Short communication

Total tract nutrient digestion of steers consuming diets containingammonium polyacrylate

K.G. Maciorowskia,*, M.J. Cecavab, A.L. Suttonc, J.A. Pattersonc

a Department of Poultry Science, Texas A & M University, College Station, TX 77843-2472, USAb Consolidated Nutrition, Research and Technology Center, P.O. Box 2508, Ft. Wayne, IN 46801, USA

c Department of Animal Science, Purdue University, West Lafayette, IN 47906, USA

Received 18 April 1997; received in revised form 23 September 1999; accepted 30 September 1999

Abstract

One of the potential factors that may limit the ruminant animalÕs ability to digest ®ber is the reduced retention and subsequent

passage of cellulolytic microorganisms from the rumen. Bacterial passage may be decreased by an inert support. Ammonium

polyacrylate is a hygroscopic organic polymer that is non-toxic to animals and environmentally degradable. A digestibility trial was

conducted with six Holstein steers cannulated at ruminal, duodenal and ileal sites to determine if an ammonium polyacrylate gel

(GEL: 20 g ammonium polyacrylate hydrated in 2 l tap water containing 20 g glucose animalÿ1 day ÿ1) would increase total tract

nutrient digestion. Intake and digestion of organic matter were not a�ected �p > 0:10� by GEL but NDF digestibility was decreased

�p < 0:06� when GEL was consumed. Although GEL appeared to be present in the rumen samples, higher concentrations may be

needed to elicit a detectable in vivo response. Ó 2000 Elsevier Science Ltd. All rights reserved.

Keywords: Ammonium polyacrylate; Steers; Fiber; Cellulolysis; Support

1. Introduction

Polymers containing acrylamide and/or acrylate havebeen shown to be non-toxic to animals and humans andresistant to microbial attack (Seybold, 1994). Thepolymers have been investigated as soil additives todecrease erosion (Seybold, 1994), gelling agents in insectdiets (Honda et al., 1996), coagulants for protein re-covery in wastewater (Guerrero et al., 1998) and aspromoters of fungal growth in vitro through the pre-vention of spore aggregation (Wainwright et al., 1993).Cellulolytic bacteria, fungi and protozoa in the rumenare sensitive to high ruminal passage rates, washout of®ber containing attached microorganisms (Latham etal., 1979; Akin and Barton, 1983; Morris and Cole,1987; Miron et al., 1989; Bhat et al., 1990) and decreasesin ruminal pH below 6.0 (Smith et al., 1973; Mould andérskov, 1983; Hoover, 1986). A gel consisting of hy-drated ammonium polyacrylate (GEL: 20 g ammoniumpolyacrylate hydrated in 2 l of tap water containing 20 gglucose) does not contain the neurotoxin acrylamide(Seybold, 1994) and may serve as an inert support to

trap cellulolytic bacteria within the rumen when dilutionrates exceed growth rates (H�aggstr�om, 1983) or when®ber levels are low (Prigge et al., 1990). If a decrease incellulolytic numbers could result in a substantial lagtime between ®ber intake and the onset of ®ber degra-dation on a particular diet, increased cellulolytic popu-lations could colonize ingested feed more rapidly,decrease the time before the initiation of cellulolysis andincrease overall ®ber digestion. GEL may also form adi�usion barrier against a sudden decrease in pH in amethod suggested by H�aggstr�om (1983) and may bindfree hydrogen ions around the GEL with ammoniumions. As polyacrylamide has been shown to serve as thesole N source for soil bacteria (Kay-Shoemake et al.,1998), GEL may also provide a nitrogen source to at-tached bacteria. The objective of this experiment was todetermine if the concentration of GEL increased thetotal tract nutrient digestion of steers.

2. Methods

2.1. Animals and diets

Six Holstein steers with an average weight of 475 kgand ®tted with ruminal, duodenal and ileal cannulas

Bioresource Technology 73 (2000) 81±85

* Corresponding author. Tel.: +409-845-3406; fax: +409-845-1921.

E-mail address: kgm4958@tamvm1.tamu.edu (K.G. Maciorowski).

0960-8524/00/$ - see front matter Ó 2000 Elsevier Science Ltd. All rights reserved.

PII: S 0 9 6 0 - 8 5 2 4 ( 9 9 ) 0 0 1 3 8 - 8

according to procedures approved by the Purdue Ani-mal Care and Use Committee were used in a modi®edswitchback design with three periods and two treatments(�=ÿGEL). The animals were individually housed infree stalls at the Purdue University Beef Cattle ResearchCenter and were allowed a full range of movement aswell as continuous lighting, ventilation, trace mineralsalt blocks and water. The steers consumed a diet con-sisting of 50% roughage and 50% concentrate on a drymatter basis and containing between 14.1% and 14.5%crude protein (Table 1). Mineral levels were within rec-ommended NRC levels for 500 kg steers (NRC, 1984).

2.2. Feeding regimen

Periods were 21 days long and consisted of 17 daysfor adjustment and 4 days for sample collection. Steerswere o�ered diets at 0730 and 1930 and unconsumedfeed was measured before the morning feeding. If un-consumed feed exceeded approximately 1.5 kg dayÿ1

during the adjustment period, the respective steerÕs feedwas incrementally reduced by 0.1% or 0.2% units ofbody weight until feed refusals were less than 1.5 kgdayÿ1. When feed refusals were consistently less than 1.5kg dayÿ1, the steerÕs daily ration was considered to bethat steerÕs ad libitum intake. During collection periods,steers were o�ered rations at 90% of each steerÕs adlibitum intake. To form approximately 2 l of GEL, 20 gof ammonium polyacrylate was added to 2 l of tap watercontaining 20 g of glucose and allowed to hydrateovernight at 4°C. The morning ration of each treatmentanimal was top-dressed with approximately 2 l of GEL.The morning ration of each control animal was top-dressed with 20 g of glucose (Sigma, St. Louis, MO). Alldiets were then manually mixed to insure even distri-

bution before consumption. In most cases, the animalsconsumed feed containing GEL or glucose within 1 h offeeding.

2.3. Feed and intestinal sampling

During sampling periods, feed refusals and each feedcomponent were sampled daily, composited by periodand stored at 4°C until processed. Every 4 h, 300 ml ofduodenal and 200 ml of ileal digesta were sampled andcomposited by steer. Fecal grab samples were takenevery 6 h and also composited by animal. The duodenal,ileal and fecal sample collection times were advanced by1 h each day to adjust for diurnal variation in gastro-intestinal ¯ow rates. Samples were stored at )20°C be-tween time of sampling and processing or analysis,unless otherwise noted.

2.4. Ruminal sampling procedures and assays

On the fourth day of each sampling period, ruminalcontents were sampled at 3, 6, 9 and 12 h after themorning feeding. The samples were obtained from fourdi�erent areas of the reticulorumen using a core sam-pling device (Firkins et al., 1986) and strained throughtwo layers of cheesecloth for a ®nal sample volume of150 ml. The pH of each sample was measured immedi-ately using an Orion pH meter (Orion Research, Boston,MA). Eight ml of ruminal ¯uid were added to scintil-lation vials containing 2 ml of 25% m-phosphoric acidand placed on ice for short chain fatty acid (SCFA)analysis by gas chromatography (Wachenheim andPatterson, 1992). Fifty ml of ruminal ¯uid were pouredinto bottles containing 3 ml of 6 N HCl, placed on iceand transported to the lab for the determination of

Table 1

Composition of diet fed to steers

Ingredients % of DM Chemical analysis of complete diet % of DM

Alfalfa silage 40.00 Crude proteina ;b 14.30

Chopped alfalfa hayc 10.00 ADFg 19.30

Cracked corn 40.21 NDFg 31.53

Soybean meal (48%) 8.60 AIAg 0.38

Trace mineralized saltd 0.50 Calcium 0.75

Dicalcium phosphate 0.40 Phosphorus 0.36

Se 200 premixe 0.16 Potassium 1.42

Vitamin ADEK premixf 0.10 Magnesium 0.21

Vitamin E premixg 0.03 Sulfur 0.22

a Calculated as Kjeldahl N * 6.25.b Acid detergent ®ber (ADF), neutral detergent ®ber (NDF) and acid insoluble ash (AIA) were calculated as the average of analyzed values of three

periods.c Ground in a tub grinder to give an average particle length of 7 cm.d g/100 g: NaCl, 98; Zn, 0.35; Fe, 0.2; Mn, 0.2; Cu, 0.033; I, 0.007.e 0.2 g Se kgÿ1 premix.f kgÿ1 premix: vitamin A, 10 000 IU; vitamin D3, 2502 IU; vitamin E, 1102 IU; menadione (vitamin K precursor), 734 mg.g 20 k IU of vitamin E kgÿ1 premix.

82 K.G. Maciorowski et al. / Bioresource Technology 73 (2000) 81±85

ammonia concentration by the method of Chaney andMarbach (1962).

2.5. Exchange of ruminal contents

Ruminal contents were transferred among animals ofdi�erent treatments between sampling periods to mini-mize carryover e�ects. Feed was withheld on themorning when contents were transferred to lessen totalruminal bulk. Steers of approximately equal weight werepaired between treatments and their rumens were evac-uated using a wet/dry vacuum (Shop-Vac, Williamsport,PA and Irvine, CA). Ruminal contents were switchedwithin the pairs and reintroduced into the rumen within15 min of evacuation.

2.6. Intestinal analyses

Duodenal and ileal digesta were later thawed andmixed. A homogenous 1000 g wet weight subsample wasfreeze dried (Unitop 600 L freeze-drier, The Virtis,Gardiner, NY 12525). Feed components, duodenalsubsamples and fecal samples were analyzed for drymatter (DM) content and ground through a 1 mmscreen (no. 1 Wiley Mill, Arthur H. Thomas, Philadel-phia, PA). Organic matter analysis was performed byashing the samples overnight at 600°C. Acid detergent®ber content was determined by the method of VanSoest (1963), neutral detergent ®ber by the method ofVan Soest et al. (1991) and Kjeldahl-nitrogen content asper AOAC (1984).

2.7. Flow rate determination

Capsules containing chromium oxide were placed inthe rumen of each steer twice daily (15 g dayÿ1) throughX-shaped incisions in the ruminal cannulas for the de-termination of ¯ow rate. Freeze-dried duodenal digestaand fecal samples were analyzed for chromium contentby the method of Williams et al. (1962) using a Perkin±Elmer 460 Atomic Absorption Spectrophotometer(Perkin±Elmer, Norwalk, CT). Acid insoluble ash con-tent was determined by the method of Van Keulen andYoung (1977).

2.8. Statistical analysis

Data were analyzed by ANOVA using the generallinear model procedure of SAS for an incompleteswitchback design with two treatments (SAS, v. 6.03,Cary, NC, 1986). Sums of squares for the model wereseparated into steer, period and treatment e�ects.Analysis of ammonia, pH and SCFA concentrationsalso included the e�ect of sampling time and an inter-action term to test for time by treatment interaction.Statistical signi®cance was de®ned as a probability level

of P < 0.05 and a trend towards a particular e�ect wasde®ned as a probability level of P < 0.10.

3. Results and discussion

No signi®cant di�erences between steers fed GEL andthose fed glucose were detected for intake or digestion ofany feed fraction measured, total tract apparent digest-ibility, duodenal ¯ow, fecal excretion, ruminal pH orruminal concentrations of ammonia, butyrate or is-ovalerate (Tables 2 and 3, P > 0:10). Nitrogen ¯ow anddigestibility at the duodenum was unreasonably high,probably due to variability in duodenal ¯ow markerconcentration. Acetate, propionate, isobutyrate andvalerate concentrations signi®cantly changed over time�P < 0:05�, but did not vary between treatments�P > 0:10�. A trend towards greater fecal NDF excre-tion �P < 0:06� and a decrease in NDF digestibility�P � 0:10� was detected. GEL may have inhibited di-gestion of the NDF fraction of the feed, but the decreasemay also be due to di�culties in the analysis of NDF inthe presence of GEL. The distilled water used in theNDF assay may have hydrated GEL particles and pre-vented proper ®ltration. Since GEL was not present incontrol animals, incomplete ®ltration could produce agreater amount of apparent NDF residue and the ap-pearance of decreased feed digestion in samples fromtreated animals. This e�ect was also noted in duodenalsamples, which could not be analyzed for NDF due toan inability to ®lter the samples.

GEL may have been inappropriate as a support forcellulolytic bacteria. Nylon bag studies (data not shown)indicated that a coccobacillus resembling Fibrobactersuccinogenes was associated with GEL, but the attachedbacteria may have been non-cellulolytic in vivo. Theconcentration of GEL used in this trial may not haveprovided su�cient support to increase cellulolytic pop-ulations or a�ect rumen fermentation patterns. GELswollen in tap water shrinks about 10-fold when im-mersed in a high-mineral solution such as ruminal ¯uid(preliminary data not shown) and may be sensitive tophysical breakdown (Seybold, 1994). The di�culties in®ltering the NDF fraction suggest that GEL was pre-sent, but as GEL resembled the color of surroundingruminal ¯uid when immersed in vitro, it was di�cult todetect visually. Due to the limited number of cannulatedand ®stulated steers available, funding restrictions andthe limited time allotted for the study, though, only theconcentration of GEL suggested by the manufacturer(Red Sea Construction) was evaluated. GEL may bee�ective at higher doses or with animals with a greatermetabolic demand for energy, such as high producingdairy cattle. Future studies with in vitro continuousfermentors containing mixed ruminal microorganismscould investigate the e�ect of GEL concentration

K.G. Maciorowski et al. / Bioresource Technology 73 (2000) 81±85 83

Table 2

E�ect of GEL on nutrient digestion in steers

GEL

())a (+)b SEMc P-value

Item �n � 6�DM 9240 9270 440 0.97

OM 8600 8630 410 0.96

NDFd 2920 2910 130 0.96

ADFe 1800 1790 80 0.93

N 212 212 10 0.98

Flow at duodenum (g dayÿ1)

DM 4460 3540 410 0.14

OM 3960 3000 490 0.18

Fecal excretion (g dayÿ1)

DM 2080 2330 180 0.35

OM 1860 2080 160 0.39

NDF 1040 1290 80 0.06

ADF 590 730 70 0.16

N 53 60 4 0.25

Nutrients digested (g dayÿ1)

DM 7160 6940 430 0.72

OM 6740 6550 400 0.76

Apparent preduodenal digestibility (% of intake)

DM 50.8 61.5 4.9 0.15

OM 53.0 65.1 5.4 0.15

Apparent total tract digestibility (% of intake)

DM 77.3 74.9 2.2 0.46

OM 78.9 75.9 2.2 0.51

NDF 64.3 56.3 3.0 0.10

ADF 66.8 60.2 3.1 0.16

N 74.9 71.8 2.3 0.38

a 20 g glucose top dressed at 0730 feeding.b Two l of GEL (20 g ammonium polyacrylate added to 2 l tap water containing 20 g glucose and allowed to hydrate overnight at 4°C) top dressed at

0730 feeding.c Standard error of the mean.d Neutral detergent ®ber residue.e Acid detergent ®ber residue.

Table 3

E�ect of GEL on ruminal characteristics of steers

Hours post feeding

parameter (n� 6)

()GEL)a (+GEL)b SEMc

3 6 9 12 3 6 9 12

NH3±N (mg dlÿ1) 9.8 9.4 7.3 9.9 9.4 9.5 9.1 9.3 0.9

pH 6.1 6.2 6.3 6.3 6.2 6.2 6.2 6.3 0.1

Acetate (mM) 61.6 58.6 54.6 53.7 62.3 64.0 56.6 55.3 3.0

Propionate (mM) 15.9 15.4 13.4 14.5 16.2 16.5 14.4 14.9 0.8

Isobutyrate (mM) 1.0 1.0 0.9 0.9 1.0 1.1 0.9 0.9 0.1

Butyrate (mM) 10.4 10.3 8.6 9.4 10.4 10.7 9.4 9.0 0.7

Isovalerate (mM) 0.8 0.8 0.6 0.8 0.8 0.8 0.6 0.8 0.1

Valerate (mM) 1.3 1.3 1.0 1.0 1.3 1.3 1.1 1.0 0.1

Total SCFA (mM) 91.0 87.4 79.1 80.3 92.0 93.4 83.0 81.9 4.5

a 20 g glucose top dressed at 0730 feeding.b Two l of GEL (20 g ammonium polyacrylate added to 2 l tap water containing 20 g glucose and allowed to hydrate overnight at 4°C) top dressed at

0730 feeding.c Standard error of the mean.

84 K.G. Maciorowski et al. / Bioresource Technology 73 (2000) 81±85

without having to rely upon expensive and labor inten-sive in vivo trials.

Acknowledgements

This work was supported by Purdue University De-partment of Animal Science Hatch funds and the sup-port of Red Sea Construction The authors would like tothank P. Boccazzi, P.A. Jaynes, D. Mcintyre and R.Pender for technical assistance.

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