EFFECT OF SUPPLEMENTING RUMINALLY UNDEGRADABLE FIBER TO FEEDLOT STEERS ON FECAL NUTRIENT FRACTIONS AND FECAL AMMONIA EMISSIONS

Effect of Supplementing Ruminally Undegradable Fiber To Feedlot Steers on Fecal Nutrient Fractions and Fecal Ammonia Emissions

Sharon Escue, Marc Bauer, Sergio Soto-Navarro, Trent Gilberry, and Greg Lardy

NDSU Department of Animal and Range Sciences

Abstract

Four beef steers were used in a 4 x 4 Latin square to evaluate effects of estimated ruminally undegradable fiber (RUF) on fecal nutrient fractions and NH₃ volatilization. Treatments were: corn control (CORN), barley (BAR), corn with corn bran (CB), and corn with confection sunflower hulls (CSH). Estimates of RUF were based on in vitro fiber digestiblities. Diets were formulated to provide RUF equal to BAR. Diets were fed as a TMR, including 7.5 percent grass hay, grain and fiber source. Steers were adapted to diets for 9 days followed by 5 days of collection, including total fecal collections. Twice per period, feces (3.5 cm deep, evenly packed) was placed in chambers for NH₃ collection. A 0.1 N HCl trap captured NH₃ for analysis. Feed, orts and fecal samples were analyzed for DM, ash, CP, ADF, NDF, and P, in addition, feces were analyzed for total C and soluble N. Treatment affected (P ≤ 0.05), fecal OM, ADF, NDF, P, total C, and C:N. Confection sunflower hull addition tended to lower fecal total N (P = 0.06) and soluble N (P = 0.06). Fecal C:N were CORN, 19.01; BAR, 18.03; CB, 20.67; and CSH, 22.44. These results suggest fecal N produced from CB and CSH diets is more likely to be organically bound. Barley produced feces higher in total N and soluble N (similar to CORN) and lower OM and C:N, indicating that N was in more volatile forms. Treatment did not affect volatilization of NH₃ (P = 0.3). Feces with higher C:N has potential to capture more N. Feces analyzed in this study was free of urinary N, perhaps explaining lack of an effect on NH₃ volatilization.

Key Words: Fiber, Ammonia, Steer

Introduction

The majority (80 to 90%) of N consumed by feedlot cattle is excreted (Giger-Reverdin et al., 1991), much of this N is subject to volatilization loss. Volatilized NH₃ returns to the earth via rainfall, dry deposition and direct absorption (CAST, 2002) and can enrich terrestrial and aquatic systems. Excessive N can cause loss of species diversity, acidify soils and water bodies, contribute to surface water eutrophication, contaminate groundwater, and increase loss of N₂O to the atmosphere. It may be possible to lower NH₃ emissions from feedlot cattle through dietary manipulation. Erickson et al. (2002) partially replaced corn with corn bran in feedlot diets and reported higher manure C:N and OM, increasing ability to capture N. Other studies have shown diet type can shift excretion of N from volatile urinary forms to more stable forms of fecal N (Bierman et al., 1999; Giger-Reverdin et al., 1991) through stimulation of hindgut fermentation.

The large intestine plays a very important role in digestion of structural carbohydrates. Ulyatt et al. (1975) report that 5 to 30 percent of digestible cellulose is fermented in the large intestine, and more hemicellulose. Hindgut fermentation can alter excretion of N by increasing production of microbial protein and increasing fecal OM.

Ruminally undegradable fiber (RUF) may have potential to alter N excretion and lower NH₃ loss. Barley is a commonly used high fiber feed grain. Corn bran and confection sunflower hulls are also high in fiber. These feedstuffs may have potential to increase hindgut fermentation or increase fecal C:N and OM.

Partially replacing corn with sunflower hulls results in decreased digestibility of DM and ADF (Park et al., 1982). Park et al. (1997) reported sunflower hulls could safely be fed to cattle up to 30 percent DMI.

The objective of this study was to evaluate effects of estimated RUF from barley, corn bran and confection sunflower hulls on fecal nutrient fractions and NH₃ volatilization.

Materials and Methods

Animals and Housing

Four Angus cross steers (324 ± 8 kg) were randomly assigned to dietary treatments in a 4 x 4 Latin square. All animals were cared for in accordance with protocols which were approved by the NDSU Institutional Animal Care and Use Committee. Steers were penned individually during diet adaptation then placed in metabolism stalls for collection periods.

Dietary Treatments

Treatments included: corn control (CORN), barley (BAR), corn with corn bran (CB), and corn with confection sunflower hulls (CSH). Diets were formulated to provide a minimum of 12 percent CP with adequate DIP (NRC, 1996). Actual nutrient composition of the diets after laboratory analysis is shown in Table 1. The basal diet was a total mixed ration (TMR) composed of a 92.5 percent corn or barley grain-based concentrate and 7.5 percent grass hay (DM basis; Table 1). Ruminal degradability estimates (Escue et al., 2004) were used to formulate CB and CSH to provide the equal estimates of fiber to the hindgut as BAR. Confection sunflower hulls were ground to increase palatability; corn and barley were coarse rolled. Diets were fed once per day for ad libitum intake, targeting 10 percent feed refusal. Water was available freely throughout the study.

Table 1. Total mixed ration composition and laboratory analysis of nutrient composition.
			Treatment¹
Ingredient			CORN			BAR		CB		CSH

TMR composition (% DM)
Barley				-	83.0		-		-
Corn				81.0	-		65.0		69.0
Corn bran				-	-		16.8		-
Confection sunflower hulls				-	-		-		10.6
Grass hay				7.5	7.5		7.5		7.5
De-sugared molasses				5.0	5.0		5.0		5.0

Supplement
	Finely ground corn			0.56	0.57		0.11		0.40
	Soybean meal			2.93	1.71		2.56		4.56
	Limestone			1.88	1.84		1.77		1.78
	Urea			0.75	-		0.75		0.75
	Dicalcium phosphate			-	-		0.13		0.03
	Salt			0.25	0.25		0.25		0.25
	Mineral premix²			0.06	0.06		0.06		0.06
	Vitamin E premix³			0.02	0.02		0.02		0.02
	Vitamin A and D premix⁴			0.02	0.02		0.02		0.02
	Monensin premix⁵			0.02	0.02		0.02		0.02
	Tylosin premix⁶			0.01	0.01		0.01		0.01


Laboratory Analysis (% DM)
Ash		4.55			5.84		4.47		5.24
CP		13.41			12.47		13.37		13.08
ADF		5.47			8.61		7.65		12.16
NDF		14.08			23.19		23.44		22.11
Fat		2.64			1.73		2.55		2.57
Ca		0.66			0.89		0.71		0.92
P		0.28			0.34		0.27		0.26

Sample Collection and Analysis

Experimental period was 15 days in length, with 8 days for diet adaptation and 5 days for sample collection. Total fecal collections were achieved utilizing chutes. Chutes were attached to steers using harnesses similar to those used for fecal bags. The open end of chutes was placed inside plastic garbage bags and secured to fecal pans, ensuring capture of all fecal material. Total fecal output was weighed daily and sub-sampled at 10 percent for lab analyses. On day one and day four of collection, feces were reserved for chamber analysis. Fecal samples were stored at 20º C until the collection period was completed, mixed in a rotary mixer, and sub-sampled again. Orts were weighed and sub-sampled daily. Samples of TMR were taken at mixing, and TMR ingredients were also sampled. Feed, orts, and fecal samples were dried at 55º C for 48 hours, and analyzed for ash, CP, ADF, NDF, and P. Feces were also analyzed for total C and soluble N.

Chamber Design and Measurements

Feces were placed in chambers (3.5 cm depth, evenly packed) for NH₃ emission collection over 72 hours. Chambers were modeled after McGinn et al. (2002). Calibrated intake and outlet fans drew air into and out of the chambers at the same rate, minimizing pressure gradient from ambient air to chamber air. Air from the chambers was subsampled by pumping (Brailsford and Company, Inc, model TD3LS7, Rye, NY) through an acid trap of 0.1 N HCl to capture NH₃. Acid was changed at 24 hours intervals and analyzed for ammonium using phenol-hypochlorite Bethelot reaction (Broderick and Kang, 1980).

Statistics

Fecal composition data were analyzed by the GLM procedure of SAS (SAS Inst., Cary, NC). The model contained effects for animal, period, and treatment. When significant (P < 0.10), means were separated by LSD. Ammonia emissions data was analyzed by the GLM and mixed procedures of SAS. The mixed model contained effects for period, treatment, day of emissions collection (day), and treatment x day. The random variable was animal and the repeated variable was day.

Results and Discussion

Mean daily DMI were 11.2 ± 1.8, 9.8 ± 1.3, 10.9 ± 1.2, and 9.9 ± 1.3 kg/d for CORN, BAR, CB, and CSH, respectively.

Treatment affected (P < 0.05) fecal ash, OM, ADF, NDF, P, total C, and C:N. Treatment tended to effect total N (P = 0.06), and soluble N (P = 0.08) (Table 2).

Table 2. Treatment effects on fecal fractions (% DM).

	Treatment¹
Item	CORN		BAR		CB		CSH		SE
Ash	7.92^ab		11.14^b		7.74^ab		7.11^a		0.412
OM	92.08^b		88.86^a		92.26^b		92.89^b		0.412
ADF	13.07^a		24.38^c		18.02^b		27.97^d		1.129
NDF	29.54^a		49.69^c		44.91^b		46.44^b		1.698
P	0.71^ab		0.98^b		0.57^ab		0.54^a		0.054
C	47.70^b		45.33^a		47.73^b		47.80^b		0.572
C:N	19.01^a		18.03^a		20.67^ab		22.44^b		0.910
N	2.53^f		2.52^ef		2.31^ef		2.15^e		0.093
Soluble N		2.37^f		2.26^f		1.82^ef		1.62^e		0.193

Fecal ADF and NDF values were lowest (P < 0.01) for CORN. Fecal N was higher (P = 0.06) for CORN than CSH, and soluble N was similar to BAR but higher (P = 0.08) than CSH. Fecal C:N from CORN was similar (P > 0.10) to BAR. Fecal ash from CORN was similar (P > 0.10) to CB. OM and C values were similar (P > 0.10) to CB.

Barley used in this study was 7 percent ADF and 22 percent NDF (DM basis). Escue et al. (2004) reported extent of digestion for barley as 87 percent and 64 percent for NDF. Estimates barley RUF were 51 percent for ADF and 87 percent for NDF (Escue et al., 2004). These estimates indicate that the majority of barley fiber should be available for hindgut fermentation.

Barley RUF did not perform equally to RUF from CB and CSH. Fecal ADF and NDF were different (P < 0.01) than all other treatments. Fecal N was similar (P > 0.10) to CB, and soluble N was similar (P > 0.10) to CORN. Fecal C was higher (P = 0.05) than all other treatments, and C:N was similar (P > 0.10) to CORN. Fecal ash was higher (P < 0.01) than CSH, and BAR fecal OM was lower (P < 0.01) than all other treatments. Fecal P was also highest (P < 0.01) from BAR.

Corn bran used in this study was 16 percent ADF and 65 percent NDF (DM basis). Escue et al. (2004) reported extent of digestion for corn bran as 95 percent for both ADF and NDF. Estimates of corn bran RUF were 67 percent for ADF and 72 percent for NDF (Escue et al., 2004). These estimates indicate that corn bran has much potential to stimulate hindgut fermentation, and should deliver more RUF to the hindgut than barley.

Addition of corn bran RUF produced fecal NDF values similar (P > 0.10) to CSH. Fecal ADF from CB was different (P < 0.01) than all other treatments. Fecal N and soluble N were similar (P > 0.10) to other treatments. Fecal C:N was numerically raised by CB, however values were statistically similar to other treatments (P > 0.10). Fecal C was similar (P > 0.10) to CORN and CSH. Fecal ash, OM, and P from CB were similar (P > 0.10) to other treatments as well.

These results tended to confirm our hypothesis that corn bran addition would increase hindgut fermentation, potentially increasing microbial utilization of N before excretion and shifting fecal N towards organic forms. Perhaps a greater dietary corn bran inclusion level would cause more significant differences in fecal N fractions.

Confection sunflower hulls used in this study were 67 percent ADF and 86 percent NDF (DM basis). Escue et al. (2004) reported extent of digestion for confection sunflower hulls to be 15 percent for ADF and 10 percent for NDF. Estimates of confection sunflower hull RUF were 91 percent for ADF and 95 percent for NDF (Escue et al., 2004). These estimates indicate that confection sunflower hull fiber should bypass both rumen and hindgut fermentation, increasing the OM and C:N of feces.

Addition of confection sunflower hulls caused the highest (P < 0.01) fecal ADF. Fecal NDF was similar (P > 0.10) to CB. Fecal N was lower (P = 0.06) than CORN but similar to BAR and CB. Soluble N was lower (P = 0.08) than CORN and BAR, but similar to CB. Fecal C:N from CSH was higher (P = 0.04) than CORN and BAR, but similar to CB. Fecal C and OM were similar (P > 0.10) to CORN and CB. Fecal ash and P were lower (P < 0.01) than BAR.

This indicates that RUF from CSH may shift fecal N towards organically bound forms. In agreement with Park et al. (1982), addition of confection sunflower hulls lowered ADF digestion, resulting in the highest fecal ADF across diets. This finding confirms our hypothesis that more confection sunflower hull RUF would leave the animal intact, increasing fecal C:N over the corn control.

Treatment did not affect volatilization of NH₃ (P = 0.30). Feces with higher C:N has potential to capture more N. The added RUF treatments (CB and CSH) raised C:N over corn and barley treatments. Manure NH₃ primarily arises from urinary urea. Feces analyzed in this study were free of urinary N, perhaps explaining lack of an effect on NH₃ volatilization.

Implications

Dietary addition of digestible fiber, which bypasses the rumen, may show promise in reducing NH₃ volatilization from feedlot cattle. Results of this study indicate that confection sunflower hulls may reduce fecal N fractions and increase fecal C:N when compared to corn-based finishing diets. Corn bran may also be used; however more research must be done to determine optimum dietary inclusion levels.

Literature Cited

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CAST. 2002. Animal diet modification to decrease the potential for nitrogen and phosphorus pollution. Issue Paper No. 21. Council for Agricultural Science and Technology, Ames, Iowa.

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Park, C. S., G. D. Marx, Y. S. Moon, D. Wiesenborn, K. C. Chang, and V. L. Hofman. 1997. Alternative uses of sunflower. Pages 765-807 in Sunflower Technol. and Prod. Agron. Monograph no. 35. Am. Soc. Agron., Crop Sci. Soc. Am, Soil Sci. Soc Am, Madison, Wisconsin.

Ulyatt, M. J., D. W. Dellow, C. S. W. Reid, and T. Bauchop. 1975. Structure and function of the large intestine of ruminants. Pages 119-133 in Digestion and Metabolism in the Ruminant: Proc. 4^th Int. Symp. Ruminant Physiology. I. W. McDonald, and A. C. I. Warner, eds. The University of New England Publishing Unit, Armidale, NSW, Australia.

Treatment1

TMR composition (% DM)

Treatment¹