Biomedical subjects

R A Merkel

Publications and source records attributed to R A Merkel.

At least 37 records · Page 2Linked to original sources

PubMed1991

Body composition of animals treated with partitioning agents: implications for human health.

Excess fat in meat products has been identified as a dietary problem by public health officials. The meat animal industry has responded during the last 25 years to concerns about excess fat intake from animal products by implementing strategies to depress fat deposition and increase lean (protein) tissue gain in meat animals. The most successful strategy to date is the use of large, late-maturing animals for meat production. At desired market weights, these animals are much leaner than smaller, early-maturing animals. In addition, exogenous agents such as anabolic steroids (FDA approved for cattle) have been used to increase lean gain and depress fat deposition in cattle. Growth hormone (GH) and beta-adrenergic agonists (beta AA) are not yet approved by the FDA, but if/when approved would also markedly increase lean gain and depress fat deposition. Both GH and beta AA are called partitioning agents because they partition nutrients and energy toward lean (protein) accretion and dramatically lower fat deposition. Contingent on approval by the FDA and subsequent adoption of partitioning agents by the animal industry would result in meat products containing less and 30% of total calories from fat.

Adrenergic beta-Agonists↗

PubMed1991

Administration of growth hormone to pigs alters the relative amount of insulin-like growth factor-I mRNA in liver and skeletal muscle.

The relative amount of insulin-like growth factor-I (IGF-I) mRNA was determined in the liver and skeletal muscle of market weight crossbred barrows (castrated male pigs) using a solution hybridization-nuclease protection assay. Pigs were given either 50 micrograms recombinant porcine GH per kg body weight or vehicle daily for 24 days i.m. They were fed corn-soybean meal diets containing either 140 or 200 g crude protein/kg (low or high protein). The percentage of muscle in the carcasses of pigs given GH was greater (P less than 0.01) than that of controls. Relative to controls, GH increased (P less than 0.05) the amount of liver IGF-I mRNA by 2.7-fold in pigs fed the low protein diet and 3.0-fold in pigs fed the high protein diet. The amount of IGF-I mRNA in the muscles of GH-treated pigs was 77% and 84% of control pigs in those fed the low and high protein diets respectively (P less than 0.08). GH increased (P less than 0.001) the serum concentration of IGF-I 1.6-fold in pigs fed the low protein diet and 2.0-fold in those fed the high protein diet. These results indicate that the administration of GH to pigs influences the relative amount of liver IGF-I mRNA. The increased amount of liver IGF-I mRNA and the increased serum IGF-I concentrations suggest that IGF-I plays an endocrine role in mediating GH-induced muscle hypertrophy in pigs.

Animals↗

PubMed1990

Ractopamine increases total and myofibrillar protein synthesis in cultured rat myotubes.

The ability of the phenethanolamine (beta-adrenergic agonist) ractopamine to stimulate cellular protein accretion and protein synthesis in cultured muscle cells was evaluated. ELC5 myoblasts (a subclone of rat L6 cells) were proliferated in culture (Dulbecco's Modified Eagle Medium plus 10% fetal bovine serum at 37 degrees C) to confluency and then allowed to differentiate to form myotubes. Myotubes were then further incubated in the presence of 10(-9), 10(-8), 10(-7), 10(-6) or 10(-5) mol/L ractopamine. A significant (p less than 0.05) response in cellular protein accretion was observed for the 10(-6) and 10(-5) concentrations when compared to 10(-8) and 10(-9) mol/L ractopamine. Ractopamine at 0 and 10(-6) mol/L was used to examine the effect of the beta agonist on [35S]methionine incorporation (protein synthesis) into total cellular protein, 43-kDa proteins and myosin heavy-chain (200 kDa) protein. Protein synthesis in response to beta agonist treatment was measured at 4, 24, 48, 72 and 96 h after ractopamine addition to the ELC5 myotubes in culture. Ractopamine (10(-6) mol/L) increased [35S]methionine incorporation (apparent protein synthesis) at 24 h (p less than 0.01), 48 h (p less than 0.05), 72 h (p less than 0.01) and 96 h (p less than 0.05) in cultured ELC5 muscle cells. Ractopamine also increased apparent protein synthesis rate of the 43-kDa proteins (p less than 0.05) and myosin heavy-chain protein (200 kDa) (p less than 0.05). These results indicate that ractopamine-enhanced ELC5 myotube protein accretion is mediated, at least in part, by stimulating cellular protein synthesis.

Adrenergic beta-Agonists↗

PubMed1990

Skeletal muscle alpha-actin synthesis is increased pretranslationally in pigs fed the phenethanolamine ractopamine.

Ractopamine [1-(4-hydroxyphenyl-2-(1-methyl-3-(4-hydroxyphenyl)propylamino)ethanol] enhances protein accretion in skeletal muscle (sm) of pigs. Experiments were conducted to elucidate fractional protein synthesis (FSR) and mRNA abundance for alpha-actin in sm of pigs fed a 16% protein diet containing 20 parts/million ractopamine for 21 days. Pigs were infused for 6 h with [14C]lysine (80 microCi/h.pig); after infusion pigs were killed, and longissimus dorsi muscle samples were obtained for RNA isolation and measurement of [14C]lysine incorporation. FSR was determined in vivo by incorporation of [14C]lysine from the muscle free amino acid pool into purified sm alpha-actin. FSR of sm alpha-actin was 55% greater in ractopamine-treated pigs than in controls. Relative mRNA abundance of alpha-actin was determined by dot blot hybridization of 0.1-0.4 microgram RNA to human sm alpha-actin [32P]cDNA probe. Longissimus dorsi alpha-actin mRNA abundance was 2-fold greater in pigs fed ractopamine. Sm RNA was translated in vitro using a cell-free assay to determine pretranslational effects on other muscle proteins. Effects of ractopamine on muscle protein synthesis are not specific to sm alpha-actin, because other muscle proteins also were increased using the in vitro translation assay. These results indicate that the increase in sm accretion in pigs fed ractopamine is due in part to an increase in myofibrillar protein synthesis and that some of the increase can be accounted for by an increase in mRNA abundance for sm alpha-actin.

Actins↗

PubMed1990

Effects of phenethanolamines and propranolol on the proliferation of cultured chick breast muscle satellite cells.

Satellite cells were isolated from 20-d embryonic chick breast muscle via a Percoll density gradient fractionation technique. Culturing of these cells gave rise to at least 89% fusion (myotube nuclei number/total nuclei number). Proliferation of cultured satellite cells (indicated by myotube nuclei number) was increased in a dose-dependent manner when fibroblast growth factor (FGF) was included in the medium (25 to 200 ng/ml). Similar cultures were used to examine the effects of ractopamine and isoproterenol on satellite cell proliferation. Ractopamine and isoproterenol were added to culture medium (10(-11) to 10(-4) M) 24 h after initial plating. After a 72-h treatment period, the treatments were removed and replaced with a medium to promote fusion for 48 h. Cells then were fixed and stained, and myotube and total nuclei were counted. In later experiments, ractopamine and isoproterenol each increased (P less than .01) myotube nuclei number vs that observed in control cultures by 2.3 and 2.1 times, respectively. Similar differences were observed with total nuclei number. The number of myotube nuclei observed in cultures treated with 10(-6) M ractopamine or isoproterenol was reduced (P less than .01) by 25.4 and 23.6%, respectively, when propranolol, a beta adrenergic antagonist, was included at 10(-5) M with the respective agonist. These results indicate that ractopamine and isoproterenol each enhance the proliferative activity of chick satellite cells in culture and that the beta adrenergic receptor mediates this proliferative effect.

Adrenergic beta-Agonists↗

PubMed1989

Muscle protein metabolism in finishing pigs fed ractopamine.

Forty crossbred barrows (average initial weight, 66.4 kg) were utilized to determine the effects of ractopamine (a phenethanolamine/beta adrenergic agonist) on protein accretion and synthesis, activities of cathepsins B, H, L and calcium-dependent proteinase and nucleic acid content of semitendinosus muscle (ST). All pigs were offered a 16% protein, mineral and vitamin fortified corn-soybean meal diet supplemented with either 0 or 20 ppm ractopamine for 14, 21, 28, 35 or 42 d. Protein synthesis (fractional rates) was studied in pigs at d 21 and 35; ST protease activities, protein and nucleic acid content were measured on d 14, 28 and 42. Ractopamine increased (P less than .01) ST total protein content and maintained RNA muscle concentration and total ST muscle RNA content. DNA content (mg/g ST) declined (P less than .05) upon ractopamine feeding, but total DNA per muscle remained unchanged except for d 42, when the ST muscles were largest. Fractional accretion rates (FAR) were 1.0 and 1.2% for control and ractopamine-fed pigs, respectively. Fractional protein synthesis rate (FSR) was higher (P less than .06) in ractopamine-fed pigs (6.1%/d) than in control pigs (4.4%/d). Fractional protein synthesis rate could account for the observed muscle hypertrophy and increased FAR. Estimated fractional breakdown rates (FBR = FSR - FAR) were 3.4%/d and 4.9%/d for control and ractopamine-fed pigs, respectively. The activities of the catheptic proteases and calcium-dependent proteinase were not affected by the treatments.

Adrenergic beta-Agonists↗

PubMed1988

Leucine degradation in sheep.

1. In vitro leucine catabolism in adipose tissue, skeletal muscle, kidney and liver homogenates was studied in sheep. 2. In Expt 1, Suffolk X Targhee ram lambs were slaughtered at 1, 28, 56, 84, 112, 140, 168, 196, 224 and 365 d of age. In Expt 2, 5-month-old crossbred wethers were fed on 80, 120 or 180 g crude protein (nitrogen X 6.25)/kg diets for 4 weeks or fed on 120 g crude protein/kg for 4 weeks and then fasted for 48 or 96 h before slaughter. Leucine catabolism was assayed in tissue homogenates for Expts 1 and 2. 3. Leucine deamination (per unit protein) was highest in skeletal muscle at day 1 and then declined; liver exhibited an activity pattern akin to muscle while kidney activity tended to rise over the duration of the study. Adipose tissue in vitro leucine deamination was higher at all ages studied and 9- to 50-fold higher than all other tissues at 365 d. Leucine decarboxylation (per unit protein) was highest at day 1 in muscle and declined to low levels (P less than 0.01) after 28 d; liver and kidney decarboxylation activities were higher than muscle at all ages with kidney showing the highest activity. Whilst adipose had high initial activity it declined significantly (P less than 0.01) by day 28 and remained low. 4. Dietary protein intake had no effect on leucine deamination in any tissue. Leucine decarboxylation tended to increase with protein intake for all tissues except kidney.(ABSTRACT TRUNCATED AT 250 WORDS)

Adipose Tissue↗

PubMed1988

The relationship between composition of gain and circulating hormones in growing beef bulls fed three dietary crude protein levels.

Twenty-one Simmental crossbred bulls (311 +/- 11 kg, 9 mo of age) were used to determine the effect of feeding 10, 12 or 14% CP on concentration of hormones in blood and the relationship of these hormones to composition of gain. Six bulls were slaughtered on d 0 to provide an estimate of initial carcass composition (9-11 rib section). Remaining bulls were assigned to dietary treatments. Blood samples were collected every 30 min from 0800 to 2000 on d 0, 66, 136 and 202 of treatment; bulls were slaughtered on d 203. Across all treatments, growth hormone (GH) declined (P less than .05) from d 0 to d 202. Free insulin-like growth factor I (IGF-I) was lowest (P less than .05) on d 0. In four randomly selected bulls, IGF-I fluctuated during the 12-h sampling periods. Within each treatment group, insulin was greatest on d 202 (P less than .05). Testosterone (T) increased from d 0 to d 66, then declined. Cortisol (C) was lowest on d 66. Thyroid hormones increased (P less than .05) after d 0. Growth hormone and IGF-I were correlated negatively with carcass fat percentage, fat accretion rate and fat thickness. IGF-I concentrations were correlated positively with percentage of carcass protein. Testosterone:cortisol ratio was not related to composition, but high T coupled with low C may be related to carcass leanness (mean carcass fat = 24.4%). These data suggest that GH and IGF-I are the hormones most related to composition of gain in growing beef bulls.

Animals↗

PubMed1988

Measurement of protein turnover in skeletal muscle strips.

Isolated porcine and bovine muscle strips were incubated in Krebs Ringer bicarbonate buffer to determine in vitro protein synthesis (PS) and protein degradation (PD) rates to validate the in vitro system for use with livestock species. The addition of 5X plasma concentrations of amino acids to the medium stimulated PS 30%. Addition of 3.5 mM leucine to a leucine-deficient buffer supplemented with amino acids decreased PD 37% and stimulated PS 24%. The addition of .1 U/ml insulin reduced PD 28% and increased PS 30%. Protein degradation was elevated in longitudinally split rat soleus and extensor digitorum longus muscles compared to their contralateral intact muscles. Muscle strips must be removed within 15 min of exsanguination because PD rates become greatly elevated thereafter. ATP concentrations declined during incubation, but the addition of ATP or creatine had no effect on either PD or PS. Neither PD nor PS was affected by the addition of transferrin, fetuin, ascorbate, dexamethasone or indomethacin to the incubation medium. However, muscle strips were sensitive to the addition of triiodothyronine (T3), PD was increased up to 75% as T3 concentration was increased, and PS rates doubled compared to controls. Serum from mature barrows or gilts had no effect on protein turnover, but the addition of 10% and 15% serum from boars increased both PD and PS. With fasted pigs a continual decline in PS occurred over 5 d, whereas PD was elevated at 3 d and then declined to rates comparable to the fed state after 5 d. These data suggest that the in vitro system has application for assessing relative changes that occur in vivo following nutritional, physiological and endocrinological manipulation.

Animals↗

PubMed1988

The effects of dietary crude protein level on rate, efficiency and composition of gain of growing beef bulls.

Two experiments were conducted to evaluate the effects of dietary CP level on rate, efficiency and composition of gain of growing beef bulls. In Exp. 1, 59 bulls (333 +/- 15.8 kg) were used. Eleven bulls were slaughtered on d 0 to provide an estimate of initial carcass composition (9-10-11 rib section chemical analyses), and remaining bulls were assigned to treatment diets containing 10, 12 or 14% dietary CP. Bulls fed the 10% CP diet grew slower (P less than .05) than bulls fed the 12 or 14% CP diets, although dry matter intake and feed-to-gain ratio did not differ. Bulls fed the 12% CP diet had fatter carcasses (P less than .05) than bulls fed the 10 or 14% CP diets and had greater daily fat accretion than bulls fed the 10% CP diet. In Exp. 2, 60 bulls (318 +/- 9.0 kg) were used. Bulls were assigned to initial slaughter (n = 6) or to one of three dietary treatments, 10, 12 or 14% CP, and were slaughtered after feeding for 66, 136 or 202 d (n = 6 . treatment -1 . slaughter time -1). Bulls fed 10% CP diets had lower (P less than .05) rates of carcass protein accretion during d 0 to 136 and d 0 to 202. Carcass fat gain was similar among treatments over the entire experiment, although bulls fed the 14% CP diet gained more fat during d 0 to 136 than bulls fed the other treatments.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗

PubMed1988

Proliferation of skeletal muscle satellite cells after castration and administration of testosterone propionate.

Thirty-six neonatal pigs were randomly assigned to the following treatment groups: sham implanted gonadally intact males (B), sham-implanted castrated males (C), or castrated males implanted with testosterone propionate (C + TP). Four pigs from each group were sacrificed at 7, 14, or 21 days of age after a 6-hr continuous infusion of [3H]thymidine. Myofibers isolated from the triceps brachii were prepared for satellite cell enumeration by light microscope autoradiography. A developmental decline in labeled myofiber nuclei occurred in all groups, however, the greatest decline occurred in C (P less than 0.01). A treatment-by-age interaction was observed for percentage of labeled nuclei. Castration reduced total and labeled nuclei per millimeter myofiber (P less than 0.05), and C + TP had a higher percentage of labeled nuclei than C (2.8 vs 2.2%; P less than 0.05). Since triceps brachii muscles from 21 day B and C + TP were 120% (P less than 0.05) of C, the results indicate that postnatal growth of skeletal muscle is dependent on satellite cell mitotic activity and that testosterone enhances this activity in neonatal pigs.

Animals↗

PubMed1987

Applications of hormones in the metabolic regulation of growth and lactation in ruminants.

Exogenous natural and synthetic estrogenic and androgenic steroid hormones are used commercially to stimulate metabolic processes associated with increased rate and efficiency of body growth in ruminants. However, mechanisms of action of steroid hormone-induced effects on metabolism are relatively unknown. Application of peptide hormones to muscle growth, fat deposition, and lactation has lagged because of lack of sufficient quantities of the hormones. However, with recombinant DNA technology synthesis of large quantities of peptide hormones is now feasible. Most efforts have focused on growth hormone (GH), growth hormone-releasing factor (GRF), and prolactin (PRL) effects on lactation. For example, administration of GH or GRF stimulates yields of milk, milk fat, protein, and lactose as much as 41% in cattle. The mechanism of GH action probably involves somatomedin C acting at extramammary sites and (or) directly at the mammary cell. PRL is lactogenic but has no significant effect on established lactation in cattle. Daily exposure of cattle to 16 h light and 8 h of darkness stimulates milk yield and body growth and reduces fat accretion in the carcass, but the hormonal signals responsible for these photoperiod-induced responses are unknown. Photoperiod manipulations are relatively easy to apply to ruminants, but development of suitable delivery systems for animals will greatly enhance application of peptide hormones to further studies of metabolism as well as commercial livestock production systems.

Animals↗

PubMed1986

Effects of photoperiod on growth, carcass composition, prolactin, growth hormone and cortisol in prepubertal and postpubertal Holstein heifers.

Effects of photoperiod on growth, carcass composition and serum concentrations of prolactin, growth hormone and cortisol were determined in prepubertal and postpubertal Holstein heifers. Forty-two prepubertal (avg body wt 84 +/- 3.0 kg) and 42 postpubertal (avg body wt 303 +/- 7.1 kg) Holstein heifers were utilized. Ten prepubertal and 10 postpubertal heifers were slaughtered before treatment began to obtain initial carcass data. The remaining 32 prepubertal and 32 postpubertal heifers were paired by body weight and randomly assigned to short-day (8 h of light: 16 h of dark) or long-day (16 h of light: 8 h of dark) photoperiods. After exposure to treatments for an average of 139 d, 10 prepubertal and 10 postpubertal heifers from each photoperiod treatment were slaughtered. In prepubertal heifers, photoperiod did not affect (P greater than .10) average daily body weight gain, carcass weight, carcass composition, accretion of carcass fat and carcass protein, or serum concentrations of prolactin, growth hormone or cortisol. However, prepubertal heifers exposed to long-day photoperiods had reduced (P less than .01) urinary N tau-methylhistidine excretion compared with heifers given short-day photoperiods. Postpubertal heifers exposed to short-day photoperiods had greater average body weight daily gain than animals exposed to long-day photoperiods. Although there was no effect of photoperiod (P greater than .10) on carcass or fat depot weights, postpubertal heifers exposed to short days had greater (P = .06) percentages of fat and reduced (P = .07) percentages of protein in the soft tissue of the 9-10-11 rib sections. Fat accretion was greater (P less than .05) in carcasses of postpubertal heifers exposed to short days than heifers given long-day photoperiods, but there was no effect (P greater than .10) of photoperiod on protein accretion. Photoperiod did not affect serum concentrations of growth hormone and cortisol, but serum prolactin tended (P less than .10) to be greater in postpubertal heifers exposed to long days. Under the conditions of this experiment, we conclude that exposure to short-day photoperiods stimulated body weight gain and fat accretion in postpubertal but not prepubertal Holstein heifers.

Animals↗

PubMed1985

Skeletal muscle protein turnover in young male pigs.

A 6-h continuous infusion of L-[U-14C]tyrosine was used to estimate fractional protein synthesis rates (FSR) in the longissimus dorsi (LD), semitendinosus (ST) and brachialis (BR) muscles of intact male pigs weighing 22 or 45 kg. The FSR was approximately 20% lower for pigs at 45 kg (4.2 vs. 5.2%/d, 5.2 vs. 6.4%/d and 5.1 vs. 6.4%/d for the LD, ST and BR muscles, respectively) compared with pigs at 22 kg. Fractional protein accretion or growth rates (FGR) were estimated over a 2-wk period. At 22 kg, FGR for the LD, ST and BR were 0.7, 2.4 and 1.7%/d, respectively; at 45 kg, FGR for these muscles were 1.7, 1.9 and 0.7%/d. Fractional protein breakdown rates (FBR) derived by difference (FBR = FSR - FGR) were 44, 16 and 8% lower for the LD, ST and BR muscles, respectively, at 45 kg compared with those at 22 kg. Therefore, it is suggested that muscle growth rate is modulated by alterations in FBR. By using the fractional rates found in these muscles to determine total-muscle protein synthesized or degraded in pigs at 22 and 45 kg, the proportion of protein retained was approximately 28% of that synthesized by the pigs at each weight. Since individual skeletal muscles of the pigs differed in protein turnover rates during postnatal growth and development, selection of a muscle(s) for turnover rates in growth studies is critical.

Animals↗

PubMed1985

Muscle growth and satellite cell proliferative activity in obese (OB/OB) mice.

Muscle growth of male obese (ob/ob) and lean mice at 2, 3, 5 and 8 wk were analyzed on the basis of weights of gastrocnemius, plantaris and soleus muscles from each hind leg. The carcasses (prepared by removing skin, viscera, head, feet and tail) were analyzed for fat content so that the effect of phenotype on the relationship between muscle weight and fat-free carcass weight could be assessed. For each age group the obese mice had less muscle relative to fat-free carcass weight than lean mice, with the difference being significant at 3 wk (P less than .05) and 8 wk (P less than .025). The proliferative activity of muscle satellite cells in 2- and 3-wk-old obese and lean mice was measured on isolated muscle fibers by autoradiography. Muscle fiber diameter and number of nuclei/unit length were unaffected by phenotype, but the proportion of muscle nuclei showing proliferative activity was lower (P less than .01) in obese than in lean mice at 2 wk (1.05 vs 1.93%, respectively) and 3 wk of age (.23 vs .59%, respectively). These results are consistent with the suggestion that muscle growth is limited by satellite-cell proliferative activity, although direct evidence for a cause and effect relationship is not provided.

Adipose Tissue↗

PubMed1985

Developmental comparisons of boars and barrows: I. Growth rate, carcass and muscle characteristics.

The rate of gain, carcass measurements and three muscles were evaluated in 65 crossbred boars representing 13 litters that were allotted at 4 wk of age to slaughter weight and treatment groups as follows: 1) 105 kg, castrated; 2) 105 kg, intact; 3) 118 kg, intact; 4) 132 kg, intact and 5) 145 kg, intact. One barrow and four boars within a litter constituted a replicate and each replicate was penned separately. The growth rate of all boars to 105 kg constituted one group and was compared with the growth rate of barrows to 105 kg live body weight. Average daily gain from 4 wk until 105 kg did not differ significantly between boars and barrows. Growth rate of the boars continued at an increasing rate until they reached 87.3 kg live weight, while maximum daily gain of barrows occurred at 76.3 kg live weight or 11 kg less than that of boars. At 105 kg, boars had 31.3% less 10th rib backfat thickness and 2.9% greater carcass length than barrows, but longissimus muscle area did not differ. Barrows had greater backfat thickness at 105 kg than 145-kg boars. As live weight increased from 105 to 145 kg, carcass length, 10th rib backfat thickness and longissimus area of boars increased (P less than .01) linearly. Fat-free muscle weights of the brachialis (BR), semitendinosus (ST) and longissimus (L) did not differ between boars and barrows at 105 kg. Boars at 105 kg had 1.3 and 1.7% more moisture in the BR and ST, respectively, than barrows. Percentage protein, total intramuscular fat and fiber diameter in the BR, ST and L muscles did not differ between boars and barrows at 105 kg or with increasing live weight in boars. Total RNA increased linearly (P less than .05) in the BR and ST as boars increased in live weight from 105 to 145 kg.

Adipose Tissue↗

PubMed1985

Developmental comparisons of boars and barrows: II. Body composition and bone development.

Differences in total carcass bone, muscle and fat, and linear measurements of the tibia and radius were evaluated in barrows at 105 kg and boars at 105, 118, 132 and 145 kg live body weight. The carcasses of five replicates were physically separated into skin, bone and soft tissues, and the linear measurements of the tibia and radius were obtained on seven replicates. At live weight of 105 kg, boars did not differ significantly in fat-free muscle, but they had 33.2% less fat, 11% greater bone weight and 14% greater skin weight than barrows. At 145 kg, boars had total carcass fat weight comparable with 105-kg barrows. Fat-free muscle, bone and skin weight of boars increased at linear rates of .41, .083 and .104 kg/kg of body weight increase from 105 to 145 kg, respectively. At 105 kg, density and length of the tibia and radius did not differ between boars and barrows. The tibia of boars were heavier than those of barrows at 105 kg, resulting in a greater ratio of tibia weight to length (indirect measure of bone thickness). As boars increased in live weight from 105 to 145 kg, total weight and length of the tibia and radius increased linearly. The ratio of weight to length of the tibia and radius increased during this 40-kg weight gain, indicating that weight of both bones increased at a greater rate than length. These results indicate that boars and barrows have the same weight of total carcass fat when boars are 40 kg heavier than the barrows. The greater bone weight of boar carcasses compared with barrows is due to greater bone thickness.

Adipose Tissue↗

PubMed1984

Genetic obesity and the muscle satellite cell.

The nuclear content of skeletal muscles from lean and obese (ob/ob) male mice was investigated. Four lean and four ob/ob mice were examined at 2, 3, 5, 8, and 16 weeks of age. Differences in body weight between the two phenotypes were significant after 5 weeks of age. For all ages in the soleus and after 3 weeks of age in the gastrocnemius, muscle wet weight and length were less in ob/ob mice than in lean mice. Age did not influence the incidence of myonuclei in fiber cross sections for either muscle. Compared to lean mice the incidence of myonuclei per fiber cross section was significantly lower for ob/ob mice in the soleus muscle but not in the gastrocnemius muscle. The incidence of satellite cells in fiber cross sections and the percentage of nuclei within the basal lamina that were satellite cell nuclei decreased as age increased. Muscle fibers of ob/ob mice contained fewer myonuclei either because of shorter muscle length (gastrocnemius), or because of the combined effect of shorter muscle length and fewer myonuclei per unit length (soleus). The lower apparent number of myonuclei in the muscles of ob/ob mice was associated with a lower apparent number of satellite cells.

Age Factors↗