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USDA, ARS, US Meat Animal Research Center, Clay Center, NE 68933-0166
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Abstract |
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 Top Abstract INTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONLITERATURE CITED |
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Key Words: beef steer • odor • protein oscillation
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INTRODUCTION |
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TopAbstractINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONLITERATURE CITED |
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).
One proposed means of improving N retention is by oscillation of the dietary CP concentrations. Cole (1999) noted an increase in N retention in lambs by oscillation of the CP concentration of the diet over 48-h intervals. However, Ludden et al. (2002) did not notice an improvement in N retention with oscillation of CP concentrations when feeding relatively high dietary CP concentrations (13 to 17%). Because the diets of Ludden et al. (2002) were all likely in excess of the needs of those lambs, this may have masked any effect of oscillation of the diets on N metabolism due to the increased amounts of N that needed to be excreted. Ludden et al. (2002) also noted that there was a decrease in overall N digestibility when lambs were fed oscillating CP diets, which caused a shift of N excretion from urinary N to fecal N. Although there are reports of limited effects on overall feedlot productivity and quality when finishing steers were fed oscillating CP diets instead of diets with static concentrations of CP (Cole et al., 2003; Ludden et al., 2003), there has been little investigation into other areas of socio-environmental concern, such as odor production.
The objective of this study was to determine the effect of oscillation of the dietary CP on the overall feedlot performance and production of odorous compounds in manure. A companion paper (Archibeque et al., 2007) addresses the effects of oscillation of the dietary CP on nutrient retention and ammonia emissions.
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MATERIALS AND METHODS |
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TopAbstractINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONLITERATURE CITED |
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Steers were fed once daily to allow ad libitum access to feed throughout the experiment. Feed (100 g) was collected each day and composited on a weekly basis for chemical analysis. Orts were collected weekly, weighed, and subsampled for chemical analysis. All diets were formulated to meet or exceed NRC (2000) recommendations for growing beef steers (Table 1), with the exception of CP, which was adjusted among treatment diets by the inclusion of soybean meal. Steers were adjusted to the finishing ration by combining the medium diet with the initial growing ration (66% corn silage, 29.5% dry-rolled corn, and 4.5% supplement; 11.6% CP, DM basis) by substituting 25% of the diet at a time in a weekly step-up fashion. When steers were adjusted to the finishing ration, the pens were then assigned to the low (9.1% CP), medium (11.8% CP), high (14.9% CP), or oscillating CP diets (6 pens/treatment), with treatments blocked by location within the barn. Alternating feeding of low and high at 48-h intervals (fed low for 2 d, followed by 2 d of high) generated the oscillating diet.
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) using a Technicon Autoanalyzer (Method #339-01, Technicon Autoanalyzer System, Tarrytown, NY). This blood collection scheme allowed for representation of either the first day of receiving a low and high diet, or the second day of receiving a low and high diet in the 4-d oscillating dietary period. Linear and quadratic regressions of weight on days on feed for each individual steer were derived based on the measured BW to provide the weights used for the calculations of ADG and G:F (based on the sum of animals within a pen).
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, quality grade, adjusted fat thickness, % KPH fat, and LM area, were assessed and collected by an independent trained consultant. Yield grades were calculated for individual carcasses (USDA, 1997).
Collection and Analysis of Microbial Shedding
Escherichia coli and coliform levels in the feces were enumerated as a means of determining any potential effects of the oscillation of the dietary protein on enteric bacterial populations. Rectal feces samples were collected on d 147 and 149 from 1 randomly chosen steer from each pen, with a different steer selected on each day. Each fecal sample (5 g) was measured into a sterile sample bag (Spiral Biotech, Norwood, MA), 45 mL of 2% buffered peptone water was added, and the bag contents were mixed using a Stomacher Circulator (200 rpm, 1 min; Model 400, Seward Limited, London, UK). These initial dilutions were serially diluted further in buffered peptone water as needed, and 1-mL volumes were plated in duplicate onto Petrifilm E. coli/coliform count plates (3M Microbiology Products, St. Paul, MN). After incubation at 37°C for 24 h, characteristic E. coli and coliform colonies were enumerated (Berry et al., 2006).
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, sieved through a screen (4 mm), and dried for 2 d at 37°C. Fecal composite samples were collected from each of the 24 pens. At least 5 fresh (noncrusted) fecal pats from each pen were used to form the fecal composite for a particular pen.
Manure slurry incubations 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 urine-to-feces ratio determined in the supporting balance study (Archibeque et al., 2007). Before preparing the manure slurry, frozen, acid-preserved urine collected during a balance study with the same treatments (Archibeque et al., 2007) was thawed and neutralized with 10 M NaOH. Manure slurries were incubated at room temperature (approximately 23°C) in stoppered 0.5-L flasks containing N2 in the headspace.
Three manure slurry samples were collected on d 0 (initial), 3, 7, 14, 21, 28, and 35, and for each individual day; the first sample 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). The second sample was analyzed for pH, water-soluble fermentation products, and intermediates (alcohols, VFA, aromatic ring-containing compounds, L-lactate, and free glucose), starch, and 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, ca-prylate, 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 the 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 a 2-µL volume 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 remaining after drying the third sample overnight at 105°C was determined by autoclaving in H2O to extract the 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 (SAS Inst. Inc., Cary, NC) was used for statistical analysis of data. For data related to feedlot and carcass characteristics and microbial shedding, the model included treatment, with pen as the experimental unit. The data related to manure slurries and PUN were treated as a repeated measures model that included treatment, day, and treatment x day using the AR(1) error structure and pen as the experimental unit. Additional analyses with steer as the experimental unit were conducted for data collected from individual animals to optimize our potential for detecting impairment in production with the oscillating treatment. This model included the dam’s sire line, dam’s dam line, weaning age, days on feed, and treatment, with steer as the experimental unit. When treatment effects were significant (P < 0.05), a difference was determined and least squares means were separated using a protected Student’s t-test. A tendency for treatment to elicit a response was noted at P < 0.10.
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RESULTS |
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TopAbstractINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONLITERATURE CITED |
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). As designed, the steers fed the low diet consumed the least (P < 0.01) amount of N, the steers fed medium and oscillating consumed similar intermediate amounts, and the steers fed high had the largest intake of dietary N. After 121 d and throughout d 149, PUN (Figure 1) reflected N intake with the steers fed low having the lowest concentration, medium and oscillating having intermediate concentrations, and those fed high having the greatest concentrations. However, within treatments, there was a marked decrease in PUN concentrations for the low, medium, and high fed steers and an increase in PUN concentrations for the steers fed oscillating between d 182 and 184. With the exception of d 182 and 184, there were no differences in PUN concentration of the steers fed oscillating within a 2-d cycle (d 121 vs. 123 or d 147 vs. 149).
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0.03) for steers fed low, but relatively unchanged when steers were fed medium, high, or oscillating. There was no difference in G:F among steers fed medium, high, or oscillating, but G:F was reduced (P = 0.01) in steers fed low. Carcass characteristics were very similar for steers fed medium, high, and oscillating, but steers fed low had lower amounts of carcass fat content than those fed the other 3 diets, as evidenced by a tendency (P < 0.10) for lower marbling scores and KPH fat percentage in steers fed low. Additionally, adjusted fat thickness was smaller (P < 0.001) in steers fed low, which was accompanied by a similar decrease (P < 0.04) in yield grade compared with steers fed the other 3 treatment diets. When the data was analyzed with steer as the experimental unit, very similar results were realized, with no detectable differences (P > 0.10) in performance characteristics between steers fed the medium or oscillating diet.
Manure Characteristics
There were no differences (P > 0.17) in the enumeration of microbial populations that may be indicators of populations that are of concern from a food safety standpoint. The populations of generic E. coli ranged from 5.94 to 6.33 log cfu/g of feces, and the total coliform counts ranged from 6.06 to 6.54 log cfu/g of feces.
Several differences were noted in the chemical characteristics of manure slurries from steers fed the various treatment diets that were incubated for 35 d (Table 3). Most of the chemical characteristics exhibited a treatment x day interaction (Figures 2 and 3). There was a decrease (P < 0.01) in the nonsoluble CP in the slurries from steers fed low by d 20 of incubations, yet the concentrations were relatively similar among the other 3 treatments. Unlike nonsoluble CP, there were much more dramatic differences in the ammonia plus ammonium (NHx) concentrations of the slurries. Throughout the incubations, there was no difference in the NHx concentrations of the slurries from the steers fed low or medium, but there were greater (P < 0.01) concentrations of NHx in both the slurries of the steers fed high or oscillating. Although initially the NHx concentrations were lower in slurries from steers fed oscillating than those fed high, by d 28 of incubation, the NHx concentrations were similar between the slurries from steers fed high or oscillating. There was a numerical increase in the branched-chain VFA concentrations that reflected the CP concentration for low, medium, and high, but the branched-chain VFA concentrations of the slurries from steers fed oscillating continued to increase throughout the incubation until they were greater (P < 0.01) than any of the other treatment groups. The slurries from steers fed oscillating had the greatest total VFA concentrations throughout the incubation and appeared to continue to accumulate (P < 0.01) by d 35, whereas there appeared to be a plateau in VFA concentrations in the slurries from steers fed low or high. However, the total VFA concentrations in slurries from steers fed medium also increased up to d 35, but not to the extent seen in steers fed oscillating. Total aromatic concentrations were much greater (P < 0.01) throughout the incubations in slurries from steers fed high (124 to 269% of the concentrations in the other slurries). The slurries from steers fed oscillating had a greater concentration of aromatics than the slurries from steers fed low or medium, although to a much lesser extent (120 to 174% of the concentrations in the low and medium slurries). There was a decrease in pH over time in all slurries, yet the pH was lowest in the slurries from steers fed low and greatest in steers fed oscillating (P < 0.01).
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DISCUSSION |
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TopAbstractINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONLITERATURE CITED |
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; Cole, 1999; Archibeque et al., 2007). This improvement in the efficiency of N utilization may serve to provide a viable means to mitigate the release of N into the environment. However, care must be taken when altering a production system to address specific environmental issues to ensure that production, quality, and other socio-environmental aspects are not also altered in an undesirable fashion.
The effects of oscillation of the dietary CP on feedlot performance in our study were similar to those of Collins and Pritchard (1992), Cole et al. (2003), and Ludden et al. (2003) who also did not observe a significant difference in DMI or ADG compared with steers fed similar amounts of total N on a continuous basis. However, there are several factors that may affect the efficacy of oscillation of the dietary CP to improve N utilization. Although there has been a much greater consistency in the results from ruminants fed high concentrate diets (Cole, 1999; Cole et al., 2003; Ludden et al., 2003), oscillation of the dietary CP has had much more variable results in ruminants fed high roughage diets (Collins and Pritchard, 1992; Simpson et al., 2001; Ludden et al., 2002). Although this variability in results may be caused by several factors, such as timing of CP oscillations and excesses or deficiencies in CP relative to the animal’s requirements, it is likely due to factors affecting N recycling to the gut. Cole (1999) hypothesized that the improvement in N retention by oscillation of the dietary CP is due to a greater proportion of recycled urea moving into the rumen rather than the large intestine. Nitrogen recycling to the rumen is affected by carbohydrate fermentation in the gastrointestinal tract (Huntington, 1989). Greater transfer of endogenous urea to the rumen, as opposed to the hindgut, when ruminants are fed a high concentrate diet may be due to greater numbers and activity of ureolytic bacteria adhering to the ruminal epithelium and to lower ammonia concentrations in the rumen (Cheng and Wallace, 1979; Egan, 1980; Kennedy et al., 1981; Javorsky et al., 1987). In ruminants fed forage-based diets, there is less potential N recycling to the rumen, where it could be utilized by the animal if it is captured by ruminal microbes and made available for absorption as AA. Additionally, the synchronization of fermentable energy and N, which is critical for use of ammonia (Petit and Veira, 1994; Kolver et al., 1998; Olson et al., 1999), could be deficient in the forage-fed ruminant. The lack of change in PUN within a 4-d oscillation cycle (2 d of low and 2 d of high) could be due to the limited rate of turnover of the PUN pool or to an overall buffering capacity of the gastrointestinal tract. We are uncertain why there were such wide variations in the PUN data on d 182 and 184.
Cole et al. (2003) noted a tendency for carcasses of steers fed oscillating CP diets to have a lower percentage of carcasses grading Low Choice or better than the carcasses of steers fed a comparable amount of CP on a continual basis. We did not see a similar trend in our study; in fact, steers fed oscillating had numerically greater quality grades than those fed medium, suggesting that the negative impact on carcass quality noted by Cole et al. (2003) may have been related to other factors.
Another aspect of carcass quality is E. coli O157:H7 contamination. Although we did not test directly for this strain, we observed very little difference in the indicator organisms that we did enumerate, suggesting very limited effects on potential pathogen populations.
An unexpected result from our study was the increased production of odorous compounds in the manure slurries of steers fed oscillating. This is likely a result of increased N recycling to the gastrointestinal tract as discussed above. We speculate that as N recycling to the gastrointestinal tract increased, there was a concomitant increase in microbial activity and growth (Wolin et al., 1959; Bond and Russell, 1996). As microbial activity and growth proceeded at a greater rate, there was an increased utilization of starch to support this process. This observation was supported by the overall similarities in starch reduction in the manure slurries from steers fed high and those fed oscillating. Much as one would expect with increased starch fermentation, there was also a modest increase in the production of VFA in the slurries from the cattle fed oscillating. However, as the starch source was depleted, the microbes would be forced to utilize a different energy source (i.e., protein). As more protein was fermented to provide for the energy needs of the microbes, there was a simultaneous increase in the production of the products associated with protein fermentation, NHx and branched-chain VFA (Mackie et al., 1998). Although a significant amount of the NHx in the manure may be from urea hydrolysis, urinary N was very similar between the medium and oscillating groups (Archibeque et al., 2007), lessening the chance that this was a primary source of the difference between the 2 diets. Additionally, this increase in protein fermentation byproducts is of particular importance because branched-chain VFA have a very low odor threshold (Zahn et al., 2001a) and NHx has a high potential for movement throughout ecosystems (Hutchinson et al., 1982).
Malodor has always been associated with animal production, but as the concentration of animals within production facilities increases and as urban sprawl and development into previously agrarian areas brings humans into a continually closer proximity with animal production, animal malodor is receiving increased attention. However, there is a great deal of difficulty associated with relating the concentrations of odorous compounds in waste materials from animal production facilities with the human perception of odor. Although it is generally accepted that the concentrations of airborne VFA and volatile aromatic compounds are correlated with odor (Zahn et al., 1997, 2001a; Zhu et al., 1997), currently there is very little consensus in the odor detection threshold of humans for various compounds, which have been reported to vary by as much as 400-fold for some compounds (Sutton et al., 1999; Zahn et al., 2001a; Le et al., 2005), nor in the multitude of interactions of these compounds in varying concentrations with the human perception of odor. Additionally, a substantial proportion of the literature is focused on the production of odor from nonruminants (Le et al., 2005). The type of malodor from ruminants and nonruminants is different (O’Neill and Phillips, 1992), and diet may have very different impacts upon the production of malodor from various species. These differences in malodor production arise from inherent differences in management, the types and amounts of digestion of various feedstuffs, the overall nutrient utilization, and microflora present in the feces of these different species (Mackie et al., 1998). These differences in malodor production from various species make extrapolation from assessments of swine or poultry odor to cattle manure problematic. Additionally, numerous factors, including pH, moisture, surface area, temperature, and wind currents may also contribute to the rate of compound dissipation from animal facilities (Zahn et al., 2001b). As such, a great deal more research in this area, particularly in regards to odorous compound production from cattle manures and their subsequent relation to the human perception of odor are warranted before speculation about the possible impact of concentration changes in manure and the overall impact upon odor perception.
Although previous research has indicated that oscillation of the dietary protein may be an effective means of improving N retention and reducing N excretion from feedlot cattle, our data suggest that there may be several undesirable side effects, such as increased production of odorous compounds in manure. In addition, there appeared to be a shift in the form of manure N to a more mobile and potentially volatile form, NHx, when steers were fed diets with oscillation of the dietary CP. Although total N excretions (not directly measured in this study) may be reduced by feeding oscillation of the dietary CP, the N that is excreted may be in a more labile and deleterious form. These effects will need to be taken into account and addressed to warrant the implementation of oscillation of the dietary protein concentrations to reduce N excretion into the environment.
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Footnotes |
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2 The author acknowledges the secretarial assistance of J. Byrkit and the technical assistance of C. Felber, C. Haussler, and T. Post.
3 Present address: Dept. Anim. Sci., Colorado State Univ., Ft. Collins, CO 80523-1171.
4 Corresponding author: cal.ferrell{at}ars.usda.gov
Received for publication April 4, 2006. Accepted for publication January 26, 2007.
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LITERATURE CITED |
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TopAbstractINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONLITERATURE CITED |
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  C. K. Reynolds and N. B. Kristensen Nitrogen recycling through the gut and the nitrogen economy of ruminants: An asynchronous symbiosis J Anim Sci, April 1, 2008; 86(14_suppl): E293 - E305. [Abstract] [Full Text] [PDF]
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N. A. Cole and R. W. Todd Opportunities to enhance performance and efficiency through nutrient synchrony in concentrate-fed ruminants J Anim Sci, April 1, 2008; 86(14_suppl): E318 - E333. [Abstract] [Full Text] [PDF]
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S. L. Archibeque, H. C. Freetly, N. A. Cole, and C. L. Ferrell The influence of oscillating dietary protein concentrations on finishing cattle. II. Nutrient retention and ammonia emissions J Anim Sci, June 1, 2007; 85(6): 1496 - 1503. [Abstract] [Full Text] [PDF]
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