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ANIMAL NUTRITION |
Department of Animal Sciences, The Ohio State University, Wooster 44691
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Abstract |
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 Top Abstract INTRODUCTIONMATERIALS AND METHODSRESULTS AND DISCUSSIONLITERATURE CITED |
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Choice– were 10% greater for NA steers, although these trends were not significant (P = 0.11 and 0.13, respectively). Backfat thickness and yield grade were not affected (P > 0.26) by vitamin A supplementation. Composition of the LM was not affected (P > 0.15) by vitamin A or SB supplementation. Serum retinol at slaughter was 44% lower (P < 0.01) for steers fed NA than for steers supplemented with vitamin A (23.0 vs. 41.1 µg/dL). A vitamin A x SB interaction occurred (P < 0.05) for adipose cellularity in the i.m. depot; when no SB was fed, vitamin A supplementation decreased cell density and increased cell size. However, when SB was fed, vitamin A supplementation did not affect adipose cellularity. Adipose cellularity at the s.c. depot was not affected (P > 0.18) by vitamin A or SB treatments. Fatty acid profile of the LM was not affected by vitamin A (P > 0.05), but SB increased (P < 0.05) PUFA (7.88 vs. 4.30 g/100 g). It was concluded that feeding NA tended to increase marbling without affecting back-fat and yield grade. It appeared that NA induced hyperplasia in the i.m. but not in the s.c. fat depot.
Key Words: beef • marbling • roasted soybean • vitamin A
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INTRODUCTION |
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TopAbstractINTRODUCTIONMATERIALS AND METHODSRESULTS AND DISCUSSIONLITERATURE CITED |
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). The mechanisms controlling the site of fat deposition within the carcass are not well understood.
Retinoic acid, a bioactive vitamin A isoform, inhibits adipocyte differentiation (Sato et al., 1980). Adipocyte differentiation is important in i.m. fat deposition because the i.m. depot grows largely by hyperplasia (Cianzio et al., 1985). Low levels of serum retinol have been correlated with increased i.m. fat deposition in Wagyu cattle (Oka et al., 1998). To our knowledge there is no information regarding the effects of feeding vitamin A in concentrations less than NRC (1996) recommendations on marbling in US cattle.
Conjugated linoleic acid is a group of positional and geometric fatty acid isomers that have multiple, beneficial, human health effects and that are found almost exclusively in ruminant products (Parodi, 1999). Increasing the content of CLA in beef may improve the demand for beef products as the perception of consumers of beef as a healthy product increases.
Conflicting data have been published regarding the effects of retinol on stearoyl-CoA desaturase (SCD) enzyme activity, which is important in the endogenous synthesis of CLA (Alam and Alam, 1985; Daniel et al., 2004). Dietary vitamin A concentration may influence desaturase activity and the CLA content of beef. Feeding roasted soybeans (SB) increases CLA in milk (Dhiman et al., 1997), and it could increase the CLA content of beef. Feeding SB may interact with retinol to modify the fatty acid profile and the CLA content of beef.
The objectives of this experiment were to 1) determine the effect of dietary vitamin A supplementation on marbling; 2) determine the effect of feeding SB on the CLA content of beef; and 3) detect potential additive effects of dietary vitamin A and SB supplementation on marbling and CLA content of beef.
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MATERIALS AND METHODS |
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TopAbstractINTRODUCTIONMATERIALS AND METHODSRESULTS AND DISCUSSIONLITERATURE CITED |
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). Research procedures were approved by the Animal Care Committee of The Ohio State University.
One hundred sixty-eight Angus-crossbred steers (initial BW = 295 ± 1.8 kg) were randomly allotted to one of the following dietary treatments, in a 2 x 2 factorial arrangement: no supplemental vitamin A, no roasted soybeans (NANS); no vitamin A, roasted soybeans (20% of the diet on a DM basis; NASB); with supplemental (2,700 IU/kg) vitamin A, no roasted soybeans (WANS); and with supplemental vitamin A, roasted soybeans (WASB). To ensure that vitamin A supplementation exceeded the published requirements (NRC, 1996), 2,700 IU of vitamin A/kg of DM were added to the supplemental vitamin A treatments. Vitamin A equivalents from basal ingredients were calculated (NRC, 1996) to be < 1,300 IU/kg of DM. Diets were formulated to be isonitrogenous (Tables 1 and 2).
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Initial and final BW were determined using average BW measured on 2 consecutive days. Steers were weighed before feeding at 0800 and were not withheld from feed or water. Interim BW were determined at 14-d intervals.
The feeding period was divided into a backgrounding and a finishing phase. During the backgrounding phase, growth rate was limited to 1.1 kg/d to extend the duration of the trial and to allow time for hepatic vitamin A stores to be depleted. Growth rate was controlled by feeding a prescribed amount of feed to achieve a BW gain of 1.1 kg/d (NRC, 1996). The amount of feed delivered was adjusted every 14 d based on the average BW of steers in each pen. After 84 d, the steers were switched to the finishing phase feeding regimen. During the finishing phase, steers were offered feed for ad libi-tum access until the end of the trial. Backfat depth was determined by ultrasound (Classic Ultrasound Equipment, Classic Medical Supply, Tequesta, FL) on d 1, 84, and 154 by a certified ultrasound technician.
Feed samples were analyzed weekly for DM content to allow determination of DMI. Feed samples also were collected every 2 wk throughout the experiment and were stored frozen until analyzed for nutrient content. Composite feed samples were freeze-dried, ground to pass a 1-mm screen, and analyzed for DM, OM, N, and ether extract (EE; AOAC, 1996). Diet vitamin A content was calculated using the NRC (1996) tabular values for feed ingredients.
Two steers per pen were selected at the beginning of the trial, and 10 mL of blood was collected from these steers by jugular venipuncture every 28 d to determine serum vitamin A concentrations. Tubes containing blood samples were immediately wrapped in aluminum foil to avoid light damage and were kept on ice until serum was harvested. Serum was obtained by centrifuging the blood samples at 2,200 x g at 4°C for 10 min. Samples were frozen at –20°C until vitamin A analyses were performed. Serum vitamin A levels were analyzed according to the procedures of Weiss et al. (1995), with modifications. Briefly, the samples were extracted with hexane, and the extracted samples were dried under N2 gas at 37°C, reconstituted with ethanol, and injected into a HPLC equipped with a reverse-phase column (Supelcosil LC-18, 25 cm x 4.6 mm; Supelco Inc., Bellefonte, PA). The solvent used was initially 75% water and 25% methanol and then was changed linearly to 100% methanol over 2 min. The flow rate was 1.8 mL/min. All-trans retinol obtained from Sigma Chemical Co. (St. Louis, MO) was used as the standard. All procedures were performed in the dark to avoid light damage to the retinol. The assay CV was less than 5%, and the limit of detection was 0.5 µg/dL.
Steers were slaughtered when the average BW of all animals was estimated to be 590 kg. Slaughtering was completed within a 2-wk period. Days on feed were kept constant across treatments. Hot carcass weight, backfat thickness, LM area, and KPH % were determined by trained Ohio State University personnel. Carcass yield grade was calculated (USDA, 1997). Quality grade and marbling score were determined by a USDA official. Carcass characteristics were measured after a 48-h chill.
Two steers per pen were selected for carcass sample collection. Selected steers had the BW closest to the average pen BW at slaughter. Samples from the 9th to 11th thoracic rib of the right side of the carcass were collected, deboned, ground thrice, and analyzed for moisture, N, and EE (AOAC, 1996). Final empty body composition of the edible carcass was estimated using the procedures of Hankins and Howe (1946) and the equations of Garrett and Hinman (1969). Longissimus muscle samples from the 11th to 12th thoracic rib were collected, trimmed of external fat, ground 3 times (model #4822, Hobart Co., Troy, OH), and analyzed for moisture, N, and EE content (AOAC, 1996). Additionally, fatty acids in LM and adipose tissue were extracted and methylated by alkaline transesterification and analyzed as described by Kramer et al. (1997). Methyl esters of fatty acids were separated on a 0.25 mm x 100 m, fused silica column (Supelco Inc.) using a Hewlett-Packard 5890 gas chromatograph with automated injection and data reduction (HP 3365 Chemstation software, Hewlett Packard Co., Santa Clarita, CA). Standards for the CLA isomers c9, t11; t10, c12; and t9, t11 were obtained from Matreya Inc. (Pleasant Gap, PA).
Subcutaneous and intramuscular adipose tissue was collected from the 6th to 8th thoracic rib after a 48-h chill. These samples were snap-frozen in liquid N2 and stored at –20°C until adipose cellularity analyses were performed. To determine adipocyte size and number, frozen adipose tissue samples were fixed and sectioned at a thickness of 6 to 8 µm in a CM1900 Leica cryostat (Meyer Instruments Inc., Houston, TX). Samples were stained with a hematoxylin-eosin solution (Merck, Darmstadt, Germany) and mounted on Superfrost Plus slides (Fisher, Pittsburgh, PA). Adipocyte number and mean adipocyte diameter were determined by computerized image analysis (Image-Pro Plus v. 4.5, Media Cybernetics Inc., Silver Spring, MD). Adipocyte presence in the samples was confirmed by staining an additional slide with Sudan IV dye (Culling, 1974).
Liver retinol stores were determined in 2 steers per pen at slaughter. Liver samples were collected immediately after the steers were eviscerated, and were snap-frozen in liquid N2, immediately placed on ice, and protected from light damage. Samples were stored at –80°C before retinol analysis. Before retinol extraction, liver samples were saponified by heating them at 70°C for 10 min with 5 mL of 50% KOH solution (Indyk, 1988). Samples were then extracted twice with hexane (10 mL each time). The extracts were combined, and 5 mL of H°O was added to allow for phase separation. After sample centrifugation at 2,200 x g for 10 min, a 5-mL aliquot of the extract was dried at 37°C under N2 gas. Samples was reconstituted with ethanol and analyzed by HPLC, as described for the serum samples.
The data were analyzed statistically using the MIXED procedure (SAS Inst. Inc., Cary, NC). Serum retinol and ultrasound backfat data were analyzed as a completely randomized design with repeated measures. The model included terms for vitamin A level, SB inclusion, days on feed at the time of sample collection, and their respective interactions. The error structure used was unstructured because it resulted in the lowest Bayesian criteria. Time effects were partitioned into linear, quadratic, and cubic contrasts.
Feedlot performance, carcass characteristics, muscle fatty acid composition, and adipose cellularity data were analyzed as a completely randomized design. The model included the fixed effects of vitamin A level and SB inclusion and their interaction. For the cellularity data, fat depot (i.m. or s.c.), and its respective interactions also were included in the model. Treatment means were compared using the PDIFF statement of SAS when protected by a significant (P < 0.05) F-value. Pen averages were used as the experimental unit for all statistical analyses.
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RESULTS AND DISCUSSION |
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TopAbstractINTRODUCTIONMATERIALS AND METHODSRESULTS AND DISCUSSIONLITERATURE CITED |
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) were similar (P > 0.10) between vitamin A levels. Steers fed NA diets had slightly lower (3%) ADG than those fed WA diets (P = 0.08). Further research is warranted to determine if this small effect of vitamin A on growth rate is biologically relevant.
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recommends dietary vitamin A concentration of 2,200 IU/kg of DM for feedlot cattle. This recommendation was established in 1976 (NRC, 1976). The recommendation was based on sparse published information (Perry et al., 1965, 1968; Eaton et al., 1972), and no reports on the requirements of growing cattle have been published since that time. High moisture corn was fed in this experiment because it was assumed to contain insignificant amounts of vitamin A precursors as a result of carotenoid degradation during storage of high moisture corn (NRC, 1996). However, no data have been published reporting changes in corn carotenoid content during the fermentative process that accompanies storage of high moisture corn. Further research is warranted to determine whether feeding diets without supplemental vitamin A during the finishing period affects cattle health and immune status. Accurate characterization of provitamin A carotenoids in feed ingredients also is required to precisely define the actual vitamin A requirement of feedlot cattle. Roasted soybean inclusion reduced (P < 0.05) DMI and increased (P = 0.06) feed efficiency for the total trial reflecting the greater energy density of the diet when roasted soybeans were fed. Average daily gain tended to be reduced only slightly with SB, suggesting that 20% SB did not change energy intake by cattle.
Hot carcass weight, carcass characteristics (except KPH %), and USDA quality and yield grades (Table 4) were not affected by SB inclusion (all P > 0.15). Roasted soybean inclusion tended to increase (P = 0.07) KPH % from 1.93 to 2.07. Hot carcass weight was similar (P = 0.58) between NA and WA confirming that the vitamin A effects on cattle growth were negligible. Carcass quality grade tended (P = 0.07) to be improved in NA because marbling scores were increased from small to modest in this group. Pyatt et al. (2005) reported that feeding low vitamin A diets did not increase marbling in steers and heifers. However, in those experiments low vitamin A diets were not below NRC (1996) requirements as opposed to the low vitamin A diets fed in this experiment. Thus, it can be speculated that in order to increase marbling, vitamin A levels in the diet need to be below NRC (1996) recommendations.
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Feeding NA numerically increased the percentage of carcasses grading Choice– or above (89.5 vs. 81.8%, P = 0.12) and those grading Choiceo or above (52.4 vs. 45.7%, P = 0.32). Although these differences were not statistically significant, they may have important implications for the beef industry. Numerous branded beef programs offer economic incentives for carcasses grading Choiceo (USDA Agricultural Marketing Service, 2006). To illustrate the importance of these findings, utilizing a grid-pricing formula published by the USDA Market News Service for the week of July 11, 2005 (USDA, 2005), NA steers were valued approximately $8.00/animal more than WA steers.
Edible carcass and LM composition data are presented in Table 5. Composition of edible carcass and LM were not affected by vitamin A or SB (P > 0.10). Edible carcass EE content was not affected (P = 0.22) by vitamin A. This was expected based on the similar USDA yield grade of NA and WA steers. Considering the trend for increased marbling scores and carcass quality grades in NA steers, it was expected that the EE of longissimus muscle would be greater in NA than in WA steers. However, the EE content in LM of NA and WA steers was almost identical. Marbling score and carcass USDA quality grade were determined in all experimental animals, whereas muscle composition analyses were performed in a subset of steers (2/pen). It is possible that our ability to confirm the effects of vitamin A on i.m. fat deposition was compromised by reducing the number of samples analyzed.
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). Serum retinol of WA steers was maintained or increased as days on feed increased, whereas NA steers had significantly lower serum retinol levels than WA steers from d 56 to 168. Differences in serum retinol levels between WA and NA steers increased over time, and at the end of the experiment WA steers had almost twice the serum retinol as NA steers (WA = 41.1 vs. NA = 23.1 µg/dL, P < 0.01). Liver retinol content at slaughter confirmed the serum retinol observations. Steers fed NA had significantly lower retinol stores in the liver than WA steers (6.5 vs. 77.8 µg/g, P < 0.01). Roasted soybean inclusion did not affect hepatic vitamin A stores (NS = 42.4 vs. SB = 41.9 µg/g, P > 0.10). It was concluded that vitamin A status (liver and serum concentrations) in NA steers was reduced to levels that appeared to enhance marbling and carcass quality grade without affecting animal health or performance.
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). Scarce information is available about the depletion kinetics of retinol in feedlot cattle. Further research in this area is advised because it is likely that hepatic vitamin A stores need to be depleted in order to observe the effects of feeding low vitamin A diets on marbling scores.
Japanese authors reported that serum retinol and the intramuscular fat content in cattle are correlated (Torii et al., 1996; Adachi et al., 1999). Pyatt and Berger (2005) hypothesized that seasonal variations of beef carcass quality grades in the United States may be explained, at least partially, by intake of vitamin A prior the feedlot phase. Marbling scores and serum retinol at slaughter observed in our experiment were negatively correlated (–0.45, P < 0.05). The regression of these 2 variables seems to confirm those Japanese reports: y = 646.6 – 1.64x (P = 0.03), where y = marbling score, and x = serum retinol on d 168 (µg/dL). Conversely, the regression of serum retinol at slaughter and intramuscular EE was not significant (P > 0.05). It is likely that the reduced number of observations for intramuscular EE (n = 48) compared with marbling scores and carcass quality grades (n = 168) caused this discrepancy. Alternatively, serum retinol at slaughter may not be a good predictor of the i.m. fat content in feedlot steers as some authors have suggested (Matsuda et al., 2004).
A vitamin A x SB x adipose depot interaction (P < 0.05) for adipocyte density and cell size distribution was detected. Dietary treatments affected the cellularity of the i.m. fat depot but not that of the s.c. depot (Tables 6 and 7, respectively). This observation provides evidence that dietary management could be used to specifically affect the i.m. depot without affecting the s.c. depot.
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; Lee et al., 2003). Further research is advised to determine the potential of utilizing SB as an adipocyte-differentiation regulator.
To further characterize the vitamin A x SB effects on i.m. adipocyte differentiation, the adipocyte size distribution pattern is presented in Figure 2. Steers fed WANS had a greater proportion of cells with a mean diameter of 110 µm or more, whereas the other 3 treatments had more of the smaller cells (P < 0.05). Steers fed NANS, NASB, and WASB had approximately 10% of the measured cells with a mean diameter of 80 µm, compared with 7% in the WANS steers (P < 0.05). This difference has biological relevance; it has been reported that when adipocytes reach a mean diameter of 80 µm, a signal is triggered for a new population of adipocytes to differentiate (Schoonmaker et al., 2004), thus stimulating hyperplasia in the depot.
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In the s.c. fat depot, adipocyte cellularity was not affected (P > 0.05) by dietary treatment. Adipocyte size distribution pattern was similar among treatments (Figure 3). These data support the carcass data, reflecting that dietary vitamin A concentration does not affect s.c. fat deposition. The presumed mechanism of action of low vitamin A diets is to release the inhibition for adipocyte differentiation (Villaroya, 1998; Ribot et al., 2001). This may affect the i.m. depot in which hyperplasia takes place during the finishing period (Albrecht et al., 2006). However, when cattle are placed in the feedlot, most hyperplasia in the s.c. fat depot is completed, and this depot grows mainly by hypertrophy, or the enlargement of existing fat cells (Hood and Allen, 1973). The results of our experiment seem to confirm this observation.
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) was not significant (P > 0.10). The desaturase activity index is an indirect measurement that reflects changes in the activity of SCD based on substrate to product ratios (Corl et al., 2001; Smith et al., 2002). It was hypothesized that dietary vitamin A concentration and SB inclusion would interact to affect SCD activity, thus modifying the muscle fatty acid profile. Our results do not support this hypothesis. Therefore, vitamin A and SB main effects are presented (Table 8) and discussed. Feeding NA did not affect (P > 0.10) the concentration of total CLA in muscle fatty acids. The activity of SCD appeared not to be affected (P > 0.05) by supplemental vitamin A, based on the similar activity index values when NA and WA diets were fed. Despite the trend for greater marbling in NA steers, when CLA were expressed as mg/100 g of muscle, dietary vitamin A did not affect (P = 0.68) CLA concentration in muscle (NA = 42.3 vs. WA = 39.2 mg of CLA/100 g of muscle).
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). Proportions of SFA in muscle were slightly reduced with SB (46.55 vs. 45.02%; P < 0.01). Thus, SB increased muscle PUFA and reduced MUFA and saturated fats without affecting muscle CLA.
Most rumenic acid is synthesized endogenously in animal tissues by the desaturation of vaccenic acid (Palmquist et al., 2004). Even though the SCD activity was not affected by the vitamin A x SB interaction, the rumenic acid to vaccenic acid ratio tended (P = 0.09) to be affected by a dietary vitamin A concentration x SB interaction. When SB was included, feeding NA diets tended (P = 0.10) to reduce the rumenic to vaccenic acid ratio (NASB = 0.33 vs. WASB = 0.43), suggesting that vitamin A supplementation may have reduced SCD activity. Lucchi et al. (2005) reported that human patients with reduced serum retinol had increased serum CLA suggesting reduced desaturase activity. When no SB was included, dietary vitamin A concentration did not affect this ratio (NANS = 0.42 vs. WANS = 0.38; P = 0.44). However, contrary to our hypothesis, rumenic acid level in muscle was not affected by the vitamin A x SB interaction or by the vitamin A and SB main effects (all P > 0.10). It remains unclear whether dietary vitamin A concentration and SB inclusion affect SCD activity.
A significant vitamin A x SB interaction (P < 0.01) was observed for the trans-10 C18:1 fatty acid content in muscle. Steers fed NASB had more than twice the trans-10 C18:1 than did the other treatments (NASB = 6.0 vs. NANS 2.0, WANS 2.4, and WASB 2.7; P < 0.01). The trans-10 C18:1 isomer appears in the rumen during the biohydrogenation process of linoleic acid to stearic acid. This isomer is commonly found when high-concentrate, low-forage diets such as the ones used in this experiment are fed (Griinari and Bauman, 1999; Madron et al., 2002). It was expected that with SB inclusion, an increase in fatty acids intermediate in the linoleic acid biohydrogenation pathway (e.g., CLA) would be observed. However, the lack of response in trans-10 C18:1 in the WASB treatment was not expected. To our knowledge no data have been reported regarding the effects of vitamin A supplementation on rumen biohydrogenation. The vitamin A x SB interaction on trans-10 C18:1 suggests that dietary vitamin A level may affect cis-9, cis-12 C18:2 biohydrogenation in the rumen when SB are fed. However, the absence of a significant vitamin A x SB interaction in other biohydrogenation intermediates of cis-9, cis-12 C18:2 (e.g., trans-11 C18:1 and trans-10, cis-12 C18:2) and the lack of response of these intermediates to dietary vitamin A concentration (vitamin A main effect, P > 0.05) were believed to be due to vitamin A not having an effect on biohydrogenation of cis-9, cis-12 C18:2 in the rumen.
Dietary treatment effects on s.c. fatty acid composition are presented in Table 9. The vitamin A x SB interaction for total CLA and desaturase activity index was not significant (P > 0.10), and therefore main effects are presented and discussed. As observed in the LM fatty acid composition, SB inclusion increased PUFA (P < 0.01) due to increases in linoleic (C18:2), linolenic (18:3, n-3, and n-6), and 20:2 fatty acids (all P < 0.05). Total SFA were not reduced in s.c. fat, but MUFA were significantly (P = 0.01) reduced by SB inclusion. Whole roasted soybeans provide a good source of PUFA that can resist to some extent ruminal biohydrogenation and thus be stored in ruminant tissues. As in the LM, increases in PUFA in s.c. fat may have been responsible for the slight but significant (P < 0.01) reduction in desaturase activity index.
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In conclusion, adipose cellularity and carcass data suggest that hyperplasia took place in the intramuscular depot when diets were not supplemented with vitamin A and that these changes affected the carcass USDA quality grade but not yield grade. No vitamin A x SB interaction or vitamin A main effect were detected for muscle fatty acid profile. Dietary inclusion of SB did not affect carcass characteristics but improved the beef fatty acid profile by increasing muscle PUFA while reducing SFA.
1 Corresponding author: loerch.1{at}osu.edu
Received for publication November 27, 2006. Accepted for publication April 18, 2007.
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LITERATURE CITED |
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TopAbstractINTRODUCTIONMATERIALS AND METHODSRESULTS AND DISCUSSIONLITERATURE CITED |
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9–desaturase in the production of cis-9, trans-11 CLA. J. Nutr. Biochem. 12:622–630.[CrossRef][Medline]
2 expression. Obes. Res. 9:500–509.[Medline]9 desaturase index and stearoyl coenzyme A desaturase enzyme activity in porcine subcutaneous adipose tissue. J. Anim. Sci. 80:2110–2115.This article has been cited by other articles:
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  M. A. Gorocica-Buenfil, F. L. Fluharty, and S. C. Loerch Effect of vitamin A restriction on carcass characteristics and immune status of beef steers J Anim Sci, July 1, 2008; 86(7): 1609 - 1616. [Abstract] [Full Text] [PDF]
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B. W. Hess, G. E. Moss, and D. C. Rule A decade of developments in the area of fat supplementation research with beef cattle and sheep J Anim Sci, April 1, 2008; 86(14_suppl): E188 - E204. [Abstract] [Full Text] [PDF]
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M. A. Gorocica-Buenfil, F. L. Fluharty, T. Bohn, S. J. Schwartz, and S. C. Loerch Effect of low vitamin A diets with high-moisture or dry corn on marbling and adipose tissue fatty acid composition of beef steers J Anim Sci, December 1, 2007; 85(12): 3355 - 3366. [Abstract] [Full Text] [PDF]
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M. A. Gorocica-Buenfil, F. L. Fluharty, C. K. Reynolds, and S. C. Loerch Effect of dietary vitamin A restriction on marbling and conjugated linoleic acid content in Holstein steers J Anim Sci, September 1, 2007; 85(9): 2243 - 2255. [Abstract] [Full Text] [PDF]
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