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ANIMAL PRODUCTION |
* ARS, USDA, Conservation and Production Research Laboratory, Bushland, TX 79012;
and
Department of Animal Science and Food Technology, Texas Tech University, Lubbock 79409; and
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Texas Agricultural Experiment Station, Amarillo 79106
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Abstract |
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 Top Abstract IntroductionMaterials and MethodsResults and DiscussionLiterature Cited |
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Key Words: Air Quality • Ammonia • Beef Cattle • Diet • Emissions • Feedyards • Protein
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Introduction |
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TopAbstractIntroductionMaterials and MethodsResults and DiscussionLiterature Cited |
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). However, factors such as urine pH and soil moisture (Luebes et al., 1974), or chemical composition of excreted urine (Whitehead et al., 1989) can also affect NH3-N emissions.
Typical feed yard finishing diets for beef cattle contain approximately 13 to 13.5% CP and are routinely supplemented with 0.5 to 1.0% urea to provide adequate ruminally degradable intake protein (DIP; Galyean and Gleghorn, 2001). Altering the concentration and ruminal degradability of N in the diet can potentially affect the quantity and form of N excreted by cattle. In general, as N intake increases, excretion of urinary urea N increases (Gueye et al., 2003b; McBride et al., 2003), and as the dietary ratio of DIP:ruminally undegradeable intake protein increases, urinary N excretion increases (Cecava and Hancock, 1994; Gueye et al., 2003b; McBride et al., 2003).
Few studies have examined mechanisms that control ammonia emissions from beef cattle feedlots. A greater understanding of the factors controlling NH3-N emissions from feedlots would aid in the development of prediction models and in the development of methods to control these emissions. To that end, this study was conducted to determine the effects of dietary CP concentration and degradability on potential NH3-N losses from feces and urine of beef cattle fed high-concentrate finishing diets.
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Materials and Methods |
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TopAbstractIntroductionMaterials and MethodsResults and DiscussionLiterature Cited |
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). Fifty-four crossbred steers (average initial BW = 315 kg) were used in the study. One-half of the steers were located at the USDA-ARS/Texas Agric. Exp. Stn. experimental feedlot at Bushland, TX, and the other half was located at the Texas Tech University Research Center in New Deal. All procedures were the same at both locations. Steers were randomly assigned to one of nine dietary treatments in a 3 x 3 factorial arrangement. Main treatment effects were three formulated dietary CP concentrations (11.5, 13, and 14.5% on a DM basis) and three supplemental urea:cottonseed meal ratios (100:0, 50:50, and 0:100 of supplemental N; Table 1). With the exception of the protein fraction, all diets were formulated to meet the nutrient requirements for finishing beef steers gaining in excess of 1.6 kg/d (NRC, 2000). All diets contained 90% concentrate and 10% alfalfa (DM basis) and corn was steam-flaked. Between urine and fecal collection periods, steers at the USDA/Texas Agric. Exp. Stn. facility were housed in open-lot pens (nine steers per pen) and were individually fed their experimental diets once daily at 0800 in Calan headgates (American Calan, Northwood, NH), whereas steers at Texas Tech University were housed and fed individually in 1.5 m x 2.4 m, soil-surfaced pens. All steers were trained to lead with a halter and adapted to individual tiestalls (1.2 m x 2.5 m) and urine collection harnesses before the study began.
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; McBride et al., 2003).
In Vitro Ammonia Emissions
The in vitro NH3-N emission system has been described (Shi et al., 2001). Briefly, the system was comprised of 48 sealed polyethylene chambers (20 cm x 20 cm x 12 cm deep), each attached to two NH3-N trapping bottles containing 100 mL of 0.9 M sulfuric acid and a vacuum system to pull air through the chambers and NH3-N traps at a rate of approximately 3 L/min. To each chamber was added 1,550 g (as-is basis) of screened soil (Pullman clay loam) followed by the feces and urine excretion of one steer (two chambers per steer). On average, the soil initially added to the chambers had a pH of 7.68, was 91.7% DM (SEM = 0.36), and contained 0.10% N (SEM = 0.0011), 1.69% C (SEM = 0.005), 24 ppm ammonia + ammonium-N (NHx-N; SEM = 0.06), and 53 ppm nitrates + nitrites (NOx-N; SEM = 2.2) on a DM basis. The quantity of urine and feces added to each chamber was equal to 1% of the daily excretion by the steer during the nutrient balance trial. Because a total of nine in vitro NH3-N runs were required, four chambers containing common feces and urine were included in each run to correct for run-to-run variation in NH3-N emissions caused by differences in temperature, atmospheric NH3-N, air flow rate, or other factors. Two "blank" chambers containing soil but no feces or urine were included in each run to correct for atmospheric NH3-N contamination.
Acid traps were replaced with fresh traps each day for 3 d, and then at 2-d intervals until d 7 of collection. At the conclusion of the run, the media in each chamber was thoroughly mixed and a sample was obtained and stored frozen for later laboratory analyses. Chambers were weighed at the start and end of the incubations and DM and total N loss were determined by difference.
Laboratory Analyses
Feces, soil, and media (soil + feces + urine mixture) samples were analyzed for DM by drying to a constant weight at 60°C in a forced-draft oven. The pH of feces, soil, and media were determined by mixing 5 g of soil or feces with 5 mL of deionized water. The mixture was stirred, allowed to stand for 1 min, and the pH determined using a combination electrode. The C and N contents of soil, feces, urine, and ending media were determined using a Carbon-Nitrogen Analyzer (Vario Max CN, Elementar Americas, Inc., Mt. Laural, NJ.). The N content of acid traps was determined colorimetrically using a flow injection analyzer (Lachet Instruments Quick Chem FIA+8000, Milwaukee, WI; Method 10-107-06-2-E, 2001: USEPA [1983] Method 351.2). Initial soil and fecal samples, and ending media samples were extracted with 2 M KCl (20 mL/2 g of air-dry sample) and filtered (Whatman No. 42 filter paper). The NHx-N content of the filtrate was determined by the phenate method (Lachat Method 12-107-06-1-A, 2001; USEPA [1983] Method 365.34), and the NOx-N content was determined by Cd reduction (Lachat Method 12-107-04-1-B, 2001; USEPA [1983] Method 353.2) using the flow injection analyzer. Urinary and serum urea-N concentrations were determined colorimetrically using a commercial kit (Sigma Diagnostics, St. Louis, MO; Procedure 640).
Statistical Analyses
Data were analyzed as a split-plot design with treatments in a 3 x 3 factorial arrangement using the GLM procedure of SAS (SAS Inst., Inc., Cary, NC). Factors included in the initial model were location (Bushland or Texas Tech), in vitro ammonia run (1 to 9), fecal collection period (d 30, 75, or 120 on feed), diet combinations, and all two-, three- and four-way interactions. Days on feed, and dietary CP and urea concentration effects were tested using steer nested within diet as the error term. Least squares means, calculated using NH3-N run as a covariant, were compared using PDIFF if a significant (P < 0.05) F-test was obtained. Regressions of N applications vs. ammonia emitted were determined using the stepwise procedure of PROC REG of SAS.
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Results and Discussion |
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TopAbstractIntroductionMaterials and MethodsResults and DiscussionLiterature Cited |
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Effects of Dietary Protein
Total daily N intake and DIP-N intake increased (P < 0.05) as dietary CP concentration increased (Table 2). Nitrogen intake was greater (P < 0.05) for steers fed the 50:50 urea:cottonseed meal supplement than for steers fed no urea; steers fed the 100% urea supplement were intermediate. Degradable N intakes increased (P < 0.05) with increasing dietary urea. Serum urea-N concentrations of steers increased with increasing dietary CP concentration. These results agree with previous studies (Johnson and Preston, 1995; Cole et al., 2003). As dietary CP concentration increased from 11.5 to 13%, the quantity of urinary N excreted increased (data not shown); thus, the quantity of urinary N added to the chambers increased (P < 0.05). The lower urinary N addition from steers fed the 14.5% CP diet than the 13% CP diet was due in part to lower DMI of steers fed the 14.5% CP diet (6.48 vs. 6.90 kg/d), which resulted in similar N intakes and an apparent shift in N excretion to the feces. Thus, total N application, as well as urinary urea N applications, to the chambers were similar for the 13 and 14.5% diets and were greater (P < 0.05) than for the 11.5% CP diet. Fecal N excretions, and thus additions, were greater for the 0% urea diet than for the 50 or 100% diets, whereas urinary N and urinary urea N excretion and additions increased with increasing dietary urea concentration (P < 0.05).
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). Fecal N concentration and urinary N, C, and urea-N concentration increased (P < 0.05) as dietary CP concentration increased. Urea-N comprised from 67 to 91% of total urinary N. These values agree with Petersen et al. (1998), who noted that 64 to 94% of urinary N was urea. Similarly, Smits et al. (1995) noted a 42% increase in urinary urea concentration when the CP concentration of lactating dairy cow diets increased from 14.4 to 19.8%. The pH of feces from steers fed the 11.5% CP diet was lower (P < 0.05) than for steers fed the 13 and 14.5% diets. This could have been due to differences in the quantity of starch entering the lower gut for fermentation and/or to differences in dietary calcium carbonate concentrations. Fecal C and NHx-N and urinary pH were not affected by dietary CP concentration. In contrast to our results, Tomlinson et al. (1996) noted that fecal NHx-N concentration increased as dietary CP concentration increased in dairy cows. However, in agreement with our results, Tomlinson et al. (1996) noted an increase in fecal N, urinary total N, and urinary urea-N concentration as dietary CP concentration increased.
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, who noted that fecal NHx-N concentration decreased as ruminal degradability of the dietary CP increased.
The quantity of NH3-N lost over the 7-d in vitro incubation period, in vitro NH3-N losses as a percentage of urinary N applied, and total in vitro N losses (determined by difference) were greater (P < 0.05) from steers fed the 13 and 14.5% CP diets than from steers fed the 11.5% CP diet (Table 4).However, total in vitro N lost as a percentage of urinary N applied was greater (P < 0.05) for the 11.5% CP diet than the 13 and 14.5% CP diets. This tends to contrast with results of Paul et al. (1998) using dairy cattle slurry. They noted a 40% decrease in 48-h in vitro NH3-N losses when dietary CP was decreased from 16.4 to 12.3% in one trial, and a 20% decrease in NH3-N loss when dietary CP was decreased from 18.3 to 15.3% in a second trial. In their study, the lower in vitro NH3-N production was caused by both a decrease in the amount of N excreted as well as a decrease in the proportion of excreted N that volatilized. The somewhat lower in vitro NH3-N emissions from urine + feces of steers fed the 14.5% CP diet than from steers fed the 13% CP diet was unexpected because a greater proportion of urinary N was from urea on the 14.5% diet. However, portions of the nonurea N in urine could have been NHx-N, which could volatilize rapidly. The pH of feces, urine, and soil did not differ (Table 3
) and thus should not have affected NH3-N volatilization. Whitehead et al. (1989) reported that hippuric acid content could significantly affect NH3-N volatilization losses from artificial urines. Adding hippuric acid to a urea solution similar to urine increased NH3-N losses by 5 to 10 times. Thus, unmeasured factors such as hippuric acid content might explain the lack of large differences in ammonia losses between the 13 and 14.5% diets.
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noted that considerable quantities of N volatilized from swine waste lagoons as dinitrogen gas rather than as NH3-N. Using soil columns treated with urine, Stewart (1970) reported that 2 to 40% of urinary N was lost as NOx-N in the soil. Koops et al. (1997) noted that approximately 2.2% of urinary N excreted onto pastures was lost as nitrous oxide through nitrification and denitrification. Cumulative 7-d in vitro NH3-N losses increased (P < 0.05) with increasing dietary urea concentration. In vitro C losses were less (P < 0.05) from the 50% urea than from the 100% urea supplement diets; however, the reason for this difference is not apparent. No other factors were affected by dietary urea concentration.
A relatively small percentage of the urinary N added to the chambers was actually lost as NH3-N (3.90 ± 0.11%). This finding tends to contrast with the results of Stewart (1970), who noted that 25 to 90% of urinary N additions to soil columns were lost as NH3-N. Similarly, a number of studies of urine additions to pastures and slurry additions to cropland suggest urinary N losses as NH3-N in the range of 4 to 50% of N applied (Ryden et al., 1987; Jarvis et al., 1989, Lockyer and Whitehead, 1990). Kellems et al. (1979) noted that more than 95% of urinary N was volatilized as NH3-N from cattle manure slurries. However, Kellems et al. (1979) did not use any soil in their incubation flasks; therefore, the medium used was probably not representative of a typical feedlot surface. Using micrometeorology methods, Hutchinson et al. (1982) reported that hourly NH3-N losses from a Colorado feed yard ranged from 0.64 to 2.37 kg of N/ha. This amounted to approximately 50% of urinary N excretion or 25% of total N excretion (approximately 20% of N fed). Using a total N balance method, Erickson and Klopfenstein (2001a,b) reported that total N volatilization losses from a Nebraska experimental feedlot were 40 to 50% of N intake during the winter and 60% of N intake during the summer. The large differences in values between Hutchinson et al. (1982) and Erickson and Klopfenstein (2001a,b) could be accounted for by losses of dinitrogen gas (Kumar and Aggarwal, 1998; Harper et al., 2000).
These large variations in apparent gaseous NH3-N losses are probably due to a number of factors including the methodology used, turnover rate of air in chambers, atmospheric environment, and soil characteristics. Several studies have demonstrated that NH3-N emissions measured using chambers or wind tunnels increase linearly as air turnover rate increases up to a maximum of 15 turnovers/min (Kissel et al., 1977; Whitehead and Raistrick, 1991). In our study, the flow rate used was approximately 1.2 turnovers per min. Thus, although relative comparisons of NH3-N losses from different treatments should be valid, the actual quantities emitted will be lower than would be noted under normal feedlot conditions.
Ammonia + ammonium-N concentrations in ending media were greater in the 13 and 14.5% CP diets than in the 11.5% CP diet (Table 5). On average, the ratio of NHx-N in the media to gaseous NH3-N losses was greater (P < 0.05) for the 11.5% CP diet than the 13 and 14.5% CP diets. Ammonia + ammonium-N concentrations and the total quantity of NHx-N also increased with increasing dietary urea (P < 0.05). The pH of the ending media was high enough so that it should not have prevented conversion of soil NH4-N to the more volatile NH3-N. Thus, the accumulation of NHx-N in the soil may have been due to other factors including high soil cation exchange capacity or low soil moisture (Fenn and Kissel, 1976). Concentrations of NOx-N in the ending media were not affected by diet and were similar to initial soil concentrations (53 ppm); thus, little if any of the added N accumulated as NOx-Nin the soil. In the present study, the cumulative quantity of NHx-N was 77.4 ± 1.23% of urinary-N applied and 99.7 ± 1.43% of urinary urea-N applied, whereas NOx- N represented less than 4% of applied N. In contrast, using soil columns and periodic additions of urine, Stewart (1970) reported that up to 40% of urinary N applied accumulated as NOx-N in the soil column. Thompson and Fillery (1998) noted that up to 65% of urea-N applied to grass pastures was accounted for in soil NOx-N and 0.2 to 49% was as soil NHx-N. In the studies of Stewart (1970) and Thompson and Fillery (1998), no feces or other source of ureolytic bacteria was added to the soil. With added feces, there may be a more rapid hydrolysis of urea to NH4-N as well as a more rapid uptake of NHx-N by fecal bacteria. Thus, less NOx-N might accumulate. In addition, the difference in soil depth (30 vs. 2.5 cm; Fenn and Kissel, 1976) and moisture content (Catchpoole et al., 1983; Pandrangi et al., 2003) of the Stewart (1970) soil and our soil may have also been factors. However, the ending media moisture concentration in this trial was similar to that in samples from actual feedyard surfaces (Mason, 2004).
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. As days on feed increased, serum urea-N increased (P < 0.05); however, total N intake and DIP-N intake were not affected. The quantity of feces N added to the chambers was greater on d 75 than on d 120, with d 30 being intermediate. Nonetheless, the quantity of urinary N, urinary urea-N, and total N added to the chambers and proportion of added N that was urea-N increased with days on feed (P < 0.05). The relatively high (12.4 mg/100 mL) serum urea N concentrations of steers during the sampling period at 120 d on feed suggest that CP was being fed in excess of requirements (Johnson and Preston, 1995; Cole et al., 2003).
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). Urinary N, C, and urea-N concentrations increased (P < 0.05) with days on feed. Cumulative in vitro NH3-N losses, total N losses, and C losses increased as days on feed increased (Table 8; P < 0.05). This was apparently due to both greater urinary N applications as well as a greater proportion of urinary N being lost as NH3-N (P < 0.01) as days on feed increased. As noted earlier, this is potentially due to differences in other metabolites such as hippuric acid in the urine. As steers approach their market or mature weight, protein deposition decreases (NRC, 2000). Thus, if CP intake remains the same as animals increase in BW, as it did in this study, the proportion and quantity of dietary N excreted in the urine and the proportion of urinary N that is urea-N increase. This potentially leads to increased NH3-N emissions. Ammonia-N losses accounted for less (P < 0.05) of the total N loss on d 30 than on d 75 and 120. Total in vitro DM and C losses also increased (P < 0.05) with days on feed. The exact reason for these differences is not apparent, but it could relate to both the quantity of urea hydrolyzed and to the quantity and form of carbohydrates that were present in the feces added to the chambers.
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). However, the soil NHx- N:gaseous NH3-N ratio decreased with days on feed (P < 0.05). This may have been due in part to the differences in pH. As the pH increases, a greater proportion of the NH4-N formed from hydrolysis of urinary urea could escape as NH3-N. Media NHx-N, as a percentage of total media N, increased (P < 0.05) with increasing days on feed. Nitrate concentrations in the ending media were not affected by days on feed.
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. There was no apparent correlation between fecal N applied and in vitro NH3-N losses (r2 < 0.01). Petersen et al. (1998) also noted minimal NH3-N losses from dung pats on pastures, whereas 3 to 52% of urinary N was lost as NH3-N. With feces and urine from dairy cows, Paul et al. (1998) reported that the primary source of NH3-N emission was the urine fraction. Ammonia-N losses in their study were 0.33 mg of NH3-N/kg of wet feces and 4.99 mg of NH3-N/kg of urine. Obviously, the quantity of urinary N excreted had a major effect on in vitro gaseous NH3-N emissions in the present study; however, other factors also had a major effect, accounting for at least 31% of the variation in NH3-N losses. Regressions determined for the individual sampling periods indicated that as the days on feed increased, the slope of the regression equation increased (Table 10). Ammonia-N emission was also highly correlated with urinary urea-N application, although the r2 value tended to be lower (0.58) than for total urinary N application. This would be expected because urinary urea-N concentrations were correlated (r2 = 0.20; P < 0.001) to total urinary N.
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; as cited by Paul et al., 1998) also noted a significant relationship between NH3-N emissions from dairy manure and serum urea N (r2 = 0.64) in dairy cows.
The in vitro NH3-N emissions in this study demonstrate that potential daily NH3-N emissions from beef cattle feces and urine can be affected by the CP and urea concentration of the diet; however, effects on animal performance also must be considered. Based on the results of the complete N balance trial (Gueye et al., 2003a; McBride et al., 2003) and two performance trials (Gleghorn et al., 2004) using the same diets as used in this trial, the actual CP requirement for optimal performance and maximal N retention was between 11.5 and 13% CP. If dietary protein concentrations are decreased to the point that animal performance is adversely affected, then total ammonia emissions could be increased because animals require more days on feed to reach market weight and condition. As animals grow and mature, the CP required in the diet (as a percentage of DM) decreases. Thus, when the same diet is fed throughout the feeding period, potential ammonia emissions may increase with days on feed. This suggests that the use of phase feeding could potentially decrease ammonia emissions from beef cattle feed yards.
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Footnotes |
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2 The mention of trade or manufacturer names is made for information only and does not imply an endorsement, recommendation, or exclusion by ARS-USDA, the Texas Agric. Exp. Stn., or Texas Tech Univ.
3 Appreciation is extended to J. Herring and A. Mason for assistance in conducting these studies.
4 Correspondence: P.O. Drawer 10 (phone: 806-356-5748; fax: 806-356-5750; e-mail: nacole{at}cprl.ars.usda.gov).
Received for publication June 10, 2004. Accepted for publication November 29, 2004.
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TopAbstractIntroductionMaterials and MethodsResults and DiscussionLiterature Cited |
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