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Effect of source and amount of energy and rate of growth in the growing phase on adipocyte cellularity and lipogenic enzyme activity in the intramuscular and subcutaneous fat depots of Holstein steers¹

Department of Animal Sciences, The Ohio State University, Wooster 44691

Abstract

Seventy-three Holstein steers (initial BW 138.5 ± 4.3 kg; approximately 3 mo of age) were allotted by BW to one of three growing-phase treatments to determine the effect of source and amount of energy on feedlot performance, and characteristics of subcutaneous (s.c.) and intramuscular (i.m.) adipose tissue. Treatment diets were 1) high concentrate fed ad libitum (ALC); 2) high forage fed ad libitum for 55 d, then a mid-level forage diet fed ad libitum for 98 d (ALF); or 3) limit-fed high concentrate to achieve a gain of 0.8 kg/d for 55 d, then to achieve a gain of 1.2 kg/d for 98 d (LFC). All steers were fed the ALC diet from d 154 to slaughter. Eight steers per treatment were selected after an average of 145 and 334 d on feed for determination of adipocyte cellularity and lipogenic enzyme activity at the end of the growing and finishing phases, respectively. Remaining steers were slaughtered after an average of 334 d on feed. At initial slaughter, ALC steers had a two- to threefold greater (P < 0.05) s.c. fat depth, and 1.9-fold greater (P < 0.01) longissimus muscle ether extract than steers in other groups. At final slaughter, LFC steers had a greater fat depth than ALF steers (P < 0.10) and had the greatest (P < 0.10) longissimus muscle ether extract. Increased fat depth for ALC steers at initial slaughter was a result of a greater (P < 0.05) mean adipocyte diameter in the s.c. depot. Mean i.m. adipocyte diameter followed the same trend (P < 0.16). The number of adipocytes per gram of s.c. fat was least for ALC and greatest for ALF (P < 0.10) at initial slaughter. Mean diameter and number of adipocytes per gram of i.m. and s.c. fat did not differ among treatments at final slaughter (after 180 d on a common finishing diet). High energy (ALC) increased activities of ATP-citrate lyase, fatty acid synthase, 6-phosphogluconate dehydrogenase, glucose-6-phosphate dehydrogenase, and malate dehydrogenase (P < 0.05), in the s.c. depot, and increased activities of ATP-citrate lyase and glucose-6-phosphate dehydrogenase (P < 0.10) in the i.m. depot at initial slaughter. Lipogenic enzyme activity in the s.c. depot at final slaughter did not differ among treatments. Glucose-6-phosphate dehydrogenase activity in the i.m. depot at final slaughter was lowest (P < 0.10) in ALF. Hypertrophy made a greater contribution to fat tissue growth than hyperplasia. Hypertrophy was affected by amount of energy, whereas hyperplasia was affected by source of energy. Differences diminished when cattle were fed the common finishing diet.

Key Words: Adipocyte Diameter • Limit-Feeding • Lipogenic Enzymes

Introduction

Strategies have not been developed that are able to maintain high levels of intramuscular fat deposition without a concurrent increase in subcutaneous fat deposition. Restricting energy intake by limit-feeding increases carcass leanness but reduces the rate of gain, increases the time required for cattle to reach market weight, and can decrease marbling scores (Plegge, 1987; Hicks et al., 1990; Murphy and Loerch, 1994). Managing bulls and implanted steers in early-weaning systems enables early intramuscular fat deposition and allows for rapid and efficient growth, but appreciable amounts of energy are still partitioned to subcutaneous fat (Myers et al., 1999; Fluharty et al., 2000; Schoonmaker et al., 2001). Thus, physiological maturity is accelerated, and carcass weights are reduced.

Smith and Crouse (1984) demonstrated that glucose provides 50 to 75% of the acetyl units for in vitro lipogenesis in the intramuscular fat depot but only 1 to 10% of the acetyl units for in vitro lipogenesis in the subcutaneous fat depot. Thus, the possibility exists that increasing blood glucose could increase intramuscular fat deposition, without markedly affecting subcutaneous fat deposition. Schoonmaker et al. (2003) demonstrated that early-weaned steers fed a high concentrate diet ad libitum from 119 to 218 d of age had elevated serum insulin at 218 d of age compared with early-weaned steers that were limit-fed concentrate or were fed forage. Elevated serum insulin may have led to an increased uptake of glucose by peripheral tissues and an increased marbling score at 218 d of age for early-weaned steers fed a high concentrate diet ad libitum. We hypothesize that the source of energy and rate of growth in the growing phase (153 d) differentially affect the growth of intramuscular and subcutaneous adipocytes. Our objective was to determine whether the site of fat deposition and adipocyte characteristics are affected by the source of energy and rate of gain in the growing phase.

Materials and Methods

Seventy-three Holstein steers, approximately 3 mo of age, were allotted to one of three growing-phase (d 0 to 153) diets: 1) 70% high-moisture corn, 15% corn silage (DM basis) fed ad libitum (ad libitum concentrate fed); 2) 60% orchardgrass haylage, 25% soy hull (DM basis) diet fed ad libitum for 55 d, and then a 25% orchardgrass haylage, 60% soy hull diet fed ad libitum for 98 d (forage fed); or 3) 70% high-moisture corn, 15% corn silage (DM basis) diet fed to achieve a gain of 0.8 kg/d for 55 d and then to achieve a gain of 1.2 kg/d for 98 d (limit-fed concentrate). The amount of feed offered to limit-fed concentrate steers was regulated according to NRC net energy equations (NRC, 1984). Limit-fed concentrate steers were weighed every 14 d, and intakes were adjusted to meet the increasing energy needs for maintenance as the steers grew (NRC, 1984). Steers on remaining treatments were weighed every 28 d. The forage-fed diet was formulated to achieve gains similar to those of the limit-fed concentrate diet. At 153 d on feed, all steers were switched to the finishing-phase (d 154 to slaughter) diet (70% concentrate, 15% corn silage [DM basis]), and intake was limited to 2% of BW for 1 wk to equalize gut-fill differences among growing-phase dietary treatments. Receiving diets were formulated to contain 16% CP to adjust for anticipated low feed intakes during feedlot adaptation. Growing-phase diets were formulated to contain 14% CP until the start of the finishing phase (Table 1). Finishing-phase diets were formulated to contain 14% CP. Steers were penned and fed individually in a totally enclosed feedlot barn (slatted concrete floor; metal gates) during the growing phase. Pens were 2.6 x 1.5 m, giving each calf 3.9 m² of floor space. Feed was delivered once daily at 0900, and feed refusals were recorded daily for each steer. For the finishing phase, steers were removed from individual pens and placed in a common pen. Feed samples were taken every 7 d throughout the trial and were composited for analysis of DM and N (AOAC, 1996). Crude protein was calculated as N x 6.25.

Steers were implanted with Compudose (25.7 mg of estradiol; provided courtesy of VetLife, Overland Park, KS) on d 28. On d 153, steers were implanted with Component TE-S (24 mg of estradiol, 120 mg of trenbolone acetate; provided courtesy of VetLife), and were scanned (Classic Ultrasound Equipment, Classic Medical Supply, Tequesta, FL) by a trained ultrasound technician for fat thickness, longissimus muscle area, and intramuscular fat percentage.

Eight steers per treatment (48 total) were selected for determination of adipocyte cellularity and lipogenic enzyme activity at the end of the growing phase (138, 145, or 152 d on feed: initial slaughter) and at the end of the finishing phase (327, 334, or 341 d on feed: final slaughter). Treatments were equally represented at each slaughter date. To avoid confounding effects of BW, steers were each assigned (on paper) to four BW subgroups, and two steers from each BW subgroup were randomly selected for slaughter. Remaining steers were slaughtered over a 3-wk period (327, 334, and 341 d on feed). Treatments were equally represented at each slaughter date. Hot carcass weight; fat thickness; percentage of kidney, pelvic and heart fat; longissimus muscle area; and USDA quality and yield grades were determined by qualified OSU personnel 48 h after slaughter (initial and final slaughter). The longissimus muscle from the 11th to 12th rib was removed from the right side of each carcass, trimmed of external fat, ground (Hobart model #4822, Hobart Co., Troy, OH) three times and subsampled for determination of moisture and ether-extractable lipid (initial and final slaughter).

Approximately 4 g of i.m. and 4 g of s.c. adipose tissue were collected from the 9th to the 12th rib for determination of adipocyte cellularity and lipogenic enzyme activity. Samples of adipose tissue (2 g) designated for cell size and number determination were stored at -25°C in screw-cap vials until measurements could be made. Fresh portions of subcutaneous and intramuscular adipose tissue (2 g) designated for lipogenic enzyme activity determination were homogenized on ice for 15 s in 3 vol (wt/vol) of 0.1 M phosphate buffer (pH 7.4, 37°C) with a Potter-Elvehjem homogenizer at medium speed. The resulting homogenate was centrifuged at 3,000 x g for 15 min and decanted; the supernatant fraction was then centrifuged at 15,000 x g for 30 min. All centrifugations were performed at 4°C. Adipose tissue centrifugal fractions were frozen in liquid nitrogen and stored at -25°C until lipogenic enzyme activity could be determined. Fatty acid synthase, NADP-malate dehydrogenase, and ATP-citrate lyase were measured as described by Ochoa (1955), Martin et al. (1961), and Srere (1962), respectively. Glucose-6-phosphate dehydrogenase, 6-phospogluconate dehydrogenase, and isocitrate dehydrogenase were assayed as described by Bernt and Bergmeyer (1974a,b). All enzyme assays were determined in duplicate using the spectrophotometric absorbance of solutions in cuvettes at 340 nm. Slopes of the linear rates of NADPH consumption (fatty acid synthase) or production (all other enzymes) were used to calculate enzyme activities.

To determine adipocyte size and number, adipose tissue samples were sliced into 1-mm thick sections while still frozen, transferred to 25-mL scintillation vials, and fixed with 3% osmium tetroxide by the method of Etherton et al. (1977), modified as described by Prior (1983). Fixed adipose tissue samples were filtered through 250- and 10-µm screens using 0.01% Triton x-100 buffer in double-distilled water. Tissue that was collected on the 250-µm screen was discarded, and tissue that collected on the 10-µm screen was resuspended in 10 mL of 55.5% glycerol for determination of cell number and diameter. Cell number and mean cell diameter were determined by computer image analysis (Image-Pro v. 4.5, MediaCybernetics Inc., Silver Spring, MD) of 1 mL of the glycerol-adipocyte suspension in a Sedgwick-Rafter counting chamber (Thomas Scientific, Swedesboro, NJ).

Performance and carcass data were analyzed using the GLM procedures of SAS (SAS Inst. Inc., Cary, NC) for a completely randomized design comparing three treatments. The model included effects for growing-phase treatment. Means were separated using LS means with residual mean square as the error term and pen was the experimental unit. Adipocyte diameter distributions were analyzed using the MODECLUS procedures of SAS.

Results and Discussion

Weight at d 0 did not differ (P > 0.97) among treatments, but by 153 d on feed, steers fed concentrate diets ad libitum were 58 to 66 kg heavier (P < 0.01) than limit-fed concentrate and forage-fed steers (Table 2). During the growing phase (d 0 to 153), steers fed ad libitum concentrate gained weight 44.8 and 36.3% faster (P < 0.01) than forage-fed and limit-fed concentrate steers, respectively. Forage-fed and limit-fed concentrate steers achieved gains of 0.96 and 1.02 kg/d, respectively, during the growing phase. The growing phase consisted of a stepwise increase in feed intake from a target gain of 0.8 kg/d to 1.2 kg/d (limit-fed concentrate) after 55 d on feed, and a stepwise increase in concentrate level from 40 to 75% (forage-fed) after 55 d on feed. Compensatory gain did not result from this stepwise increase in energy intake. In contrast, Schoonmaker et al. (2004) demonstrated that beef-type cattle experienced an 18 and 22% increase (limit-fed concentrate and forage-fed, respectively) in predicted gain because of a stepwise increase in intake. Loerch and Fluharty (1998) also demonstrated that actual growth rate of limit-fed beef-type steers is 3 to 19% higher than predictions based on 1984 NRC net energy equations.

Daily and total DMI during the growing phase was greatest (P < 0.01) for steers fed concentrate diets ad libitum, intermediate for forage-fed steers, and lowest for limit-fed concentrate steers. Limit-fed concentrate steers were 10.3 and 39.0% more efficient (P < 0.05) in the growing phase than ad libitum concentrate-fed steers and forage-fed steers, respectively. In agreement, Schoonmaker et al. (2003, 2004) demonstrated that early-weaned cattle that were limit-fed concentrate in the growing phase were the most efficient. However, Loerch and Fluharty (1998) demonstrated that in the growing phase no difference existed for feed efficiency of normally weaned cattle that were limit-fed concentrate compared with those that were fully fed. Effects of growing-phase feeding regimens on intake during the finishing phase of the current trial could not be determined because cattle from all treatments were grouped together.

When slaughtered at the end of the growing phase (eight steers per treatment), slaughter weight (P < 0.01), hot carcass weight (P < 0.01), and longissimus muscle area (P < 0.05) were greatest for ad libitum concentrate-fed steers compared with forage-fed and limit-fed concentrate steers (Table 3). In addition, ad libitum concentrate-fed steers had two- to threefold greater (P < 0.05) fat thickness and 1.9-fold greater (P < 0.01) longissimus muscle ether extract. Subjective marbling score at the end of the growing phase was lowest (P < 0.05) for limit-fed concentrate steers, but was similar (P > 0.10) between ad libitum concentrate-fed steers and forage-fed steers. Carcass characteristics, as measured by ultrasound at the end of the growing phase on the remainder of steers, followed the same tendency (Table 4). Schoonmaker et al. (2003) demonstrated that marbling score and fat thickness, as measured by ultrasound, were similarly increased for steers fed a high concentrate diet ad libitum during the growing phase. The authors postulated that the increased marbling score at 218 d of age may have been a consequence of elevated ruminal propionate and serum insulin for steers fed a high concentrate diet ad libitum. Glucose provides 50 to 75% of the acetyl units for intramuscular fat deposition (Smith and Crouse, 1984), and elevated serum insulin would likely lead to increased uptake of glucose by peripheral tissues. However, differences in intramuscular fat percentage diminished during the finishing phase, when cattle were fed the same diet (Schoonmaker et al., 2003).

Adipose tissue can expand by cell proliferation (hyperplasia) or cell enlargement through lipid accumulation (hypertrophy). An increase in adipocyte number may be either apparent, because of preadipocytes filling with lipid, or genuine, because of differentiation or proliferation of newly stimulated preadipocytes (Hood, 1982). In the growing phase of the current trial, increased fat thickness for ad libitum concentrate-fed steers was a result of a greater (P < 0.05) mean adipocyte diameter in the subcutaneous fat depot compared with the subcutaneous fat depot of forage-fed and limit-fed concentrate steers (Table 5). Mean subcutaneous adipocyte diameter did not differ (P > 0.10) between forage-fed and limit-fed concentrate steers at the end of the growing phase. The number of adipocytes per gram of subcutaneous fat was lowest (P < 0.10) for ad libitum concentrate-fed steers; it was greatest for forage-fed steers. Limit-fed concentrate steers produced subcutaneous fat with an intermediate amount of adipocytes per gram that did not differ from ad libitum concentrate-fed and forage-fed steers. Mean diameter (P < 0.16) of intramuscular adipocytes followed the same trend, with ad libitum concentrate-fed steers producing intramuscular adipocytes with the greatest diameters. Increased longissimus muscle fat percentage at 153 d for ad libitum concentrate-fed compared with forage-fed and limit-fed concentrate steers supports this trend. The number of adipocytes per gram of intramuscular fat did not differ (P > 0.57) because of growing-phase feeding regimen. Increased adipocyte diameter (25.4 and 20.7% for subcutaneous and intramuscular fat, respectively), with a concurrent decrease in adipocytes per gram of fat tissue (49.1 and 18.0% for subcutaneous and intramuscular fat, respectively) in steers with greater amounts of subcutaneous and intramuscular fat (ad libitum concentrate-fed) compared with forage-fed and limit-fed concentrate steers indicate that hypertrophy, rather than hyperplasia, is making a larger contribution to fat deposition in Holstein steers less than 250 d of age. Characterization of adipocyte cellularity in the intramuscular fat depot has not been previously reported in cattle younger than 250 d of age. Robelin (1981) demonstrated that a 100-fold increase in subcutaneous fat tissue from 15 to 65% of mature weight was a result of a 5.6-fold increase in cell number, and a 13-fold increase in cell size. An apparent cell proliferation occurred between 15 and 25% of mature weight; lipid filling occurred from 25 to 45% of mature weight; and an increase in cell number occurred from 45 to 55%. The apparent proliferation occurred when mean cell diameter reached 80 to 90 µm.

As fat depots in the bovine animal increase beyond a certain point, further increases in diameter or volume of the adipocytes are minimal (Allen, 1976). At this point, another population of smaller adipocytes becomes evident, resulting in a biphasic adipocyte diameter distribution (Allen, 1976). An exact point when this occurs in subcutaneous and intramuscular fat depots is unknown. Robelin (1981) reported that in the subcutaneous fat depot, a new population of cells arises when adipocyte diameter is approximately 80 to 90 µm. Because age and rate of growth can be directly related, their effects on adipocyte cellularity are difficult to separate and interpret. Marbling is traditionally thought of as a late-maturing fat depot that has not fully developed when cattle are slaughtered (Hood and Allen, 1973; Cianzio et al., 1985; May et al. 1994). As a result, carcasses are produced with greater amounts of extramuscular fat and with lesser amounts of intramuscular fat. However, mechanical pressure from muscle may result in a smaller maximum adipocyte size for intramuscular compared with subcutaneous fat depots (Waters, 1909), or lipid may be preferentially deposited subcutaneously rather than intramuscularly. Hood and Allen (1973) observed that subcutaneous adipose tissue from cattle slaughtered at 1.2 cm of fat thickness still exhibited a monophasic cell distribution, whereas intramuscular adipose tissue from cattle slaughtered at 1.2 cm of fat thickness exhibited a biphasic cell distribution. Allen (1976) reported that in very obese cattle (5.1 cm of backfat), extramuscular adipose tissue will exhibit a biphasic cell distribution, indicating that hyperplasia in the subcutaneous fat depot may occur at a greater adipocyte size compared to the intramuscular fat depot.

When adipocyte size distributions were determined in the present trial at the end of the growing phase, concentrate-fed steers (ad libitum and limit-fed) already had biphasic subcutaneous (Figure 1) and intramuscular (Figure 2) adipocyte distributions (small- and medium-sized clusters), whereas forage-fed steers still had a monophasic (single size cluster) size distribution (P < 0.05) in each depot. Concentrate-fed steers (ad libitum and limit-fed, respectively) produced subcutaneous adipocytes with a mean diameter of 33.2 and 34.3 µm, for the small cluster, and 136.6 and 112.1 µm, for the medium cluster. Mean diameter for the subcutaneous fat depot of forage-fed steers was 92.9 µm. Concentrate-fed steers (ad libitum and limit-fed) produced intramuscular adipocytes with a mean diameter of 30.1 and 24.6 µm, respectively, for the small cluster, and 107.5 and 88.4 µm, respectively, for the medium cluster. Mean diameter for the intramuscular fat depot of forage-fed steers was 67.9 µm. Biphasic distributions for concentrate-fed steers (ad libitum and limit-fed) compared with forage-fed steers indicate that the source of energy may be playing a role in when a new population of cells arises. The observation that new cells arose when average cell size was approximately 90 µm is in agreement with data from Robelin (1981). However, despite achieving a diameter of 92.9 µm, a new cluster of adipocytes had not arisen in the subcutaneous depot of forage-fed steers. In contrast, a new cluster of adipocytes had arisen in the intramuscular fat depot of limit-fed concentrate steers when a mean intramuscular diameter of only 88.4 µm had been achieved. This discrepancy indicates that subcutaneous and intramuscular depots may have a different mean size when new hyperplasia occurs.

View larger version (24K): [in this window] [in a new window]   Figure 1. Effect of source of energy and rate of gain on subcutaneous adipocyte diameter in the growing phase (d 0 to 145). ALC = steers fed ad libitum concentrate during the entire trial; LFC = steers limit fed at 0.8 kg/d for 55 d, then at 1.2 kg/d for 98 d, and then fed ad libitum concentrate until slaughter; ALF = steers fed a 60% haylage diet, ad libitum forage for 55 d, then fed a 25% haylage diet, ad libitum for 98 d, and then fed ad libitum concentrate until slaughter. Small cluster of cells, open bars; medium cluster, solid bars.

View larger version (23K): [in this window] [in a new window]   Figure 2. Effect of source of energy and rate of gain on intramuscular adipocyte diameter in the growing phase (d 0 to 145). ALC = steers fed ad libitum concentrate during the entire trial; LFC = steers limit fed at 0.8 kg/d for 55 d, then at 1.2 kg/d for 98 d, and then fed ad libitum concentrate until slaughter; ALF = steers fed a 60% haylage diet, ad libitum forage for 55 d, then fed a 25% haylage diet, ad libitum for 98 d, and then fed ad libitum concentrate until slaughter. Small cluster of cells, open bars; medium cluster, solid bars.

View larger version (38K): [in this window] [in a new window]   Figure 3. Effect of source of energy and rate of gain on subcutaneous adipocyte diameter in the finishing phase (d 0 to 145). ALC = steers fed ad libitum concentrate during the entire trial; LFC = steers limit fed at 0.8 kg/d for 55 d, then at 1.2 kg/d for 98 d, and then fed ad libitum concentrate until slaughter; ALF = steers fed a 60% haylage diet, ad libitum forage for 55 d, then fed a 25% haylage diet, ad libitum for 98 d, and then fed ad libitum concentrate until slaughter. Small cluster of cells, open bars; medium cluster, solid bars; large cluster of cells, crosshatched bars.

View larger version (28K): [in this window] [in a new window]   Figure 4. Effect of source of energy and rate of gain on intramuscular adipocyte diameter in the finishing phase (d 0 to 145). ALC = steers fed ad libitum concentrate during the entire trial; LFC = steers limit fed at 0.8 kg/d for 55 d, then at 1.2 kg/d for 98 d, and then fed ad libitum concentrate until slaughter; ALF = steers fed a 60% haylage diet, ad libitum forage for 55 d, then fed a 25% haylage diet, ad libitum for 98 d, and then fed ad libitum concentrate until slaughter. Small cluster of cells, open bars; medium cluster, solid bars; large cluster of cells, crosshatched bars.

The low levels of ATP citrate lyase and NADP-malate dehydrogenase (both involved in the conversion of glucose to acetyl-CoA) that are typically present in ruminant adipose tissue imply that glucose can make little contribution to even chain fatty acid synthesis via acetyl-CoA (Hood et al., 1972). However, glucose incorporation into fatty acids and activities of relevant enzymes can be increased substantially by infusing glucose postruminally or intravenously (Bauman, 1976), indicating that fat metabolism in the ruminant is substrate dependent. The infusion of glucose into lambs dramatically increased glucose utilization for lipogenesis relative to acetate with 44- and 9-fold increases in activities of ATP-citrate lyase and NADP⁺-malate dehydrogenase. When measured at the end of the growing phase (d 145) in the current trial, activity of ATP-citrate lyase (P < 0.01), fatty acid synthase (P < 0.05), 6-phosphogluconate dehydrogenase (P < 0.05), glucose-6-phosphate dehydrogenase (P < 0.05), and malate dehydrogenase (P < 0.01) were increased approximately 10-, 2-, 2.5-, 5-, and 5-fold, respectively, in the subcutaneous fat depot in ad libitum concentrate-fed steers compared with forage-fed and limit-fed concentrate steers. Activity of isocitrate dehydrogenase in the subcutaneous fat depot did not differ between ad libitum concentrate-fed steers and forage-fed steers, but tended to be increased twofold (P < 0.11) in ad libitum concentrate-fed steers compared with limit-fed concentrate steers. Activity of ATP-citrate lyase was increased (P < 0.10) approximately 150-fold in the intramuscular fat depot of ad libitum concentrate-fed steers compared with the intramuscular fat depot of forage-fed steers at the end of the growing phase. Activity of ATP-citrate lyase in the intramuscular fat depot of limit-fed concentrate steers was intermediate, and did not differ (P > 0.10) from activity in the intramuscular fat depot of ad libitum concentrate-fed and forage-fed steers. A greater amount of propionate production for ad libitum concentrate-fed steers may have contributed to increased glucose production and the subsequent increase in enzyme activities. The observation that the intramuscular fat depot of ad libitum concentrate-fed steers had 150-fold greater ATP-citrate lyase activity compared with forage-fed steers, whereas the subcutaneous fat depot only had 20-fold greater activity, indicates that ATP-citrate lyase is playing a larger relative role in the intramuscular fat depot. However, this difference in relative contribution of lipogenic enzymes was not able to be exploited, as indicated by greater increases in subcutaneous fat rather than intramuscular fat in ad libitum concentrate-fed steers compared with limit-fed concentrate and forage-fed steers. Even though glucose only provides 1 to 10% of the acetyl units for fat deposition in the subcutaneous fat depot, compared with 50 to 75% in the intramuscular fat depot (Smith and Crouse, 1984), it is the second-largest fat depot in the body (Cianzio et al., 1985). As a result, the subcutaneous fat depot may consume more total glucose than the intramuscular fat depot, which is the smallest fat depot in the body, still causing subcutaneous fat to be deposited at a faster rate than intramuscular fat. Greater activities of ATP-citrate lyase and NADP malate dehydrogenase in the subcutaneous compared with intramuscular adipose tissue in the present study substantiate this. Activity of glucose-6-phosphate dehydrogenase in the intramuscular fat depot of ad libitum concentrate-fed steers was increased (P < 0.05) approximately 2.6-fold compared with the intramuscular fat depot of forage-fed and limit-fed concentrate steers. In agreement, Smith et al. (1984) demonstrated that ATP-citrate lyase, NADP⁺-malate dehydrogenase, and fatty acid synthase measured on biopsies of subcutaneous adipose tissue taken at 30- to 70-d intervals from British-type beef breeds were greater in concentrate-fed steers than in roughage-fed steers.

Despite differences in fat thickness in the current trial, lipogenic enzyme activity in the subcutaneous fat depot when measured at the end of the finishing phase did not differ (P > 0.33) among treatments. Perhaps this is because all steers were fed a common high concentrate diet for the 180-d finishing phase. Glucose-6-phosphate dehydrogenase activity in the intramuscular fat depot at the end of the finishing phase was decreased (P < 0.10) 37.6% in previously forage-fed compared with ad libitum concentrate-fed and limit-fed concentrate steers. Due to analytical problems, activities of ATP-citrate lyase and fatty acid synthase were not determined in the intramuscular fat depot at the end of the finishing phase.

Implications

The source of energy may play a role in when a new population of adipocytes arises (hyperplasia). Larger mean adipocyte diameter (hypertrophy) may occur as a result of increased substrate (energy from starch fermentation) and greater lipogenic enzyme activity; this is substantiated by biphasic distributions for concentrate-fed steers compared with forage-fed steers at the end of the growing phase. The amount of energy and the resultant hypertrophy of adipocytes make a larger contribution to fat deposition in Holstein steers younger than 250 d of age than do the source of energy and resultant hyperplasia of adipocytes. Increased adipocyte diameter and decreased adipocytes per gram of fat tissue in steers with the greatest amount of fat (ad libitum concentrate fed) substantiate this. When cattle are fed the same high-concentrate diet for the finishing phase, these differences diminish. Adipocyte hypertrophy also plays a dominant role in fat tissue growth in the finishing phase.

Footnotes

¹ Salaries and research support provided by state and federal funds appropriated to the Ohio Agric. Res. and Dev. Center, The Ohio State Univ. Manuscript No. 10-03AS.

² Correspondence: 114 Gerlaugh Hall, OARDC, 1680 Madison Ave. (phone: 330-263-3900; fax: 330-263-3949; e-mail: loerch.1{at}osu.edu).

Received for publication May 22, 2003. Accepted for publication September 11, 2003.

Literature Cited

Allen, C. E. 1976. Cellularity of adipose tissue in meat animals. Federation Proc. 35:2302–2307.[Medline]

AOAC. 1996. Official Methods of Analysis. 16th ed. Assoc. Offic. Anal. Chem., Arlington, VA.

Bauman, D. E. 1976. Intermediary metabolism of adipose tissue. Federation Proc. 35:2308–2313.[Medline]

Bernt, E., and H. U. Bergmeyer. 1974a. Hexokinase. Pages 473–474 in Methods of Enzyme Analysis. H. U. Bergmeyer and K. Gawehn, ed. Academic Press, New York.

Bernt, E., and H. U. Bergmeyer. 1974b. Isocitrate dehydrogenase. Pages 624–631 in Methods of Enzymatic Analysis. H. U. Bergmeyer and K. Gawehn, ed. Academic Press, New York.

Cianzio, D. S., D. G. Topel, G. B. Whitehurst, D. C. Beitz, and H. L. Self. 1985. Adipose tissue growth and cellularity: changes in bovine adipocyte size and number. J. Anim. Sci. 60:970–976.

Eguinoa, P., S. Brocklehurst, A. Arana, J. A. Mendizabal, R. G. Vernon, and A. Purroy. 2003. Lipogenic enzyme activities in different adipose depots of Pirenaican and Holstein bulls and heifers taking into account adipocyte size. J. Anim. Sci. 81:432–440.[Abstract/Free Full Text]

Etherton, T. D., E. H. Thompson, and C. E. Allen. 1977. Improved techniques for studies of adipocyte cellularity and metabolism. J. Lipid Res. 18:552–557.[Abstract]

FASS. 1998. Guide for the Care and Use of Agricultural Animals in Agricultural Research and Teaching. Consortium for Developing a Guide for the Care and Use of Agricultural Animals in Agricultural Research and Teaching. Savoy, IL.

Fluharty, F. L., T. B. Turner, S. J. Moeller, and G. D. Lowe. 2000. Effects of age at weaning and diet on growth of calves. J. Anim. Sci. 78:1759–1767.[Abstract/Free Full Text]

Hicks, R. B., F. N. Owens, D. R. Gill, J. J. Martin, and C. A. Strasia. 1990. Effects of controlled feed intake on performance and carcass characteristics of feedlot steers and heifers. J. Anim. Sci. 68:233–244.[Abstract/Free Full Text]

Hood, R. L., E. H. Thompson, and C. E. Allen. 1972. The role of acetate, propionate, and glucose as substrates for lipogenesis in bovine tissues. Int. J. Biochem. 3:598–606.

Hood, R. L., and C. E. Allen. 1973. Cellularity of bovine adipose tissue. J. Lipid Res. 14:605–610.[Abstract]

Hood, R. L., and R. F. Thornton. 1980. The effect of compensatory growth on lipogenesis in ovine carcass adipose tissue. Aust. J. Agric. Res. 31:155–161.

Hood, R. L. 1982. Relationships among growth, adipose cell size, and lipid metabolism in ruminant adipose tissue. Federation Proc. 41:2555–2561.[Medline]

Knoblich, H. V., F. L. Fluharty, and S. C. Loerch. 1997. Effects of programmed gain strategies on performance and carcass characteristics of steers. J. Anim. Sci. 75:3094–3102.[Abstract/Free Full Text]

Loerch, S. C., and F. L. Fluharty. 1998. Effects of programming intake on performance and carcass characteristics of feedlot cattle. J. Anim. Sci. 76:371–377.[Abstract/Free Full Text]

Martin, D. B., M. G. Horning, and P. R. Vagelas. 1961. Fatty acid synthesis in adipose tissue. J. Biol. Chem. 236:663–668.[Free Full Text]

May, S. G., J. W. Savell, D. K. Lunt, J. J. Wilson, J. C. Laurenz, and S. B. Smith. 1994. Evidence for preadipocyte proliferation during culture of subcutaneous and intramuscular adipose tissues from Angus and Wagyu crossbred steers. J. Anim. Sci. 72:3110–3117.[Abstract]

Murphy, T. A., and S. C. Loerch. 1994. Effects of restricted feeding of growing steers on performance, carcass characteristics, and composition. J. Anim. Sci. 72:2497–2507.[Abstract]

Myers, S. E., D. B. Faulkner, F. A. Ireland, L. L. Berger, and D. F. Parrett. 1999. Production systems comparing early weaning to normal weaning with or without creep feeding for beef steers. J. Anim. Sci. 77:300–310.[Abstract/Free Full Text]

NRC. 1984. Nutrient Requirements of Beef Cattle. 6th ed. National Academy Press, Washington, DC.

NRC. 1996. Nutrient Requirements of Beef Cattle. 7th ed. National Academy Press, Washington, DC.

Ochoa, S. 1955. Malic enzyme. Methods Enzymol. 1:735–748.

Plegge, S. D. 1987. Restricting intake of feedlot cattle. Symposium Proceedings: Feed Intake by Beef Cattle. F. N. Owens, ed. Oklahoma Agric. Exp. Sta. 121:297–301.

Prior, R. L. 1983. Lipogenesis and adipose tissue cellularity in steers switched from alfalfa hay to high concentrate diets. J. Anim. Sci. 56:483–492

Robelin, J. 1981. Cellularity of bovine adipose tissues: developmental changes from 15 to 65 percent mature weight. J. Lipid Res. 22:452–457.[Abstract]

Schoonmaker, J. P., F. L. Fluharty, S. C. Loerch, T. B. Turner, S. J. Moeller, and D. M. Wulf. 2001. Effects of weaning status and implant regimen on growth, performance, and carcass characteristics of steers. J. Anim. Sci. 79:1074–1084.[Abstract/Free Full Text]

Schoonmaker, J. P., M. J. Cecava, D. B. Faulkner, F. L. Fluharty, H. N. Zerby, and S. C. Loerch. 2003. Effect of source of energy and rate of growth on performance, carcass characteristics, ruminal fermentation, and serum glucose and insulin of early-weaned steers. J. Anim. Sci. 81:843–855.[Abstract/Free Full Text]

Schoonmaker, J. P., M. J. Cecava, F. L. Fluharty, H. N. Zerby, and S. C. Loerch. 2004. Effect of source and amount of energy, and rate of growth in the growing phase on performance and carcass characteristics of early- and normal-weaned steers. J. Anim. Sci. 82:273–282.[Abstract/Free Full Text]

Smith, S. B., and J. D. Crouse. 1984. Relative contributions of acetate, lactate and glucose to lipogenesis in bovine intramuscular and subcutaneous adipose tissue. J. Nutr. 114:792–800.

Smith, S. B., R. L. Prior, C. L. Ferrell, and H. J. Mersmann. 1984. Interrelationships among diet, age, fat deposition and lipid metabolism in growing steers. J. Nutr. 114:153–162.

Srere, P. A. 1962. Citrate cleavage enzyme. Methods Enzymol. 5:641–644

Waters, H. J. 1909. The influence of nutrition upon the animal form. Pages 70–98 in Soc. Proc. Agric. Sci. 30th Annu. Meet.

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