 33.45
13.95 22.17 23.46
10.79 20.05 23.95
10.46 10.89 9.67
9.69 11.50 11.15
12.23 16.43 15.84
7.02 12.69 14.31
76.28 100.567 102.25
65.20 85.132 88.66
50.27 73.51 86.21
1.69 1.74 1.71
2.07 1.88 1.73
2.80 1.95 1.98
2.67 1.92 1.89
0.88 1.06 1.03
0.99 1.07 0.95
1.67 1.79 1.97
1.30 1.58 1.44
89.49 102.41 95.89
H3
ES4
0.12 0.01 0.26 0.52 0.40 — — — 0.14 0.02 0.18 0.98 0.06 0.01 0.14 0.66 0.79 — — — 0.02 — — —
0.01 0.01 0.01 0.01 0.01 — — — 0.02 0.69 0.01 0.01 0.01 0.01 0.01 0.01 0.01 0.01 0.43 0.17 0.01 — — —
H × ES
0.13
0.75
0.06
0.30
0.37
0.01
H × T5
ES × T5
0.04
0.04 0.26 0.01 0.05 0.01
0.13
0.05
0.03
0.35
0.23
0.51
n = 8 animals per treatment. DM basis: 7 or 14% hay. 3 Hay: effects of 7 versus 14% hay, DM basis. 4 Energy source: effects of corn versus DDGS. 5 Time effect was detected (P < 0.05) for all measures. The P-values in the row with the item name are from the repeated measures model of SAS. When an interaction of time × main effect was suggested (P < 0.10), the SLICE option (SAS Institute, 2004) was used to determine the probability of the main effect at each time period. The SE shown is associated with the associated with the time × main effect cell means. 6 Hours postfeeding. 7 Acetate:propionate. 1 2
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