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The feeding of livestock in confinement leads to concentration of feed nutrients such as nitrogen, phosphorus, carbon, and trace minerals into a relatively small geographic area. Only a small percentage of the nutrients consumed by feedlot cattle is retained by the animal; hence, little is removed from the premises when the animal leaves the feedyard.

The accumulation of these ‘excess’ nutrients, the extraneous losses of these nutrients to ground water, surface water, and the atmosphere, and removal of accumulated manure have become significant environmental concerns to the beef cattle industry. The excretion of these nutrients also represents an economic loss to the cattle feeder.

Nutrition and management practices can influence the amount of nutrients excreted by the animal as well as influence transformations and movements of excreted nutrients (Figures 1 and 2). Efficient, integrated waste control and management systems need to be developed and implemented that are environmentally friendly, sustainable, and beneficial for feedyard owners, cattle feeders, and the general public.

The amounts and sources of nutrient losses from the feedlot can be affected appreciably by the type of confinement system (unpaved open lots, paved open lots, confinement-slotted floors, etc.) (Adriano, 1975; Vanderholm, 1975). The vast majority of beef cattle in North America are fed in open, unpaved lots; therefore, this review will concentrate on environmental issues relating primarily to that production system.


Nutrient losses from feedyards

NUTRIENTS CONSUMED AND EXCRETED

The ‘typical’ quantities of nutrients consumed and excreted by feedlot cattle are presented in Table 1 and the average nutrient composition of feedlot manure is presented in Table 2.

Based on these values, during a ‘typical’ 150 day feeding period, 1,000 head of cattle will excrete the following quantities of nutrients: 1,200 metric tons of dry matter (DM), 535 metric tons of carbon (C), 27 metric tons of nitrogen (N), 6 metric tons of calcium (Ca), 3.6 metric tons of phosphorus (P), 1.8 metric tons of magnesium (Mg), 1.2 metric tons of sulfur (S), 6.3 metric tons of chloride (Cl), 6.3 metric tons of potassium (K), 1.4 metric tons of sodium (Na), 180 g of cobalt (Co), 12 kg of copper (Cu), 718 g of iodine (I), 120 kg of iron (Fe), 60 kg of manganese (Mn), 239 g of selenium (Se), and 48 kg of zinc (Zn).





Figure 1. The nitrogen cycle in a confined animal feeding operation (Elliott and McCalla, 1973).






Figure 2. The phosphorus cycle in a confined animal feeding operation (SCS, 1992).



Nitrogen

Compared with nonruminants, ruminants have a poor efficiency of utilization of absorbed amino acids for growth (70 to 75% vs 25 to 60%, respectively).

This is attributable to several factors:

(1) Compared with nonruminants, ruminants have a larger gastrointestinal tract. The gastrointestinal tract also has a high metabolic rate, accounting for approximately 27% of total body protein synthesis (MacRae, 1996).

(2) The ruminant seems to have a very high muscle turnover rate which results in a greater percentage of dietary N being used for maintenance (MacRae, 1996).

(3)Within the rumen, bacteria are lysed, and the N within these bacteria is reused by other ruminal microbes.


This intraruminal N recycling results in a decrease in energy and N use efficiency (Firkins et al., 1992).

Ruminants also have several physiological mechanisms to improve N use efficiency. The ruminal bacterial population allows the animal to make use of nitrogenous compounds that cannot be utilized by nonruminants.

The ruminant also has the capacity to recycle N from the lower gut or tissues to the rumen via the saliva and(or) by transport from the blood across the ruminal wall (Kennedy and Milligan, 1980). Recycling is especially important to ruminants fed low-protein diets, but also may be important in synchronizing the ruminal ammonia pool with the rate of energy digestion in the rumen.

Urea recycling via the saliva seems to be directly proportional to the blood urea-N concentration and to the amount of saliva secreted (Nolan and Leng, 1972; Orskov, 1982). The amount of urea recycled via the blood seems to be inversely related to the ruminal ammonia concentration and is partially controlled by the urease activity of the microorganisms that inhabit the ruminal wall (Orskov, 1982).

Much is still unknown about N recycling, especially in animals fed high-concentrate diets. However, the National Research Council (NRC, 1985) suggested that on average, 15% of intake protein is recycled to the rumen. This value varied from 70% in cattle fed 5% crude protein (CP) diets (approximately 350 g/d at a dry matter intake of 10 kg/d), to 34% in cattle fed 10% CP diets (340 g/d), and to 12% (180 g/d) in cattle fed 15% CP diets.

In contrast to the NRC (1985) report, Bunting et al. (1989) reported that dietary protein concentration did not affect actual amounts of N transferred from plasma urea-N to the rumen (7 to 10 g daily). However, in calves fed a low-protein diet (10.2% CP) almost 40% of bacterial N was derived from plasma urea-N, whereas, approximately 12.5% of bacterial N was derived from plasma urea-N in calves fed a high-protein diet (18.8% CP).


Table 1. ‘Typical’ nutrient intakes and losses of cattle fed a high-concentrate diet in feedlots.*



* Assumes a steer eating 10 kg of dry matter daily.
†Small quantities of Se can be lost by respiration/volatilization, but this normally only occurs when the requirement is greatly exceeded.



Table 2. ‘Typical’ nutrient composition of manure, compost, and runoff from a beef cattle feedlot.



* Except for dry matter, values are on a dry matter basis.
†Fresh feces as excreted by the animal (Azevedo and Stout, 1974).
‡Air dried manure collected from an unpaved drylot. Values from Gilbertson et al., 1970; Azevedo
and Stout, 1974;Ward et al., 1978; and C.L. Fields, personnel communication.
§ From Stewart, 1995 and Eghball et al., 1997.
¶ From Clark et al., 1975.



GASEOUS LOSSES

Nitrogen

The predominant loss of N from feedlots seems to be by volatilization to the atmosphere, primarily as ammonia-N. With cattle fed on an open, unpaved lot surface, Bierman (1995) calculated that approximately 60% of N excreted was lost by volatilization. This corresponded to more than 50% of N intake.

Nitrogen excreted in the feces (30 to 50% of total excretion) is composed of undigested feed residues, microbial cells, endogenous secretions, and sloughed cells from the gastrointestinal tract. Once excreted, most of these nitrogenous residues are degraded slowly and therefore release ammonia-N into the atmosphere at a slow rate.

In contrast, urinary N (50 to 70% of total excretion) is composed primarily of urea, which is rapidly hydrolyzed to ammonia and carbon dioxide by microbes in the feces and soil. Stewart (1970) reported that 25 to 90% of urinary N was lost as ammonia within 48 h of excretion, however, these losses were affected by factors such as soil pH and moisture content.

In a typical 10,000-head feedyard, therefore, approximately 400,000 kg of ammonia-N is potentially released into the atmosphere annually. These atmospheric N losses can contribute to nuisance odors and, in some areas, to the formation of secondary particulates.

In areas with a substantial urban population and the subsequent high atmospheric concentrations of nitrous oxides (NOx) produced from burning of fossil fuels, it is estimated (Deanne Morse, UC-Davis, personal communication) that ammonia-N losses account for 20 to 40% of PM10 (particulates with an aerodynamic diameter of 10 microns or less) and for more than 40% of PM2.5 dust emissions from feedyards.

These values may be substantially lower in more rural areas where little NOx is present in the atmosphere (C. Parnell, personnel communication).

Ammonia losses to the atmosphere can also be re-dissolved in rain and surface waters downwind from the feedyard, although the distance that airborne ammonia travels appears to be limited. Miner (1975) reported that atmospheric ammonia concentrations decreased by 82 to 96% within a distance of 120 m from feedlot corrals.


Carbon

In ruminants, losses of C occur primarily via respiration as carbon dioxide and methane. These metabolic and enteric losses have received considerable attention in the past few years because of the implication that these gases contribute to the ‘greenhouse’ effect and to ‘global warming’. In cattle fed typical feedlot diets, methane emissions as a percentage of gross energy intake, are small in comparison to cattle fed high-roughage diets (3 vs 6%) (Johnson and Ward, 1996).

However, these lower methane emissions by the feedlot animal may be counteracted by increased methane emissions from the manure they produce, compared to manure of animals on pasture (Steed and Hashimoto, 1994). Methane emissions are greater from liquid manure systems than from manure collected dry in open lots (Johnson and Ward, 1996).


Odors

Most offensive odors from feedyards are released as a result of anaerobic fermentation of N-, C-, and(or) S-containing compounds in manure and runoff retention facilities.

Feedyard odors are comprised of at least 170 different volatile gases including ammonia, indoles, volatile fatty acids, amines, and alcohols. The odor threshold limit (i.e. the concentration at which the odor is detectable by the human nose) of these odor-producing compounds varies greatly.

Besides being a potential ‘nuisance’ problem, appreciable amounts of N, C, and S can leave the yard in gaseous products that can contribute to odor or acid rain concerns in some locations. In general, when the loose surface manure is wet (>35% moisture) odor emissions increase, whereas, when the surface is dry (<25% moisture) dust emissions increase (Sweeten et al., 1988).

However, the relatively low correlations noted between the surface moisture content and dust concentrations (r² = 0.27) reported by Sweeten et al. (1988) suggests other factors also play a major role in dust and odor emissions. For example, Jones et al. (1992) noted that feces with higher pH emitted less odor. In contrast, lowering the pH of urine decreases ammonia losses but may not affect actual ‘odor’ emissions.


RUNOFF/RETENTION FACILITIES

Some typical values for the nutrient composition of feedlot runoff are presented in Table 2. In general, runoff of water from feedlot surfaces is not a major environmental concern because most feedlots are required to construct retention facilities that collect and hold all the runoff from the feedyard, except in the case of extreme precipitation events (e.g. 25-year, 24 h rainfall event).

In reality, most manure nutrients that do enter lakes and streams enter these surface waters via runoff from fields fertilized with manure and(or) from intensively grazed pastures (CAST, 1996) rather than from the feedlot surface directly. Runoff retention facilities themselves can be an environmental concern due to seepage and emissions of odorous compounds.


Nitrogen

Nitrogenous compounds in feces and urine can run into lakes and streams to pollute surface waters. Gilbertson et al. (1970) reported that 3 to6%of excreted N was lost in runoff from the feedlot surface. Bierman (1995) noted similar values for diets containing 8 and 20% roughage. However, when allconcentrate diets were fed, N runoff exceeded 20% of N excreted. Only 10 to 20% of excreted N (7 to 15% of N intake) was actually collected in the manure at the conclusion of the feeding period. Nitrogen can also be lost after entering the retention facility. Vanderholm (1975) noted that 20 to 70% of N can be lost from aerated and anaerobic manure storage facilities before it is spread on fields.


Phosphorus

Phosphorus that runs into surface waters can lead to eutrophication, algae blooms, and fish kills. Bierman (1995) reported that from 2 to 5% of P consumed was lost in runoff from the feedlot surface. Vanderholm (1975) noted that P and other minerals can chemically react in anaerobic lagoons and precipitate into bottom sludges. These precipitation losses limit the nutritive value of water pumped from the lagoons, but are still recoverable if the bottom sludge is removed.


Other

Feedyard cattle excrete approximately 80% of the trace minerals they consume. The quantities of trace minerals and most macrominerals that occur in runoff or percolation from feedyard surfaces have not been quantified.

A principal concern over trace minerals in feedlot runoff is the potential toxic effects on migratory waterfowl and other wildlife that use waste retention facilities (Irwin and Dodson, 1991).

With the possible exception of Se, trace minerals that run into a waste retention facility or wetland may accumulate over time. Portions of Se can be volatilized from evaporation ponds via microbial biomethylation, a process in which microorganisms convert inorganic Se into volatile methylated Se (Gao and Tanji, 1995).

Thus, methods need to be developed that allow these minerals to be harvested from waste retention facilities.

Carbon can also be lost from runoff retention facilities as carbon dioxide and methane. However, the quantities vary greatly depending upon weather conditions and other factors.


LEACHING/PERCOLATION

Soluble nutrients can potentially percolate through the soil to contaminate ground waters. The primary ground water pollutant associated with beef cattle feeding operations is nitrate-N. Phosphorus and most other nutrients are absorbed readily by the soil, therefore they are seldom a major problem.

Bierman (1995) reported that approximately 60 to 80% of consumed P was retained within the soil of the feedlot pen. Only 25 to 35% of consumed P was collected in the manure. Elliot and McCalla (1973) reported that little or no nitrate-N leaching occurred below feedlots because of the compaction of manure and soil by the animals. However, if the feedlot was abandoned or grossly understocked, nitrate production and leaching could occur. Leaching can also occur from improperly constructed waste water retention facilities.

Sweeten et al. (1990) found no evidence of elevated nitrate concentrations in ground water beneath 23 cattle feedyards in the High Plains. Most leaching of nitrates and other water soluble nutrients seems to occur below manure stockpiles and composting facilities (CAST, 1996).


DUST

In arid cattle feeding areas, the effects of feedlot dust on cattle, employees, and the general public have become a primary concern. Dust particles with a mean diameter of less than 2.5 microns (PM2.5) can be inhaled into the lungs and cause respiratory problems for both cattle and humans (Rylander et al., 1986; Schwartz et al., 1996), although the actual severity of this problem is debated (Barnes, 1994).

Dust can act as a substrate to which acids, gases, microbes, and other organisms can attach. Based on cost figures we have obtained, a typical southwest US feedyard that uses a sprinkling system to control dust will spend from $1 to $20/head-capacity annually to control dust.

Fortunately, only about 2 to 4.4% (particle volume basis) of the dust particles emitted by beef cattle feedyards have a mean aerodynamic diameter of less than 2.5 microns (Sweeten et al., 1988).

The nutrient content of feedlot dust has not been well characterized and the quantity of dust lost from feedlots is highly debated (Sweeten et al., 1988).

Using electron microscopy, Auvermann and Coleman (personal communication) determined that the dust from Texas High Plains feedyards consisted primarily of organic particles. Nakaue et al. (1981) characterized the mineral content of dust in poultry houses and Chang and Rible (1975) characterized the nutrient content of fine and coarse manure particles in a feedlot (Table 3).

As the particle size of manure decreased, the ash, fat, N, and P content increased, suggesting that these values would be high in dust particles. As a proportion of nutrient intake, few of the nutrients excreted by cattle in feedyards leave the yard in dust particles.


Table 3. Nutrient content of broiler house dust (Nakaue et al., 1981) and small manure particles (Chang and Rible, 1975).


* Micrograms/g of dry matter unless shown.
†Air dried manure collected from an unpaved drylot. Particles < 0.053 mm accounted for 0.5%, particles 0.105–0.053 mm accounted for 1.6%, and particles > 1.0 mm accounted for 65.4% of manure samples. In freshly collected manure, the percentages were 43.9, 3.6, and 30.7%, respectively.



MANURE USE AND DISPOSAL

Land application limitations

Several factors limit the use of feedlot manure as a fertilizer for field crops. The losses of N that occur to the atmosphere and to surface or groundwater not only affect air and water quality, but also result in a final product (i.e. manure for fertilizer) that is lower in quality as a result of lower N content and a lower N:P ratio (Table 2).

Although typical fresh manure has an N:P ratio of approximately 5.5:1 (feces = 3.8:1, urine = 38:1), manure collected from feedlot pens normally has an N:P ratio of approximately 1:1 (Azevedo and Stout, 1974). Because most crops require an N:P ratio of 5:1 to 8:1, when manure is applied to fields to meet N requirements of crops, P application may be excessive.

Regulations requiring that manure be applied to land based on P content, rather than N content, are currently in practice in many countries and are beginning to come into practice in many states of the US.

Other factors such as inconsistent nutrient composition, inconsistent size (i.e. nonuniform spreading), weed seeds, foreign material, salinity, and transportation costs also are factors that limit the value of feedlot manure.


Composting

Composting has become a popular method to decrease the volume and weight of feedlot manure and to produce a product that is more acceptable to farmers as a fertilizer (fewer weed seeds, more uniform spreading, more consistent nutrient composition, etc.).

During a 100- to 120-day composting period, the weight and volume of manure can be decreased by 15 to 70% (Inbar et al., 1993; Lopez-Real and Baptista, 1996; Eghball et al., 1997). Most of this weight loss is the result of losses of C as carbon dioxide and methane: 46 to 61% of the C initially present can be lost during composting (Eghball et al., 1997, Table 2).

The amount of methane produced during composting is highly dependent upon the composting method used (Lopez-Real and Baptista, 1996) and is decreased by proper aeration. Manure composted in windrows produces significantly less methane than manure that is stored in piles and allowed to compost/ferment with minimal intervention (Lopez-Real and Baptista, 1996).

Nineteen to 45% of the N present in manure can be lost during composting (Eghball et al., 1997) although the actual N concentration in compost (DM basis) may be greater than in the uncomposted manure (Inbar et al., 1993; Lopez-Real and Baptista, 1996). The appreciable losses of C and N that occur during composting have led some to suggest that feedlot manure should not be composted before application to fields (Eghball et al., 1997; Stewart, 1995). However, these arguments are based on nutrient content alone, not the overall quality and utility of the product.

Mineral losses can also occur during composting due to runoff and(or) percolation. In studies by Eghball et al. (1997), P losses ranged from 1 to 12%, K losses ranged from 11 to 16%, Na losses ranged from 14 to 16%, Ca losses ranged from 1.2 to 1.7%, and Mg losses ranged from 1.9 to 5.7% of the amounts present when the composting process began. The pathways for these losses have not been conclusively identified.


Decreasing nutrient losses: Where do we go from here?

NITROGEN

Studies to decrease N losses by feedlot cattle have revolved around several areas:

(1) optimizing the amount of crude/metabolizable protein fed, (2) optimizing the amino acid supply in the lower gut, (3) increasing digestion of dietary protein, (4) altering the site of digestion of dietary protein, and (5) maximizing ruminal microbial protein synthesis.

Obviously, N use efficiency could be improved and N losses in feces and urine could be decreased if the animals’ requirements (ruminally digestible intake protein/NPN, small intestinal amino acid/peptide supply, etc.) are met precisely.

Unfortunately, this is difficult to do under the most controlled experimental conditions and impossible under typical feedyard conditions. Attempting to formulate the‘optimum’ diet for many lots of cattle of varying genetic backgrounds, with differing growth potentials, and in various stages of finishing is a difficult task.

The nutritionist could formulate diets based on ‘the average’ requirement of animals in the feedyard, realizing that the requirements of animals that are ‘above average’ will not be met, thereby affecting their performance adversely.

Conversely, the nutritionist may formulate diets that meet the requirements of the animals with the greatest nutrient requirements (i.e. growth potential), realizing that the latter decision will result in N wastage by cattle with lower nutrient requirements. Practically, this decision will be determined by economics, personal opinion/bias, and(or) state and federal regulations.


Nitrogen intake

Increasing the protein and(or) nonprotein-N concentration of the diet generally increases the amount of N excreted in the urine. Johnson and Preston (1995) fed steers diets containing 10, 12, 14, or 16% CP to estimate N waste based on plasma urea-N concentrations. Protein concentrations in their diets were increased by replacing steam-flaked milo (sorghum) with a cottonseed meal/urea (6:1) blend.

During each period of the feeding period, optimal performance occurred in steers with plasma urea-N concentrations of 5 to 8 mg/dL. These results agreed with those of Thomson et al. (1994), who noted that the optimal plasma urea-N concentration for protein deposition in steers was 6 to 8 mg/dL.

In both studies, these concentrations occurred with diets containing from 12 to 14% CP. Plasma urea-N concentrations increased during the feeding period, leading the authors to suggest that dietary CP concentrations could be decreased from 14 to 12% after 56 to 84 days on feed.

However, decreasing the protein content of feedlot diets can potentially have negative side effects. Several studies suggest that ammonia may serve as a renal/systemic buffer in cattle fed high-concentrate diets (Heitman and Bergman, 1978; Boukila et al., 1995). If ammonia does serve as a renal buffer in cattle fed high-concentrate diets, decreasing the dietary protein concentration could potentially lead to an increased incidence of acidosis. Thus, other systemic buffers may need to be added to the diet in order to compensate for the lowered renal buffering capacity.


Nitrogen source

The source of dietary N can have a marked effect on animal performance and nutrient excretion because of differences in the site and rate of protein digestion. With the release of the new NRC (1996) publication, source of dietary N has taken on greater importance in the formulation of beef cattle diets. We now have the capacity to balance diets for the proper amounts of ruminally degradable (DIP) and ruminally undegradable (UIP) protein.

However, because of the low ruminal degradability of most grain proteins, when formulating high-concentrate finishing diets for cattle, it is often necessary to feed excess N in order to meet the microbial requirements for DIP.

This may be exacerbated by the feeding of ionophores because they tend to increase the UIP and decrease the DIP of proteins (NRC, 1996). Similarly, animal response to estrogenic implants may interact with the ruminal degradability of the dietary protein (Cecava and Hancock, 1994). With calves fed 40% hay diets, Cummins et al. (1983) reported that when DIP was greater than 54% of CP, degraded N was wasted. However this ‘balance point’ probably varies with dietary energy and protein content.

It has long been suggested that for optimal utilization of dietary N the release of ammonia-N, amino acid-N, and peptide-N needs to be synchronized with energy released by ruminal fermentation (Henning et al., 1993). However, several studies have questioned the importance of this synchronization (Knight and Owens, 1973; Mizwicki et al., 1980; Newbold and Rust, 1992), at least with high-forage diets. Factors such as ruminal pH, feeding frequency, meal size, ruminal microbial species, N recycling from the lower gut, and N recycling within the ruminal contents may serve to ‘override’ differences in the intraruminal release of N and energy.


Energy intake

Energy intake affects N excretion in several ways. Increased energy intake can increase ruminal microbial activity and stimulate the transfer of urea from the blood to the rumen (Kennedy and Milligan, 1980).

On high-concentrate diets, considerable quantities of starch can escape digestion in the rumen and small intestine and be fermented in the large intestine. When appreciable fermentation occurs in the large intestine, urea can diffuse from the blood into the large intestine and be used by the intestinal microbes.

Thus, on highenergy diets, blood urea-N destined for excretion via the urine may be diverted to the rumen and(or) large intestine and be excreted in the feces rather than in the urine (Orskov et al., 1971). By diverting N excretion to the feces, rather than the urine, volatilization losses of N can be decreased possibly leading to a higher N:P ratio in the manure collected.

Energy intake also affects ruminal microbial protein synthesis and duodenal passage of N. Orskov (1982) noted that the N requirement of ruminal bacteria increased as dietary energy density increased with the actual requirements depending on the degradability of dietary N.

In cattle fed whole shelled corn diets, microbial protein efficiency and microbial protein yield decreased as the dietary roughage content decreased from 21 to 0% (Cole et al., 1976). Similarly, microbial efficiency and yield were decreased in cattle fed steam-flaked corn compared with cattle fed dryrolled corn.

Tucker andWatts (1993) fed cattle high-concentrate (5% hay) diets containing dry-rolled milo, steam-flaked milo, dry-rolled barley, or steam-flaked barley.

As expected, steam-flaking milo decreased total manure excretion, dry matter excretion, and fecal starch content, and improved feed efficiency (Table 4). In contrast, steam flaking barley did not affect manure excretion although it improved feed efficiency. The addition of two commercial ‘odor suppressants’ to the dry-rolled milo diets did not affect performance or manure excretion.

Bierman (1995) fed diets containing 10% (all concentrate), 13% (7.5% roughage), or 28% wet corn gluten feed (WCGF, 41.5%of diet DM) neutral detergent fiber (Figure 3). Forty-five to 57% of the N fed was lost to volatilization.

This amounted to 8 to 12 kg of ammonia N lost per head over the 87 day feeding period. Only 5 to 15%of feed N was recovered in the manure removed from the pens.


Table 4. Manure excretion and performance of cattle fed 95% concentrate diets containing dry-rolled milo, steam-flaked milo, dry-rolled barley and steam-flaked barley (Tucker and Watts, 1993).





Ruminal escape amino acids

Ruminally protected amino acids have been studied and available for many years. Newer ‘ruminally protected’ amino acids have shown more promise, at least in dairy cattle. Klemesrud et al. (1996) fed diets with various concentrations of ‘ruminally protected’ lysine and methionine. Maximum daily gain was obtained when 2.53 g of lysine/steer daily was fed. In general, optimal feed efficiency seemed to occur when calves were fed 1 g of lysine and 0.3 g of methionine daily. Providing methionine alone did not affect performance.


Intermittent protein supplementation

Several studies have indicated that providing pasture cattle with protein supplement every other day, rather than daily, does not adversely affect performance (Brown et al., 1995). Krehbiel et al. (1996) noted that providing ewes maintained on brome hay (7.7% CP) with protein supplement at 72 h intervals did not increase N recycling to the rumen; however, they concluded that the interval of protein supplementation may affect the pattern of absorption of nitrogenous compounds from the gastrointestinal tract.

We conducted two studies to evaluate nutrition and management regimens that can decrease N excretion and(or) divert N excretion from the urine to the feces in order to reduce volatile N losses. We hypothesized that feeding diets that are alternatively adequate and deficient in protein could result in increased N recycling between the rumen and lower gut, improved efficiency of N utilization, and decreased urinary N excretion (Cole, 1997).

Two nutrient balance trials were conducted using lambs fed 90% concentrate diets containing 10, 12.5, or 15% CP. In addition, one group was fed the 10 and 15% diets on alternating days and a fifth group was fed the 10 and 15% diets every 2 days.

In Trial 1 the supplemental protein was provided by cottonseed meal and in Trial 2 it was provided by a 50:50 blend (N basis) of urea and cottonseed meal. In Trial 1, N retention was increased 38% (P < 0.05) by alternating protein concentrations at 2 day intervals compared to continuously feeding the 12.5% CP diet (Table 5, Cole, 1997).

In Trial 2, N metabolism was not significantly affected suggesting that the ruminal degradability of the dietary protein might affect the results.





Figure 3. Nitrogen losses from feedlot pens with cattle fed diets containing 28% wet corn gluten feed (WCGF), 13% (7.5% roughage), or 10% (all concentrate) neutral detergent fiber (Bierman, 1995).



Ammonia volatilization from the feedlot surface and waste retention facilities can be decreased by addition of certain additives such as bedding and minerals including superphosphate, phosphoric acid, S-containing compounds (aluminum sulfate, etc.) or calcium chloride (Miner, 1975).

Some of these have been used successfully with poultry litter, but their use in beef cattle feedlots has not been evaluated thoroughly. Unfortunately, each of these methods has distinct disadvantages (increased manure mass, increased manure P, increased sulfate emissions, etc.) that may limit their use in beef cattle feedlots.


Table 5. Daily nitrogen metabolism of lambs fed a high-concentrate diet with constant or intermittent protein supplementation (Cole, 1997).*


* Supplemental N provided by cottonseed meal.
†Protein concentration alternated between 10 and 15% on a daily basis.
‡ Protein concentration alternated between 10 and 15% on a 2-day basis.
§ Linear effect of dietary crude protein content (P < 0.01).
¶Linear effect of dietary crude protein content (P < 0.05).
** Treatment 12.5% CP different from protein alternated on a 2-day basis (P < 0.05).



PHOSPHORUS

Because of the high concentrate levels currently fed to most feedlot cattle, 60 to 80% of the P in feedyard diets comes from the grain portion of the diet.

In general, the amounts of P in the normal ration ingredients are sufficient to meet the animal’s P requirement, therefore, the amounts of supplemental P required are small or nil. Thus, decreasing P losses via decreasing the quantity of P fed becomes difficult unless low-P grain sources become available.

To decrease P losses to the environment, it will be necessary to improve P utilization and to increase the amounts of P retained by the animal.

One method is to use estrogenic implants (Niemann et al., 1997).

Increasing the efficiency of utilization of grain P could also lead to a decrease in P excretion by feedlot cattle. As much as 70% of the P in cereal grains is in the form of phytate-P (Nelson et al., 1968), a combination of penta-, tetra-, tri-, di-, and mono-phosphates of inositol (Mags, 1982).

Phytate-P has a low availability to nonruminants, however, ruminal bacteria can hydrolyze phytate-P and make it available to the animal and ruminal microbes (Reid et al., 1947; Raun et al., 1956; Tillman and Brethour, 1958). The phytase produced by cellulose-fermenting cultures of ruminal bacteria has a pH optimum of about 5.5, with little or no activity at a pH of 4.5 (Raun et al., 1956).

In cattle limitfed high concentrate diets it seems that essentially all dietary phytate is hydrolyzed during passage through the gut (Nelson et al., 1976). However, it is not clear if microbial phytase is active in the rumen of feedlot cattle fed high-concentrate diets ad libitum.

The availability of phytate-P is only about 67% of the availability of P in dicalcium phosphate (Lofgreen, 1960; Hansard and Barth, 1962) suggesting that the utilization of phytate-P can be improved in ruminants. Therefore, through the use of phytase enzymes or low-phytate cereal grains, it might be possible to improve the utilization of dietary P by feedlot cattle and decrease the amounts of P excreted to the environment.


CARBON

In the 1970s a considerable amount of research was conducted to decrease enteric methane production of ruminants to improve energetic efficiency.Most of the research revolved around the feeding of chemicals (chloral hydrate, etc.) that were selectively toxic to ruminal methanogenic bacteria. In general, it seemed that the methanogenic bacteria were able to adapt to these chemicals and thus, the decrease in ruminal methane production was transient (Johnson, 1974; Cole and McCrosky, 1975).

In addition, the low methane production by cattle fed high-concentrate diets limited the quantity of energy that could be conserved by preventing ruminal methanogenesis. Ruminal methanogenesis occurs primarily via reduction of carbon dioxide to methane by a unique group of ruminal bacteria.

Recently, Miller (1994) has proposed colonization of the rumen with selective acetate-producing bacteria (acetogens) that can effectively compete with ruminal methanogens for hydrogen, and thus, shift the flow of hydrogen from reduction of carbon dioxide to methane to reduction of carbon dioxide to acetate. Such a system could potentially increase the efficiency of energy utilization by ruminants and decrease enteric methane emissions.

A similar treatment might also have the capacity to decrease methane emissions from manure stockpiles, composting facilities and lagoons. By developing improved composting methods and additives, it may be possible to produce compost of higher quality while decreasing the losses of C and N to the atmosphere.


TRACE MINERALS

By feeding more biologically available sources of trace minerals, it would be possible to decrease the amounts of these minerals supplemented in the diet, and thus decrease the quantities that are excreted to the environment.

For many years the bioavailability of trace minerals for ruminants has received little attention. Practically, minerals were a minor cost and it was often more economically feasible to feed excesses of a mineral with lower bioavailability than to feed a more expensive mineral with a higher availability. In addition, the bioavailability of different trace mineral sources for ruminants has not been thoroughly researched and values in the literature vary greatly. Some values for bioavailability of trace mineral sources, summarized from the papers of Albin (1988), Greene (1995), and Spears (1996) are presented in Table 6.

In general, the sulfate forms of Co, Cu, Fe, Mn, and Zn tend to be the most available inorganic forms of the mineral. Organic sources of these minerals tend to have greater availability than the sulfate forms. Selenium is normally supplemented as sodium selenite ((Na₂SeO₃) and sometimes as sodium selenate ((Na₂SeO₄). The relative bioavailability of the selenate form seems to be equal to or slightly greater (133%) than the selenite form (Henry et al., 1988). Swedish studies indicate that organic forms of Se (selenomethionine and a high selenium-yeast product) are approximately twice as available as sodium selenite for cattle (Pehrson et al., 1989).


Table 6. Relative bioavailability of trace minerals from different inorganic and organic sources in relation to the availability of the sulfate form (Albin, 1988; Greene, 1995; Spears, 1996).





DUST AND ODORS

Currently, feedlot dust and odors are controlled primarily by changing/controlling the moisture content of the feedlot surface. This is done by use of sprinklers, water trucks, mounds in pens, varying the stocking density, frequent scraping of pens, and other methods.

Unfortunately, the success of these methods is highly dependent upon weather conditions, the methods are usually not entirely successful, each method can add a substantial cost to the feedyard operation, and the return on the investment may be nil.

Some methods that might be used in the future to control dust and odor include the following: (1) Feed additives that, when excreted, prevent the breakdown of urea to ammonia, bind fine dust particles, and(or) decrease other anaerobic fermentation in manure; (2) Soil amendments that can be applied to the feedlot surface to prevent ammonia, C, and(or) S volatilization and(or) bind fine dust particles; (3) Lagoon additives that decrease release of N, C, and S from lagoons; and (4) Dietary regimens that increase nutrient recycling in the animal and thus decrease the quantity of nutrients that must be imported to the feedlot.

References

Adriano, D.C. 1975. Chemical characteristics of beef feedlot manures as influenced by housing type. Proc. ASAE 3rd Inter. Symp. On Livestock Wastes. pp. 347–350.

Albin, R.C. 1988. Trace mineral sources for beef cattle. Proc. Plains Nutrition Council Symposium on Trace Minerals in Beef Cattle Nutrition, Sept. 15, 1988, Amarillo, TX. pp. 1B–13B.

Azevedo, J. and P.R. Stout. 1974. Farm Animal Manures: An overview of their role in the agricultural environment. Univ. Of Calif., Davis Manual # 44.

Barnes, P.J. 1994. Air Pollution and asthma. Postgrad. Med. J. 70:319–325.

Bierman, S. 1995. Nutritional effects on waste management. MS Thesis, Univ. of Nebraska, Lincoln.

Boukila, B., J.R. Seoane and J.F. Bernier. 1995. Effects of dietary hydroxides on intake, digestion, rumen fermentation and acid-base balance in sheep fed a high-barley diet. Can. J. Anim. Sci. 75:359–369.

Brown, D.R., F.C. Hinds and R.M. Collins. 1995. Effect of supplementation frequency on diet digestion and nitrogen metabolism of growing lambs fed low-quality forage. Prof. Anim. Sci. 12:24–27.

Bunting, L.D., J.A. Boling and C.T. MacKown. 1989. Effect of dietary protein level on nitrogen metabolism in the growing bovine: 1. Nitrogen recycling and intestinal protein supply in calves. J. Anim. Sci. 67:810–819.

CAST. 1996. Integrated AnimalWaste Management. Council for Agricultural Science and Technology Task Force Report No. 128, Nov. 1996.

Cecava, M.J. and D.L. Hancock. 1994. Effects of anabolic steroids on nitrogen metabolism and growth of steers fed corn silage and corn-based diets supplemented with urea or combination of soybean meal and feathermeal. J. Anim. Sci. 72:515–522.

Chang, A.C. and J.M. Rible. 1975. Particle-size distribution of livestock wastes. Proc. ASAS 3rd Internat. Symp. on LivestockWastes, April 21–24, 1975, Urbana-Champaign, IL. pp. 339–343.

Clark, R.N., C.B. Gilbertson and H.R. Duke. 1975. Quantity and quality of beef feedyard runoff in the great plains. Proc. ASAE 3rd Inter. Symp. On Livestock Wastes. pp. 429–431.

Cole, N.A. 1997. Nitrogen retention of lambs fed alternating dietary protein concentrations. J. Anim. Sci. 75 (Suppl. 1): 273. (Abstr.).

Cole, N.A. and J.E. McCrosky. 1975. Effects of hemiacetal of chloral and starch on the performance of beef steers. J. Anim. Sci. 41:1735–1741.

Cole, N.A., R.R. Johnson, F.N. Owens and J.R. Males. 1976. Influence of roughage level and corn processing method on microbial protein synthesis by beef steers. J. Anim. Sci. 43:497–503.

Cummins, K.A., J.E. Nocek, C.E. Polan and J.H. Herbein. 1983. Nitrogen degradability and microbial protein synthesis in calves fed diets of varying degradability defined by the bag technique. J. Dairy Sci. 66:2356–2364.

Eghball, B., J.F. Power, J.E. Gilley and J.W. Doran. 1997. Nutrient, carbon, and mass loss during composting of beef cattle feedlot manure. J. Environ. Qual. 26:189–193.

Elliott, L.F. and T.M. McCalla. 1973. The fate of nitrogen from animal wastes. In: Proceedings of Professional Conference on Nitrogen in the Environment. p. 86.

Firkins, J.L.,W.P.Weiss and E.J. Piwonka. 1992. Quantification of intraruminal recycling of microbial nitrogen using nitrogen-15. J. Anim. Sci. 70:3223–3233.

Gao, S. and K.K. Tanji. 1995. Model for biomethylation and volatilization of selenium from agricultural evaporation ponds. J. Environ. Quality 24:191–197.

Gilbertson, C.B., T.M. McCalla, J.R. Ellis, O.E. Cross andW.R.Woods. 1970. The effect of animal density and surface slope on characteristics of runoff, solid wastes and nitrate movement on unpaved beef feedlots. Beef Feedlot Waste: NE Agric. Exp. Stat. Bull. # 508.

Greene, L.W. 1995. The nutritional value of inorganic and organic mineral sources. Proc. Of the Plains Nutrition Council Symposium ‘Update on Mineral Nutrition of Beef Cattle.’ Nov 10, 1995. Lubbock, TX. Public. TAMUS-AREC-95–2.

Hansard, S.L. and J. Barth. 1962. Effects of dietary phytin and of calcium levels upon absorption and excretion of minerals by lambs. J. Anim. Sci. 21:384 (Abstr.).

Heitmann, R.N. and B.N. Bergman. 1978. Glutamine metabolism, interorgan transport and glycogenicity in sheep. Am. J. Physiol. 234:E197–E203.

Henning, P.H., D.G. Steyn and H.H. Meissner. 1993. Effect of synchronization of energy and nitrogen supply on ruminal characteristics and microbial growth. J. Anim. Sci. 71:2516–2528.

Henry, P., M. Echevarria, C. Ammerman and P. Rao. 1988. Estimation of the relative biological availability of inorganic selenium sources for ruminants using tissue uptake of selenium. J. Anim. Sci. 66:2306–2314.

Inbar,Y.,Y. Hadar andY. Chen. 1993. Recycling of cattle manure: The composting process and characterization of maturity. J. Environ. Qual. 22: 857–863.

Irwin, R.J. and S. Dodson. 1991. Contaminants in Buffalo Lake National Wildlife Refuge, Texas. U.S. Fish andWildlife Service, Dept. Of Interior. Johnson, D.E. 1974. Adaptational responses in nitrogen and energy balance of lambs fed a methane inhibitor. J. Anim. Sci. 38:154–162.

Johnson, J.W. and R.L. Preston. 1995. Minimizing nitrogen waste by measuring plasma urea-N levels in steers fed different dietary crude protein levels. Texas Tech Univ. Res. Rept. # T-5–356: 62–63.

Johnson, D.L. and G.W. Ward. 1996. Estimates of animal methane emissions. Environ. Monitoring and Assessment 42:133–141.

Jones, M., P.J.Watts, S.C. Lott, R.W. Tucker and R.J. Smith. 1992.Amobile dynamic olfactometer for feedlot odor studies. ASAE Paper No. 92–4515. St. Joseph, MO, MI:ASAE.

Kennedy, P.M. and L.P. Milligan. 1980. The degradation and utilization of endogenous urea in the gastrointestinal tract of ruminants; A review. Can. J. Anim. Sci. 60:205–221.

Klemesrud, M.J., T.J. Klopfenstein, R.A. Stock, A.J. Lewis and D.W. Herold. 1996. Ruminal escape lysine for feedlot cattle. J. Anim. Sci. 74 (Suppl. 1): 276.

Krehbiel, C.R., C.L. Ferrell and H.C. Freetly. 1996. Frequency of protein supplementation on net portal and hepatic flux of nutrients in mature ewes consuming low quality forage. J. Anim. Sci. 74 (Suppl. 1):265.

Knight,W.M. and F.N. Owens. 1973. Interval urea infusion for lambs. J. Anim. Sci. 36:145–152.

Lofgreen, G.P. 1960. The availability of the phosphorus in dicalcium phosphate, bonemeal, soft phosphate and calcium phosphate for mature wethers. J. Nutr. 70:58–65.

Lopez-Real, J. and M. Baptista. 1996. A preliminary comparative study of three manure composting systems and their influence on process parameters and methane emissions. Compost Sci. And Util. 4:71–82.

MacRae, J.C. 1996. Advancing our understanding of amino acid utilization and metabolism in ruminant tissues. In: E.T. Kornegay (Ed.) Nutrient Management of Food Animals to Enhance and Protect the Environment. CRC Press, Inc. Boca Raton, FL. pp. 73–89.

Mags, J.A. 1982. Phytate: Its chemistry, occurrence, food interactions, nutritional significance, and methods of analysis. J. Agric. Fd. Chem. 30:1–9.

Miller, T.L. 1994. Ecology of methane production and hydrogen sinks in the rumen. Proc. Soc. Nutr. Physiol. 3:176 (Abstr.).

Miner, J.R. 1975. Evaluation of alternative approaches to control odors from animal feedlots. Idaho Research Foundation, Moscow, Idaho.

Mizwicki, K.L., F.N. Owens, K. Poling and G. Burnett. 1980. Timed ammonia release for steers. J. Anim. Sci. 51:698–703.

Nakaue, H.S., J.K. Koelliker, D.R. Buhler and G.H. Arscott. 1981. Distribution of inorganic elements in poultry house dust. Poultry Sci. 60:1386–1391.

Niemann, D.R.,W.S. Ramsey, L.W. Greene and D.F.Waldron. 1997. Zeranol reduces P excretion in feedlot lambs. J. Anim. Sci. 75 (Suppl. 1) 265 (Abstr.).

Nelson, T.S., L.W. Ferrara and N.L. Storer. 1968. Phytate phosphorus content of feed ingredients derived from plants. Poultry Sci. 47:1372–1374.

Nelson, T.S., L.B. Daniels, J.R. Hall and L.G. Shields. 1976. Hydrolysis of natural phytate phosphorus in the digestive tract of calves. J. Anim. Sci. 42:1509–1512.

Newbold, J.R. and S.R. Rust. 1992. Effect of asynchronous nitrogen and energy supply on growth of ruminal bacteria in batch culture. J. Anim. Sci. 70:538–546.

Nolan, J.V. and R.A. Leng. 1972. Dynamic aspects of ammonia and urea metabolism in sheep. Br. J. Nutr. 27:177–194.

NRC, 1985. Ruminant Nitrogen Usage. National Academy Press,Washington, DC. NRC. 1996. Nutrient Requirements of Beef Cattle (7th Ed.). National Academy Press, Washington, DC.

Orskov, E.R. 1982. Protein Nutrition in Ruminants. Academic Press, New York.

Orskov, E.R., C. Fraser and I. McDonald. 1971. Digestion of concentrates in sheep. 3. Effects of rumen fermentation of barley and maize diets on protein digestion. Br. J. Nutr. 26:477–486.

Pehrson, B., M. Knutsson and M. Gyllensward. 1989. Glutathione peroxidase activity in heifers fed diets supplemented with organic and inorganic selenium compounds. Swed. J. Agric. Res. 19:53–60.

Raun, A., E. Cheng andW. Burroughs. 1956. Phytate phosphorus hydrolysis and availability to rumen microorganisms. J. Agric. Fd. Chem. 4:869–871.

Reid, R.L., M.C. Franklin and E.G. Hallsworth. 1947. The utilization of phytate phosphorus by sheep. Australian Vet. J. 23:136–140.

Rylander, R., Y. Peterson and K.J. Donham. 1986. Health effects of organic dusts from the farm environment. Proc. of the Inter.Workshop in Skokloster, Sweden, April 23–25, 1985. Amer. J. Indust. Med. 10:196–316.

Schwartz, J., D.W. Dockery and L.M. Neas. 1996. Is daily mortality associated specifically with fine particles? J. Air andWaste Management Assoc. 46:927–939.

SCS. 1992. Soil Conservation Service AgricultureWaste Management Field Handbook. National Engineering Handbook.

Spears, J.W. 1996. Optimizing mineral levels and sources for farm animals. In: E.T. Kornegay (Ed.) Nutrient Management of Food Animals to Enhance and Protect the Environment. CRC Press – Lewis Publishers, Boca Raton. pp. 259–275.

Steed, J. and A.G. Hashimoto. 1994. Methane emissions form typical manure management systems. Bioresource Tech. 50:123–130.

Stewart, B.A. 1970.Volatilization and nitrification of nitrogen from urine under simulated cattle feedlot conditions. Environ. Sci. Tech. 4:579–582.

Stewart, B.A. 1995. Agronomic benefits of compost. Proc. Symp. on Innovations and New Horizons in Livestock and Poultry Manure Management. Austin, TX. Sept. 6–7, 1995. pp. 88–94.

Sweeten, J.M., C.B. Parnell, R.S. Etheredge and D. Osborne. 1988. Dust emissions in cattle feedlots. In:Veterinary Clinics of North America: Food Animal Practice 4 (No. 3):557–578.

Sweeten, J.M., H.D. Pennington, D. Seale, R. Wilson, R.M. Seymour, A.W. Wyatt, J.S.Cochran and B.W. Auvermann. 1990. Well water analysis from 26 cattle feedyards in Castro, Deaf Smith, Parmer, and Randall Counties, Texas. Texas Agricultural Extension Service, College Station, TX.

Thomson, D.U., R.L. Preston and S.J. Bartle. 1994. Influence of protein source and level on the performance and carcass characteristics of finishing beef steers. Texas Tech Univ. Res. Rept. # T-5–342: 28–30.

Tillman, A.D. and J. R. Brethour. 1958. Utilization of phytin phosphorus by sheep. J. Anim. Sci. 17:104–112.

Tucker, R.W. and P.J. Watts. 1993. Waste minimization in cattle feedlots by ration modification. Trans. ASAE 36:1461–1466.

Vanderholm, D.H. 1975. Nutrient losses from livestock waste during storage, treatment and handling. Proc. ASAE 3rd Inter. Symp. On Livestock Wastes, pp. 282–285.

Ward, G.M., T.V. Muscato, D.A. Hill and R.W. Hansen. 1978. Chemical composition of feedlot manures. J. Environ. Quality 7:159–164.

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