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ANIMAL NUTRITION |
USDA-ARS, US Meat Animal Research Center, Clay Center, NE 68933-0166
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Abstract |
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0.23) between treatments. Compared with feeding DRC, feeding HMC decreased (P = 0.02) starch intake from 5,407 to 4,846 g/d, decreased (P < 0.01) fecal excretion of starch from 448 to 292 g/d, and increased (P = 0.03) starch digestibility from 91.7 to 94.1%. Nitrogen intake was greater (P < 0.01) for steers fed DRC than HMC in both studies, but N retention did not differ (P = 0.55). Heat production and energy retention did not differ between the 2 treatments (P 0.55). In manure slurries incubated for 35 d with soil and water, total VFA concentration was lower (P < 0.01) in manure from steers fed HMC (1,625 µmol/g of DM) compared with steers fed DRC (3,041 µmol/g of DM). Lower initial (d 0) starch concentrations and greater initial pH was also observed in the slurries from the HMC manure. By d 3 of slurry incubation, there was an increase (P < 0.01) in free glucose and L-lactic acid in the DRC slurries but not in the HMC slurries. During manure incubation, alcohol and VFA content increased (P < 0.01) and pH declined, but to a lesser extent (P < 0.01) in the HMC slurries. However, branched-chain VFA increased more (P < 0.01) in the HMC slurries than in the DRC slurries. These data suggest that feeding HMC instead of DRC decreased fecal starch and production of some potentially odorous compounds in a finishing cattle system but had little impact on animal productivity.
Key Words: beef steer • odor compound • starch • volatile fatty acid
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INTRODUCTION |
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TopAbstractINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONIMPLICATIONSLITERATURE CITED |
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,b) than dry-rolled corn (DRC) and has improved beef cattle performance and efficiency in some studies (Ladely et al., 1995), whereas other studies reported decreased DMI and ADG with no change in efficiency (Owens et al., 1997).
Odors are an increasingly difficult and pressing problem for the agricultural industry. This problem will continue to grow as suburban development encroaches upon areas that are primarily used for agricultural purposes and as animal production sites may be required to feed greater numbers of animals on smaller areas of land. Odors from confinement livestock feeding operations are produced primarily via an incomplete fermentation of livestock manure by bacteria (Mackie et al., 1998). This manure contains many nutrients that may be utilized by bacteria, such as starch, proteins, NPN, lipids, and nonstarch polysaccharides. Miller and Varel (2001, 2003) demonstrated that malodorous VFA are dominant cattle manure fermentation products in feedlot situations and are produced primarily by incomplete fermentation of starch. Therefore, feedlot management and feeding practices that influence the use and excretion or both of starch by cattle may significantly affect the production of odor from these systems.
The purpose of this study was to determine whether steers fed high-concentrate diets with less rumen-escape starch and a greater total tract starch digestibility will release quantifiably less starch in their manure than steers fed diets greater in rumen-escape starch and if the decrease in fecal starch would result in decreased odorous compound production from these manures.
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MATERIALS AND METHODS |
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TopAbstractINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONIMPLICATIONSLITERATURE CITED |
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These experimental procedures were approved by the US Meat Animal Research Center Animal Care and Use Committee. In Exp. 1, 8 steers (447 ± 22 kg of BW) sired by Charolais bulls bred to 3/4 Angus 1/4 Piedmontese dams were trained to be used in a nutrient balance study. Adaptation to diets began when steers were 325 to 356 d of age. Steers were housed in individual stalls and were adapted to close human contact. During adaptation, steers were housed in 2 open, dirt pens and were separated by dietary treatment. Steers were fed a HMC- (ensiled for >120 d) or DRC-based finishing diet (Table 1) in a crossover design; 4 steers were on each diet for 25 d. Data were collected, then diets were switched so that the steers received the other diets for 28 d, and data were collected again. The HMC was grown, ground through a tub grinder equipped with 2.54-cm screen, and ensiled on the US Meat Animal Research Center, and the DRC was purchased from a local supplier. The same feed mixtures were delivered daily for use by steers in Exp. 1 and Exp. 2.
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Composited feed, ort, and fecal samples were weighed, dried in a forced air oven (55°C), weighed again, and then ground with a Wiley Mill (Arthur Thomas Co., Philadelphia, PA) fitted with a 1-mm screen. A subsample of feed, orts, and feces were dried at 70°C for determination of DM. Concentrations of N (Leco CN-2000 carbon/nitrogen analyzer, Leco Corporation, St. Joseph, MI) and P (HNO3 digestion and subsequent color development using the Fiske chemical method; Fiske and SubbaRow, 1925) were determined in feed, orts, feces, and urine for determination of nutrient balance. Urinary urea N was measured (Marsh et al., 1965) using a Technicon Autoanalyzer (Method #339-01, Technicon Autoanalyzer System, Tarrytown, NY). Gross energy was determined for feed, orts, and feces by bomb calorimetry (Parr 1241, Parr Instrument Co., Moline, IL). Urinary GE was estimated from N content as described by Blaxter (1962).
Immediately after the balance trial, O2, Co2, and CH4 exchanges were measured for 6 h, and heat production was calculated with indirect calorimetry as previously described by Eisemann and Nienaber (1990). Fresh feed and water were placed in the head-box calorimeters before the indirect calorimetry measurement to allow steers ad libitum access to their respective diets and water during the measurement.
The feedlot study was conducted for 124 d at the beef cattle feedlot on the USDA-ARS, US Meat Animal Research Center located in south-central Nebraska (–98° longitude, 40.6° N latitude). One hundred fifty crossbred (varying percentages of Angus, Hereford, Pinzgauer, and Red Poll) yearling steers were used in Exp. 2 to assess feedlot performance and carcass characteristics as well as odorous compound production. Before initiation of the study, steers were treated with a modified live bovine rhinotracheitis-virus diarrhea-parainfluenza3-respiratory syncytial virus vaccine (Bovi-Shield Gold 5, Pfizer Animal Health, Exton, PA) and dewormed with moxidectin (Cydectin, Fort Dodge Animal Health, Overland Park, KS). All pens were open lots, and feeding occurred by pen (15 steers/pen); thus pen was the experimental unit (n = 5 pens/diet) for dietary treatment effects related to intake.
Throughout the experiment, steers were fed once a day to allow ad libitum access to feed. One hundred grams of feed was collected each day and composited on a weekly basis for chemical analysis. Orts were collected weekly, weighed, and subsampled for chemical analysis. On d 0, steers weighed 363 ± 33 kg. As a subplot effect, 5 steers in each pen were implanted with trenbolone-acetate (TBA, Finaplix-H, Intervet Inc., Millsboro, DE), estradiol benzoate/progesterone (estradiol, Synovex-S, Fort Dodge Animal Health), or no implant. The 3 implant strategies were used to evaluate the effects of diet over a low (no implant), intermediate (TBA), or high (estradiol) growth rate.
Steers were weighed on consecutive days at the initiation and termination of the study. In addition, steers were weighed at 4-wk intervals throughout the experiment. Blood was collected by jugular venipuncture into heparinized tubes at each of the weighing events and analyzed for urea N as previously described. Steers were weighed before their morning feeding. To provide the beginning and final weights used for the calculations of ADG and G:F, quadratic regressions of BW vs. days on feed for each individual were derived based on the measured weights. Linear daily gains throughout the experiment were calculated as the first derivative of the regression of BW on time.
At the end of the feeding period, steers were shipped to a commercial abattoir (Swift and Co., Grand Island, NE) for slaughter. Individual carcass data, including HCW, marbling score, adjusted fat thickness, KPH, and LM area, were collected by an independent trained consultant. Dressing percent, quality grade, and yield grade were calculated as described by the USDA (1997).
Collection and Analysis of Feedlot Fecal Samples
Cattle feedlot soil (Hastings silt-loam) was collected from the surface soil (top 2 cm) in a feedlot drainage ditch outside of the pens, sieved through a screen (4 mm), and dried for 2 d at 37°C. Fresh fecal composite samples were collected from each of the 10 pens (n = 5/treatment) after 123 d of treatment. At least 9 fresh (noncrusted) fecal pats from each pen were used to form the fecal composite for each pen.
Manure slurry incubations (400 g) were prepared in a blender using fresh fecal composite (30% by weight), feedlot soil (5% by weight), and a mixture of urine and water (65% by weight). The amount of urine used in the slurry was determined based upon the average urine-to-feces ratio for each dietary treatment determined in the balance study. Before preparing the manure slurry, frozen, acid-preserved urine collected during the balance study was thawed and neutralized to pH 7 with 10 M NaOH. Manure slurry was incubated at room temperature in stoppered 0.5-L flasks containing a N2 headspace.
Three slurry subsamples were collected on d 0 (initial), 3, 7, 14, 21, 28, and 35. The first subsample was analyzed for DM and OM content by mass loss after drying overnight at 105°C and by mass loss-on-ignition at 425°C overnight, respectively (Nelson and Sommers, 1996). A second subsample was also analyzed for pH, water-soluble fermentation products and intermediates (alcohols, VFA, aromatic ring-containing compounds, L-lactate, and free glucose), starch, and nonsoluble protein content in a stepwise manner as previously described (Miller and Berry, 2005). Total alcohol, L-lactate, and free glucose were determined using the membrane-immobilized alcohol, L-lactate, and glucose oxidase enzyme system, respectively, of the YSI Model 2700 autoanalyzer (Yellow Springs Instrument Company, Yellow Springs, OH). Other fermentation products (propanol, isobutanol, butanol, pentanol, hexanol, acetate, propionate, isobutyrate, butyrate, isovalerate, valerate, isocaproate, caproate, heptanoate, caprylate, phenol, 
-cresol, 4-ethyl phenol, indole, skatole, benzoate, phenylacetate, and phenylpropionate) were quantified using a Hewlett Packard 6890 gas chromatograph (Agilent Technologies, Palo Alto, CA) equipped with flame ionization and mass-selective detectors. Liquid extract (0.5 mL) was added to a 2-mL vial with ethyl butyrate as an internal standard (1 mM final concentration), 100 µL of 3 M HCl, and 800 µL of ether. The vials were crimp-capped, shaken for 1 min, and 2 µL from the upper ether phase was injected by autoinjector into a split/splitless inlet operated at 275°C and at a 30:1 split. Temperature, pressure, and detection conditions have been previously reported (Miller and Berry, 2005). The starch content of the dried ground fecal material in the third subsample was determined by autoclaving in H2O to extract starch, converting the starch to free glucose during a 2-h digestion with amyloglucosidase, and then measuring the liberated monomeric glucose using the YSI Model 2700 autoanalyzer.
Statistical Analysis
The MIXED procedure of SAS (SAS Inst. Inc., Cary, NC) was used for statistical analysis of data. For Exp. 1 (n = 16 observations), the model included the independent variables; steer, period, and grain type; steer and period were treated as random effects. The model for Exp. 2 performance and carcass data (n = 148 observations) included grain type, implant treatment, and the 2-way interaction with pen(grain) treated as a random effect. The model for intake and initial manure (n = 10 observations) composition data included grain type. The model for manure slurry composition over the 35-d incubation included grain type, days of incubation as a repeated measure. When treatment effects were significant (P < 0.05), a difference was determined, and a tendency for treatment to elicit a response was noted when P < 0.10. Least square means are reported, and when a difference was noted due to implant or the 2-way interaction of grain x implant, all possible single df tests were used for mean separation.
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RESULTS |
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TopAbstractINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONIMPLICATIONSLITERATURE CITED |
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In Exp. 1 (Table 2), steers fed the HMC diet consumed similar amounts of DM (P = 0.16) but less (P = 0.02) starch than those fed the DRC diet. This was accompanied by a concomitant increase (P = 0.03) in starch digestibility and a decrease (P < 0.01) in fecal starch for steers fed HMC compared with steers fed DRC.
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Phosphorus intake tended (P = 0.06) to be greater in steers fed HMC than in steers fed DRC. However, there were no differences in fecal (P = 0.33) or urinary (P = 0.37) excretion of P between the 2 dietary groups, which resulted in an increase (P = 0.01) in the amount of P retained by steers fed HMC compared with steers fed DRC. The relationship between N and P in manure is of great importance to the value of manure as a fertilizer, and as such, the N:P ratio was decreased (P < 0.01) from 8.36 in steers fed DRC to 6.51 in steers fed HMC. However, if the urinary N is removed from the ratio due to the likely rapid degradation of the majority of urinary N to ammonia and its subsequent volatilization, the adjusted N:P ratio did not differ (P = 0.76).
Energy metabolism components also differed between the 2 dietary treatments (Table 2
). There was no difference in intake energy (P = 0.19), fecal energy (P = 0.12), and subsequently, no difference (P = 0.76) in the dietary DE of the DRC (3.44 Mcal/kg of diet) or HMC (3.45 Mcal/kg of diet). Similarly, there was no difference (P = 0.24) in the total amount of DE consumed between the 2 treatments. There was also no difference in heat production (P = 0.94) or retained energy (P = 0.56) between the 2 dietary treatments. However, urinary energy (P = 0.01) and gaseous energy (P = 0.01) losses were greater for steers fed DRC than those fed HMC. Although there was no difference (P = 0.67) in the total ME between the 2 treatments, when adjusted for DMI, the alteration in gaseous and urinary energy led to a 4% decrease (P < 0.01) in dietary ME of DRC (3.04 Mcal/kg of diet) compared with HMC (3.16 Mcal/kg of diet; data not shown).
Feedlot Study
In the feedlot study (Exp. 2), 2 steers with no implant fed DRC in separate pens died before completion of the study. Therefore, intake data are reported on an individual basis to account for the different number of steers within a given pen, although statistical analysis of intake data was analyzed with pen as the experimental unit. Steers fed HMC consumed less (P = 0.01) N (Table 3) and tended (P = 0.06) to have lower ADG than steers fed DRC. However, final live BW (P = 0.19), components of calculated growth curves and daily gain (P = 0.33; data not shown), G:F (P = 0.23), and HCW (P = 0.23) did not differ between the 2 treatment groups. There were few differences in carcass composition between the 2 diet groups; however, there was a tendency for the steers fed DRC to have a greater adjusted fat thickness (P = 0.07) and yield grade than those fed HMC (P = 0.09). Differences in blood urea nitrogen (BUN) reflected differences in N intake with the steers fed DRC having a greater (P < 0.01) BUN concentration than those fed HMC. There was an increase (P = 0.01) in BUN concentrations over time (data not shown) in both dietary groups with the steers fed DRC (6.62 to 8.70 mM) having greater BUN than those fed HMC (5.80 to 6.67 mM) throughout the feeding trial.
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). Initially, daily growth of the steers implanted with TBA was greater (P < 0.01) than the growth of nonimplanted steers but decreased below that of the nonimplanted steers after d 73, resulting in no overall difference. Final live BW of steers implanted with estradiol was greater (P = 0.02) than those with a TBA implant or no implant. Similarly, there was an increase (P = 0.02) in HCW of the steers implanted with estradiol compared with the steers implanted with TBA or those with no implant. Additionally, steers implanted with estradiol had lower (P = 0.05) BUN concentrations than those that received no implant.
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Manure Slurry Composition
Several differences between the 2 diets were noted in the manure composite samples collected during the feedlot trial (Table 4). The DRC composites had a greater (P < 0.01) initial starch content than the HMC composites. The pH was lower (P = 0.02) in the DRC composites than the HMC composites. No differences were detected in the nonsoluble CP, L-lactate, total alcohol, total branched-chain VFA, or total aromatic concentrations in the initial manure composites. However, total VFA concentrations were greater (P = 0.03) in the DRC composites than in the HMC composites.
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). Starch was rapidly depleted in both slurries during the first week of incubation. A slow continued loss of starch was observed in the DRC slurries during the following 4 wk, but starch content was essentially depleted after the first 7 d of incubation in the HMC slurries. The magnitude of starch loss (grams lost) differed between diets largely because initial starch content differed. Concurrent with starch loss, there was an increase in VFA (Figure 2), which increased to a greater extent in the DRC slurries than in the HMC slurries (Figure 2; P < 0.01). However, branched-chain VFA increased (P < 0.01) more in the HMC slurries than in the DRC slurries (Figure 3). There were limited changes in slurry nonsoluble CP (Figure 3) in the DRC slurries, but nonsoluble CP decreased (P < 0.01) during the incubation in the HMC slurries.
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) during the incubation. Fermentation intermediates, such as glucose and L-lactic acid, also rapidly increased in the DRC slurries by d 3 but then decreased to near negligible levels (time x treatment, P < 0.01; Figure 5) that were not different from initial concentrations. However, there was not a similar response in the HMC slurries, which was expected, due to the aforementioned lower starch content of those slurries. Differences between diets were also observed in pH, which decreased to a greater extent in the DRC slurries (time x treatment, P < 0.01; Figure 6). This was attributed to the increased production of lactate and VFA in the DRC slurries.
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DISCUSSION |
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TopAbstractINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONIMPLICATIONSLITERATURE CITED |
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). Many of the strategies described in the literature, particularly those designed to reduce manure malodor, involve the addition of masking, disinfecting, or oxidizing agents to manure (Miner and Stroh, 1976; Zhu et al., 1997; Varel and Miller, 2004). Unfortunately, the capacity of additives to reduce odor production is finite and may require reapplication of the compounds as they become inactivated or as odor producing microorganisms in the animal wastes adapt to the additives (Varel et al., 1999). The current study, however, focused on reducing the components in the manure that lead to the production of malodorous compounds. This approach to odor reduction not only reduces the labor costs that would be involved in application of additives to manure, but will effectively reduce the overall production of odor from manure.
Care must be taken when altering a production system to address socio-environmental issues to ensure that production and quality are not diminished. Although there have been conflicting reports in the literature on the effects of HMC upon feedlot cattle performance, Owens et al. (1997) noted no difference in feed efficiency and modest decreases in rate of gain and DMI when cattle were fed HMC in lieu of DRC. The present studies yielded similar results; however, the decreases in gain were not large enough to cause a significant reduction in final live BW or HCW, although final live BW and HCW were numerically lower (2%) in steers fed the HMC diet compared with those fed the DRC diet. Implantation strategy was used as a subplot in this model to address potential concerns that a HMC diet may alter the effectiveness of implants. Interactions between diet type and implantation strategy on overall performance were low, and differences were likely to be of little biological importance (i.e., yield grade of 1.94 vs. 2.00), and the main effects of implants (altered ADG and HCW) were as expected (Hunt et al., 1991; Lough et al., 1993; Guiroy et al., 2002). However, a thorough description of the changes in the growth pattern associated with these different implant strategies, as depicted by the quadratic regression and daily gain throughout the finishing period, have not been reported in several previous experiments (Hunt et al., 1991; Lough et al., 1993; Guiroy et al., 2002). These data may provide information for future mathematical modeling of duration and efficacy of these implant strategies. The reduction in BUN concentration in the steers implanted with estradiol compared with those without implants may have been a result of decreased catabolism of amino acids associated with the increased growth as has been previously reported (Cecava and Hancock, 1994).
There was a small difference in the ME between the 2 diets (on a kilogram of diet basis), resulting from differences in methane production and urinary energy, but the difference may also be partially explained by a numerical difference in DMI. Krause and Combs (2003) demonstrated a decrease in ruminal pH of dairy cows from 5.82 to 5.67 when HMC was fed in lieu of DRC. Although acetate:propionate in the rumen can influence methane production (Moe and Tyrrell, 1979), Van Kessel and Russell (1996) also indicated that lower pH decreases methanogenesis. Therefore, we speculate a decrease in ruminal pH, coupled with a possible alteration in acetate:propionate, reduced methane produced by steers fed HMC- instead of DRC-based diets. Additionally, dietary protein concentrations were formulated to be near the concentrations fed in industry, which is well in excess of NRC (2000) recommendations for MP. As such, protein in excess of requirements can be degraded to yield glucogenic and lipogenic precursors, with the remaining N converted to urea, much of which is excreted. Increase in blood concentrations of urea and urinary urea excretion in steers fed DRC compared with steers fed HMC also increased the urinary energy component, which contributed to the decreased ME of the DRC diet compared with the HMC diet.
Starch digestion by ruminants fed high grain diets and subsequent starch appearance in feces may be influenced by multiple factors. These factors have been extensively reviewed (Rooney and Pflugfelder, 1986; Huntington, 1997; Owens et al., 1997) and include grain species or varieties, grain processing, and dietary additives. The current study utilized course-ground, high-moisture, ensiled corn grain, which has a decreased total starch content (due to the ensiling process) and greater total starch tract digestibility (Rooney and Pflugfelder, 1986; Huntington, 1997) than DRC. Therefore, there is a potential to decrease fecal starch by substituting HMC for DRC due to greater starch digestion within the animal and less total starch entering the system. This was of particular concern because starch from DRC has a high total tract digestibility (92.2%; Huntington, 1997). Our data support previous findings and demonstrated an overall reduction in fecal starch of about 35% when HMC was fed instead of DRC. Other methods of diet manipulation may be available to elicit an even greater reduction in fecal starch. For example, if we assume that steers fed steam-flaked corn will consume 7.25% less DM (Zinn et al., 2002) than those fed DRC, and that starch from steam-flaked corn has a digestibility of 98.9% (Huntington, 1997), then approximately 77 g/d of fecal starch is expected. This is equivalent to an 83% reduction in fecal starch compared with steers fed a DRC diet. Although results may vary extensively, this approach also offers a plausible method to reduce fecal starch from feedlot cattle without reducing performance due to the improved use of steam-flaked corn relative to DRC (Zinn, 1987; Barajas and Zinn, 1998; Scott et al., 2003). The ability to use such methods will vary because of other factors, such as availability of HMC, steam-flaked corn, or other grain sources for feedlot systems.
Miller and Varel (2001; 2003) indicated that for beef cattle consuming typical feedlot finishing diets, VFA were the predominant malodorous compounds produced during manure fermentation, and fecal starch was the primary source of malodorous VFA accumulation in manure slurries. Those data support our observation that a feeding regimen that decreased fecal starch (HMC diet) reduced VFA and other volatile compounds in the fresh manure and reduced the production of VFA and other odorous fermentation products during manure incubation. Although there was no similar difference in DM digestibility as has been previously reported (Oba and Allen, 2003), it is unlikely that the remaining OM would contribute to volatile odorous compound production before the manure is incorporated into a fertilizer system. This assumption is based on the "plateauing" of odorous compound production observed in the slurry incubations. However, it should be noted that initial starch concentrations (d 0) in the slurry samples were lower than those reported in the feces of cattle in the balance study. This is likely due to addition of additional components such as soil, physical disruption of fecal material during the blending process, and possible starch digestion within the slurry before the initial sample was taken (approximately 2 h after processing). The simultaneous spike in the concentrations of glucose and lactate in the manure slurries from the steers fed DRC further corroborate the concept that fermented starch passed through its intermediary metabolites (monomeric glucose and lactic acid) before it was finally converted to VFA and alcohol. However, as the primary fermentable energy source (starch) was decreased in the feces, there was an apparent increase in the amount of branched-chain VFA production. Branched-chain VFA are a product of branched-chain AA fermentation (Mackie et al., 1998). The increase in branched-chain VFA in the HMC slurries likely was the result of microbial use of alternative energy sources by bacteria when less starch was available. Decreases in nonsoluble CP during the incubation are consistent with these observations. This is of particular importance because branched-chain VFA have a very low odor threshold (Zahn et al., 2001). However, the incubated slurries from steers fed the HMC had a greater pH than DRC. Greater pH is expected to increase the content of ionized VFA (nonprotonated conjugate base), which have lower volatility (Derikx et al., 1994). This is expected to reduce the amount of malodorous compounds volatilized, which could further reduce the inherent malodor of manure. Sensory panel assessment to assess if reducing starch excretion decreases the human perception of odor in cattle manure is warranted.
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Footnotes |
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2 These data were reported in part in the Proceedings of the Symposium on the State of the Science of Animal Manure and Waste Management, January 5–7, 2005, San Antonio, TX.
3 The authors acknowledge the secretarial assistance of Jackie Byrkit and the technical assistance of Cindy Felber, Chris Haussler, and Ty Post.
4 Corresponding author: ferrell{at}email.marc.usda.gov
Received for publication August 19, 2005. Accepted for publication January 30, 2006.
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