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Site and extent of digestion, duodenal flow, and intestinal disappearance of total and esterified fatty acids in sheep fed a high-concentrate diet supplemented with high-linoleate safflower oil

University of Wyoming, Laramie 82071-3684

	Abstract

Top Abstract INTRODUCTION MATERIALS AND METHODS RESULTS AND DISCUSSION IMPLICATIONS LITERATURE CITED

 
Our objective was to determine duodenal and ileal flows of total and esterified fatty acids and to determine ruminal fermentation characteristics and site and extent of nutrient digestion in sheep fed an 80% concentrate diet supplemented with high-linoleate (77%) safflower oil at 0, 3, 6, and 9% of DM. Oil was infused intraruminally along with an isonitrogenous basal diet (fed at 2% of BW) that contained bromegrass hay, cracked corn, corn gluten meal, urea, and limestone. Four crossbred wethers (BW = 44.3 ± 15.7 kg) fitted with ruminal, duodenal, and ileal cannulas were used in a 4 x 4 Latin square experiment, in which 14 d of dietary adaptation were followed by 4 d of duodenal, ileal, and ruminal sampling. Fatty acid intake increased (linear, P = 0.004 to 0.001) with increased dietary safflower oil. Digestibilities of OM, NDF, and N were not affected (P = 0.09 to 0.65) by increased dietary safflower oil. For total fatty acids (free plus esterified) and esterified fatty acids, duodenal flow of most fatty acids, including 18:2c-9,c-12, increased (P = 0.006 to 0.05) with increased dietary oil. Within each treatment, duodenal flow of total and esterified 18:2c-9,c-12 was similar (P = 0.32), indicating that duodenal flow of this fatty acid occurred because most of it remained esterified. Duodenal flow of esterified 18:1t-11 increased (P = 0.08) with increased dietary safflower oil, indicating that reesterification of ruminal fatty acids occurred. Apparent small intestinal disappearance of most fatty acids was not affected (P = 0.19 to 0.98) by increased dietary safflower oil, but increased (P = 0.05) for 18:2c-9,c-12, which ranged from 87.0 to 97.4%, and for 18:2c-9,t-11 (P = 0.03), which ranged from 37.9% with no added oil to 99.2% with supplemental oil. For esterified fatty acids, apparent small intestinal disappearance was from 80% for 18:3c-9,c-12,c-15 at the greatest level of dietary oil up to 100% for 18:1t-11 and 18:1c-12 with 0% oil. We concluded that duodenal flow of 18:2c-9,c-12 was predominately associated with the esterified fraction, suggesting that the extent of ruminal lipolysis was decreased with increased dietary high-linoleate safflower oil. Furthermore, biohydrogenation intermediates observed in the esterified fatty acids indicated that some reesterification occurred, and the high level of apparent absorption of esterified fatty acids indicated that intestinal lipolysis did not limit overall digestion of the fatty acids fed to the sheep.

Key Words: biohydrodgenation • dietary fat • lipids • ovine

	INTRODUCTION

Top Abstract INTRODUCTION MATERIALS AND METHODS RESULTS AND DISCUSSION IMPLICATIONS LITERATURE CITED

 
Triacylglycerols consumed by sheep are rapidly hydrolyzed in the rumen, and unsaturated fatty acids are saturated through biohydrogenation (Jenkins, 1993). However, feeding high-concentrate diets can result in decreased biohydrogenation, which can lead to greater unsaturated fatty acid concentrations in tissues (Latham et al., 1972; Leat, 1977). Kucuk et al. (2001) reported greater duodenal flow of unsaturated fatty acids in sheep fed a high-concentrate diet compared with sheep fed a high-forage diet when total dietary fat was adjusted to 6% with soybean oil. Kucuk et al. (2004) subsequently determined that 9.4% soybean oil in a high-concentrate diet for lambs increased duodenal flow of linoleic acid (18:2c-9,c-12) by 48% compared with lambs fed a diet with no oil supplement. The increased duodenal flow of 18:2c-9,c-12 with soybean oil supplementation noted by Kucuk et al. (2004) might have occurred because of either less ruminal hydrolysis of dietary esterified 18:2c-9,c-12 or less ruminal biohydrogenation of free 18:2c-9,c-12.

Other studies have demonstrated that biohydrogenation of 18:2c-9,c-12 is rapid (Harfoot and Hazlewood, 1997) and that the free acid (carboxyl group) is required for biohydrogenation to be initiated. Protection of fatty acids from biohydrogenation has been demonstrated by esterification to substances not easily hydrolyzed in the rumen (Jenkins and Adams, 2002). We hypothesized that the increased duodenal flow of 18:2c-9,c-12 that occurs in lambs fed high-linoleate vegetable oil occurs from increased duodenal flow of esterified 18:2c-9,c-12. Our objectives were to determine duodenal and ileal flow of total and esterified fatty acids and to evaluate ruminal digestion and duodenal flow of other nutrients in lambs fed a high-concentrate diet supplemented with up to 9% of DM as high-linoleate safflower oil.

	MATERIALS AND METHODS

Top Abstract INTRODUCTION MATERIALS AND METHODS RESULTS AND DISCUSSION IMPLICATIONS LITERATURE CITED

 
Animals, Diets, and Sampling

Four crossbred wether lambs (BW = 44.3 ± 15.7 kg) were fitted with ruminal, duodenal (inserted cranial to the common bile and pancreatic duct), and ileal T-type cannulas. Lambs were housed in metabolism crates (1.4 x 0.6 m) within a temperature-controlled room (22°C) under continuous lighting. Fresh water and trace-mineralized salt (Iofix T-M, Morton Salt, Chicago, IL) were available ad libitum throughout the study. Guaranteed analysis of salt blocks indicated NaCl at 97.1% along with the following (in ppm): Zn, 3,500; Mn, 2,800; Fe, 1,750; Cu, 350 to 450; I, 70; and Co, 70. All procedures were conducted in accordance with an approved University of Wyoming Institutional Animal Care and Use Committee protocol.

Lambs were assigned to one of 4 dietary treatments in a 4 x 4 Latin square. Diets consisted of the basal diet plus 0, 3, 6, or 9% high-linoleate (77% linoleic acid) safflower oil (DM basis). The basal diet was formulated on a DM basis to meet the maintenance requirements of a 40-kg finishing lamb (NRC, 1985) and included bromegrass hay, cracked corn, corn gluten meal, urea, and limestone (Table 1). Diets were fed at 2% of initial BW in 2 equal allotments at 0600 and 1800. To ensure that supplemental oil was completely consumed, high-linoleate safflower oil was infused intraruminally immediately after feeding. Intraruminal infusion of the oil was considered to be comparable with ingestion because oil infusion and diet consumption occurred simultaneously.

On d 17 of each collection period, 100 mL of whole ruminal contents was collected from each wether immediately before feeding (0-h sampling time). Additional ruminal contents were collected at 3, 6, 9, 12, 15, 18, 21, 24, 36, and 48 h thereafter. Ruminal pH was determined immediately for each fresh ruminal sample. Ruminal contents were then strained through 4 layers of cheesecloth, and 10 mL of the strained fluid was acidified with 0.1 mL of 7.2 N H₂SO₄ and frozen for later VFA analysis. The remaining whole ruminal contents were placed in a blender (Hamilton Beach/Proctor Silex, Washington, NC) with an equal volume of 0.9% NaCl (wt/vol) solution and homogenized for 1 min to dislodge particulate-associated bacteria. The homogenized solution was then strained through 8 layers of cheesecloth and frozen for later bacterial isolation by differential centrifugation (Merchen et al., 1986). The resulting bacterial isolate was lyophilized and ground with a mortar and pestle for subsequent laboratory analysis.

Sample Processing and Analysis

Feed, ruminal (including bacterial isolates), duodenal, ileal, and fecal samples were prepared for analysis as described by Kucuk et al. (2001, 2004). Feed, duodenal, ileal, and fecal samples were analyzed for DM and ash; feed was analyzed for crude fat by ether extraction (AOAC, 1990) and for N content (Leco model FP-528 Nitrogen determinator, LECO, St. Joseph, MI). Neutral and acid detergent fiber contents of feed and NDF content of fecal and duodenal digesta were determined using an ANKOM 200 fiber analyzer (ANKOM Technology, Fairport, NY). Duodenal, ileal, and fecal samples were prepared for analysis of Cr according to Hill and Anderson (1958). Chromium concentration was determined by atomic absorption spectrophotometry (Model 210 VDT atomic absorption spectrophotometer, Buck Scientific, Norwalk, CT) using an air plus acetylene flame. Ruminal NH₃ concentrations were determined by the phenol-hypochlorite procedure (Broderick and Kang, 1980). Ruminal fluid was analyzed for VFA concentration (Goetsch and Galyean, 1983) using a Hewlett-Packard 5890 gas liquid chromatograph (Hewlett-Packard, Avondale, PA) 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 carrier gas with a column flow rate of 20 mL/min. Injector and flame ionization detector temperatures were 250°C.

Duplicate samples of feed (1.0 g), duodenal (1.0 g), and ileal (4.0 g) contents; feces (4.0 g); and ruminal bacteria (0.20 g) were subjected to total lipid extraction for 4 h in chloroform, methanol, and water (1:2:0.8 vol/vol/vol) in 16- x 125-mm screw-capped tubes (Rule, 1997). Each extraction tube contained 2.0 mg of tritride-canoylglycerol as the internal standard (Sigma Chemical Co., St. Louis, MO). Fatty acid methyl esters of the feed (Table 2) were prepared using methanolic HCl as described by Kucuk et al. (2001). Lipid extracts of duodenal, ileal, and fecal samples were dried under N₂ at 22°C and redissolved in 2.0 mL of chloroform; then, 1.0 mL was transferred into a separate tube. Both subsamples were then dried under N₂.

Therefore, for each subsample in duplicate, one lipid extract was subjected to methyl esterification using 2.0 mL of 1.09 N HCl in methanol, and the other duplicate extract was subjected to methyl esterification using 2.0 mL of 0.2 N KOH in methanol (Murrieta et al., 2003). Thus, fatty acid methyl esters of one-half of the lipid extract represented total fatty acids (free plus esterified), and the other half represented esterified fatty acids. Fatty acid methyl esters were extracted in 3.0 mL of hexane and transferred to GLC vials containing a 1.0-mm bed of anhydrous sodium sulfate. Fatty acid quantification and identification were accomplished using GLC as described by Murrieta et al. (2003). For this analysis, a 100-m capillary column, designed for cis and trans isomer separation, was used (SP2560, Supelco).

In addition to quantifying duodenal flow of total and esterified fatty acids, we determined the fatty acid profile within each major lipid class: neutral, free, and polar lipids. However, samples had to be pooled to obtain sufficient lipid for a meaningful fatty acid analysis of the neutral and polar lipid fractions. To accomplish this fractionation, total lipid extracts were subjected to solid phase extraction using a 6.0-mL solid phase, NH₂ extraction column (Phenomenex, Torrance, CA). Approximately 45 mg of lipid was loaded onto the column in 0.7 mL of chloroform. Neutral lipids were eluted from the column with 12.0 mL of a 4:1 (vol/vol) mixture of chloroform:2-propanol. The neutral lipid fraction was contaminated with FFA; therefore, the initial neutral lipid fraction was loaded onto a fresh column and eluted with the chloroform:2-propanol mixture. Free fatty acids were eluted from the original column with 12.0 mL of 2% acetic acid in diethyl ether, and polar lipids were eluted with 12.0 mL of methanol. Cross-contamination of each fraction was not apparent as determined by TLC using 80:20:1 (vol/vol/vol/) petroleum ether, diethyl ether, and acetetic acid, respectively, as the developing solvent. Each lipid fraction was dried under N₂, and methyl esters were prepared using 1.09 N HCl in methanol. Fatty acid methyl esters were extracted in 1.0 mL of hexane, concentrated to 0.5 mL by evaporation under N₂, and transferred to a GLC vial containing a 1.0-mm bed of anhydrous sodium sulfate. Fatty acid methyl esters were separated and identified as described previously except that a 2.0-µL injection was used.

Calculations and Statistical Analysis

Organic matter flow was calculated by dividing the amount of Cr dosed by the concentration of Cr in the sample (duodenal, ileal, and fecal). Digesta flow of N, NDF, and individual fatty acids was calculated by multiplying nutrient concentration of OM at each site by OM flow. Bacterial isolates were used to calculate true ruminal OM digestibility as follows: [OM intake – (duodenal OM flow – duodenal microbial OM flow)/OM intake] x 100. Apparent small intestinal fatty acid disappearance was calculated as the difference between duodenal flow and ileal flow of fatty acid expressed as a percentage of the fatty acid duodenal flow.

All data were normalized to a constant BW of 50 kg. as the lambs grew at variable rates because of the difference in energy consumption throughout the experiment. All data except ruminal fermentation data were analyzed using the GLM procedures of SAS for a Latin square (Version 8.0, 1998, SAS Inst., Inc., Cary, NC). The main plot was diet tested against animal x diet. Ruminal fermentation data (pH, NH₃, and VFA) were analyzed using the MIXED procedure of SAS (Version 8.0, 1998). 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. No treatment x time interaction (P = 0.80) for ruminal pH was observed; therefore, only treatment effects were reported. When F-tests were significant, single degree of freedom orthogonal polynomial contrasts (Steel and Torrie, 1980) were used to determine linear, quadratic, and cubic effects of level of oil supplementation.

	RESULTS AND DISCUSSION

Top Abstract INTRODUCTION MATERIALS AND METHODS RESULTS AND DISCUSSION IMPLICATIONS LITERATURE CITED

 
Intake, Digestion, and VFA

By experimental design, intake of total and individual fatty acids increased (linear, P < 0.004) with increasing level of dietary safflower oil (Table 3). Intake of 18:2c-9,c-12 was the most substantial because high-linoleate safflower oil was fed. Similarly, OM intake increased (linear, P < 0.001), but NDF and N intake did not change (P = 1.00), with increased dietary safflower oil because all treatments received the same basal diet at 2% of BW.

Increased dietary safflower oil did not affect ruminal pH (P = 0.41; Table 4). The average pH across treatments was 6.0, which suggests that the extent of fermentation of OM and NDF was not affected by increasing levels of dietary safflower oil. Extent of NDF fermentation was not expected to be altered because cellulolysis is not inhibited until pH decreases to <6.0 (Van Soest, 1994).

Linear decreases in molar proportions of isobutyrate and isovalerate (P = 0.03 and 0.05, respectively), but not of butyrate or valerate (P = 0.73 to 0.93), were observed with increased dietary safflower oil. The effect of dietary safflower oil on these VFA was unexpected because CP intake by all wethers was normalized for BW, and bacterial metabolism of the branched-chain amino acids, valine and leucine, results in the branched-chain VFA isobutryrate and isovalerate, respectively (Hespell and Smith, 1983).

Increased dietary safflower oil did not affect (P = 0.21) ruminal NH₃ (data not shown). In the current study, ruminal NH₃ concentrations were 1.40 mg/dL for the 9% safflower oil diet to 4.19 mg/dL for the 0% oil diet. The lack of effect on ruminal NH₃ concentration was expected because true ruminal N digestion was not affected as dietary oil increased.

Duodenal Flow of Total Fatty Acids

Except for duodenal flow of 18:2 c-9,c-11 (P = 0.28), duodenal flow of all individual and total fatty acids increased (linear, P = 0.006 to 0.05) with increased dietary safflower oil (Table 5). Increased duodenal flow of 16:0 could be attributed to increased dietary intake as well as microbial fatty acid contributions (Pantoja et al., 1996). There was a 2.2-fold increase in duodenal flow of 18:0 from the 0 to the 6% oil diets; little further increase in duodenal flow was observed when dietary safflower oil was increased to 9%. The magnitude of increase in duodenal flow of 18:0 from 0 to 6% dietary oil indicated that biohydrogenation of dietary unsaturated fatty acids was occurring; however, duodenal flow of 18:0 leveled off between the 6 and 9% oil diets, suggesting that the extent of biohydrogenation was lower with the 9% safflower oil diet. Other researchers (Pantoja et al., 1996; Duckett et al., 2002; Kucuk et al., 2004) have also observed increased duodenal flow of 16:0 and 18:0 with fat supplementation.

Our study was predicated on the observation of Kucuk et al. (2004), who noted a 2-fold (1.90 to 3.88 g/d) increase in the duodenal flow of 18:2c-9,c-12 when sheep were fed a high-concentrate diet supplemented with increasing levels (0 to 9.4%) of soybean oil. In the current study, high-linoleate safflower oil was used instead of soybean oil (58% 18:2c-9,c-12) to assure a similar or greater magnitude of increase in duodenal flow of this fatty acid as was observed by Kucuk et al. (2004). A 5-fold increase (P = 0.01) in the duodenal flow of 18:2c-9,c-12 was observed from 0 to 9% added safflower oil. Duodenal flow of linolenic acid (18:3c-9,c-12,c-15) also increased (P = 0.02) with increased dietary safflower oil, suggesting that the extent of lipolysis and/or biohydrogenation was decreased with increasing levels of dietary safflower oil. Conversely, Duckett et al. (2002) did not observe an increase in the duodenal flow of either 18:2c-9,c-12 or 18:3c-9,c-12,c-15 when feeding beef steers a 79% corn diet supplemented with either high-oil corn or corn oil. However, the level of oil inclusion used by Duckett et al. (2002) was approximately 5% less, and the concentration of 18:2 c-9,c-12 was much lower, than in the current study.

With the exception of 18:2c-9,c-11, duodenal flow of all of the CLA isomers identified increased (linear, P = 0.02 to 0.05) with increased dietary safflower oil. Conjugated linoleic acid has several potential health benefits, and natural CLA isomers can only be found in ruminant products (Bauman et al., 2003). The CLA isomer 18:2t-10,c-12 was increased the most of any of the CLA isomers. Duckett et al. (2002) also observed that 18:2t-10,c-12 had the greatest increase, and the increase was only observed for diets with high lipid content (high-oil corn) vs. lower lipid levels (2.4% added corn oil). Similarly, Kucuk et al. (2004) observed increases in all identified CLA isomers with increased dietary soybean oil; 18:2t-10,c-12 showed the greatest increase. Griinari and Bauman (1999) proposed that the production of 18:2c-9,t-10 involved 18:2c-9,t-10 isomerase in ruminal bacteria, resulting in the formation of the 18:2t-10,c-12 conjugated double bond structure as one of the biohydrogenation intermediates.

Duodenal Flow of Esterified Fatty Acids

Duodenal flow of esterified 16:0 and 18:0 increased (linear, P = 0.04 and 0.05, respectively) with increased dietary safflower oil (Table 5). As dietary safflower oil increased, duodenal flow of esterified 16:0 increased 0.5-fold, which was much lower than the increased duodenal flow observed for total 16:0. A change of similar magnitude in duodenal flow of 18:0 was also observed when total 18:0 and esterified 18:0 duodenal flow values were contrasted. The increases in esterified 16:0 and 18:0 were expected because of the increased consumption of 16:0 and 18:0 with increased dietary safflower oil. However, the increases might also be attributed to de novo synthesis.

Duodenal flow of esterified 18:1t-11 tended to increase (linear, P = 0.08), and duodenal flow of esterified 18:1c-12 increased (linear, P = 0.04), with increased dietary safflower oil, which was a surprising observation because to become a biohydrogenation intermediate, its precursor would have had to be in the free fatty acid form. This indicates reesterification of a portion of the 18:1t-11 and 18:1c-12 to a glycerol backbone occurred within the rumen, possibly as part of rumen bacterial cell membranes. Harfoot and Hazlewood (1997) concluded that both ruminal protozoa and bacteria incorporate preformed fatty acids into their cellular lipids. Jenkins (1993) calculated the extent of microbial lipid synthesis in the rumen from a variety of reports and estimated that for every 100 g of lipid entering the rumen about 8 g were lost because of incorporation into microbial cells. Rumen microbial fatty acid analysis (data not shown) revealed that total 18:1t-11 tended to increase (linear, P = 0.07), and total 18:1c-12 increased (linear, P = 0.001), with increasing dietary safflower oil. Within the esterified fraction, duodenal flow of microbial 18:1t-11 (linear, P = 0.03) and 18:1c-12 (P = 0.01) were increased (data not shown), further supporting the conclusion that reesterification of fatty acids and microbial incorporation of preformed fatty acids into microbial membranes occurred.

Duodenal flow of esterified linoleic acid (18:2c-9,c-12) increased (linear, P = 0.007) with increased dietary safflower oil. When duodenal flow of total 18:2c-9,c-12 and esterified 18:2c-9,c-12 were compared by paired t-test, there was no difference (P = 0.32) in duodenal flow between the 2 forms. Free linoleic acid is rapidly hydrogenated within the rumen; thus, it is possible that initiation of fatty acid hydrolysis might have decreased because of saturation of the microbial enzyme system. Therefore, to increase the availability of 18:2c-9,c-12 for intestinal absorption, it must remain esterified.

Very little CLA was detected in the esterified fatty acids. Nevertheless, esterified 18:2t-10,c-12 tended (P = 0.07) to increase with increased dietary safflower oil, but the other CLA isomers were not affected (P = 0.21 to 0.50). Duodenal flow of esterified 18:3c-9,c-12,c-15 also increased (P = 0.02) with increased dietary safflower oil. In contrast to the duodenal flow of total 18:3c-9,c-12,c-15, which increased 3-fold, duodenal flow of esterified 18:3c-9,c-12,c-15 increased 2-fold with increased dietary safflower oil. However, at each dietary level of safflower oil, total and esterified 18:3c-9,c-12,c-15 in the duodenal contents were of similar magnitude. Thus, it is likely that duodenal flow of this fatty acid was not biohydrogenated because a large portion existed in the esterified form.

Solid Phase Lipid Extraction

Weight percentages of fatty acids extracted from the duodenal contents that were observed in the neutral lipid, polar lipid, and FFA fractions are shown in Table 6. There were insufficient duodenal contents from each animal to allow for quantitative comparisons. However, the results clearly indicate the pattern of distribution of fatty acids within each fraction. The neutral lipid fraction was composed primarily of triacylglycerols, but di- and, to a lesser extent, monoaclyglyerols were also present.

The presence of 18:1t-11 in the neutral and polar lipid fractions further indicates that fatty acid reesterification occurred within the rumen because 18:1t-11, a biohydrogenation intermediate, could only be present if its precursor was a free fatty acid, and the presence of a free carboxyl group is absolutely required for hydrogenation to take place (Hazlewood et al., 1976). Harfoot (1981) provided insight on uptake of long-chain fatty acids by ruminal bacteria and the fractions in which they have been observed. After ruminal bacteria were incubated with ¹⁴C-linolenic acid, the proportion of ¹⁴C appearing in the sterol ester fraction as C18:2 fatty acids was 16%, as C18:1 fatty acids was 23% and 18:0 was 61%. Within the polar lipid fraction, ¹⁴C was present in all C18 fatty acids with 14% as C18:2 and 32% as C18:1 fatty acids. Therefore, we can conclude that the presence of 18:1t-11 within the polar lipid fraction observed in the current study represented microbial incorporation, and the presence of 18:2c-9,c-12 within the neutral fraction likely represented aclyglycerols of the feed component, which indicates a decrease in extent of lipolysis and, thus, biohydrogenation.

Apparent Small Intestinal Fatty Acid Disappearance

Ileal flow of fatty acids represents the amount of fatty acids that did not disappear between the duodenum and ileum; therefore, an estimation of apparent absorption can be made. Ileal flow of most individual, total, and esterified fatty acids were not affected by increased dietary safflower oil (data not shown).

Total Fatty Acids. Except for 18:2c-9,c-12 and 18:2c-9,t-11, apparent small intestinal disappearance (Table 7) of most individual fatty acids was not affected (P = 0.19 to 0.90) by increased dietary safflower oil. There was, however, a linear increase in small intestinal disappearance of 18:2c-9,c-12 (P = 0.05) and 18:2c-9,t-11 (P = 0.03) as dietary safflower oil increased. Kucuk et al. (2004) observed a quadratic increase in disappearance of 18:2c-9,c-12 from the small intestine but did not observe an increase in that of 18:2c-9,t-11 until soybean oil was included in the diet at 6.4%. Conversely, others have observed a linear decrease in small intestinal total fatty acid digestion with increasing level of fat supplementation (Zinn, 1989; Pantoja et al., 1996; Elliott et al., 1999). Contrasting results were likely attributable to differences in duodenal flow of saturated fatty acids, because Kucuk et al. (2004) reported decreased apparent disappearance of total fatty acids as the duodenal flow of stearate increased. Moreover, intestinal absorption of unsaturated fatty acids is greater compared with saturated fatty acids (Doreau and Chilliard, 1997).

According to Noble (1981), absorption of fatty acids from large amounts of unhydrolyzed triacylglycerols that reach the small intestine may be delayed until they reach the mid jejunum because pancreatic lipase has an optimal pH of 7.5 and the pH in the distal duodenum is about 5.0. Thus, acylglycerols may not be as readily digested, which may decrease absorption. However, results of the current study are not in agreement with the conclusion of Noble (1981) because all esterified fatty acids within the duodenal contents were apparently absorbed at 80% for 18:3c-9,c-12,c-15 at the greatest level of dietary safflower oil up to 100% for 18:1t-11 and 18:1c-12 with 0% dietary safflower oil. Thus, in the current study, the physical and chemical properties of the dietary triaclyglycerols had minimal effects on apparent absorption of fatty acids by the small intestine.

In conclusion, increasing levels of dietary safflower oil increased the duodenal flow of linoleic acid along with other unsaturated fatty acids, indicating that the extent of ruminal biohydrogenation was decreased. Duodenal flow of linoleic acid associated with total fatty acids was similar to duodenal flow of linoleic acid associated with esterified fatty acids. Thus, we further conclude that the extent of ruminal lipolysis was also decreased with increased level of dietary safflower oil because of the requirement for a free carboxyl group for initiation of biohydrogenation and concomitant loss of linoleic acid. Additionally, the observation of biohydrogenation intermediates in the esterified pool of fatty acids indicated that reesterification of ruminal fatty acids was occurring, thus contributing to duodenal flow of biohydrogenation intermediates. Finally, at the levels of high-linoleate safflower oil fed, apparent disappearance, and thus apparent absorption, of fatty acids ranged from 80 to 100%, indicating that intestinal lipolysis did not limit overall digestion of the fatty acids fed to the sheep.

	IMPLICATIONS

Top Abstract INTRODUCTION MATERIALS AND METHODS RESULTS AND DISCUSSION IMPLICATIONS LITERATURE CITED

 
Producing ruminant meat and dairy products that are enriched with unsaturated fatty acids, such as various n-3, n-6, and conjugated linoleic acid, is desired. By feeding large dietary proportions of high-linoleate vegetable oils in high-concentrate diets, greater levels of linoleic acid and other polyunsaturated fatty acids will be available for incorporation into ruminant-derived food products.

	Footnotes

 
¹ Current address: Northern Great Plains Research Laboratory, Mandan, ND 58554.

² Corresponding author: dcrule{at}uwyo.edu

Received for publication August 18, 2005. Accepted for publication October 5, 2005.

	LITERATURE CITED

Top Abstract INTRODUCTION MATERIALS AND METHODS RESULTS AND DISCUSSION IMPLICATIONS LITERATURE CITED

 


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

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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, M. W. Pariza, and G. J. Nelson ed. AOCS Press, Champaign, IL.

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