Subcutaneous and intramuscular adipose tissue stearoyl-coenzyme A desaturase gene expression and fatty acid composition in calf- and yearling-fed Angus steers

We proposed that stearoyl-CoA desaturase (SCD) activity dictates fatty acid composition of adipose tissue and muscle in beef cattle, regardless of ruminal or hepatic fatty acid hydrogenation or desaturation. Twelve Angus steers were assigned to a calf-fed (CF) group and slaughtered at weaning (8 mo of age; n=4), 12 mo of age (n=4), or 16 mo of age (n=4). Twelve steers were assigned to a yearling-fed (YF) group and slaughtered at 12 mo of age (n=4), 16 mo of age (n=4), and 17.5 mo of age (n=4; 525 kg, market weight). Data were analyzed based on time on the corn-based finishing diet, with terminal age as a covariate, and orthogonal polynomial contrasts were tested on the main effects of treatment group and time on the finishing diet. Fatty acids from duodenal digesta, plasma, liver, LM, and subcutaneous and intramuscular adipose tissue were measured, and SCD gene expression was measured in intramuscular and subcutaneous adipose tissues. In duodenal digesta, palmitic and linoleic acids increased by 100% over the sampling period, α-linolenic acid decreased over the sampling period, and trans-vaccenic acid was greater in YF than in CF steers (all P < 0.01). The proportion of α-linolenic acid decreased over time in all tissues, including liver. The SCD index (ratio of SCD fatty acid products to SCD fatty acid substrates) increased over time in LM and in intramuscular and subcutaneous adipose tissues. The SCD:glyceraldehyde 3-phosphate dehydrogenase mRNA ratio was virtually undetectable at the initial sampling periods in subcutaneous adipose tissue of YF and CF steers, and it increased over time (P < 0.01). The SCD index and SCD:glyceraldehyde 3-phosphate dehydrogenase ratio were greater in intramuscular adipose tissue of CF steers than in that of YF steers. The SCD index did not change over time in liver and decreased over time in duodenal digesta. We conclude that, unlike essential fatty acids, the SFA and MUFA composition of adipose tissue is regulated by adipose tissue fatty acid desaturation, with little contribution from hepatic or duodenal fatty acids.     

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.     

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.     

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.     

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.     

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.     

Relationship between fatty acid-binding protein activity and marbling scores in bovine longissimus muscle

Studies were conducted in an attempt to establish a relationship between fatty acid-binding protein (FABP) activity and marbling score in bovine longissimus muscle. Longissimus muscle was obtained from four 20-mo-old Charolais-Hereford crossbred heifers, three 16-mo-old Angus steers, and four 18-mo-old Angus steers. Immediately after slaughter, longissimus muscles were removed for the extraction of FABP. Supernatant (S104) fractions containing 41.3 to 144 mg of protein (depending on animal group) were eluted over Sephadex columns, and elution fractions were analyzed for the binding of radiolabeled palmitoyl-coenzyme A (CoA). Specific activities of FABP were 23, 32, and 101 nmol palmitoyl-CoA bound/mg protein for the Charolais-Hereford, 16-mo-old Angus, and 18-mo-old Angus cattle, respectively. These preliminary results suggested that longissimus muscle FABP activity was positively correlated with marbling score. To test specifically for this possibility, longissimus muscle was obtained at slaughter from each of four Wagyu steers, Angus heifers and Braford heifers. Marbling scores taken at the 12th-13th rib junction were Sm45, Sm43, and SI50 for the Wagyu, Angus, and Braford cattle, respectively. Interfascicular adipose tissue was exhaustively removed from sections of the 5th to 8th thoracic region of the longissimus muscle to eliminate any contribution of adipose tissue to FABP activity. For each animal, 300 mg of the S104 were eluted over Sephadex columns. Specific activities for the Wagyu, Angus, and Braford longissimus muscle FABP were 3.1, 3.8, and 3.9 pmol palmitoyl-CoA bound/mg protein, respectively, and were not different (P greater than .05) among the three animal groups.(ABSTRACT TRUNCATED AT 250 WORDS)     

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.     

Effects of feeding whole cottonseed and cottonseed products on performance and carcass characteristics of finishing beef cattle

Three experiments were conducted to determine the effects of whole cottonseed or cottonseed products on performance and carcass characteristics of beef cattle. In Exp. 1, 120 beef steers (initial BW = 381 +/- 31.7 kg) were fed steam-flaked corn-based finishing diets with 10% (DM basis) basal roughage, and whole cottonseed or individual cottonseed components (cottonseed hulls, meal, and oil). Over the entire feeding period, ADG did not differ (P = 0.95), but DMI increased (P = 0.07) and G:F decreased (P = 0.06) for steers fed the cottonseed diets compared with the control diet. Dressing percent (P = 0.02) and marbling scores (P = 0.02) of carcasses from steers fed the cottonseed diets were less than for steers fed the control diet. In Exp. 2, 150 beef steers (initial BW = 364 +/- 9.9 kg) were used to determine the effects of whole cottonseed or pelleted cottonseed (PCS) on performance and carcass characteristics. Cattle were fed steam-flaked corn-based finishing diets in which whole cottonseed or PCS replaced all of the dietary roughage, supplemental fat, and supplemental natural protein of the control diet. Over the entire feeding period, steers fed the cottonseed diets had lower (P = 0.04) DMI and greater (P < 0.01) G:F than steers fed the control diet. Carcass characteristics did not differ (P = 0.16 to 0.96) among dietary treatments. In Exp. 3, 150 beef heifers (initial BW = 331 +/- 17.1 kg) were used to determine the effects of PCS or delinted, whole cottonseed (DLCS) on performance and carcass characteristics. Heifers were fed rolled corn-based finishing diets in which cottonseed replaced the dietary roughage, supplemental fat, and all or part of the supplemental natural protein of the control diet. Over the entire feeding period, ADG, DMI, and G:F of heifers fed the control diet did not differ (P = 0.19 to 0.80) from those of the cottonseed diets; however, heifers fed the diets containing PCS had greater ADG (P = 0.03) and G:F (P = 0.09) than heifers fed diets containing DLCS. Carcass characteristics of heifers fed the control diet did not differ (P > or = 0.28) from those fed the cottonseed diets. Heifers fed the diets containing PCS had greater (P < or = 0.03) HCW, dressing percent, and LM area than those fed DLCS. Based on our results, whole cottonseed, or products derived from processing whole cottonseed, can replace feedstuffs commonly used in beef cattle finishing diets with no adverse effects on animal performance or carcass characteristics.     

Lipogenesis in acute and 48-hour cultures of bovine intramuscular and subcutaneous adipose tissue explants

In this study, the interactions among breed of cattle, adipose tissue site and specific incubation conditions were investigated. Subcutaneous and i.m. adipose tissues were obtained from 10 Angus and 9 Santa Gertrudis steers immediately postmortem. Adipose tissue explants were incubated acutely for 2 h immediately at slaughter or after being cultured 48 h with or without 1 mU/ml insulin and 30 mg/ml bovine serum albumin; the incorporation of 14C-labeled acetate and glucose (5 mM, plus 5 mM unlabeled lactate) into lipid fractions was measured. AT the same chronological age, Angus steers had a more youthful lean maturity score, higher USDA marbling score and higher USDA quality grade (P less than .05) than did carcasses from Santa Gertrudis steers. The lower marbling score of the Santa Gertrudis steers was paralleled by smaller i.m. adipocytes (P less than .05) relative to Angus steers. Pentose cycle reductase and NADP-malate dehydrogenase activities were greater in Angus i.m. adipose tissue than in Santa Gertrudis i.m. adipose tissue, which would provide more reducing equivalents (NADPH) and glycerol for fatty acid biosynthesis and triacylglycerol esterification. Correspondingly, Angus i.m. adipose tissue exhibited a greater rate of lipogenesis from acetate and glucose (P less than .05) than did Santa Gertrudis i.m. adipose tissue in acute incubations. The presence of insulin resulted in higher rates of lipogenesis from acetate in Angus s.c. adipose tissue than in Santa Gertrudis s.c. adipose tissue after 48 h of explant culture. These data indicate that i.m. and s.c. adipose tissues exhibit aspects of lipid metabolism unique to each tissue and suggest that breed-related differences in adipose tissues may explain the divergent responses to insulin observed in different laboratories.     

Effects of restricted and ad libitum intake of diets containing wheat middlings on site and extent of digestion in steers

A 5 x 5 Latin square design was used to determine the effects of restricted and ad libitum intake of diets containing wheat middlings on the site and extent of digestion compared to ad libitum intake of a corn-based diet and ad libitum intake of chopped alfalfa hay. Five ruminally and duodenally cannulated Angus steers (519 +/- 41.5 kg BW) were used to compare five dietary treatments. The five treatments were as follows: ad libitum access to a corn-based finishing diet (control), the control diet with 25 percentage units of the corn and soybean meal replaced with wheat middlings offered ad libitum (WM), the WM diet restricted to 75% of predicted ad libitum intake (RWM), the RWM diet with wheat middlings replaced with ammoniated wheat middlings (RNWM), and ad libitum access to a chopped alfalfa hay diet. Although RWM steers were fed to consume 75% of ad libitum intake, RWM steers consumed 15.5% less DM than WM. Steers fed ad libitum hay consumed 28.6, 31.7, and 37.2% less (P < 0.01) DM, OM, and nitrogen than RWM steers. No differences in apparent or true ruminal digestibility were observed among steers fed the control vs WM, WM vs RWM, RWM vs RNWM, or RWM vs hay diets. However, the steers fed the hay diet had 32.5, 33.4, and 36.9% lower (P < 0.01) apparent total tract digestibilities of DM, OM, and N than those fed the RWM diet. Average ruminal pH was lower (P < 0.01) for control steers than those fed the WM diet and for those fed RWM compared to the hay diet. The acetate:propionate ratio was higher for cattle fed hay vs the RWM diet. Microbial DM and OM flow to the small intestine was higher (P < 0.02) for steers fed the RWM diet than those fed the hay diet. In addition, bacterial N flow to the small intestine was higher (P < 0.01) for cattle receiving the RWM diet than the hay diet. Feeding diets containing 25 percentage units of wheat middlings at 75% ad libitum intake had no effect on ruminal digestibility.     

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 adding poultry fat in the finishing diet of steers on performance, carcass characteristics, sensory traits, and fatty acid profiles

Use of poultry fat in the finishing diets of steers has not been studied as a potential source of added energy. Therefore, 60 Angus crossbred steers were fed 1 of 3 dietary treatments consisting of 1) a corn-soybean meal control diet devoid of added fat; 2) the control diet formulated with 4% tallow; or 3) the control diet formulated with 4% poultry fat. Addition of fat did not (P = 0.17) affect ADG for the 112-d study. The inclusion of tallow in the diet reduced (P < 0.05) ADFI of steers compared with those on the control diet; however, ADFI of steers fed poultry fat did not differ from those fed the control (P = 0.06) or the tallow (P = 0.36) diets. At d 55, steers consuming either fat source had improved (P < 0.05) G:F compared with steers fed the control diet. For the entire 112 d, steers consuming the poultry fat diet gained more efficiently (P < 0.05) than the control steers, and the tallow-fed steers were intermediate and not different from the other groups (P > or = 0.14). The inclusion of fat in the diet did not (P > or = 0.15) affect carcass characteristics. Steaks from the steers consuming diets with added fat were darker (lower L* value; P < 0.05) than the controls; however, dietary treatments did not (P > or = 0.10) affect any other objective color measurements or discoloration scores during retail display. Thiobarbituric acid reactive substances for LM steaks did not differ (P = 0.21) by dietary treatment. The cooked LM steaks from steers fed poultry fat did not (P > or = 0.80) differ in juiciness or flavor intensity from steaks of steers fed the control or tallow diets. There were also no differences (P = 0.18) in off flavors as a result of added dietary fat. In the LM and adipose tissue, percentages of total SFA were increased (P = 0.05) by adding supplemental fat to the diet, regardless of source. In the LM, total MUFA were decreased (P = 0.02) by adding supplemental fat. Conversely, diet did not (P > or = 0.14) affect the proportions of total PUFA in either tissue or total MUFA in the adipose tissue. Results indicated that replacing beef tallow in finishing diets with poultry fat, a more economical energy source, had no detrimental effects on growth performance, carcass characteristics, retail display life, fatty acid profiles, or palatability.     

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.     

Early-weaning and postweaning nutritional management affect feedlot performance, carcass merit, and the relationship of 12th-rib fat, marbling score, and feed efficiency among Angus and Wagyu heifers

Twelve 3/4 Angus (Angus) and 12 Wagyu-cross (1/2 Wagyu x 1/2 Angus) (Wagyu) heifers were weaned at 180 d of age and grazed on endophyte-infected tall fescue for 16 mo before entering the feedlot as 2-yr-olds. Twelve 3/4 Angus heifer calves and 12 Wagyu-cross heifer calves from the following year's calf crop were weaned at 142 +/- 4.1 d of age, immediately adjusted to an 80% concentrate diet, and finished as calves. All heifers were fed a common finishing diet until an estimated 50% of their respective group would grade USDA low Prime or better based on ultrasound predictions. Ultrasound measurements of s.c. and i.m. fat depots were recorded at 60-d intervals throughout the finishing period. Heifers finished as calves had higher (P = 0.02) marbling scores at any given fat thickness and gained more efficiently (P < or = 0.01) at any given marbling score than heifers finished as 2-yr-olds. Gain:feed decreased quadratically (P < or = 0.05) as 12th-rib fat thickness increased for Angus and Wagyu heifers. Gain:feed decreased linearly (P < or = 0.01) for Wagyu calves and quadratically (P < or = 0.01) for Angus calves as 12th-rib fat thickness increased. However, these differences in slope were not different (P = 0.34) as a result of breed among heifers finished as calves. Marbling score increased linearly (P < or = 0.01) as 12th-rib fat thickness increased for Angus and Wagyu heifers finished as 2-yrolds or as calves. However, Wagyu heifers, regardless of age at feedlot entry, had a higher marbling score (P < or = 0.05) at any given 12th-rib fat thickness than Angus heifers. Finishing early-weaned heifers as calves as opposed to 2-yr-olds results in i.m. fat deposition during a period of more efficient growth. Additionally, including Wagyu genetics into the breeding of early-weaned heifers finished as calves or as 2-yr-olds results in higher marbling scores at any 12th-rib fat thickness.     

Effects of phase-feeding of crude protein on performance, carcass characteristics, serum urea nitrogen concentrations, and manure nitrogen of finishing beef steers

As cattle mature, the dietary protein requirement, as a percentage of the diet, decreases. Thus, decreasing the dietary CP concentration during the latter part of the finishing period might decrease feed costs and N losses to the environment. Three hundred eighteen medium-framed crossbred steers (315 +/- 5 kg) fed 90% (DM basis) concentrate, steam-flaked, corn-based diets were used to evaluate the effect of phase-feeding of CP on performance and carcass characteristics, serum urea N concentrations, and manure characteristics. Steers were blocked by BW and assigned randomly to 36 feedlot pens (8 to 10 steers per pen). After a 21-d step-up period, the following dietary treatments (DM basis) were assigned randomly to pens within a weight block: 1) 11.5% CP diet fed throughout; 2) 13% CP diet fed throughout; 3) switched from an 11.5 to a 10% CP diet when approximately 56 d remained in the feeding period; 4) switched from a 13 to an 11.5% CP diet when 56 d remained; 5) switched from a 13 to a 10% CP diet when 56 d remained; and 6) switched from a 13 to an 11.5% CP diet when 28 d remained. Blocks of cattle were slaughtered when approximately 60% of the cattle within the weight block were visually estimated to grade USDA Choice (average days on feed = 182). Nitrogen volatilization losses were estimated by the change in the N:P ratio of the diet and pen surface manure. Cattle switched from 13 to 10% CP diets with 56 d remaining on feed or from 13 to 11.5% CP with only 28 d remaining on feed had lower (P < 0.05) ADG, DMI, and G:F than steers fed a 13% CP diet throughout. Steers on the phase-feeding regimens had lower (P = 0.05) ADG and DMI during the last 56 d on feed than steers fed 13.0% CP diet throughout. Carcass characteristics were not affected by dietary regimen. Performance by cattle fed a constant 11.5% CP diet did not differ from those fed a 13% CP diet. Serum urea N concentrations increased (P < 0.05) with increasing dietary CP concentrations. Phase-feeding decreased estimated N excretion by 1.5 to 3.8 kg/steer and nitrogen volatilization losses by 3 to 5 kg/steer. The results suggest that modest changes in dietary CP concentration in the latter portion of the feeding period may have relatively small effects on overall beef cattle performance, but that decreasing dietary CP to 10% of DM would adversely affect performance of cattle fed high-concentrate, steam-flaked, corn-based diets.     

Soybean hulls as a primary ingredient in forage-free diets for limit-fed growing cattle

In Exp. 1, 300 heifers (260 kg initial BW) were used to compare growth performance of cattle fed forage-free diets containing predominantly soybean hulls with that of cattle receiving roughage- and corn-based diets and to determine whether cattle fed soybean hull-based diets would respond to supplementation with methionine hydroxy analogue (MHA), lipid-coated betaine, or concentrated separator by-product (CSB; a source of betaine). Treatments included 1) a roughage-based diet fed at 2.75% of BW, 2) a corn-based diet fed at 1.5% of BW, 3) a corn-based diet fed at 2.25% of BW, 4) a soybean hull-based diet fed at 1.5% of BW (SH1.5), 5) a soybean hull-based diet fed at 2.25% of BW (SH2.25), 6) SH1.5 top-dressed with 11.4 g/d Alimet (10 g/d MHA), 7) SH2.25 top-dressed with 11.4 g/d Alimet, 8) SH2.25 top-dressed with 7 g/d of a lipid-coated betaine product (4.2 g/d betaine), and 9) SH2.25 top-dressed with 250 g/d CSB (15.5 g/d betaine). Supplemental MHA, betaine, and CSB did not change DMI, ADG, or gain:feed ratio for cattle fed soybean hulls. Heifers fed soybean hull-based diets gained 29% slower (P < 0.05) and had 27% lower gain:feed ratios than heifers fed the corn-based diets. Cattle fed soybean hull-based diets had gains that were lower (P < 0.05) than those of cattle fed the roughage-based diets, but gain:feed ratios were similar because cattle were fed less of the soybean hull-based diets. Roughage-fed cattle had similar gains but 25% lower (P < 0.05) gain:feed ratios than cattle fed the corn-based diets. In Exp. 2, degradation by ruminal microbes of betaine in anhydrous betaine, betaine-HCl, feed-grade betaine, lipid-coated betaine, and CSB was evaluated in vitro using ruminal inocula collected from steers fed a high-grain or high-roughage diet. The roughage diet led to less betaine disappearance than the grain diet. More betaine was degraded from CSB than from other sources, perhaps because sugars provided by CSB stimulated fermentation, but no large differences occurred among the other four sources. Betaine from all sources was extensively degraded, although some betaine may escape ruminal degradation.     

Tolerance of cattle to increased dietary sulfur and effect of dietary cation-anion balance

The objective of this study was to determine if dietary cation-anion balance (DCAB) affects the concentration of S that can be tolerated by growing and finishing cattle without adversely affecting performance. Angus cross and Bradford steers (n=114; average initial BW=252.8 kg) were blocked by BW and breed, and randomly assigned within a block to treatment. The design was a 3 × 2 factorial arrangement of treatments with S (from NH(4)SO(4)) supplemented at 0, 0.15, or 0.30% of DM, and NaHCO(3) added at 0 or 1.0% of DM. Each treatment consisted of 3 pens containing 5 steers and 1 pen containing 4 steers. Steers were used in an 84-d growing study followed by a finishing study. A corn silage-based diet was fed during the growing study and a corn-based diet was fed during the finishing study. Steers were not randomized between experiments. The analyzed concentrations of S in the growing diets were 0.12, 0.30, and 0.46%, whereas the analyzed concentrations of S in the finishing diets were 0.13, 0.31, and 0.46% for treatments supplemented with 0, 0.15, and 0.30% S, respectively. Increasing DCAB by approximately 15 mEq/100 g of DM, by the addition of NaHCO(3,) did not affect (P > 0.36) performance during the growing or finishing studies. During the growing study DMI was not affected (P=0.29) by dietary S. Steers fed diets containing 0.30% S had greater ADG (P=0.02) and G:F (P=0.01) than those receiving 0.46% S, but similar (P > 0.36) performance to steers fed 0.12% S. During the finishing study, steers fed diets containing 0.46% S had less ADG than steers fed 0.13 (P=0.004) or 0.31% S (P=0.07), whereas ADG did not differ (P=0.18) among steers fed 0.13 and 0.31% S. Steers fed diets containing 0.31 (P=0.01) or 0.46% S (P=0.001) had less DMI than controls, but G:F was not affected (P=0.52) by S during the finishing study. Carcass characteristics did not differ (P > 0.18) among steers fed diets containing 0.13 and 0.31% S. Steers receiving diets containing 0.46% S had decreased HCW (P=0.001), quality (P=0.02), and yield grades (P=0.04) than steers receiving 0.13% S. Plasma Cu concentrations on d 101 of the finishing phase and liver Cu concentrations at slaughter were greater (P ≤ 0.05) in control steers compared with those fed diets containing 0.31 or 0.46% S. This study indicates that steers fed growing diets can tolerate up to 0.46% S with minimum effects on performance. Finishing steers tolerated diets containing 0.31% S without adverse affects on ADG or G:F. However, 0.46% S greatly decreased ADG and DMI, and increasing DCAB did not prevent these depressions.     

Growth,carcass characteristics,muscle conjugated linoleic acid (CLA) content,and response to intravenous glucose challenge in high percentage Wagyu,Wagyu x Limousin,and Limousin steers fed sunflower oil-containing diet

The effect of breed and diet on insulin response to glucose challenge and its relation to intramuscular fat deposition was determined in 36 steers with 12 each of greater than 87% Wagyu (referred to as Wagyu), Wagyu x Limousin, and Limousin breeds. Weaned steers were blocked by weight into heavy, medium, and light calves and placed in six pens with two pens per weight type and with two steers of each breed per pen. Three pens with steers from each weightclass were fed backgrounding and finishing diets for 259 d, while the other three pens were fed the same diets where 6% of the barley grain was replaced with sunflower oil. Prior to initiation of the finishing phase of the study the intravenous glucose tolerance test (VGTIT) was conducted in all steers. Once steers were judged as carrying adequate 12th-rib fat, based on weight and days on feed, they were harvested and graded and samples of the longissimus muscle were procured for determination of fat content and fatty acid composition. Dietary oil improved (P = 0.011; 0.06) ADG and feed conversion efficiency of steers during the latter part of backgrounding and only ADG during early part ofthe finishing period. Generally percent kidney, pelvic, and heart fat was the only adiposity assessment increased (P = 0.003) by dietary oil. The IVGTT results indicated that insulin response to intravenous glucose was lower in Limousin steers than in Wagyu steers. Dietary oil decreased (P = 0.052) fasting plasma insulin concentration in Wagyu steers compared with Limousin steers. The correlation coefficients among the IVGTT measures and intramuscular fat content or marbling score were less than 0.4, and only a negative trend existed between fasting insulin and USDA marbling scores. However, the carcasses of the Wagyu steers graded US Choice, and 66% of the Wagyu carcasses graded US Prime, which were substantially better than the quality grades obtained for the carcasses from the other breed types. Dietary oil did not affect muscle fat content but increased (P = 0.01) conjugated linoleic acid (CLA) concentrations by 339%. Results indicated that IVGTT measures were not appropriate indices of marbling potential in cattle and that dietary oil can enhance CLA content of beef.