Lipogenesis and stearoyl-CoA desaturase gene expression and enzyme activity in adipose tissue of short- and long-fed Angus and Wagyu steers fed corn- or hay-based diets

Angus and Wagyu steers consuming high-roughage diets exhibit large differences in adipose tissue fatty acid composition, but there are no differences in terminal measures of stearoyl-CoA desaturase (SCD) activity or gene expression. Also, adipose tissue lipids of cattle fed corn-based diets have greater MUFA:SFA ratios than cattle fed hay-based diets. We hypothesized that any changes in SCD gene expression and activity would precede similar changes in adipose tissue lipogenesis between short- and long-fed endpoints. Furthermore, changes in SCD activity and gene expression between production endpoints would differ between corn- and hay-fed steers and between Wagyu and Angus steers. Angus (n = 8) and Wagyu (n = 8) steers were fed a corn-based diet for 8 mo (short-fed; 16 mo of age) or 16 mo (long-fed; 24 mo of age), whereas another group of Angus (n = 8) and Wagyu (n = 8) steers was fed a hay-based diet for 12 mo (short-fed; 20 mo of age) or 20 mo (long-fed; 28 mo of age) to match the end point BW of the corn-fed steers. Acetate incorporation into lipids in vitro was greater (P < 0.01) in corn-fed steers than in hay-fed steers and tended (P = 0.06) to be greater in Wagyu than in Angus s.c. adipose tissue because the rate in Wagyu was twice that of Angus adipose tissue in the corn-fed, short-fed steers. There were diet x end point interactions for lipogenesis in i.m. and s.c. adipose tissues (both P < 0.01) because lipogenesis was 60 to 90% lower in the long-fed cattle than in short-fed cattle fed the corn-based diet. The greatest SCD enzyme activity in Angus s.c. adipose tissue was observed at 24 mo of age (corn-based diet), but activity in Wagyu adipose tissue was greatest at 28 mo of age (hay-based diet; breed x diet x end point interaction, P = 0.08). For short- vs. long-fed endpoints in Angus, s.c. adipose tissue SCD activity was less (hay diet) or the same (corn diet). Conversely, SCD gene expression was greatest in long-fed Wagyu steers fed the hay- or corn-based diets (breed x end point interaction; P < 0.01). Contrary to our hypotheses, SCD activity increased over time, whereas lipogenesis from acetate decreased. However, the developmental pattern of SCD gene expression and activity differed markedly between hay-fed Angus and Wagyu adipose tissues, which may explain the differences in the MUFA:SFA ratios observed in adipose tissues from these cattle.     

Adipogenic gene expression and fatty acid composition in subcutaneous adipose tissue depots of Angus steers between 9 and 16 months of age

We have demonstrated that among carcass adipose tissue depots, brisket subcutaneous adipose tissue contains the greatest concentration of MUFA and lowest concentration of SFA. Therefore, we hypothesized that brisket subcutaneous adipose tissue depots would exhibit greater adipogenic gene expression over time than other major subcutaneous adipose tissue depots. Four Angus steers, each at 9, 12, 14, and 16 mo of age, were harvested and fresh subcutaneous adipose tissue samples were collected from over the brisket, chuck, rib, loin, sirloin, round, flank, and plate. Relative gene expression for C/EBPβ, PPARγ, carnitine palmitoyltransferase-1 beta (CPT-1β), stearoyl-coenzyme A desaturase (SCD), AMP-activated protein kinase alpha (AMPKα), and G-coupled protein receptor 43 (GPR43) was analyzed by quantitative real-time PCR. Expression of C/EBPβ, PPARγ, and CPT-1β was greatest at 12 to 14 mo of age (all P < 0.0001) and declined to very low abundance by 16 mo of age in all depots. Expression of PPARγ and CPT-1β was greater (P < 0.03) in flank, rib, and sirloin subcutaneous adipose tissues than in brisket and round adipose tissues. The expression of the SCD gene did not differ among the 4 age groups (P = 0.95). The palmitoleic:stearic acid ratio (an estimate of SCD activity) was greater (P < 0.001) in the subcutaneous adipose tissues from brisket, plate, and round than in the loin, rib, and sirloin. Conversely, subcutaneous adipose tissue from the loin, rib, and sirloin had greater (P < 0.001) SCD gene expression than the brisket, plate, and round. In general, subcutaneous adipose tissues with the highest concentration of MUFA and least SFA consistently exhibited the least SCD gene expression and adipogenic gene expression. We conclude that MUFA in the brisket and other depots with large SCD indices were deposited before 9 mo of age, during a time when the subcutaneous adipocytes were highly differentiated.     

Adiposity of calf- and yearling-fed Brangus steers raised to constant-age and constant-body weight endpoints

We tested the hypothesis that fatty acid biosynthesis and adipocyte diameter and volume would be greater in s.c. and i.m. adipose tissues of calf-fed steers than in yearling-fed steers at a constant BW, due to the greater time on feed for the calf-fed steers. Conversely, we predicted that the capacity for s.c. and i.m. preadipocytes to divide, as estimated by 3H-thymidine incorporation into DNA, would be greater in the less mature adipose tissues of calf-fed steers and in yearling-fed steers at 16 mo of age than in yearling-fed steers fed to 18 mo of age. Brangus steers were fed a corn-based finishing diet as calves (calf-fed; n = 9) or yearlings (n = 4) to 16 mo of age (CA yearling-fed); another group of yearlings (n = 5) was fed to a constant-BW end point of 530 kg (CW yearling-fed). Both groups of yearling-fed steers had free access to native pasture until 12 mo of age. At slaughter, the fifth to eighth thoracic rib section of the LM was removed, and fresh s.c. and i.m. adipose tissues were removed for in vitro incubations. There were no differences in the number of s.c. adipocytes/g or mean peak volumes of adipocytes across production groups (P > or = 0.14). However, s.c. adipose tissue of CA yearling-fed steers contained greater proportions of smaller adipocytes (<1,500 pL) than calffed or CW yearling-fed steers, and similar results were observed for i.m. adipose tissue. Acetate incorporation into total lipids was greater (P = 0.02) in s.c. adipose tissue of CA yearling-fed steers than in calf-fed or CW yearling-fed steers, and tended to be different (P = 0.10) across production groups in i.m. adipose tissue. The production system x cell fraction interaction was significant (P = 0.03) for s.c. adipose tissue DNA synthesis, which was greatest in adipocytes from CA yearling-fed steers, whereas there were no differences across production system in stromal vascular (SV) DNA synthesis. For i.m. adipose tissue, DNA synthesis was greatest in adipocytes and SV cells from CA yearling-fed calves, and was greater in SV cells than in adipocytes (both P = 0.01). Therefore, stage of adipose tissue development more strongly influenced fatty acid synthesis, adipocyte volume, and DNA synthesis than age at sampling, final BW, or time on the finishing diet.     

Adiposity, fatty acid composition, and delta-9 desaturase activity during growth in beef cattle

Oleic acid (18:1n‐9) is the most abundant fatty acid in bovine adipose tissue. Because most of the lipid in bovine muscle is contributed by intramuscular adipocytes, oleic acid also is the predominant fatty acid in beef. In many species, the concentration of oleic acid in adipose tissue is dictated by the average concentration of oleic acid in the diet, but in ruminant species such as beef cattle, oleic acid is hydrogenated largely to stearic acid by ruminal microorganisms. In these species, the concentration of oleic acid in adipose tissue is dependent upon the activity of Δ⁹ desaturase, encoded by the stearoyl coenzyme A desaturase (SCD) gene. Expression of the SCD gene is essential for bovine preadipocyte differentiation, and desaturase gene expression and catalytic activity increase dramatically as adipose tissue mass increases after weaning. Feeding a hay‐based diet to American Wagyu steers to a typical Japanese bodyweight endpoint (650 kg) markedly stimulated desaturase enzyme activity as well as the accumulation of both oleic acid and intramuscular lipid, but the increase in oleic acid and intramuscular lipid was much less in hay‐fed Angus steers. Increasing the concentration of oleic acid improves the palatability and healthiness of beef, and Korean Hanwoo and Japanese Black (and American Wagyu) seem especially well adapted to accumulate oleic acid in their adipose tissue.     

Postnatal development of stearoyl coenzyme A desaturase gene expression and adiposity in bovine subcutaneous adipose tissue

This investigation addressed the hypothesis that stearoyl coenzyme A desaturase (SCD) gene expression would serve as a postnatal marker of adipocyte differentiation in bovine s.c. adipose tissue. Samples of tailhead s.c. adipose tissue were obtained by biopsy from preweaning steer calves 2.5 wk, 5 mo, and 7.5 mo of age and from yearling steers 12 mo of age. Samples also were obtained at slaughter when the steers were 18 mo of age. The steers sampled as yearlings were fed native pasture from weaning until 12 mo of age, and the steers sampled at slaughter were fed a high-concentrate diet from 12 to 18 mo of age. Major peak adipocyte volumes for the 2.5-wk-, 5-mo-, and 7.5-mo-old steers were 14, 270, and 700 pL, respectively (P < .001). The steers did not gain weight during pasture feeding, and at 12 mo of age peak adipocyte volume had decreased (P = .009) to 270 pL. At this time, a second, smaller population of adipocytes had appeared with a peak volume of 115 pL. At slaughter, adjusted fat thickness of the steers was 1.60 +/- .13 cm, the USDA yield grade of the carcasses was 3.51 +/- .31, and peak adipocyte volume had increased (P = .01) to over 2,500 pL. The number of adipocytes per 100 mg of adipose tissue doubled (P = .006) between 2.5 wk and 5 mo of age, concurrent with the nearly 20-fold increase in peak adipocyte volume, indicating that this was a period of apparent adipocyte hyperplasia. Uncoupling protein mRNA was undetectable at all stages of postnatal growth, indicating that differentiating tailhead s.c. adipocytes do not acquire brown adipocyte characteristics postnatally. Lipogenesis expressed on a cellular basis was low in all preweaning samples and increased significantly above preweaning values only in the 18-mo-old steers. Stearoyl coenzyme A desaturase mRNA concentration also was low in all preweaning samples, but it peaked (P = .07) at 12 mo of age. Because the peak in SCD mRNA concentration preceded a significant rise in lipogenesis and lipid filling, we conclude that the level SCD gene expression may be indicative of the extent of terminal differentiation in bovine tailhead s.c. adipose tissue.     

Fatty acid indices of stearoyl-CoA desaturase do not reflect actual stearoyl-CoA desaturase enzyme activities in adipose tissues of beef steers finished with corn-, flaxseed-, or sorghum-based diets

We hypothesized that stearoyl-CoA desaturase (SCD) enzyme activity would not correlate with fatty acid indices of SCD activity in steers fed different grains. Forty-five Angus steers (358 +/- 26 kg BW) were individually fed for 107 d diets differing in whole cottonseed (WCS) supplementation (0, 5, or 15% of DM) and grain source (rolled corn, flaxseed plus rolled corn, or ground sorghum grain) in a 3 x 3 factorial arrangement. Flaxseed- and corn-fed steers had greater (P < 0.01) G:F (0.119 and 0.108, respectively) than sorghum-fed steers (0.093). Marbling score was decreased by WCS (P = 0.04), and LM area was decreased (P < 0.01) by sorghum. Plasma 14:0, 16:0, 16:1n-7, and 18:2n-6 were greatest in corn-fed steers, whereas plasma 18:3n-3 and 20:5n-3 were greatest in the flax-seed-fed steers (P < 0.01). Plasma 18:1trans-11 was least in sorghum-fed steers, and plasma cis-9,trans-11 CLA was barely detectable, in spite of high intestinal mucosal SCD enzyme activity (118 to 141 nmol*g tissue(-1).7 min(-1)). Interfascicular (i.f.) and s.c. cis-9,trans-11 CLA remained unchanged (P > or = 0.25) by treatment, although 18:1trans-11 was increased (P < or = 0.02) in steers fed corn or flaxseed. Steers fed flaxseed also had greater (P < 0.01) i.f. and s.c. concentrations of 18:3n-3 than steers fed the other grain sources. Oleic acid (18:1n-9) was least and total SFA were greatest (P < 0.01) in i.f. adipose tissue of steers fed 15% WCS. Lipogenesis from acetate in s.c. adipose tissue was greater (P < 0.01) in flaxseed-fed steers than in the corn- or sorghum-fed steers. Steers fed flaxseed or corn had larger i.f. mean adipocyte volumes (P < 0.01) than those fed sorghum and tended (P = 0.07) to have larger s.c. adipocyte volumes. Several fatty acid indices of SCD enzyme activity were decreased (P < or = 0.03) by WCS in i.f. adipose tissue, including the 18:2cis-9,trans-11/ 18:1trans-11 ratio. The 18:2cis-9,trans-11/18:1trans-11 ratio also tended to be decreased (P = 0.09) in s.c. adipose tissue by flaxseed; however, SCD enzyme activities in i.f. and s.c. adipose tissue were not affected by dietary WCS (P > or = 0.47) or grain source (P > or = 0.37). Differences in SFA seemed to be independent of SCD enzyme activity in both adipose tissues, suggesting that duodenal concentrations of fatty acids were more important in determining tissue fatty acid concentrations than endogenous desaturation by SCD.     

Insulin and dexamethasone regulate stearoyl-CoA desaturase mRNA levels and fatty acid synthesis in ovine adipose tissue explants

Sheep adipose tissue explants were maintained in culture for 24 h in the presence of insulin, dexamethasone, or insulin and dexamethasone, and stearoyl-CoA desaturase (SCD) messenger RNA (mRNA) levels and fatty acid synthesis were measured. Insulin increased SCD mRNA levels (P = 0.008) and synthesis of both saturated (P = 0.07) and unsaturated (P < 0.001) fatty acids but had the greatest effect on unsaturated fatty acid synthesis, resulting in the overall production of a greater (P < 0.001) proportion of monounsaturated fat. Dexamethasone, alone, had the opposite effect but actually potentiated the effect of insulin in stimulating SCD expression and both saturated and monounsaturated fatty acid synthesis, without affecting the relative proportions of each. Across adipose tissue depots, the effect of hormones was similar, although the increase in SCD mRNA levels (P = 0.008) and monounsaturated fatty acid synthesis (P < 0.001) was greater in subcutaneous adipose tissue than in the internal (omental and perirenal) depots. These data clearly show that, in ovine adipose tissue, changes in SCD gene expression in response to insulin and dexamethasone are associated with changes in monounsaturated fatty acid synthesis and suggest that it may be possible to develop strategies to manipulate sheep tissues to produce a less-saturated fatty acid profile.     

Fatty acid composition of muscle and adipose tissue from crossbred bulls and steers

Fatty acid composition of total lipid extracts of muscle and adipose samples from crossbred bulls (N = 34) and steers (N = 35) was determined by gas-liquid chromatography. Samples of semitendinosus, triceps brachii and longissimus muscle and of subcutaneous and perinephric adipose tissue were excised from the right side of each carcass. In addition, thin-layer chromatography was utilized to obtain phospholipid and triacylglycerol fractions from total lipid extracts of semitendinosus and longissimus muscle and subcutaneous adipose tissue from 10 bull and steer cohorts (N = 20). The most prominent sex condition effect was in percentage of total poly-unsaturated fatty acids (PUFA). Bull tissues contained higher (P less than .01) percentages of PUFA than those of steers at all sampling sites. This reflected higher percentages of linoleate (C18:2), linolenate (C18:3) and arachidonate (C20:4) in bull tissues. Most of the PUFA were present as phospholipids in muscle samples. The fatty acid composition of muscle phospholipids was similar regardless of sex condition or muscle sampled. Total lipid extracts of semitendinosus and triceps brachii muscles of both bulls and steers contained from 6 to 10% more unsaturated fatty acids (UFA) compared with M. longissimus. Muscle triacylglycerols contained relatively high percentages of saturated fatty acids (SFA). Semitendinosus and longissimus samples from steers contained higher (P less than .05 and P less than .01, respectively) percentages of total SFA than those from bulls. Steer samples contained slightly higher percentages of palmitic acid (C16:0) compared with bulls at all sampling sites, and this difference was significant for M. longissimus. The fat:lean ratio of muscle tissue is the major factor that determines fatty acid composition.     

Effects of dietary copper on the expression of lipogenic genes and metabolic hormones in steers

An experiment was conducted to determine the effects of Cu supplementation on performance, subcutaneous adipose tissue mRNA expression of acetyl CoA carboxylase (ACC), stearoyl CoA desaturase (SCD), uncoupling protein 2 (UCP2), and leptin in growing and finishing steers. Forty-eight purebred Angus steers were allotted to one of five treatments: 1) control (no supplemental Cu); 2) 10 mg Cu/kg DM from CuSO4; 3) 10 mg Cu/kg DM from a Cu amino acid complex (Availa Cu); 4) 20 mg Cu/kg DM from CuSO4; 5) 20 mg Cu/kg DM from Availa Cu. Steers were fed an alfalfa hay corn-based diet for 56 d (basal diet contained 7.1 mg Cu/kg DM) and switched to a high-concentrate diet for 144 d (basal diet contained 6.1 mg Cu/kg DM). Blood samples were obtained every 28 d throughout the entire experiment. On d 112 of the finishing period, subcutaneous adipose tissue biopsies were obtained from the tailhead of three animals per treatment and analyzed for ACC, SCD, UCP2, and leptin mRNA expression. Animal performance was not affected by Cu supplementation during the growing phase. Steers receiving 10 mg Cu/kg DM from Availa Cu had higher (P < 0.05) ending body weights and tended (P < 0.10) to have higher ADG than steers receiving 10 mg Cu/kg DM from CuSO4 during the finishing phase. Serum concentrations of nonesterified fatty acid and insulin were not affected by Cu supplementation. Steers receiving supplemental Cu tended (P < 0.11) to have less backfat relative to controls. However, dietary Cu did not influence the level of subcutaneous adipose tissue ACC and SCD mRNA. Neither UCP2 nor leptin gene expression was affected by Cu supplementation. These results indicate that dietary Cu supplementation (10 to 20 mg Cu/kg DM diet) may alter lipid metabolism of subcutaneous adipose tissue; however, it does not seem to affect expression of certain lipogenic genes.     

Effects of in vitro ronnel on metabolic activity in subcutaneous adipose tissue and skeletal muscle from steers

Ronnel [0,0-dimethyl 0-(2,4,5-trichlorophenyl) phosphorothioate] is an organophosphate pesticide with growth-promoting properties. Experiments were conducted to determine effects of ronnel on oxidation of and fatty acid synthesis from acetate and glucose as indices of metabolic activity in subcutaneous adipose tissue and skeletal muscle from 6-, 12- and 18-mo-old steers. Ronnel depressed metabolic activity in adipose tissue from 6- and 12-mo-old steers without concomitantly decreasing metabolic activity in skeletal muscle. Production of CO2 and fatty acids from acetate and glucose in tissues from 18-mo-old steers was influenced less by ronnel than in tissues from younger steers. Interactions of ronnel with thyroxine or growth hormone on acetate oxidation and conversion to fatty acids in adipose tissue also were investigated. Thyroxine increased acetate oxidation and decreased fatty acid synthesis. Ronnel interfered with the metabolic effects of thyroxine. Growth hormone, with or without ronnel, did not affect metabolic activity of adipose tissue. Ronnel seemingly alters the partitioning of acetate and glucose between major metabolic processes in adipose tissue and skeletal muscle.     

Ruminal biohydrogenation of fatty acids from high-oleate sunflower seeds.

The objective of these experiments was to examine methods of modifying the fatty acid composition of bovine tissues. In the first experiment, four steers were fitted with duodenal fistulas and were assigned to four diets in a Latin square design. The steers were fed a control diet or the same diet containing 10% high-oleate partially crushed sunflower seeds, serum-coated sunflower seeds, and heat-treated, serum-coated sunflower seeds for 5 d. Samples of digesta and feces were collected on d 5. The inclusion of sunflower seeds (plain or serum-coated) in the diet increased (P less than .05) the digesta concentration of stearate. The percentage of stearate in the digesta and feces was increased (P less than .05) from 51 to 67% and from 64 to 74%, respectively, when steers were fed the untreated sunflower seed. The fecal concentration of oleate was increased (P less than .05) by dietary sunflower seeds in steers that were fed the serum-coated, unheated sunflower seeds. In a second experiment, heifers (four per group) were fed a corn-based control diet or diets containing 10% of high-oleate sunflower oil encapsulated with calcium alginate, either plain, coated with blood meal, or with blood meal integrated into the pellet. After 50 d on treatment, samples of perianal adipose tissue were obtained by biopsy. The fatty acid composition of the adipose tissue was not modified by the inclusion of the encapsulated oleate in the diet. In summary, limited ruminal bypass of sunflower seed oleate was accomplished with sunflower seed but not with encapsulated oleate.     

Lipogenesis and adipose tissue cellularity in steers switched from alfalfa hay to high concentrate diets

An experiment was conducted to 1) evaluate the effects of diet (alfalfa hay vs high concentrate) on adipose tissue cellularity and rates of in vitro lipogenesis and 2) determine if there was a relationship between in vitro lipogenic rates from acetate and lactate and rates of L- or D-lactate disappearance from plasma. Number of adipose cells/g of tissue decreased with time on experiment; however, hay-fed steers had fewer, but larger cells/g of subcutaneous adipose tissue compared with concentrate-fed steers (.78 +/- .04 vs 1.20 +/- .13 X 10(-6)/g, respectively). These results, however, are likely due to a higher (approximately 25%) intake of dry matter and metabolizable energy by the hay-fed steers. Carcass data obtained at slaughter (460 kg) indicated that the concentrate-fed steers had as much or more adipose tissue compared with the hay-fed steers. Characteristics describing D- or L-lactate disappearance from plasma were not highly correlated with lactate utilization for fatty acid synthesis. Utilization of acetate as a substrate for fatty acid synthesis in vitro was correlated (r = .64) with the rate of lactate utilization for fatty acid synthesis.     

Effect of breed on fatty acid composition and stearoyl-CoA desaturase protein expression in the Semimembranosus muscle and subcutaneous adipose tissue of cattle

The present study investigated (i) the effect of breed on the expression of stearoyl-CoA desaturase (SCD) protein and fatty acid composition in Semimembranosus muscle and subcutaneous adipose tissue of beef cattle and (ii) the relationship between SCD expression, cis-9, trans-11 conjugated linoleic acid (CLA) content, and monounsaturated fatty acid (MUFA) level. The study was conducted on the following breeds: Longhorn (L), Charolais cross with Holstein–Friesian (CX), Hereford (H), Belted Galloway (BG) and Beef Shorthorn (BS). Significant breed differences in the total fatty acid content, saturated fatty acid (SFA) level, MUFA and n−3 PUFA content were observed in subcutaneous adipose tissue but not in muscle. In the case of CLA, the breed differences were observed in both muscle and subcutaneous adipose tissue, with the highest level in L and the lowest level in H. In the case of subcutaneous adipose tissue, the breed with the highest CLA content (L) also had the highest SCD protein expression. The breed-specific pattern of SCD expression in subcutaneous adipose tissue was similar to the breed-specific pattern of one of the products of an SCD-catalysed reaction, C16:1 (BS < BG < H < CX < L). It has been concluded that (i) the mechanisms regulating SCD protein expression and CLA level in beef cattle are tissue-specific; (ii) breed-specific variations in SCD expression might contribute to breed variations in MUFA and CLA content in subcutaneous adipose tissue but not in Semimembranosus muscle.     

Adipose tissue growth and cellularity: changes in bovine adipocyte size and number

Forty crossbred steers of similar birth date and fed the same growing-finishing diet were used to study adipocyte changes in six fat depots during growth from 11 to 19 mo of age. Steers were slaughtered at 2-mo intervals. Adipose tissue samples were obtained from kidney, mesenteric and brisket fat and subcutaneous, intermuscular and intramuscular fat from the 10th to 12th rib section. The osmium tetroxide fixation technique was used for determination of cell size and number. Except for three brisket fat samples, distributions of adipocyte diameters from six different fat depots were monophasic during the age range considered in this study. At 17 mo of age, the mean adipocyte diameter, in decreasing order, was: kidney fat greater than mesenteric greater than subcutaneous greater than intermuscular greater than intramuscular greater than brisket fat. Fat deposition during growth to 19 mo of age occurred mainly by hypertrophy of adipocytes. An apparent cell hyperplasia occurred in the intramuscular fat depot from 11 to 15 mo and in the brisket fat depot after 15 mo of age. Based on cellularity characteristics, evidence exists to classify intramuscular and brisket fat depots as late-developing ones. Cell number/gram of intramuscular adipose tissue was a better predictor of marbling score than was fat cell diameter.     

Effect of dietary energy source on in vitro substrate utilization and insulin sensitivity of muscle and adipose tissues of Angus and Wagyu steers

Angus (n = 8; 210 kg of BW) and 7/8 Wagyu (n = 8; 174 kg of BW) steers were used to evaluate the effects of dietary energy source on muscle and adipose tissue metabolism and insulin sensitivity. Steers were assigned to either a grain-based (corn) or hay-based (hay) diet and fed to similar final BW. At slaughter, LM and s.c. and i.m. adipose tissue samples were collected. Portions of the LM and adipose tissues were placed immediately in liquid N for later measurement of glycolytic intermediates. Fresh LM and s.c. and i.m. adipose tissues were incubated with [U-(14)C]glucose to assess glucose metabolism in vitro. All in vitro measures were in the presence of 0 or 500 ng/mL of insulin. Also, s.c. and i.m. adipose tissues were incubated with [1-(14)C]acetate to quantify lipid synthesis in vitro. Glucose-6-phosphate and fructose-6-phosphate concentrations were 12.6- and 2.4-fold greater in muscle than in s.c. and i.m. adipose tissues, respectively. Diet did not affect acetate incorporation into fatty acids (P = 0.86). Insulin did not increase conversion of glucose to CO(2), lactate, or total lipid in steers fed hay but caused an increase (per cell) of 97 to 110% in glucose conversion to CO(2), 46 to 54% in glucose conversion to lactate, and 65 to 160% in glucose conversion to total lipid content in adipose tissue from steers fed corn. On a per-cell basis, s.c. adipose tissue had 37% greater glucose oxidation than i.m. adipose (P = 0.04) and 290% greater acetate incorporation into fatty acids than i.m. adipose (P = 0.04). Insulin addition to s.c. adipose tissue from corn-fed steers failed to stimulate glucose incorporation into fatty acids, but exposing i.m. adipose tissue from corn-fed steers to insulin resulted in a 165% increase in glucose incorporation into fatty acids. These results suggest that feeding hay limited both glucose supply and tissue capacity to increase glucose utilization in response to insulin without altering acetate conversion to fatty acids. Because s.c. adipose tissue consistently utilized more acetate and oxidized more glucose than did i.m. adipose, these results suggest that hay-based diets may alter i.m. adipose tissue metabolism with less effect on s.c. adipose tissue.     

Effect of level of endophyte infection, nitrogen fertilization rate, grazing period, and paddock exchange on some chemical properties of four bovine tissues.

Three grazing experiments were conducted to determine the effect of level of endophyte infection, rate of N fertilization of tall fescue grass, grazing period, and paddock exchange on selected chemical properties of four bovine carcass tissues. Samples of semitendinosus and longissimus muscle and of subcutaneous and perinephric adipose tissue were excised from the left side of each carcass. In Exp. 1, percentage of stearic acid was higher (P less than .05) and percentages of palmitoleic and oleic acid were lower (P less than .05) in all tissues from steers grazed on LELN Au-Triumph fescue than in tissues from steers grazed on LELN KY-31 fescue. Grazing periods of 175 or 245 d or paddock exchange (Exp. 2) had no significant effect on proximate composition of semitendinosus and longissimus muscles; however, moisture content was higher (P less than .05) in the semitendinosus muscle from steers grazed on 100% (100E) endophyte-infected KY-31 fescue. Forage treatment, grazing period, and paddock exchange (Exp. 2 and 3) had no significant effect on percentage of saturated fatty acids in the subcutaneous, semitendinosus, and longissimus tissue samples. In Exp. 2 and 3, percentages of saturated fatty acids were higher (P less than .05) in subcutaneous and perinephric adipose tissue samples from steers grazed on 100E than in samples from steers grazed on zero endophyte (OE) fescue.(ABSTRACT TRUNCATED AT 250 WORDS)     

Comparison of muscle fatty acid profiles and cholesterol concentrations of bison,beef cattle,elk, and chicken

The objective of this study was to compare fatty acid weight percentages and cholesterol concentrations of longissimus dorsi (LD), semitendinosus (ST), and supraspinatus (SS) muscles (n = 10 for each) of range bison (31 mo of age), feedlot-finished bison (18 mo of age), range beef cows (4 to 7 yr of age), feedlot steers (18 mo of age), free-ranging cow elk (3 to 5 yr of age), and chicken breast. Lipids were analyzed by capillary GLC. Total saturated fatty acids (SFA) were greater (P < 0.01) in range bison than in feedlot bison and were greater (P < 0.01) in SS of range beef cattle than in feedlot steers. Muscles of elk and range bison were similar (P > 0.05) in SAT. In LD, polyunsaturated fatty acids (PUFA) were highest (P < 0.01) for elk and range bison and lowest (P < 0.01) for feedlot steers within each muscle. Range bison and range beef cows had greater (P < 0.01) PUFA in LD and ST than feedlot bison or steers, respectively. Range-fed animals had higher (P < 0.01) n-3 fatty acids than feedlot-fed animals or chicken breast. Chicken breast n-6 fatty acids were greater (P < 0.01) than for muscles from bison, beef, or elk. Elk had higher (P < 0.01) n-6 fatty acids than bison or beef cattle; however, range-fed animals had higher (P < 0.01) n-6 fatty acids than feedlot-fed animals in ST. Conjugated linoleic acid (CLA, 18:2cis-9, trans-11) in LD was greatest (P < 0.01) for range beef cows (0.4%), and lowest for chicken breast and elk (mean = 0.1%). In ST, CLA was greatest (P < 0.01) for range and feedlot bison and range beef cows (mean = 0.4%) and lowest for elk and chicken breast (mean = 0.1%). Also, SS CLA was greatest (P < 0.01) for range beef cows (0.5%) and lowest for chicken breast (0.1%). Mean total fatty acid concentration (g/100 g tissue) for all muscles was highest (P < 0.01) for feedlot bison and feedlot cattle and lowest (P < 0.01) for range bison, range beef cows, elk, and chicken. Chicken breast cholesterol (mg/100 g tissue) was higher (P < 0.01) than LD and ST cholesterol, which were lowest (P < 0.01; 43.8) for range bison and intermediate for the other species. Cholesterol in SS was highest (P < 0.01) for feedlot bison and steers, which were similar to chicken breast (mean = 61.2 vs 52.8 for the mean of the other species). We conclude that lipid composition of bison muscle varies with feeding regimen, and range-fed bison had muscle lipid composition similar to that of forage-fed beef cows and wild elk.     

Effects of timing and duration of dietary vitamin A reduction on carcass quality of finishing beef cattle

Two feedlot studies were conducted to investigate the timing and duration of supplemental vitamin A withdrawal from feedlot cattle (Bos taurus) diets to reduce intramuscular adipose tissue vitamin A concentration and improve carcass quality. In Exp. 1, Angus crossbred steers (n = 84, BW = 211 ± 4 kg) were allotted to 4 treatments: no supplemental vitamin A for 227 d, no supplemental vitamin A for 112 d followed by 115 d of supplemental vitamin A, supplemental vitamin A for 112 d followed by no supplemental vitamin A for 115 d, or supplemental vitamin A for 227 d. In Exp. 2, Angus crossbred steers (n = 80, BW = 210 ± 5 kg) were allotted to 4 treatments: early weaning with or without supplemental vitamin A, and traditional weaning with or without supplemental vitamin A. In both experiments, serum vitamin A concentrations were greatest (P < 0.05) 56 d after cattle were weaned and placed in the feedlot, regardless of feedlot dietary vitamin A concentration. Hepatic vitamin A stores were dramatically decreased (P < 0.05) in the first 56 d and remained depressed as long as steers were not supplemented with vitamin A. At the end of the finishing period, vitamin A concentrations were less in intramuscular than subcutaneous adipose tissue. Growth was not affected by finishing cattle without supplemental dietary vitamin A (P > 0.10). Dietary vitamin A supplementation did not affect USDA yield grades. However, in Exp. 2, cattle without supplemental vitamin A had greater (P < 0.001) ether extractable lipid in the LM. Ether extractable lipid in the LM or marbling scores were enhanced when intramuscular adipose tissue vitamin A concentration was reduced in response to feeding diets without supplemental vitamin A.     

Adipogenic differentiation state-specific gene expression as related to bovine carcass adiposity

Genetic regulation of the site of fat deposition is not well defined. The objective of this study was to investigate adipogenic differentiation state-specific gene expression in feedlot cattle (>75% Angus; <25% Simmental parentage) of varying adipose accretion patterns. Four groups of 4 steers were selected via ultrasound for the following adipose tissue characteristics: low subcutaneous-low intramuscular (LSQ-LIM), low subcutaneous-high intramuscular (LSQ-HIM), high subcutaneous-low intramuscular (HSQ-LIM), and high subcutaneous-high intramuscular (HSQ-HIM). Adipose tissue from the subcutaneous (SQ) and intramuscular (IM) depots was collected at slaughter. The relative expression of adipogenic genes was evaluated using quantitative PCR. Data were analyzed using the mixed model of SAS, and gene expression data were analyzed using covariate analysis with ribosomal protein L19 as the covariate. No interactions (P > 0.10) were observed between IM and SQ adipose tissue depots for any of the variables measured. Therefore, only the main effects of high and low accretion within a depot and the effects of depot are reported. Steers with LIM had smaller mean diameter IM adipocytes (P < 0.001) than HIM steers. Steers with HSQ had larger mean diameter SQ adipocytes (P < 0.001) than LSQ. However, there were no differences (P > 0.10) in any of the genes measured due to high or low adipose accretion. Preadipogenic delta-like kinase1 mRNA was greater in the IM than the SQ adipose tissue; conversely, differentiating and adipogenic genes, lipoprotein lipase, PPARγ, fatty acid synthetase, and fatty acid binding protein 4 were greater (P < 0.001) in the SQ than the IM depot. Intramuscular adipocytes were smaller than SQ adipocytes and had greater expression of the preadipogenic gene, indicating that more hyperplasia was occurring. Meanwhile, SQ adipose tissue contained much larger (P < 0.001) adipocytes that had a greater expression (P < 0.001) of differentiating and adipogenic genes than did the IM adipose tissue, indicating more cells were undergoing differentiation and hypertrophy. Adipogenic differentiation state-specific gene expression was not different in cattle with various phenotypes, but adipogenesis in the SQ and IM adipose tissues seems to occur independently.     

Corn oil supplementation to steers grazing endophyte-free tall fescue. II. Effects on longissimus muscle and subcutaneous adipose fatty acid composition and stearoyl-CoA desaturase activity and expression

Eighteen steers were used to evaluate the effect of supplemental corn oil level to steers grazing endophyte-free tall fescue on fatty acid composition of LM, stearoyl CoA desaturase (SCD) activity and expression as well as cellularity in s.c. adipose. Corn oil was supplemented (g/kg of BW) at 0 (none), 0.75 (medium), and 1.5 (high). Cottonseed hulls were used as a carrier for the corn oil and were supplemented according to pasture availability (0.7 to 1% of BW). Steers were finished on a rotationally grazed, tall fescue pasture for 116 d. Fatty acid composition of LM, s.c. adipose, and diet was determined by GLC. Total linoleic acid intake increased linearly (P < 0.01) with corn oil supplementation (90.7, 265.1, and 406.7 g in none, medium, and high, respectively). Oil supplementation linearly reduced (P < 0.05) myristic, palmitic, and linolenic acid percentage in LM and s.c. adipose. Vaccenic acid (C18:1 t11; VA) percentage was 46 and 32% greater (linear, P = 0.02; quadratic, P = 0.01) for medium and high, respectively, than none, regardless of tissue. Effect of oil supplementation on CLA cis-9, trans-11 was affected by type of adipose tissue (P < 0.01). In the LM, CLA cis-9, trans-11 isomer was 25% greater for medium than for none and intermediate for high, whereas CLA cis-9, trans-11 CLA isomer was 48 and 33% greater in s.c. adipose tissue for medium and high than for none, respectively. Corn oil linearly increased (P 0.05) the percentage of total SFA, MUFA, or PUFA but linearly increased (P = 0.03) n-6:n-3 ratio from 2.4 to 2.9 in none and high, respectively. Among tissues, total SFA and MUFA were greater in s.c. adipose than LM, whereas total PUFA, n-6, and n-3 fatty acids and the n-6:n-3 ratio were lower. Trans-10 octadecenoic acid, VA, and CLA trans-10, cis-12 were greater (P < 0.01) in s.c. adipose than in LM. Oil supplementation did not alter (P > 0.05) stearoyl CoA desaturase activity or mRNA expression. Corn oil supplementation to grazing steers reduced the percentages of highly atherogenic fatty acids (myristic and palmitic acids) and increased the percentages of antiatherogenic and anticarcinogenic fatty acids (VA and cis-9, trans-11 CLA).