J. Anim. Sci. 2005. 83:2806-2814
© 2005 American Society of Animal Science
Effects of pasteurization of potato slurry by-product fed in corn-or barley-based beef finishing diets1
J. I. Szasz*,
C. W. Hunt*,2,
O. A. Turgeon, Jr.
,*,
P. A. Szasz* and
K. A. Johnson
* Department of Animal and Veterinary Science, University of Idaho, Moscow 83844-2330;
and
Koers-Turgeon Consulting Service, Inc., Amarillo, TX 79188; and
and
Department of Animal Sciences, Washington State University, Pullman 99164
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Abstract
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Pasteurization of vegetable by-products such as potato slurry (PS) before feeding may be necessary to prevent the spread of pathogens and beef carcass blemishes. We hypothesized that pasteurization would increase ruminal fermentability of PS starch. Four ruminally cannulated crossbred beef steers (initial BW = 432) were used in a 4 x 4 Latin square experiment with a 2 x 2 factorial arrangement of treatments to examine the main effects and interactions of pasteurization (54.4° C for 2 h) of PS and grain type (GT; dry-rolled corn and barley) on ruminal and total tract digestion of beef finishing diets. Diets contained 7% alfalfa hay and 14% PS (DM basis) and were fed ad libitum three times daily. Corn-based diets had 71.7% corn, whereas barley-based diets had 60% barley and 11.7% corn. Pasteurization resulted in greater (P = 0.004) soluble, rapidly degradable starch (34.3 vs. 26.7% for pasteurized and nonpasteurized PS, respectively). Ruminal fluid pH was more acidic (P < 0.07) for corn-based diets than for barley-based diets (P = 0.07) at 0200 and 2100 (sample time x GT; P < 0.05). Ruminal fluid pH was more acidic (P = 0.06) at 1400 for corn-based diets containing pasteurized PS compared with other dietary treatments (sample time x pasteurization x GT; P = 0.04). Minimum and maximum ruminal pH were greater (P < 0.10) for barley-based diets than for corn-based diets. Ruminal fluid pH was < 6.0 for a greater (P = 0.04) proportion of the day for corn-based compared with barley-based diets. In vitro incubation measurements revealed that pasteurization of PS resulted in lower (P = 0.06) ruminal fluid ammonia N concentration. Ruminal fluid ammonia N concentration was lower (P = 0.11) for barley-based diets than for corn-based diets. Steers fed barley-based diets had greater (P = 0.02) DMI and lesser (P < 0.05) total tract digestibility of DM and ADF compared with steers fed corn diets. Pasteurization increased (P = 0.10) total tract starch digestibility. Results indicate pasteurization increased rapidly degradable starch, ruminal starch fermentability, and total tract starch digestibility of PS. Grain type interacted with pasteurization such that feeding corn-based diets containing pasteurized PS resulted in periodic reductions in ruminal pH. Feeding management may be more critical when feeding pasteurized PS in beef finishing diets.
Key Words: Cattle • Feedlot • Fermentation • Gelatinization
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Introduction
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Potato by-products represent an opportunity for cattle feeders in the Pacific Northwest because potato byproducts are a low-cost yet energy-dense dietary ingredient. Potato slurry (PS) is a common potato by-product; however, PS contaminated with Taenia saginata (beef tapeworm) ova has been implicated in some cysticercosis outbreaks (Hancock et al., 1989
; Yoder et al., 1994). Although pasteurization has been used to kill T. saginata ova (Hancock, 2002), effects of pasteurizing on feeding value of PS are unknown. Nevertheless, heat treatment increases ruminal fermentability of feed grains (Rooney and Pflugfelder, 1986; McNiven et al., 1995), primarily as a result of gelatinization of starch. Therefore, pasteurization may result in similar effects, thus modifying the feeding characteristics of PS.
Corn and barley are common grains used in beef finishing diets. Differences exist between corn and barley with regard to ruminal starch fermentation. Barley exhibits a greater rate of ruminal starch fermentation compared with corn (Owens et al., 1986). Forty percent of starch in corn escaped ruminal fermentation compared with only 10% of barley starch (Orskov, 1986). The starch component of corn is fermented more slowly and continuously in the rumen, resulting in greater starch flow to the small intestine (Brake et al., 1989). Because pasteurization may increase ruminal starch degradability of PS, pasteurization effects may interact with grain type (GT) in high-energy finishing diets. Therefore, the objectives of this study were to measure the main effects and interactions of PS pasteurization and GT on digestion of beef finishing diets.
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Materials and Methods
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In Vitro Starch Disappearance
Potato slurry was obtained from a commercial beef feedlot located in Washington State (Beef Northwest, Quincy, WA). Slurry was previously obtained by the feedlot from a local potato processing plant (Lamb Weston, Quincy, WA). Potato slurry was stored in an earthen pit and pasteurized using a commercial milk pasteurization unit. Pasteurization was accomplished by heating the slurry via heat exchangers to 54.4° C for 10 min. Pasteurized and nonpasteurized slurry samples were lyophilized and ground using a mortar and pestle. In vitro disappearance measurements of lyophilized potato slurries were conducted using methods described by Hristov et al. (2002). Triplicate samples (0.5 g) of lyophilized PS (pasteurized and nonpasteurized) were weighed into 125-mL Erlenmeyer flasks (three flasks/PS treatment/incubation time). McDougall’s buffer (McDougall, 1948) was prepared 1 d before initiating the trial. After preparation of the buffer, CO2 was added using a porous silica probe until the pH of the solution reached 6.8. The solution was then stored at 39° C. On the day of the trial, 2.5 g of glucose and 117 mg of 2-mercaptoethanol were added to the buffer, and lyophilized PS samples were hydrated by adding 20 mL of the buffer solution to flasks. Flasks were then stored at 39° C.
One ruminally cannulated Holstein cow (fed twice daily ad libitum a diet consisting of 40% alfalfa hay and 60% corn-barley mix on a DM basis) served as the source of ruminal inoculum. Two hours after the a.m. feeding, a representative sample of ruminal contents was obtained from the donor cow. The sample was mixed, and a subsample of ruminal contents was squeezed through two layers of cheesecloth until 2.0 L of ruminal fluid were obtained. Ruminal contents remaining on the cheesecloth were then washed with 2.0 L of buffer and squeezed through two layers of cheesecloth; the two filtrates were then combined. Filtrate was stored in a prewarmed insulated container for transport to the laboratory. Ruminal fluid solution was stored in a 39° C oven for 45 min to allow low density particulate to rise. Particulate was subsequently removed using a vacuum. Samples were inoculated by adding 40 mL of the ruminal fluid plus buffer solution to the flasks. Flasks were then vigorously stirred. Blank flasks containing only the ruminal fluid plus buffer solution were incubated at each time point to correct for microbial and feed particulate contamination.
Flasks were briefly flushed with CO2 to remove O2 and then capped with stoppers equipped with one-way valves and incubated for 0, 1, 2, 4, 8, 12, 16, 20, and 24 h at 39° C under continuous agitation in a forced-air oven. Zero-hour flasks received only 40 mL of buffer solution followed by agitation for only 15 min. After incubation periods, flasks were removed from the incubator, and formalin (0.6 mL) was added to halt microbial fermentation. Flasks and contents were then stored in an ice bath until further processing. Contents of each flask were transferred to a 100-mL centrifuge tube and centrifuged at low speed (2,200 x g) for 15 min. Supernatant was discarded, and the sediment was transferred after mixing it with distilled water into 120-mL pre-weighed sample cups. Sample cups containing residues were then dried at 55° C for 48 h. Dry sample cups were weighed, and residues were analyzed for starch (AOAC, 1990; total starch assay kit obtained from Megazyme Intl. Ireland Ltd., Wicklow, Ireland). In vitro starch disappearance (IVSD) was calculated as the amount of starch that disappeared during in vitro incubation (blank corrected).
In vitro starch disappearance values were applied to the following equation (Orskov and McDonald, 1979) using the NLIN procedure of SAS (Version 8, SAS Inst., Inc., Cary, NC):
where p = starch that disappeared at time t (%); a = soluble, rapidly degradable fraction (%); b = potentially degradable fraction (%); c = rate at which b disappeared per hour; and t = incubation time (h).
Effective starch degradability (ED) was determined using the equation
where a, b, and c are constants from the nonlinear kinetics model, and k is the fractional outflow rate, assumed to be 5.0%/h. Differences in starch disappearance for each time of incubation and in kinetic parameters of starch disappearance were detected using the TTEST procedure of SAS.
Metabolism Study
Animals, Feeding, and Experimental Timeline.
Four ruminally and duodenally cannulated crossbred steers (approximate mean BW = 450 kg) were used in a 4 x 4 Latin square design to evaluate the effects of pasteurization of PS fed in corn- or barley-based finishing diets on ruminal and total tract digestion. Duodenal T-type cannulas were placed within 20 cm caudal to the pyloric sphincter (Streeter et al., 1991). Animals were housed in individual pens (approximately 25 m2) and were allowed ad libitum access to fresh water. Pens had concrete floors, and one-half of each pen was indoors with rubber mats on the floors. Solid waste was removed from each pen daily.
Dietary treatments consisted of corn- or barley-based (blend of 60% barley and 40% corn on a DM basis) finishing diets containing unpasteurized or pasteurized PS; chemical and ingredient composition of diets is shown in Table 1. Diets were prepared daily at 0600 as a total mixed ration and were offered in three equal portions at 0700, 1100, and 1500 to simulate feeding practices at commercial beef feedlots. All diets were formulated to contain sodium monensin and tylosin (33 and 11 mg/kg, respectively; Elanco Animal Health, Indianapolis, IN). Potato slurry was monitored daily for DM, and adjustments to as-fed ingredient amounts were made accordingly. Other dietary ingredients were more static in DM content; therefore, weekly DM analyses were used for adjusting as-fed percentages of each ingredient. Feed offered, diet DM, and orts were recorded daily. Experimental periods lasted 21 d. Animals were allowed to adapt to their respective dietary treatment for 10 d (d 1 to 10) followed by measurement of DMI for 7 d (d 11 to 17). Each experimental period concluded with a 4-d sample collection period (d 18 to 21). Experimental procedures were approved by the University of Idaho Institutional Animal Care and Use Committee (Protocol number 2003–45).
Ruminal Fermentation.
On d 18, ruminal fluid pH was obtained at 0200, 0700, 0800, 0900, 1000, 1200, 1400, 1600, 1800, 2100, and 2300. Ruminal fluid pH was measured by submersing a combination pH electrode (Model SA720; Orion, Boston, MA) into the rumen. A numerical integration method was used to approximate the sum of time ruminal fluid pH was below a given value; computations were made using a DATA step macro in SAS (SAS Inst., Inc.). Ruminal contents were obtained at 0700, 1000, 1400, and 2100 and strained through two layers of cheesecloth to collect approximately 120 mL of ruminal fluid. Fluid was stored on ice and then centrifuged (2,000 x g for 5 min at 4° C) to remove feed particulate. After centrifugation, an aliquot of supernatant (85 mL) was placed into a 120-mL sample cup containing 7 mL of chilled 65% trichloroacetic acid solution and was vigorously swirled. This sample was stored on ice for 30 min and then frozen. Upon thawing and centrifugation (20,000 x g for 15 min), samples were analyzed for ammonia N concentration via spectrophotometry (Lachat AE Quikchem, Milwaukee, WI) according to the procedures of Broderick and Kang (1980). Another aliquot (10 mL) was added to a 15-mL sample cup containing 2 mL of 25% meta-H2PO4 and was vigorously swirled. This sample was immediately frozen and, upon subsequent thawing and centrifugation (20,000 x g for 15 min), was analyzed for VFA concentration by gas chromatography (Supelco, 1998; Model 6890, Hewlett Packard, Palo Alto, CA).
Intake and Digestibility.
Six fecal samples (approximately 500 g) and six duodenal samples (approximately 500 mL) were obtained on d 19 through 21 to represent every 4-h period within a 24-h feeding cycle. Duodenal samples were composited by animal within period and frozen at –20° C until further processing. Subsequently, duodenal samples were lyophilized and ground using a mortar and pestle. Fresh fecal samples were transferred to a forced-air oven and dried at 55° C for 72 h, composited by animal within period, and ground to pass through a 2-mm screen using a Udy cyclone mill (Udy Corp., Fort Collins, CO). Ground duodenal and fecal samples were analyzed for DM, ash (AOAC, 1990), starch, ADF (Van Soest et al., 1991 as modified by Komarek, 1993), GE by bomb calorimetry (1261 Isoperibol Calorimeter; Parr Instrument Co., Moline IL), and acid detergent insoluble ash (Bodine et al., 2002). Total tract nutrient digestibilities were calculated using acid detergent insoluble ash as an internal marker with the computations of Merchen (1988).
Statistical Analysis.
Data were analyzed as a 4 x 4 Latin square design with a 2 x 2 factorial treatment arrangement using the MIXED procedure of SAS. The statistical model was
where µ = overall mean, 
I = random effect of steer (i = 1 to 4), ß j = fixed effect of period (i = 1 to 4), 
k = fixed effect of pasteurization, 
l = fixed effect of GT, kl = fixed effect interaction term, and 
ij(k) = residual error term, which was distributed normally.
Similarly, a mixed linear model (using the MIXED procedure) was used to analyze ruminal fluid variables measured over time (Littell et al., 1998). Effects within the previous model were retained along with the inclusion of a sampling time effect and the resulting interactions. Different covariance matrix structures were assessed for the given data in an iterative process; the best-fitting structure was then selected based on the Bayesian information criterion (Schwartz, 1978). In the event that an interaction between PS and GT was detected, means were compared using Tukey’s honestly significant difference procedure.
Characterization of Grains and Potato By-Product.
Pasteurized and nonpasteurized PS used during the metabolism study were from the same source described for the in vitro study. Potato slurries were stored in 208-L drums equipped with lids and plastic liners. Samples of PS were obtained daily during each collection period and were then composited within PS type (pasteurized and nonpasteurized). Composited samples were lyophilized and ground using a mortar and pestle. Ground samples were then analyzed for DM, ash, N (AOAC, 1990), NPN (AOAC, 1990), starch, ADF, Ca, P, K, and Mg (AOAC, 1990). Compositions of PS are shown in Table 2.
Characterization of grains is shown in Table 3. Barley was a two-row Baronesse variety and had a bulk density of 0.64 kg/L (49.6 lb/bu), and corn was purchased as US grade No. 2 from a nearby grain elevator and had a bulk density of 0.71 kg/L (55 lb/bu). Samples of whole grain were ground to pass through a 2-mm screen using a Udy cyclone mill, and chemical composition was analyzed using the aforementioned procedures. Grains used in the experimental diets were dry-rolled (Farm-King model Y100, Buhler Industries Inc., Winnipeg, Canada); roller position was maintained at a gap required to fracture every kernel. Bulk density was monitored weekly on pre- and post-processed grain samples, and the processing index was calculated according to Wang et al. (2003). Particle size distribution of processed grains was determined by a dry sieving method using an analytical sieve shaker (Retsch model AS200, Rheinische, Germany) equipped with US Standard Sieves (4.75, 3.35, 2.0, and 0.85 mm) arranged in descending order above a collection pan (< 0.85 mm). Geometric mean diameter (dgw) and standard deviation (Sgw) were determined by applying the following equations to the fraction of weight passing through sieves (Baker and Herrman, 2002):
where di = geometric mean diameter of sieve i and Wi = weight fraction on sieve i. Surface area (SA) was estimated using the equation:
where ß s = shape coefficient for calculating SA of particles (fixed at 6), ß v = shape coefficient for calculating volume of particles (fixed at 1), and 
= specific weight of material (fixed at 1.32; Pfost and Headley, 1976, as cited by Baker and Herrman, 2002).
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Results and Discussion
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In Vitro Starch Disappearance
In vitro starch disappearance of both pasteurized and nonpasteurized PS was rapid and extensive, having 99% disappearance by 16 h of incubation (Table 4). Disappearance of starch at 0 and 2 h of incubation was greater (P < 0.10) for pasteurized PS than for nonpasteurized PS. No differences because of PS substrate type were observed at any other incubation times. The kinetic model explained a considerable portion of the variation in IVSD (R2 = 0.96 to 0.98). The soluble, rapidly degradable fraction was greater (P = 0.004) for pasteurized PS than for nonpasteurized PS (34.3 and 26.7%, respectively); these values correspond reasonably well with our observed 0-h IVSD values. Extent of IVSD was reached at 24 h; therefore, the kinetics model was constrained so that the soluble, rapidly degradable fraction plus the insoluble, potentially degradable fraction would not exceed 100%. As a result, the greater soluble, rapidly degradable fraction was compensated by a lower (P = 0.004) insoluble, potentially degradable fraction for pasteurized compared with non-pasteurized PS. The rate at which the insoluble, potentially degradable fraction degraded was not affected by PS substrate type. Effective starch degradability tended to be greater (P = 0.15) for pasteurized than for nonpasteurized PS.
Our findings parallel those of Monteils et al. (2002), who reported 38% soluble starch for potato peelings. Monteils et al. (2002) also noted potato peelings had in situ starch disappearances of 50 and 96% at 1 and 12 h of incubation, respectively, which is similar to starch disappearances for PS used in the current study (40.0 and 94.9% for 1 and 12 h of incubation, respectively). Heat treatment, in combination with excess water, typically results in gelatinization of starch. The gelatinization process involves hydration of starch granules followed by subsequent deterioration of swollen starch crystallites (Belitz and Grosch, 1999). Indeed, gelatinization depends on thermal energy, but arguably more important to this process is the water content of the suspension itself. For instance, dried starch heated at temperatures of 180° C with 1 to 3% water undergoes only minor changes, whereas starch in a solution containing 60% water completely gelatinizes at temperatures as low as 70° C (Belitz and Grosch, 1999). For this reason, we hypothesized that pasteurization of PS would result in improved starch use. However, because of the high degree of fermentability of uncooked PS, we found that pasteurization only increased the soluble (rapidly fermentable) starch fraction of PS.
Metabolism Study
Ruminal Fermentation.
A sampling time x pasteurization x GT interaction was detected (P = 0.04) for ruminal fluid pH. Accordingly, main effects and interactions were tested across individual sample times (Figure 1). At 1400, steers fed corn-based diets containing pasteurized PS had a more acidic (P = 0.06) ruminal fluid pH compared with steers fed the other diets. Ruminal fluid pH was also more acidic (P < 0.07) for corn-based diets compared with barley-based diets at 0200 and 2100; these sample times were all > 6 h after the most recent feeding. Pasteurization of PS resulted in more acidic (P = 0.08) ruminal fluid pH at 0200. Minimum ruminal fluid pH was lower (P = 0.10) for corn-based diets than for barley-based diets (Table 5). Maximum pH was greater (P = 0.04) for steers fed barley-based diets than for steers fed corn-based diets. Variation in ruminal fluid pH (reported as CV) was similar between dietary treatments. Ruminal fluid pH was < 5.5 and was similar across dietary treatments; however, the time spent below pH 6.0 was greater (P = 0.04) for corn-based diets compared with barley-based diets.
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Figure 1. Effect of pasteurization of potato slurry (PS) and grain type (GT; corn or barley) on ruminal fluid pH (pasteurization x GT x sampling time; P = 0.04). Values are expressed as least squares means. Arrows indicate time of feeding. aMain effect of GT (P = 0.07). bMain effect of pasteurization (P = 0.08). cCorn-based diet containing pasteurized PS compared with other dietary treatments (pasteurization x GT; P = 0.06).
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Table 5. Effect of pasteurization of potato slurry (PS) and grain type on ruminal ammonia N and VFA concentrations and pH
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Radunz et al. (2003) fed corn-based beef finishing diets containing 11.4% (DM basis) potato-processing waste and found that mean ruminal fluid pH was 6.02. This value is numerically greater than the mean ruminal fluid pH for our corn-based diets (5.59). Increased fermentability of pasteurized PS, as indicated by the in vitro results, likely resulted in more rapid production of organic acids and a decrease in ruminal fluid pH. Because corn and barley differ in degree of starch fermentability, we hypothesized that GT may interact with pasteurization, thereby altering ruminal fermentation; however, we hypothesized barley would have an additive effect on ruminal starch fermentation. On the contrary, corn fed in combination with pasteurized PS produced lower ruminal fluid pH after the last feeding of the day. Presumably, this response was due to 7.7% more starch for corn-based diets compared with barley-based diets, thereby resulting in greater production of organic acids. To ensure diets were isonitrogenous, corn-based diets were supplemented with 0.3% urea (DM basis). Therefore, ruminal fluid ammonia N concentration was greater (P = 0.11) for corn-based diets than for barley-based diets (Table 5
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Pasteurization reduced (P = 0.06) ammonia N concentration in ruminal fluid, which is consistent with the observation that pasteurized PS is more ruminally fermentable. Total VFA concentration was not affected by pasteurization (Table 5); however, steers fed corn-based diets tended (P = 0.13) to have greater total VFA compared with those fed barley-based diets. Pasteurization of PS reduced (P = 0.03) molar proportions of acetate. A time x treatment interaction was detected (P < 0.001) for ruminal fluid propionate (Figure 2). At 1000, barley-based diets containing nonpasteurized PS resulted in a lower (P < 0.05) molar proportion of propionate compared with barley-based diets containing pasteurized PS and corn-based diets containing nonpasteurized PS (pasteurization x GT; P = 0.003). At 1400, molar proportion of propionate was greater (P = 0.07) for corn-based diets than for barley-based diets. Numerically greater molar proportions of acetate resulted in greater (P = 0.05) acetate:propionate for barley-based diets containing nonpasteurized PS (pasteurization x GT; P = 0.09).
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Figure 2. Effect of pasteurization of potato slurry (PS) and grain type (GT; corn and barley) on ruminal propionate concentration (pasteurization x GT x sampling time; P < 0.001). Values are expressed as least squares means. Arrows indicate time of feeding. a,b,cDifferent letters indicate significant (P < 0.07) differences (pasteurization x GT; P = 0.003). Nonpasteurized PS + barley vs. others (P < 0.05; pasteurization x GT; P = 0.08).
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Intake and Digestibility.
Pasteurization of PS did not affect intake of DM, starch, or ADF (Table 6). Steers fed corn-based diets consumed less (P = 0.02) DM than did steers fed barley-based diets. Digestibility of DM was not affected by pasteurization of PS; however, DM and ADF digestibilities were greater (P < 0.05) for corn-based diets than for barley-based diets. Intake of DM and ADF was greater (P < 0.05) for barley-based diets compared with corn-based diets. Pasteurization increased total tract ADF (P = 0.02) and starch (P = 0.10) digestibility. Starch digestibility and intake were not affected by GT. Dry matter and starch digested daily were not affected by dietary treatment. Whereas the amount of ADF digested daily was not impacted by GT, cattle fed diets containing pasteurized PS had a greater (P = 0.02) amount of ADF digested than did those fed diets containing nonpasteurized PS. Intake of DE was not affected by dietary treatment.
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Table 6. Effect of pasteurization of potato slurry (PS) and grain type on total tract nutrient digestibility and DE content
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Surber and Bowman (1998) compared dry-rolled corn and barley in beef finishing diets and noted that total tract starch digestibility for barley diets was 5% greater compared with corn diets (99.3 and 94.6%, respectively). Similarly, Feng et al. (1995) fed beef steers diets containing barley or corn and found that total tract starch digestibility was 4.7% greater for barley vs. corn diets (96.0 and 91.7%, respectively). In contrast, Spicer et al. (1986) fed beef steers barley-based or corn-based finishing diets and found that total tract starch digestibility was similar between the two diets, averaging 99.2%. In the current study, total tract starch digestibility was similar between corn-based and barley-based diets, averaging 96.9%. These digestibility coefficients also parallel other reports investigating dry-rolled corn-based (96.1%; Cooper et al., 2002) and barley-based finishing diets (95.8%; Zinn et al., 1996). Nevertheless, inconsistent reports from studies comparing corn and barley may be due to the relatively large variation in barley quality. Zinn et al. (1996) reported that digestibility of ADF in barley hulls was only 6.4%, whereas Oliveros et al. (1987) reported DM digestibility of corn bran was 59.9%. Therefore, greater ADF digestibility for corn-based compared with barley-based diets should be expected. Accordingly, the discrepancy in DM digestibility between corn-based and barley-based diets might be explained by differences in ADF digestibility between the two grains.
Greater DM digestibility for corn-based diets resulted in a 17% improvement (P < 0.001) in dietary DE content compared with barley-based diets. In cattle fed high concentrate diets, chemical factors are largely responsible for limitations in feed intake (Grovum, 1987). Such limitations are likely mediated through greater ruminal fermentation via hypertonicity of ruminal fluid and/or increased propionate absorption in the liver (Allen, 2000). In accordance with this phenomenon, steers fed corn-based diets consumed less (P = 0.02) DM compared with those fed barley-based diets. Consequently, DE intake was similar across dietary treatments. Improved total tract starch digestibility as a result of pasteurization of PS is consistent with ruminal fluid and IVSD, which indicated that pasteurization increased the fermentability of PS. The cause of improved total tract ADF digestibility as a result of pasteurization of PS is not readily apparent.
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Implications
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Beef finishing diets containing a high level of fermentable starch often present a risk for ruminal acidosis and other ruminal disorders. Potato slurry has a very rapid ruminal fermentation rate, which is further increased by pasteurization as evidenced by our in vitro data. The general lack of interactions between potato slurry pasteurization and grain type for our in vivo data suggests that the increased fermentation rate of the already highly fermentable starch found in potato slurry does not pose a significant added risk of ruminal disruption. Therefore, feeding management is likely more critical when feeding pasteurized potato slurry to feedlot cattle.
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Footnotes
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1 Special thanks to Beef Northwest Feeders (Boardman and Nyssa, OR and Quincy, WA), SDK Labs (Hutchinson, KS), and Elanco Animal Health (Indianapolis, IN). 
2 Correspondence: 209 Agricultural Science (phone: 208-885-6932; fax: 208-885-6420; e-mail: chunt{at}uidaho.edu).
Received for publication December 30, 2004.
Accepted for publication September 12, 2005.
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Abstract
Introduction
