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J. Anim. Sci. 2004. 82:2985-2994
© 2004 American Society of Animal Science

ANIMAL NUTRITION

Soybean oil supplementation of a high-concentrate diet does not affect site and extent of organic matter, starch, neutral detergent fiber, or nitrogen digestion, but influences both ruminal metabolism and intestinal flow of fatty acids in limit-fed lambs

O. Kucuk1, B. W. Hess and D. C. Rule2

University of Wyoming, Laramie 82071-3684


   Abstract
Top
 Abstract
Introduction
 Materials and Methods
 Results and Discussion
 Implications
 Literature Cited
 
Our objective was to measure ruminal fermentation characteristics and site and extent of nutrient digestion in sheep limit-fed an 81.6% (DM basis) concentrate diet supplemented with increasing levels of soybean oil. Eight white-faced wether lambs (39.9 ± 3.0 kg BW) fitted with ruminal, duodenal, and ileal cannulas were used in a replicated 4 x 4 Latin square experiment. Diets were formulated to contain 15.0% CP (DM basis) and included bromegrass hay (18.4%), cracked corn, soybean oil, corn gluten meal, urea, and limestone. Soybean oil was added to diets at 0, 3.2, 6.3, and 9.4% of dietary DM. The diet was limit-fed at 1.4% of BW. After 14 d of dietary adaptation, Cr2O3 (2.5 g) was dosed at each feeding for 7 d followed by ruminal, duodenal, ileal, and fecal sample collections for 3 d. Digestibilities of OM, starch, NDF, and N were not affected (P = 0.13 to 0.95) by increasing dietary soybean oil level. Means for true ruminal (percentage of intake), lower-tract (percentage entering the duodenum), and total-tract (percentage of intake) digestibility for each nutrient were (mean ± SEM): OM = 50.7 ± 4.66%, 71.6 ± 2.58%, and 82.7 ± 0.93%; starch = 92.0 ± 1.94%, 96.1 ± 0.70%, and 99.8 ± 0.05%; NDF = 36.7 ± 6.75%, 50.9 ± 7.58%, and 71.7 ± 1.93%; and N = 31.6 ± 9.93%, 84.1 ± 1.50%, and 81.0 ± 1.10%, respectively. Total VFA concentration was greatest in sheep fed 6.3% soybean oil and least in sheep fed 9.4% soybean oil (cubic, P = 0.01). Duodenal flow of fatty acids from the diet and those metabolized within the rumen increased (linear, P < 0.001) with increasing dietary soybean oil level. Ileal flow of 16:0, 17:0, 18:0, 18:1trans, and 18:1cis-9 fatty acids increased (P ≤ 0.04) with increasing dietary soybean oil level. Apparent small intestinal disappearance of 18:0 decreased (linear, P = 0.004) as dietary soybean oil increased, and with 9.4% dietary soybean oil, nearly half the duodenal 18:0 was observed at the ileum; thus, the true energy value of the soybean oil decreased with increasing oil supplementation. We conclude that supplementation of a high-concentrate diet with increasing amounts of soybean oil in limit-fed sheep resulted in a trade off between loss of potential dietary energy from the fat and gain of important PUFA and biohydrogenation intermediates, but without a marked influence on digestibility of other important macronutrients.

Key Words: Conjugated Linoleic Acid • Fatty Acid Absorption • Nutrient Absorption • Sheep • Trans-Fatty Acids


   Introduction
Top
 Abstract
 Introduction
Materials and Methods
 Results and Discussion
 Implications
 Literature Cited
 
Enduring periods of limited forage availability may require replacing forage and limit-feeding relatively high-concentrate diets that contain fat to enhance dietary energy density. However, diets with less than 10% fat can decrease ruminal digestion of structural carbohydrates by 50% or more, and unsaturated fatty acids can cause greater disruption of fermentation than saturated fatty acids (Jenkins, 1993Go). However, soybean oil fed at approximately 3% of the diet DM did not adversely affect nutrient digestion in sheep limit-fed either high-forage or high-concentrate diets (Kucuk et al., 2003Go). Furthermore, inclusion of 3.6% yellow grease in a limit-fed, 58% corn diet did not adversely affect total-tract digestion of DM, OM, NDF, and ADF in steers (Tjardes et al., 1998Go). Loss of unsaturated fatty acids through biohydrogenation poses additional problems to the supplementation strategy when these fatty acids are desired. However, limit-feeding an 80% concentrate diet resulted in greater duodenal flow of linoleic and transvaccenic acids than with a high-forage diet when 3% soybean oil was supplemented (Kucuk et al., 2001Go). Thus, limit-feeding sheep with a high-concentrate diet that contains supplemental vegetable oil would be expected to provide additional dietary energy without a negative effect on nutrient digestion. We hypothesized that along with enhancing duodenal flow of dietary unsaturated fatty acids and conjugated linoleic acid (CLA) precursors by oil supplementation, digestibilities of other nutrients may not be compromised when soybean oil is included in a high-concentrate diet that is limit-fed. The objective of the current study was to determine ruminal fermentation characteristics and intestinal flow of fatty acids in sheep limit-fed an 81.6% concentrate diet supplemented with increasing levels of soybean oil.


   Materials and Methods
Top
 Abstract
 Introduction
 Materials and Methods
Results and Discussion
 Implications
 Literature Cited
 
Animals, Diets, and Sampling
Eight white-faced wether lambs (39.9 ± 3.0 kg of initial BW) were fitted with ruminal cannulas, duodenal (inserted proximal to the common bile and pancreatic duct), and ileal T-type cannulas. Wethers were housed in a temperature-controlled room (22°C) under continuous lighting. Fresh water and trace mineral salt (Iofix T-M, Morton Salt, Chicago, IL) were available for ad libitum consumption throughout the study. Guaranteed analysis of salt blocks indicated a composition as follows (percentage of DM): NaCl (98 to 95%), Zn (not less than 0.350%), Mn (not less than 0.280%), Fe (not less than 0.175%), Cu (not less than 0.035%), and I and Co (not less than 0.007%). All procedures were conducted under protocols approved by the University of Wyoming Institutional Animal Care and Use Committee.

Lambs were assigned to one of four dietary treatments in a replicated 4 x 4 Latin square. Diets were formulated on a DM basis to be isonitrogenous (not isocaloric) and to meet the CP requirements of a 40-kg finishing lamb (NRC, 1985Go). Diets consisted of 0.0, 3.2, 6.3, or 9.4% (DM basis) added soybean oil (Table 1Go). Soybean oil was used because it is rich in unsaturated fatty acids, especially 18:2cis-9, cis-12. Soybean oil, delivered by top-dressing rations immediately before feeding, replaced corn as the level of dietary soybean oil was increased. Corn gluten meal was increased with increased dietary soybean oil to account for decreased CP with the decrease in corn. Daily rations were limit-fed at 1.4% of initial BW (DM basis) in two equal allotments at 0630 and 1830.


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  		Table 1. Ingredient and chemical composition of diets fed to wethers
 
Each experimental period lasted 25 d, with the first 14 d used for adaptation to the respective diet. Concentrate mix, hay, and soybean oil samples were collected daily for later analysis. From d 15 to 23, Cr2O3 was dosed (2.5 g/d) via gelatin capsules into the rumen twice daily at each feeding for use as an indigestible marker of digesta flow. Sample collections were 4 d in duration. At the morning feeding on d 22, duodenal (50 mL) and fresh fecal grab samples were collected at 6-h intervals. Collection times were advanced 3 h on d 23 to provide one sample for every 3-h interval in a theoretical 24-h period. Duodenal and fecal samples were composited on approximately equal volume bases by wether within period and were frozen immediately (–5°C). On d 24 of each sampling period, 100 mL of whole ruminal contents was collected from each wether immediately before feeding at 0630 (0-h sampling time). Ruminal pH was measured immediately on the 0-h sample. After pH measurement, ruminal samples were strained through four layers of cheesecloth, and 10 mL of the strained ruminal fluid was acidified with 0.1 mL of 7.2 N H2SO4 and stored frozen for later VFA analysis. Remaining ruminal contents were placed into 3.78-L plastic jugs containing 200 mL of formalin (9 g of NaCl/L of 37% formaldehyde) on an equal-volume basis and stored at 4°C for later isolation of ruminal bacteria. Following initial collection of ruminal contents, 50 g of Yb-labeled feedstuffs (40.8 g of corn and 9.2 g of bromegrass hay; Teeter et al., 1984Go) and 50 mL of CoEDTA (Uden et al., 1980Go) were dosed into the rumen of each sheep for estimation of digesta passage rates. Ruminal contents were collected at 3, 6, 9, 12, 15, 18 h, and processed similar to the 0-h sample. Additional ruminal samples were collected at 24, 36, and 48 h for Yb and Co determination, and thus were not acidified.

Sample Processing and Analyses
Feed, ruminal, duodenal, ileal, and fecal samples were prepared for analysis as described by Kucuk et al. (2001Go, 2003)Go. Ruminal fluid was analyzed for VFA concentration (Goetsch and Galyean, 1983Go) using a Hewlett Packard (Palo Alto, CA) 5890 Series II gas chromatograph equipped with a 15 m x 0.53 mm (i.d.) column (Nukol, Supelco, Bellefonte, PA) with an initial oven temperature of 110°C to a final temperature of 150°C at 8°C/min. Helium was used as the carrier gas with a column flow rate of 20 mL/min. Injector and detector temperatures were 250°C.

Feed, duodenal, and fecal samples were analyzed for DM, ash, Kjeldahl N (AOAC, 1990Go), starch (MacRae and Armstrong, 1968Go), and NDF (by nonsequential methods of Goering and Van Soest [1970]Go but without decalin, NaSO3, or ethoxyethanol). Crude fat in the concentrate mix and hay was determined according to AOAC (1990)Go. Ileal samples were analyzed for DM and ash (AOAC, 1990)Go to determine OM for fatty acid ileal flow calculations. Ileal flow of N, starch, and NDF was not determined. Isolated ruminal microorganisms were analyzed for DM, ash, and Kjeldahl N (AOAC, 1990)Go. Purine content of duodenal digesta and bacterial composites were determined according to Zinn and Owens (1986)Go. Duodenal, ileal, and fecal samples were prepared for analysis of chromium content according to Hill and Anderson (1958)Go. Chromium assay was by atomic absorption spectroscopy (model 210 VDT atomic absorption spectrometer, E. Norwalk, CT) using an air-acetylene flame. After extracting Yb from ground ruminal samples with 0.05 M EDTA containing 3.8 g of KCl/L as an ionization buffer (Teeter et al., 1984Go), Yb concentration was determined by atomic absorption spectroscopy with an air-acetylene and nitrous oxide flame. Cobalt concentration was determined by atomic absorption spectroscopy with an air-acetylene flame (Hart and Polan, 1984Go). Ruminal fluid supernatant was analyzed for NH3 by the phenol-hypo-chlorite procedure (Broderick and Kang, 1980Go). Fatty acid methyl esters of total lipids of feed, duodenal, and ileal samples (100 mg) were prepared and analyzed by GLC as described by Kucuk et al. (2001)Go.

Calculations and Statistical Analyses
Nutrient flows were calculated as described by Kucuk et al. (2001Go, 2003)Go. Nitrogen flow was apparent. Ruminal fluid and particulate passage rates were calculated by regressing the natural logarithm of Yb and Co concentration against sampling time after dosing (Uden et al., 1980Go).

All data were analyzed by ANOVA using the MIXED procedure of SAS (Version 4.1, release 7.0; SAS Inst., Inc., Cary, NC) for a Latin square. Compound symmetry was determined to be the most desirable covariance structure according to the Akaike’s Information Criterion. Animal was designated as the random effect for all analyses. Ruminal data (pH, NH3, and VFA) were analyzed using animal x period x diet as the subject index. Treatment x time interactions were detected (P ≤ 0.05) for acetate and propionate molar proportions and acetate:propionate ratio, but not for pH, NH3, or other VFA data; therefore, only treatment means were represented for the latter variables. Treatment means were calculated using the LSMEANS option of MIXED of SAS. When F-tests were significant, single-df orthogonal contrasts (Steel and Torrie, 1980Go) were used to determine linear, quadratic, and cubic effects of soybean oil levels. Because crude fat level increments were not equal in each diet (i.e., 3.5, 6, 9, 12% of DM), coefficients for orthogonal polynomials were generated using the Interactive Matrix Language procedure of SAS for unequal spacing.


   Results and Discussion
Top
 Abstract
 Introduction
 Materials and Methods
 Results and Discussion
Implications
 Literature Cited
 
Intake, Digestibility, and Fermentation
By design, intake of fatty acids increased (linear, P < 0.001) with increasing dietary soybean oil level (Table 2Go). As a consequence of increased oil intake, OM intake increased (cubic, P < 0.01). However, intake of starch and NDF decreased (cubic, P < 0.01) because of the decrease in dietary corn as dietary soybean oil increased. Intake of N changed very little; however, as dietary soybean oil level increased, a cubic (P < 0.001) change in N intake was observed.


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  		Table 2. Intake of total fatty acids, OM, starch, NDF, and N by wethers limit-fed a high-concentrate diet with different levels of soybean oil
 
Digestibilities of OM, starch, NDF, and N were not affected (P = 0.13 to 0.95) by increasing dietary soybean oil level (data not shown). Overall means for true ruminal (percentage of intake), lower-tract (percentage entering the duodenum), and total-tract (percentage of intake) digestibility for each nutrient were (mean ± SEM): OM = 50.7 ± 4.66% (P = 0.93), 71.6 ± 2.58% (P = 0.78), and 82.7 ± 0.93% (P = 0.23); starch = 92.0 ± 1.94% (P = 0.86), 96.1 ± 0.70% (P = 0.30), and 99.8 ± 0.05% (P = 0.31); NDF = 36.7 ± 6.75% (P = 0.95), 50.9 ± 7.58% (P = 0.83), and 71.7 ± 1.93% (P = 0.29); and N = 31.6 ± 9.93% (P = 0.34), 84.1 ± 1.50% (P = 0.13) and 81.0 ± 1.10 (P = 0.23), respectively. Of the nutrients evaluated, NDF digestibility would have been expected to decrease with increased dietary soybean oil because fiber digestibility is adversely affected by dietary fat (Jenkins, 1993Go). Zinn (1989)Go reported lower ADF digestibility in cattle fed a fat-supplemented (8%), high-concentrate diet without restriction. On the other hand, Tjardes et al. (1998)Go did not observe lower ADF digestibility in cattle that were limit-fed a fat-supplemented diet containing 58% corn. Thus, limit-feeding a high-concentrate diet may decrease the adverse effects that fat supplementation can have on fiber digestibility.

Ruminal ammonia (mean = 2.73 ± 0.30 mg/dL, P = 0.76) and particulate passage rate (mean = 2.97 ± 0.24 %/h, P = 0.69) were not affected by increased dietary soybean oil (Table 3Go). Brokaw et al. (2001)Go suggested that increased ruminal NH3 for cattle receiving supplemental soybean oil was attributed to decreased demand for NH3-N uptake to support microbial protein synthesis. Neither duodenal flow of microbial N (mean = 4.71 ± 0.44 g/d, P = 0.39) nor microbial efficiency (21.5 ± 3.82 g of microbial N flow/kg of OM truly fermented, P = 0.85) was affected by dietary treatment in the current study. Therefore, similar ruminal NH3 across dietary treatments was to be expected. This result suggests that when sheep are limit-fed a high-concentrate diet, dietary fat up to 9% will not alter the ruminal digestion of protein or the turnover of ammonia. Jenkins and Fotouhi (1990)Go reported decreased ruminal ammonia concentrations in sheep fed a diet supplemented with 2.4% corn oil; however, the current study focused on a limit-fed, high-concentrate diet, whereas Jenkins and Fotouhi (1990)Go reported their findings on sheep fed at 90% ad libitum of a diet containing 56% concentrates.


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  		Table 3. Ruminal NH3 concentration, particulate and fluid passage rates, pH, and VFA of wethers limit-fed a high-concentrate diet with different levels of soybean oil
 
A cubic response (P = 0.02) to increased dietary soybean oil was observed for fluid passage rate because, when dietary soybean oil was increased from 3.2 to 6.3%, and then to 9.4%, fluid passage rate increased by 31%, and then decreased by 10%, respectively. Changes in both VFA concentrations and osmotic balance were shown to be associated with fluid dilution rate (Estell and Galyean, 1985Go). A change in osmotic balance can affect water intake, which will increase fluid dilution rate if water intake increases (Estell and Galyean, 1985Go). In the current study, there was a cubic response to diet in total VFA concentrations (discussed below), which was similar to the response observed for fluid passage rate.

Ruminal pH was not changed (P = 0.31) with increasing dietary soybean oil level. Total ruminal VFA concentrations changed (cubic, P = 0.01) with increased dietary soybean oil by decreasing by 7.4% when soybean oil was increased from 0 to 3.2%, then increasing by 20.5% when soybean oil was increased to 6.3%, and finally decreasing by 32.2% when dietary soybean oil was increased to 9.4%. The lack of change in pH was unexpected in view of the altered total ruminal VFA concentrations that occurred as dietary soybean oil was increased. The most pronounced effects on VFA concentration occurred with the 6.3% soybean oil diet. The calculated ratio of starch to NDF in the current study (from results shown in Table 1Go) decreased slightly as dietary soybean oil level increased, although the ratio was maintained near 1.9:1. Thus, in the current study, with a nearly 2:1 starch:NDF ratio in limit-fed diets, 6.3% soybean oil supported the greatest level of ruminal fermentation, and 9.4% soybean oil supported the lowest level of ruminal fermentation. However, this apparent difference in fermentation characteristics did not affect overall OM digestibility.

An interaction between ruminal sampling hour and diet was observed for ruminal acetate (P < 0.001), pro-pionate (P = 0.05), and acetate:propionate ratio (P < 0.001). However, these interactions did not preclude the evaluation of main effects because the response was due to changes in magnitude over time within treatment, and not to changes in ranking of treatments. Specifically, from 0 to 21 h, the concentration of acetate decreased (P < 0.001) by 8.2, 4.3, and 5.2 mmol/100 mol for the 0, 3.2, and 6.3% soybean oil diets, respectively. For the 9.4% soybean oil diet, there was no change (P = 0.49) in acetate concentration from 0 to 21 h. Propionate increased (P ≤ 0.003) by 10.0, 5.0, and 5.9 mmol/100 mol from 0 to 21 h for the 0, 3.2, and 6.3% soybean oil diets, respectively. Again, no change (P = 0.27) occurred for the 9.4% soybean oil diet. Acetate:propionate ratio decreased (P < 0.001) by 0.8, 0.3, and 0.4 for the 0, 3.2, and 6.3% soybean oil diets, respectively, but no change (P = 0.29) was observed for acetate:propionate ratio over time for the 9.4% soybean oil diet. Thus, molar proportions of acetate and propionate, and the acetate:propionate ratio were not affected (P = 0.35 to 0.88) by increasing dietary soybean oil level. Propionate molar proportions were expected to increase from conversion of glycerol to propionate, with the glycerol supplied from hydrolysis of dietary triacylglycerol (Chalupa et al., 1986Go). From the results presented in Tables 1Go and 2Go, it can be calculated that the supplemental soybean oil could have provided up to 0.0175, 0.0361, and 0.0546 mol/d of propionate from glycerol, assuming all of the soybean oil fatty acids were hydrolyzed, and the average fatty acid molecular weight was 276 g/mole. The lack of change in ruminal propionate with increased soybean oil indicates, in part, that triacylglycerol hydrolysis may not have been complete.

Molar proportions of butyrate and isobutyrate were not affected (P = 0.30 to 0.71) by dietary soybean oil. Both valerate and isovalerate molar proportions increased (linear, P < 0.001) equally as dietary soybean oil level increased. Valerate and isovalerate arise from the metabolism of branched-chain AA (Maeng and Baldwin, 1976Go; Argyle and Baldwin, 1989Go). Content of branched-chain AA is much greater for corn gluten meal than for corn grain (NRC, 1982Go). The level of corn gluten meal increased as level of dietary soybean oil increased; thus, greater molar proportions of isoacids as dietary soybean oil increased may reflect ruminal degradation of corn gluten meal branched-chain AA.

Duodenal and Ileal Fatty Acid Flow
Table 4Go shows that duodenal flow of fatty acids from the diet and those metabolized within the rumen increased (linear, P < 0.001) with increasing soybean oil level. Greater duodenal flow of 16:0 and 17:0 than expected based on dietary intake may have been from microbial fatty acid contributions, including microbial fatty acid synthesis (Pantoja et al., 1996Go).


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  		Table 4. Duodenal and ileal flow of fatty acids in wethers limit-fed a high-concentrate diet with different levels of soybean oil
 
Greater duodenal flow of 18:0 compared with its intake (Table 2Go) would be consistent with extensive bio-hydrogenation of C18 unsaturated fatty acids. Duodenal flow of 18:0 increased (linear, P < 0.001) with each increased level of soybean oil intake. Duodenal flow of 18:1trans fatty acids was over threefold greater when soybean oil was increased from 3.2 to 6.3%; however, duodenal flow of these fatty acids increased to a much lesser extent when soybean oil was increased to 9.4%. The predominant 18:1trans fatty acid observed in ruminal and duodenal contents of ruminants fed high-linoleate vegetable oil was 18:1trans-11, a common biohydrogenation intermediate. Harfoot et al. (1973)Go found that when 18:2cis-9,cis-12 is added to ruminal contents in vitro at greater than 1.0 mM, it is not completely saturated, and is associated with accumulation of 18:1trans-11. Similarly, Bateman and Jenkins (1998)Go reported a linear increase in 18:1trans-11 in ruminal contents of nonlactating cows when soybean oil was fed at 0, 2, 4, 6, and 8% of the diet. Furthermore, most of the 18:1trans fatty acids in ovine muscle lipids of animals fed diets supplemented with high-linoleate safflower seeds comprised 18:1trans-10 and 18:1trans-11 fatty acids (Bolte et al., 2002Go; Murrieta et al., 2003Go).

The sharp increase in duodenal flow of 18:0 (35%) compared with the modest increase in 18:1trans fatty acids when dietary soybean oil was increased from 6.3 to 9.4% suggests that biohydrogenation of the trans-fatty acids was progressing toward completion at the highest soybean oil levels, despite linear increases (P < 0.001) in duodenal flow of 18:1cis-9, 18:2cis-9,cis-12, and 18:3cis-9, cis-12, cis-15. Increased duodenal flow of the latter three fatty acids, in view of the likely extensive biohydrogenation, appears surprising, but is not unusual. For example, Wu et al. (1991)Go fed dairy cows 171, 240, and 296 g/d of 18:2cis-9,cis-12 in a 60% forage diet containing 0, 3, and 6% animal/vegetable blended fat, respectively, and found that duodenal flow of 18:2cis-9,cis-12 increased by 5 g/d with 3% fat, and by 9 g/d with 6% fat compared with a control diet. In the current study, duodenal flow of dietary unsaturated fatty acids suggests that initiation of unsaturated fatty acids biohydrogenation may have decreased, possibly because the microbial enzyme systems, including bacterial lipases, were saturated. Hydrolysis of dietary acylglycerols is a prerequisite for ruminal biohydrogenation because a free carboxyl group is needed for the reactions to begin (Harfoot and Hazlewood, 1988Go). The mechanism of increased duodenal flow of dietary unsaturated fatty acids (i.e., as the free acid or the esterified acid) as the level of dietary 18:1-, 18:2-, and 18:3-containing triacylglycerols increases warrants further investigation because the proportion of free to esterified fatty acids was not determined in the current study.

Of the isomers of CLA identified in the current study, only the 10-12 isomers were affected by increased dietary soybean oil. Duodenal flow of rumenic acid (18:2cis-9,trans-11) was not influenced by diet (P = 0.35). As dietary soybean oil level increased, duodenal flow of 18:2trans-10,cis-12 and 18:2cis-10,cis-12 increased (linear, P < 0.001). The low duodenal flow of 18:2cis-9,trans-11, and relatively greater duodenal flow of the other two CLA isomers was consistent with the observation that the 10-12 isomers were greater in adipose tissue and milk fat of cows fed high-grain diets (Griinari and Bauman, 1999Go). Moreover, Kucuk et al. (2001)Go reported a linear increase in the duodenal flow of 18:2cis-9,trans-11, and linear decreases in the duodenal flow of 18:2trans-10,cis-12 and 18:2cis-10, cis-12 in ewes fed increasing levels of dietary forage, also indicating that high-concentrate diets support lower duodenal flow of rumenic acid than high-forage diets. Generally, CLA was quite low in duodenal contents of the oil-supplemented animals, indicating its rapid conversion to trans-fatty acids. The CLA that is found in adipose tissue and mammary gland occurs largely from desaturation of 18:1trans fatty acids (Griinari and Bauman, 1999Go). The potential health benefits of CLA have been well documented (Pariza, 1999Go).

Duodenal flow of total fatty acids, total saturated fatty acids, and total unsaturated fatty acids increased (linear, P < 0.001) with increasing dietary soybean oil level. The greater duodenal flow of total saturated fatty acids compared with duodenal flow of total unsaturated fatty acids was a consequence of the flow of 18:0. Also, duodenal flow of total fatty acids was greater than fatty acid intake, which was the case in previous work (Kalscheur et al., 1997Go; Elliott et al., 1999Go; Kucuk et al., 2001Go). Greater duodenal flow of total fatty acids can be partially attributed to bacterial de novo fatty acid synthesis in the rumen (Doreau and Ferlay, 1994Go), as well as to the lack of aerobic catabolism of ruminal long-chain fatty acids, and low absorption efficiency of long- and medium-chain fatty acids by the ruminal epithelium (Noble, 1981Go). Although Noble (1978)Go noted that bile contamination of duodenal digesta may contribute to duodenal fatty acid flow, in the current study, the duodenal cannula was placed proximal to the entrance of the bile duct. Higher duodenal flow of fatty acids reported by Elliott et al. (1999)Go was attributed to underestimation of fatty acid contents of feed and inaccurate measurement of duodenal fatty acids, and Murphy et al. (1987)Go attributed higher duodenal fatty acid flows to inaccuracies associated with sampling and digesta markers. However, contribution of fatty acids by ruminal microbes, as well as sloughed epithelial cells should not be discounted.

Ileal flow of 16:0, 17:0, 18:0, 18:1trans, and 18:1cis-9 increased (linear, P ≤ 0.04) with increasing dietary soybean oil level. The largest values recorded were for 16:0, 18:0, 18:1trans, and 18:1cis-9, suggesting that these fatty acids were absorbed less efficiently. Ileal flow values for the CLA isomers were very low, indicating that most of these fatty acids were absorbed. Ileal flow of total fatty acids, total saturated fatty acids, and total unsaturated fatty acids increased (linear, P < 0.01) with increasing soybean oil level, a direct reflection of increased ileal flow of individual fatty acids included in these totals.

By expressing the difference between ileal and duodenal flow as a proportion of duodenal flow, apparent absorption, or disappearance, of fatty acids from the small intestine can be estimated. Results of this estimation are shown in Table 5Go. Apparent disappearance of fatty acids from the small intestine changed with the level of dietary soybean oil for only a few fatty acids. Apparent small intestinal disappearance of 18:0 decreased (linear, P = 0.004) as soybean oil level increased. With 9.4% dietary soybean oil, nearly half of the duodenal 18:0 was observed at the ileum. Considering that much of the dietary C18 unsaturated fatty acids were converted to 18:0, the energy value of the supplemented fatty acids of the 9.4% oil diet was substantially lessened by the lack of apparent absorption of these fatty acids. Consistent with our observation in limit-fed sheep, Plascencia et al. (2003)Go observed a linear decrease in postruminal fatty acid digestion in steers fed a high-concentrate diet supplemented with 0, 3, 6, and 9% yellow grease. Decreased digestion of 18:0 was responsible for the majority of the decreased postruminal fatty acid digestion, which resulted in a linear decrease in NE value of the yellow grease in their steers (Plascencia et al., 2003Go). Dry matter intake by the steers used by Plascencia et al. (2003)Go was constant across dietary treatments in which yellow grease was included at 0, 30, 60, or 90 g/kg of DM. Plascencia et al. (2003)Go concluded that intestinal fatty acid digestion was a predictable function of total fatty acid intake when fatty acid intake was expressed on a per-unit-BW basis. In the current study, total fatty acid intake (Table 2Go) of lambs was estimated to be 0.50, 0.86, 1.25, and 1.63 g/kg of BW. The change in fatty acid intake across treatment was comparable in magnitude to that described by Plascencia et al. (2003)Go. Thus, when the observed conversion of C18 unsaturated fatty acids to 18:0 is considered, the decreased apparent disappearance of 18:0 observed in the current study was the result of greater total fatty acid intake.


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  		Table 5. Apparent disappearance of fatty acids from the small intestine of wethers limit-fed a high-concentrate diet with different levels of soybean oila
 
Apparent disappearance of 18:2cis-9,cis-12 changed (quadratic, P = 0.03) with increasing dietary soybean oil level. This fatty acid increased by 9.5% from the 0 to the 3.2% soybean oil diet, whereas disappearance remained unchanged from 3.2 to 9.4% dietary soybean oil. Thus, the level of apparent absorption of supplemental 18:2cis-9,cis-12 was not altered by increased duodenal flow of this fatty acid. On the other hand, apparent absorption of 18:2cis-9,trans-11 changed (cubic, P = 0.04) as dietary soybean oil level increased. However, both duodenal flow and ileal flow of 18:2cis-9,trans-11 were very low and unaffected by diet; therefore, any detection of this fatty acid in ileal contents would greatly decrease apparent disappearance. Decreased apparent disappearance of total fatty acids (linear, P = 0.03) and saturated fatty acids (linear, P = 0.008) occurred, and can be accounted for by the decreased (linear, P = 0.004) disappearance of 18:0 as dietary soybean oil level was increased.

Generally, ruminants can absorb large quantities of lipids, with absorption efficiencies of C16 and C18 fatty acids estimated at 83 to 92% for most common diets (Noble, 1981Go). Also, absorption efficiencies of major fatty acids have been suggested to rank as follows: 18:1 > 16:0 > 18:0 (Noble, 1981Go), which is consistent with findings of the current study. Heath and Hill (1969)Go did not observe a decrease in absorption of palmitic acid from abomasal infusion of 14C-tripalmitin in sheep that consumed from 12 to 44 g/d of corn oil in a high-forage diet. In contrast, in the current study, apparent disappearance of total fatty acids decreased (linear, P = 0.05) as dietary soybean oil increased. The magnitude of apparent disappearance values for 18:1cis-9 and 18:1trans fatty acids were similar at each level of dietary soybean oil. Likewise, Bickerstaffe et al. (1972)Go did not observe preferential uptake of 18:1cis and trans isomers by the small intestine of lactating goats. However, results reported by Lennox and Garton (1968)Go suggest that 18:1trans fatty acids may be absorbed to a greater extent than 18:1cis fatty acids in sheep. Consistent with our results, Zinn (1989)Go reported linear decreases in small intestinal total fat digestion with increasing fat supplementation (0 to 8%) in a finishing diet for steers. Christensen et al. (1998)Go reported lower digestion of total fatty acids with greater dietary fat (2.77 vs. 5.86% total fatty acids) in a 50% forage diet for lactating cows, and speculated that this might be due to poor micelle formation. Similarly, Elliott et al. (1999)Go and Pantoja et al. (1996)Go reported lower small intestinal total fatty acid digestion in cattle supplemented with fat compared with cattle fed a control diet.

In general, the results of the current study suggest that as top-dressed soybean oil level is increased in the diet of limit-fed sheep, lesser amounts of fatty acids originating from the soybean oil were apparently absorbed by the small intestine. We conclude this because of the greater amounts of 18:0 that were produced and the lower ileal flow of 18:0 that occurred as duodenal flow increased. The large intestine does not absorb fatty acids, especially high-melting-point fatty acids such as 18:0 (Magee and Dalley, 1986Go). Therefore, increased levels of fatty acids originating from soybean oil would be eliminated through the feces as the dietary level is increased; thus, the true energy value of this type of oil supplement in limit-fed sheep would be expected to decrease with increased level of supplementation. Nevertheless, total dietary energy still increases with oil supplementation (Zinn, 1988Go, 1989Go; Plascencia et al., 2002Go).

Production of large amounts of 18:0 as dietary soybean oil was increased was likely responsible for its decreased apparent absorption as level of dietary oil was increased. Compared with top-dressing rations with the oil, if the intact seed protects the oil from as extensive a degree of biohydrogenation (Baldwin and Allison, 1983Go), then more total fatty acids may be absorbed. This is because for every 1% increase in proportion of 18:1 entering the small intestine of steers fed an 88% concentrate diet, there was a 1% increase in 18:0 absorbed (Zinn et al., 2000Go). The limited level of feed intake employed in the current study may have caused the lower apparent small intestinal disappearance of fatty acids. On the other hand, greater ruminal biohydrogenation of dietary fatty acids in Holstein steers fed an 88% concentrate diet, without restriction, and supplemented with 6% yellow grease also resulted in decreased small intestinal digestion of 18:0 (Zinn et al., 2000Go). Nevertheless, enhanced duodenal and ileal flow of 18:0 by the sheep in the current study did not decrease apparent absorption of unsaturated fatty acids, and did not affect digestibility of OM, starch, NDF, or N. Thus, supplementation of the diet with increased levels of soybean oil in limit-fed sheep resulted in a trade off between loss of potential dietary energy and gain of important PUFA and biohydrogenation intermediates, but without a marked effect on digestibility of other important macronutrients.


   Implications
Top
 Abstract
 Introduction
 Materials and Methods
 Results and Discussion
 Implications
Literature Cited
 
A limit-fed high-concentrate diet for sheep can be supplemented with soybean oil at levels up to about 9% without adversely affecting nutrient digestibility; however, supplementation to approximately 6% of the diet DM would be recommended because of the greater fermentation that was observed at this level of supplemental oil. Furthermore, with 9% dietary soybean oil, decreased absorption of stearic acid, and thus loss of potential dietary energy, could be a concern. Nevertheless, enough fatty acids would be absorbed at the greater levels of soybean oil supplementation that the energy value of the diet would be greater with the supplemental oil, and use of trans and conjugated unsaturated fatty acids for functions beyond energy needs would be possible.


   Footnotes
 
1 Present address: Erciyes Univ., School of Vet. Med., Dept. of Anim. Nutr. and Nutr. Diseases, Kayseri, Turkey 38090. Back

2 Correspondence: University Station (phone: 307-766-3404; fax: 307-766-2355; e-mail: dcrule{at}uwyo.edu).

Received for publication October 27, 2003. Accepted for publication June 21, 2004.


   Literature Cited
Top
 Abstract
 Introduction
 Materials and Methods
 Results and Discussion
 Implications
 Literature Cited
 


AOAC. 1990. Official Methods of Analysis. 15th ed. Assoc. Offic. Anal. Chem., Arlington, VA.

Argyle, J. L., and R. L. Baldwin. 1989. Effects of amino acids and peptides on rumen microbial growth yields. J. Dairy Sci. 72:2017–2027.

Baldwin, R. L., and M. J. Allison. 1983. Rumen metabolism. J. Anim Sci. 57(Suppl. 2):461.

Bateman, H. J., II, and T. J. Jenkins. 1998. Influence of soybean oil in high fiber diets fed to nonlactating cows on ruminal unsaturated fatty acids and nutrient digestibility. J. Dairy Sci. 81:2451–2458.[Abstract]

Bickerstaffe, R., D. E. Noakes, and E. F. Annison. 1972. Quantitative aspects of fatty acid biohydrogenation, absorption and transfer into milk fat in the lactating goat, with special reference to the cis- and trans-isomers of octadecenoate and linoleate. Biochem. J. 130:607–617.[Medline]

Bolte, M. R., B. W. Hess, W. J. Means, G. E. Moss, and D. C. Rule. 2002. Feeding lambs high-oleate or high-linoleate safflower seeds differentially influences carcass fatty acid composition. J. Anim. Sci. 80:609–616.[Abstract/Free Full Text]

Broderick, G. A., and J. H. Kang. 1980. Automated simultaneous determinations of ammonia and total amino acids in ruminal fluid and in vitro media. J. Dairy Sci. 63:64–75.

Brokaw, L., B. W. Hess, and D. C. Rule. 2001. Supplemental soybean oil or corn for beef heifers grazing summer pasture: Effects on forage intake, ruminal fermentation, and site and extent of digestion. J. Anim. Sci. 79:2704–2712.[Abstract/Free Full Text]

Chalupa, W., B. Vecchiatelli, A. Esler, D. S. Kronfeld, D. Sklan, and D. L. Palmquist. 1986. Ruminal fermentaion in vivo as influenced by long-chain fatty acids. J. Dairy Sci. 69:1293–1301.

Christensen, R. A., J. H. Clark, J. K. Drackley, and S. A. Blum. 1998. Fatty acid flow to the duodenum and in milk from cows fed diets that contained fat and nicotinic acid. J. Dairy Sci. 81:1078–1088.[Abstract]

Doreau, M., and A. Ferlay. 1994. Digestion and utilization of fatty acids by ruminants. Anim. Feed Sci. Technol. 45:379–396.

Elliott, J. P., J. K. Drackley, A. D. Beaulieu, C. G. Aldrich, and N. R. Merchen. 1999. Effects of saturation and esterification of fat sources on site and extent of digestion in steers: Digestion of fatty acids, triglycerides, and energy. J. Anim. Sci. 77:1919–1929.[Abstract/Free Full Text]

Estell, R. E., and M. L. Galyean. 1985. Relationship of rumen fluid dilution rate to rumen fermentation and dietary characteristics of beef steers. J. Anim. Sci. 60:1061–1071.

Firkins, J. L., L. L. Berger, N. R. Merchen, G. C. Fahey, Jr., and D. R. Nelson. 1986. Effects of feed intake and protein degradability on ruminal characteristics and site of digestion in steers. J. Dairy Sci. 69:2111–2123.

Goering, A. L., and P. J. Van Soest. 1970. Forage Fiber Analyses (Apparatus, Reagents, Procedures, and Some Applications). Agric. Handbook No. 379. ARS, USDA, Washington, DC.

Goetsch, A. L., and M. L. Galyean. 1983. Influence of feeding frequency on passage of fluid and particulate markers in steers fed a concentrate diet. Can. J. Anim. Sci. 63:727–730.

Griinari, J. M., and D. E. Bauman. 1999. Biosynthesis of conjugated linoleic acid and its incorporation into meat and milk in ruminants. Page 180 in Advances in Conjugated Linoleic Acid Research. Vol. 1. M. P. Yurawecz, M. M. Mossoba, J. K. G. Kramer, G. Nelson, and M. W. Pariza ed., AOCS Press, Champaign, IL.

Harfoot, C. G., and G. P. Hazlewood. 1988. Lipid metabolism in the rumen. Page 285 in The Rumen Microbial Ecosystem. P. N. Hobson ed. Elsevier Applied Science, New York, NY.

Harfoot, C. G., R. C. Noble, and J. H. Moore. 1973. Factors affecting the extent of biohyrogenation of linoleic acid by rumen microorganisms in vitro. J. Sci. Food Agric. 24:961–970.[Medline]

Hart, S. P., and C. E. Polan. 1984. Simultaneous extraction and determination of ytterbium and cobalt ethylenediaminetetraacetate complex in feces. J. Dairy Sci. 67:888–892.[Abstract/Free Full Text]

Heath, T. J., and L. N. Hill. 1969. Dietary and endogenous long-chain fatty acids in the intestine of sheep, with an appendix on their estimation in feeds, bile, and faeces. Aust. J. Biol. Sci. 22:1015–1029.[Medline]

Hill, F. W., and D. L. Anderson. 1958. Comparison of metabolizable energy and productive energy determinations with growing chicks. J. Nutr. 64:1405–1415.

Jenkins, T. C. 1993. Lipid metabolism in the rumen. J. Dairy Sci. 76:3851–3863.[Abstract/Free Full Text]

Jenkins, T. C., and N. Fotouhi. 1990. Effects of lecithin and corn oil on site of digestion, ruminal fermentation and microbial protein synthesis in sheep. J. Anim. Sci. 68:460–466.[Abstract]

Kalscheur, K. F., B. B. Teter, L. S. Piperova, and R. A. Erdman. 1997. Effect of forage concentration and buffer addition on duo-denal flow of trans-C18:1 fatty acids and milk fat production in dairy cows. J. Dairy Sci. 80:2104–2114.[Abstract]

Kucuk, O., B. W. Hess, P. A. Ludden, and D. C. Rule. 2001. Effect of forage:concentrate ratio on ruminal digestion and duodenal flow of fatty acids in ewes. J. Anim. Sci. 79:2233–2240.[Abstract/Free Full Text]

Kucuk, O., B. W. Hess, P. A. Ludden, and D. C. Rule. 2003. Potential associative effects of increasing dietary forage in limit-fed ewes fed a 6% fat diet. Sheep Goat Res. J. 18:25–33.

Lennox, A. M., and G. A. Garton. 1968. The absorption of long-chain fatty acids from the small intestine of the sheep. Br. J. Nutr. 22:247–254.[Medline]

MacRae, J. C., and D. G. Armstrong. 1968. Enzyme method for determination of alpha-linked glucose polymers in biological materials. J. Sci. Food Agric. 19:578–592.

Maeng, W. J., and R. L. Baldwin. 1976. Factors influencing rumen microbial growth rates and yields: Effects of amino acid additions to a purified diet with N from urea. J. Dairy Sci. 59:648–655.

Magee, D. F., and A. F. Dalley. 1986. Absorption. Pages 211–255 in Digestion and the Structure and Function of the Gut. Vol. 8. D. F. Magee and A. F. Dalley, ed. Karger Continuing Education Series, Basel, Switzerland.

Murphy, M., P. Uden, D. L. Palmquist, and H. Wiktorsson. 1987. Rumen and total digestibilities in lactating cows fed diets containing full-fat rapeseed. J. Dairy Sci. 70:1572–1582.

Murrieta, C. M., B. W. Hess, and D. C. Rule. 2003. Comparison of acidic and alkaline catalysts for preparation of fatty acid methyl esters from ovine muscle with emphasis on conjugated linoleic acid. Meat Sci. 65:523–529.

Noble, R. C. 1978. Digestion, absorption and transport of lipids in ruminant animals. Prog. Lipid Res. 17:55–91.[Medline]

Noble, R. C. 1981. Digestion, absorption and transport of lipids in ruminant animals. Page 57 in Lipid Metabolism in Ruminant Animals. W. W. Christie ed., Pergamon Press, New York, NY.

NRC. 1982. Pages 112–131 in United States-Canadian Tables of Feed Composition. Table 4Go. Composition of important feeds: Amino acids. Natl. Acad. Press, Washington, DC.

NRC. 1985. Nutrient Requirements of Sheep. Natl. Acad. Press, Washington, DC.

Pantoja, J., J. L. Firkins, and M. L. Eastridge. 1996. Fatty acid digestibility and lactation performance by dairy cows fed fats varying in degree of saturation. J. Dairy Sci. 79:429–437.[Abstract]

Pariza, M. W. 1999. The biological activities of conjugated linoleic acid. Page 12 in Advances in Conjugated Linoleic Acid Research, Vol. 1. M. P. Yurawecz, M. M. Mossoba, J. K. G. Kramer, M. W. Pariza, and G. J. Nelson, ed. AOCS Press, Champaign, IL.

Plascencia, A., E. G. Alvarez, M. G. Montano, M. Machado, S. Rodriguez, R. A. Ware, and R. A. Zinn. 2002. Influence of level of intake on the comparative feeding value of fat in finishing diets for feedlot cattle. Proc. West. Sec. Amer. Soc. Anim. Sci. 53:613–615.

Plascencia, A., G. D. Mendoza, C. Vasquez, and R. A. Zinn. 2003. Relationship between body weight and level of fat supplementation on fatty acid digestion in feedlot cattle. J. Anim. Sci. 81:2653–2659.[Abstract/Free Full Text]

Steel, R. G., and J. H. Torrie. 1980. Principles and Procedures of Statistics: A Biometrical Approach. 2nd ed. McGraw-Hill Book Co., New York, NY.

Tjardes, K. E., D. B. Faulkner, D. D. Buskirk, D. F. Parrett, L. L. Berger, N. R. Merchen, and F. A. Ireland. 1998. The influence of processed corn and supplemental fat on digestion of limit-fed diets and performance of beef cows. J. Anim. Sci. 76:8–17.[Abstract/Free Full Text]

Teeter, R. G., F. N. Owens, and T. L. Mader. 1984. Ytterbium chloride as a marker for particulate matter in the rumen. J. Anim. Sci. 58:465–473.[Abstract/Free Full Text]

Uden, P., P. E. Colucci, and P. J. Van Soest. 1980. Investigation of chromium, cerium, and cobalt as markers in digesta. Rate of passage studies. J. Sci. Food Agric. 31:625–632.[Medline]

Wu, Z., O. A. Ohajuruka, and D. L. Palmquist. 1991. Ruminal synthesis, biohydrogenation, and digestibility of fatty acids by dairy cows. J. Dairy Sci. 74:3025–3034.[Abstract]

Zinn, R. A. 1988. Comparative feeding value of supplemental fat in finishing diets for feedlot steers supplemented with and without monensin. J. Anim. Sci. 66:213–227.

Zinn, R. A. 1989. Influence of level and source of dietary fat on its comparative feeding value in finishing diets for feedlot steers. Metabolism. J. Anim. Sci. 67:1038–1049.

Zinn, R. A., S. K. Gulati, A. Plascencia, and J. Salinas. 2000. Influence of ruminal biohydrogenation on the feeding value of fat in finishing diets for feedlot cattle. J. Anim. Sci. 78:1738–1746.[Abstract/Free Full Text]

Zinn, R. A., and F. N. Owens. 1986. A rapid procedure for purine measurement and its use for estimating net ruminal protein synthesis. Can. J. Anim. Sci. 66:157–166.


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