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ANIMAL PRODUCTION |
* Agriculture and Agri-Food Canada, 5304 1st Ave. S., PO Box 3000, Lethbridge, Alberta, Canada, T1J 4B1; and
Agriculture and Agri-Food Canada, 6000 C&E Trail, Lacombe, Alberta, Canada, T4L 1W1
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Abstract |
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 Top Abstract MATERIALS AND METHODSRESULTS AND DISCUSSIONLITERATURE CITED |
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Key Words: carcass characteristic • conjugated linoleic acid • liver abscess • sunflower seed • trans fatty acid
Oilseeds or oils have been added to beef cattle diets to increase the concentrations of beneficial fatty acids such as CLA in meat (Mir et al., 2003b
; Sackmann et al., 2003; Gibb et al., 2004), to enhance the health advantages of beef for consumers. However, Hristov et al. (2005) indicated that safflower oil supplementation of beef finishing diets caused a shift in the biohydrogenation of PUFA from 11-trans (t)-18:1 to 10t-18:1, without affecting the CLA concentrations of meat. Although Bauchart et al. (2007) demonstrated a neutral effect of 11t-18:1 toward the risk of atherogenesis, consumption of 10t-18:1 was detrimental. Thus, it is of interest to establish whether replacing barley with sunflower seeds (SS) in the diet of finishing steers will negatively affect the content and profile of trans fats in the beef. From a beef production perspective, Gibb et al. (2004) reported that beef steers fed SS at either 9 or 14% of the diet had a reduced incidence and severity of liver abscesses. Furthermore, steers fed the barley and high linoleic acid SS diet had fewer liver abscesses compared with those fed diets containing corn and SS or those fed diets containing high oleic acid SS. Liver abscesses cost the Canadian beef industry approximately $8 million/yr in condemned livers from beef carcasses (Van Donkersgoed et al., 2001) and can negatively affect G:F ratios and ADG (Nagaraja and Chengappa, 1998). Thus, the objectives of the study were 2-fold: first, to compare the effect of replacing 15% of the diet with SS (Shah et al., 2006) or including tylosin phosphate (TP, an antibiotic currently used to reduce liver abscesses) on ADG, G:F, carcass characteristics, and incidence of liver abscesses; and second, to compare the effect on fatty acid composition, including the trans fatty acid content in muscle [pars costalis diaphragmatis (PCD)] and in subcutaneous fat (SF; from the brisket).
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MATERIALS AND METHODS |
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TopAbstractMATERIALS AND METHODSRESULTS AND DISCUSSIONLITERATURE CITED |
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Steers were maintained in the Individual Feeding Barn of the Lethbridge Research Center following the guidelines of the Canadian Council on Animal Care (1993), and the study was conducted with the approval of the Institutional Animal Care Committee.
A 2 x 2 factorial experiment with 48 (373 ± 8.4 kg) European crossbred steers (with Hereford, Angus, and Charolais genetics) was conducted to evaluate the effects of dietary SS and TP on production variables, carcass characteristics, liver abscess incidence, and muscle and subcutaneous adipose tissue fatty acid composition. Steers were fed either a control diet or an SS diet (Table 1), in which 15% of the diet was replaced with SS, where the SS replaced only barley in the control diet, as reported in Shah et al. (2006). One-half the animals within each diet received TP (Elanco, Clinton, MO) top-dressed at 11 mg/kg of DM fed. The nutrient and fatty acid compositions of the diets are provided in Table 1.
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). Daily DMI was calculated from the feed offered and the feed refused, and the ratio of the ADG (g) to DMI (kg) was calculated. At the end of the feeding period (157 d), the animals were weighed on 2 consecutive days on full feed and were processed in a commercial abattoir.
At processing, HCW and samples of PCD and SF were obtained for determination of fat content and fatty acid composition. Liver scores were obtained soon after slaughter; livers were scored for incidence (animals with abscesses) and severity on a 4-point scale (Gibb et al., 2004). At the time of grading, approximately 48 h after slaughter, the average grade of fat depth, LM area, US marbling score ["Canada A" or "US Standard" received a score of 300, "Canada AA" or "US Select" received a score of 400, and "Canada AAA" or "US Choice" received a score ranging from 500 to 700, based on whether the carcass was deemed to display a small (500), modest (600), or moderate (700) amount of marbling fat], and percent lean meat yield (Canadian Beef Grading Agency, 1995) were obtained. The total lean yield produced was calculated as the product of the carcass weight and percentage lean meat yield divided by 100, and the ratio of the total lean yield (g) to feed consumed (product of DMI and days on feed; kg) was determined.
Fatty Acid Analysis
Lipid extraction from PCD (total lipid in the muscle) and SF samples was carried out according to the procedures of Jiang et al. (1996) as modified by Shah et al. (2006). Fatty acid methyl esters were prepared (Lock and Garnsworthy, 2002) and quantified by a gas-liquid chromatograph (GC System 5890, Hewlett-Packard, Mississauga, Ontario, Canada) equipped with a flame-ionization detector and an SP-2560 fused-silica capillary column (100 m with 0.2 mm film thickness; Supelco Inc., Oakville, Ontario, Canada). Samples were loaded onto the column via 1-µL splitless injections (Kramer et al., 1997). The initial oven temperature (120°C) was held for 15 min and then increased by 5°C/min to 160°C, and held for 15 min. Next, the temperature was increased by 4°C/min to 240°C and held for 30 min. Inlet and detector temperatures were maintained at 220 and 275°C, respectively. The He carrier gas flow rate through the column was 1.7 mL/min. Hydrogen flow to the detector was 34 mL/min, air flow was 320 mL/min, and the He makeup gas flow rate was 29 mL/min. Peaks in the chromatograms were identified and quantified by using pure methyl ester standards (Sigma-Aldrich Inc., Oakville, Ontario, Canada) and reported as weight percent (wt%, mg of fatty acid/100 mg of fatty acids detected; Dhiman et al., 2000). Non-adecanoic acid methyl ester (C19:0) was used as the internal standard to determine recoveries and correction factors for individual fatty acids.
Trans Fatty Acid and CLA Analysis
Initial GLC analyses were not capable of resolving individual trans-18:1 and CLA isomers; therefore, the GLC and Ag+-ion HPLC conditions outlined by Cruz-Hernandez et al. (2004) were used, except that purification of trans isomers was not completed by using Ag+-TLC and the minor contributions of 13t-18:1 to 16t-18:1 were not accounted for (i.e., because of their overlap with cis-18:1 isomers). For the analyses of trans-18:1 and CLA, 50 mg of dried lipid was dissolved in 1 mL of toluene and methylated with 2 mL of 0.5 N sodium methoxide at 50°C for 15 min. One hundred microliters of glacial acetic acid and 1 mL of 0.88% aqueous potassium chloride were then added, and fatty acid methyl esters were extracted with 3 mL of hexane. An aliquot of fatty acid methyl ester extract was then diluted to approximately 1 mg/mL before GLC and HPLC analyses. Conjugated linoleic acid and trans-18:1 methyl esters were identified based on peak retention times by using a GLC reference standard with 4 positional CLA isomers (mixture no. UC-59M; Nu-Chek Prep Inc., Elysian, MN) and individual trans-18:1 isomers (Sigma-Aldrich Inc.). Isomers not available commercially were identified based on their retention times and relative order from chromatograms presented by Cruz-Hernandez et al. (2004).
Statistical Analysis
The experiment was a completely randomized design with a 2 x 2 factorial arrangement of treatments and was analyzed by using PROC MIXED (SAS Inst. Inc., Cary, NC) with SS, TP, and their interaction included in the model as fixed effects and steer nested in treatment as the random effect. Steer was the experimental unit because steers were penned and fed individually. Initial BW was used as a covariate for all variables. A protected LSD mean separation test was performed for effects that were significant. The liver scores were given a value of 0, 1, 2, or 4 for each animal. Because differences in severity did not exist, abscess incidence was analyzed by PROC FREQ to test for differences among treatments. The treatment x liver score matrix had many cells with zero counts, so the EXACT option was used to perform Fisher’s exact test. Treatment differences were declared significant at P < 0.05.
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RESULTS AND DISCUSSION |
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TopAbstractMATERIALS AND METHODSRESULTS AND DISCUSSIONLITERATURE CITED |
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; Table 1
). The diet containing the SS had greater CP content but substantially greater fiber components because of the substitution of SS for barley at the rate of 15% of dietary DM. The inclusion of SS not only elevated the ether extract of the SS diet compared with the control diet, but also altered the fatty acid composition. The principal differences were an increase in 18:2n-6 and a decrease in 18:3n-3, reflecting the differences in fatty acid composition of SS and barley. Steer Growth and Carcass Characteristics
The interactions of SS and TP were significant (Table 2) for all growth factors except start BW (P = 0.898) and G:F ratio (P = 0.338). For start BW, we observed that dietary SS increased (P = 0.001) the BW of the steers during the 4-wk period between randomization and initiation of the study, but reduced the G:F ratio in the study. During the 4-wk period between randomization and initiation of the study on the finishing diets, the steers were being adapted to increasing amounts of grain and SS, but for the majority of the time, they received relatively high-forage diets. Mir et al. (2002) reported that feeding high-forage backgrounding diets with sunflower oil increased the rate of gain of steers compared with the gain of steers not receiving the oil, which supports the observation of an effect of dietary SS on the BW of the steers between randomization and start weight in the present study. This increase in the rate of BW gain may be due to the effect of dietary oil, which substantially decreases ruminal protozoa, which, if present in large numbers in the rumen, can negatively affect protein availability (Ivan et al., 2001, 2004), and also decreases the viscosity in the small intestine, favoring nutrient absorption (Mir et al., 2005).
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). Consequently, ADG up to 84 and 157 d were less for SS-fed steers than for steers fed the control diet (P = 0.031 and 0.014, respectively), and ADG of steers fed the control + TP and SS + TP diets were intermediate, but not different from, these values up to 84 d. However, after 157 d the ADG of steers fed the SS + TP diet was also less than that of steers fed the control diet. Steers fed the SS and SS + TP diets began the experiment at greater BW because of their increased rate of gain during the adaptation period, but after 84 d into the study, the BW of steers fed the SS and SS + TP diets were comparable with that of steers fed the control diet. Steers fed the control + TP diet, however, had reduced BW compared with steers fed the control diet (P = 0.043), but BW were not different from those of steers fed the SS diet. After 157 d, BW of steers fed the control + TP, SS, and SS + TP diets were less (P = 0.031) than those of steers fed the control diet. However, the G:F ratio was less (P = 0.011) for the SS diet than for the control and control + TP diets. The relative slaughter weights of the steers fed each of the diets affected the HCW. Thus, carcass weights of steers fed the control diet were greater (P = 0.025) than those of steers fed the SS diet. However, the greater (P = 0.025) carcass weights of steers fed the control diet tended to be due to fat, as indicated by the trend (P = 0.083) toward a greater grade of fat depth for these animals compared with those fed the other 3 diets. Differences in LM area (P = 0.642), saleable lean meat yield (P = 0.898), or marbling score (P = 0.303) were not observed and were not attributable to SS, TP, or their interaction. As a result, the total lean yield or the product of the HCW and the percentage of lean yield divided by 100 was comparable for steers fed the treatment diets. However, when the efficiency of meat production from the diets was determined as the ratio of total lean yield to feed consumed (DMI x 157 d), the interaction indicated a trend (P = 0.059), and the ratio was greater for the SS and control + TP diets than for the control diet.
It is not known whether the CLA and some of the trans fatty acids produced as a result of dietary inclusion of SS are responsible for the trend toward a diminished grade of fat depth in steers fed the diets containing SS. Dugan et al. (1997) observed similar effects on subcutaneous adipose tissue in pigs fed synthetic CLA. In rats fed beef with increased CLA, Mir et al. (2003a) reported a decrease in adipocyte number for inguinal fat depots compared with rats fed control beef. However, Gibb et al. (2004) observed some dietary energy loss caused by increased excretion of fat in the feces in steers fed SS. The great extent of hydrolysis and biohydrogenation of PUFA in the rumen leads to decreased lipid digestibility, especially of stearic acid (Plascencia et al., 2003). The melting point of stearic acid or tristearate is approximately 69°C, which is well above the internal body temperature of animals. Thus, a substantial portion of the stearate formed is eliminated in the feces and is an energy loss for the animal.
There is concern that the use of antibiotics as a dietary ingredient in beef production may lead to the development of antibiotic-resistant bacteria (Witte, 1998). As a result, there is considerable effort to investigate safe, efficacious alternatives to antibiotics for use in beef cattle diets to prevent or reduce liver abscesses. From the perspective of the beef producers, increased starch fermentation is known to cause liver abscesses (a consequence of high starch digestion in the rumen), and merely replacing 15% of the diet with SS reduces the grain load for the animal. Because differences in severity were not observed (all noted abscesses received a score of 1, or minimal severity), the percentage of animals with an incidence of liver abscess was determined by dietary treatment. In the present study, provision of the SS diet or the SS + TP diet tended (P = 0.08 for the interaction) to reduce the liver abscess incidence to zero, and the reduction was significant compared with the control diet. A reduction in liver abscesses was observed in steers fed the diet containing barley and the high linoleic acid SS (Gibb et al., 2004), but not when the high oleic acid SS was fed. This suggests that animals on high-barley diets might benefit from supplementary linoleic acid, its elongation and desaturation products, or both, which are important for maintaining membrane integrity and immune function. Alternatively, CLA produced from dietary linoleic acid appears to be sequestered by the liver in sheep (Ivan et al., 2001); if this is true for cattle as well, CLA might improve the immune function in the liver (Hayek et al., 1999), contributing to a decreased incidence of liver abscesses. If the improvement in immune function is substantial and consistent in decreasing liver abscesses, it may be possible to eliminate the antibiotic TP from beef diets in favor of SS. This possibility requires further study.
Muscle Fatty Acid Composition
Alterations in fatty acid composition reflected those of the diets consumed (Table 3), and the interaction of SS and TP was significant only for a minor fatty acid (11c-20:1; P = 0.007); thus, the focus will be on the main effects only. For the SFA, provision of the control, SS, or SS + TP diet led to a decreased wt% of 16:0 compared with that in animals fed the control + TP diet and is indicative of decreased endogenous synthesis, but the reason for this is not apparent. The wt% of 17:0, although less than 2% of the fatty acids in muscle, was less in steers fed the SS diets. However, the wt% of 18:0 was greater in these steers and is an index of the biohydrogenation of the additional PUFA from dietary SS in the rumen. Among the PUFA in muscle, steers fed the SS diets had greater wt% of 18:2n-6 (P = 0. 001) and 20:4n-6 (P = 0.055), but less (P = 0.024) wt% of 18:3n-3. These alterations in fatty acid composition of the muscle led to declines in the percentage of MUFA in steers fed either the SS (P = 0.001) or TP (P = 0.002) diet and to decreased ratios of unsaturated fatty acids to SFA among steers fed either the SS (P = 0.001) or the TP (P = 0.027) diet. The general pattern of alterations in the wt% of fatty acids attributable to dietary SS is in agreement with previously reported information for the same muscle (Shah et al., 2006).
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), and its consumption has not been associated with atherogenesis in rabbits (Bauchart et al., 2007). Muscle from animals fed the SS diet had more total trans-18:1 (2.94 ± 0.29%) than that from animals fed the control and control + TP diets (P < 0.001), and animals fed the SS + TP diet had a further increase in total trans (4.23 ± 0.52%) compared with animals fed the SS diet (P < 0.001). This pattern was repeated for 6t–8t-18:1, 9t-18:1, and 10t-18:1. For 11t-18:1 and 12t-18:1, however, feeding the SS and TP diets increased the quantity of trans-18:1 compared with feeding the control diets (P < 0.001), but adding the TP to the SS diet did not cause a synergistic increase. Jenkins et al. (2003) reported a synergistic increase in 10t-18:1 production when monensin and soybean oil were added to a barley ration in a continuous rumen fermenter, but this was the first time an effect was demonstrated in vivo for a nonionophore antibiotic. Within the trans-18:1 isomers, 10t-18:1 and 11t-18:1 were consistently the greatest, with 10t-18:1 dominating (P = 0.004) the composition when TP was added to the diets. It is important to note, however, that in 100 g of beef, the greatest amount of total trans-18:1 was found when steers were fed the SS + TP diet. This amount was only 0.47 g/100 g (Table 4), which is considerably less than values for margarines prepared by partially hydrogenating vegetable oils.
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Biohydrogenation of PUFA along the 10t-18:1 pathway, rather than the 11t-18:1 pathway, in the rumen of cattle fed high-grain diets (Hristov et al., 2005) is of concern because this creates the opportunity for the production and deposition of atherogenic trans fatty acids, which can be exacerbated by the inclusion of dietary oil (Hristov et al., 2005). In addition, there is further concern that additive effects of TP inclusion to the diet may cause increases in trans-18:1 (particularly 10t-18:1), which might negatively affect the healthfulness of beef. In the present study, however, when steers were fed the SS diet (i.e., without TP), the quantity of total trans-18:1 was comparable with that when the control and control + TP diets were fed.
Furthermore, the inclusion of SS decreased the grain content of the diet. The SS could have affected the fermentation in the rumen, leading to a tendency toward lower acidity than can be expected in cattle fed the control finishing diets (Beauchemin et al., 2007). These 2 factors, the decrease in dietary grain content attributable to SS inclusion and the effect on fermentation, could have jointly contributed to the absence of liver abscesses in SS-fed animals. In the present study, the values for 10t-18:1 were less than those reported by Hristov et al. (2005) and may be related to the use of the SS rather than safflower oil, which may have affected the rate of availability of fatty acids for biohydrogenation between oil in the seed and the oil itself. However, the increase in CLA attributable to dietary SS in the present study was only 36% and was less than the 300% previously reported (Mir et al., 2002). This may have been due to the use of silage in the diets in the present study rather than the pea hay used in the previous study. Although the reason for the relatively poor CLA accumulation response to silage is not clear, French et al. (2000) observed this previously. Moreover, the SS were provided during the finishing period only and not from weaning, as was the case in the previous study (Mir et al., 2002), suggesting that the duration of oil provision may affect the extent of increase of CLA in muscle.
Fatty Acid Composition of SF
The fat content of the SF was greater than that of the PCD (Table 5) but was not affected by the diets provided to the steers. As observed for the PCD, the interactions between the SS and TP were not significant, and dietary SS had a greater effect on SF fatty acid composition than did TP. The general pattern of changes followed the observations noted for the PCD. Dietary SS caused an increase in the wt% of 18:0, 20:0, and 18:2n-6 but a decrease in the wt% of many other fatty acids.
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) attributable to dietary provision of the SS and SS + TP diets compared with the control and control + TP diets was comparable to that observed in the PCD for 10t-18:1 (116%), 11t-18:1 (65%), 9c,11t-CLA (39%), and 10t,12c-CLA (250%). As a result, the total percentage of trans-18:1 fatty acids was increased by 123%. The amount of trans-18:1/100 g of SF increased by 218%, from 1.82 ± 0.20 (sum of values for steers fed the control and control + TP diets) to 3.96 ± 0.36 g (in steers fed the SS and the SS + TP diets), and the amounts reflect the fat content of the SF. However, SF is rarely consumed exclusively but is added to ground beef and could affect its overall trans fatty acid content. It must be emphasized that the fatty acids presented are as wt% of detected fatty acids, as reported by Dhiman et al. (2000), and do not include the 12% contribution of glycerol to the triacylglycerol molecule and thus are exaggerated by that amount.
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It was concluded that dietary inclusion of SS to replace 15% of the diet for finishing steers reduced the occurrence of liver abscesses to zero. Although the G:F ratio was diminished by feeding SS, despite reduced feed intakes, the efficiency of conversion to meat was improved because of the trend toward a decreased grade of fat depth. Alterations in fatty acid composition were observed because of the addition of both SS and TP, and increases were observed for both CLA and trans fatty acid isomers. In general, changes in the fatty acid profiles were improved compared with when linoleic acid-rich oils were added to the diet (Hristov et al., 2005). However, there still seems to be room for improvement in the production of beef with bioactive fatty acids having beneficial properties (i.e., 11t-18:1 and 9c,11t-CLA).
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Footnotes |
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2 The authors acknowledge the funding and the donation of the sunflower seeds from Pioneer Hi-Bred (Chatham, Ontario, Canada) and financial assistance for the project from the Matching Investments Initiative of Agriculture and Agri-Food Canada. The technical help of M. A. Shah, Elysia Ma, Charmaine Ross, David Rolland, and the staff at the barn is gratefully acknowledged.
3 Corresponding author: mirp{at}agr.gc.ca
Received for publication January 16, 2008. Accepted for publication June 5, 2008.
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LITERATURE CITED |
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TopAbstractMATERIALS AND METHODSRESULTS AND DISCUSSIONLITERATURE CITED |
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9-desaturated compared with trans-12-18:1 in humans. Br. J. Nutr. 95:752–761.[CrossRef][Medline]
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