Responses to cimaterol in genetically obese and lean pigs

Twenty-four genetically obese and 24 lean barrows were allotted within genotype to either a 16% CP corn-soybean meal basal diet, the basal + .69 ppm cimaterol or the basal + 1.38 ppm cimaterol. Pigs had ad libitum access to their diets from 59.3 kg to 104.5 kg body weight. No genotype x cimaterol interactions were detected (P greater than .05). Neither genotype nor cimaterol supplementation had any effect (P greater than .05) on average daily weight gain or gain-to-feed ratio. Compared with lean pigs, obese pigs had higher fasting plasma urea nitrogen (BUN), a smaller gastrointestinal tract and a greater dressing percentage with a shorter and fatter carcass (P less than .05). Cimaterol produced a higher fasting plasma BUN, a greater dressing percentage with a leaner carcass and a higher shear force value for loin chops (P less than .05). Cimaterol also tended (P less than .10) to increase heart weight. However, no difference was observed in these measurements between pigs fed .69 or 1.38 ppm cimaterol. In lean pigs fed the basal or .69 ppm cimaterol diet, there was no difference (P greater than .05) in the 8 to 24 h postprandial whole-animal heat production. Cimaterol effectively decreased fat deposition and increased lean accretion both in genetically obese and in lean pigs; there were no differential responses to cimaterol in pigs with different propensities to deposit body fat.     

Sera from pigs infected with Sarcocystis suicanis and cachectin decrease preadipocyte differentiation in primary cell culture

The macrophage-secreted hormone cachectin depressed lipoprotein lipase activity and lipogenic enzymes in adipose cells. Cachectin reduced differentiation of preadipocytes in cultures of stromal-vascular cells from rat adipose tissue. Differentiation was measured by two methods of estimating lipid accumulation. Adipocytes were separated from the stromal-vascular cells by centrifugation and staining (oil red 0) for intracellular lipid. Lipolytic activity was measured by using esterase histochemistry. Sera from pigs that were infected with Sarcocystis suicanis showed cachectin-like activity compared with sera collected from the same animals before infection. Cachectin and sera collected from infected animals specifically decreased fat cell number without decreasing the stromal-vascular cell number.     

Effects of ractopamine on genetically obese and lean pigs

Twenty-eight genetically obese and 24 lean barrows (65.0 and 68.7 kg average BW, respectively) were allotted within genotype to a 16% CP corn-soybean meal basal diet or this basal diet + 20 ppm ractopamine (a phenethanolamine beta-adrenergic agonist) and allowed ad libitum access to feed for 48 d. Compared to lean pigs, obese pigs had lower ADG, gain to feed ratio, longissimus muscle area, predicted amount of muscle, and weights of trimmed loin and ham, ham lean, heart, spleen, kidney and gastrointestinal tract (P less than .05). Obese pigs also had shorter carcass but higher dressing percentage, backfat thickness, fat depth, fat area, untrimmed loin weight and fasting plasma urea N concentration (P less than .05). Dietary supplementation with 20 ppm ractopamine reduced daily feed intake and improved gain to feed ratio in both lean and obese pigs (P less than .05). Pigs fed ractopamine had shorter carcasses, less fat depth and fat area, smaller weights of stomach and colon plus rectum, but higher dressing percentages, longissimus muscle areas, weights of trimmed Boston butts, picnics and loins, ham lean and predicted amounts of muscle than pigs not fed ractopamine (P less than .05). Supplemental ractopamine had no effect on fasting plasma concentrations of urea N, nonesterified fatty acids, triglyceride or glucose (P greater than .05). No genotype x ractopamine interactions for the criteria described above were detected (P greater than .05). These results suggest that ractopamine will improve the efficiency of feed utilization and carcass leanness in swine with different propensities for body fat deposition.     

Cellular and enzyme-histochemical aspects of adipose tissue development in obese (Ossabaw) and lean (crossbred) pig fetuses: an ontogeny study

The cellular and enzyme-histochemical differentiation of subcutaneous adipose tissue was studied in lean and obese pig fetuses at several ages. Positive reactions for a variety of cytosolic and organellar enzyme markers indicate metabolic competence of fetal adipocytes despite their small size (12 to 15 microns). Reactions for several enzymes decreased with fetal age and may be associated with a qualitative change in activity of adipocyte organelles. Age-associated increases in two lipogenic enzymes were observed in obese adipocytes. Observations on developing cells around hair follicles in the younger fetuses indicated significant temporal lags between the appearance of detectable enzyme activities in adipocytes. Enzyme activities in order of appearance were: dehydrogenases (cytosolic and mitochondrial), lipoprotein lipase and esterase. Esterase activity and several other enzymes were never observed in lipid positive cells that were not spherical. A proportion of hair follicle associated adipocytes in 110-d-old lean fetuses were histochemically and morphologically similar to brown adipocytes in the young rat. There was no evidence for brown adipocyte like cells in obese fetuses. Finally, comparison of the enzyme-histochemical differentiation of lean and obese fetal adipocytes indicates that fetal adipocytes become sensitive to external stimuli between 70 and 90 d of gestation.     

Responsiveness to adipogenic agents in stromal-vascular cultures derived from lean and preobese pig fetuses: an ontogeny study.

Primary cultures of stromal-vascular (S-V) cells from adipose tissue were used to evaluate characteristics of preadipocytes from lean and preobese fetuses at several ages (50, 75, and 110 d). In insulin-supplemented (1 microM) cultures (serum free) there was a significant age x fetal genotype interaction (P less than .01) for glycerol-phosphate dehydrogenase specific activity (GPDH); GPDH activity was genotype-dependent at 110 d (preobese greater than lean). The responses of S-V cultures (preadipocyte development) to 2% pig serum and to insulin (serum free) were similar. Main effects of genotype and age were significant (P less than .05) for protein levels in pig serum and insulin-treated cultures. There was a significant genotype x age (P less than .05) interaction for GPDH activity and protein levels in cultures treated with dexamethasone + 3-isobutyl-1-methylxanthine (DEX-IBMX). Treatment with DEX-IBMX induced more preadipocyte development in cultures from preobese fetuses than in cultures from lean fetuses at 110 d (P less than .05). The responsiveness of S-V cultures to DEX-IBMX (enhanced development) increased considerably between 50 and 75 d regardless of fetal genotype, but there was little response in cultures form 50-d fetuses. Preadipocyte development in lean and preobese fetuses diverged between 75 and 110 d, resulting in many more preadipocytes in preobese fetuses at 110 d. Therefore, S-V cells from preobese fetuses (late term) may be inherently more sensitive to adipogenic agents than S-V cells from lean fetuses.     

Lipid mobilization by obese and lean pigs infused with the beta-adrenergic agonist isoproterenol

Generally obese and lean pigs in both the fed and fasted states were anesthetized and then acutely infused with increasing concentrations of the beta-adrenergic agonist isoproterenol. Plasma free fatty acid (FFA), blood glycerol, glucose and lactate, and heart rate were monitored during the infusion period. Data were reduced by estimating the parameters of the generalized logistic function (minimum, maximum, ED50 and slope) and subsequently analyzed to compare the lean and obese genotypes within nutritional state. Lactate data could not be fitted to this function because the upper asymptote was not approached during the experiment. The minimum plasma concentration of FFA tended (P less than .1) to be less in obese than in lean pigs. The maximum, ED50 and slope for the responses of FFA were similar for obese and lean pigs in fed pigs and in fasted pigs. In fed pigs, the minimum glycerol concentration was greater in obese than in lean pigs, and the ED50 for heart rate tended to be lower in lean than in obese pigs. All other estimated parameters for the variables were similar in fed obese and lean pigs. In fasted pigs, the maximum glucose concentration was greater in obese than in lean pigs. All other parameters for the variables were similar in fasted obese and lean pigs. The results suggest that there was no major defect in lipid mobilization in these obese pigs (only a lower minimum FFA concentration was detected) and that an increased maximum blood glucose concentration in the fasting state might contribute to the obesity.     

Carcass, muscle and meat characteristics of lean and obese pigs

Six pigs obtained from a lean selected strain and six pigs obtained from an obese selected strain were slaughtered at about 110 kg live-animal weight. Carcasses were evaluated; hams were dissected into bone, skin, fat and lean, and loin samples were obtained for fiber type characteristics, percentage of fat and moisture, collagen analysis, sensory characteristics, textural properties and objective color analysis. Carcasses from lean pigs were longer, had less backfat and larger longissimus muscle cross-sectional areas than carcasses obtained from obese pigs. Hams from lean pigs had less fat, more bone and more lean than hams from carcasses of obese pigs. The percentages and cross-sectional areas of red and white muscle fibers of the longissimus muscle from lean and obese pigs were not different. However, lean pigs had intermediate fibers that were only 79% as large (P less than .10) as intermediate muscle fibers from obese pigs. Intermediate fibers represented only 7 and 10% of total fiber area, whereas white fibers represented 84 and 79% of total fiber area in longissimus muscle of lean and obese pigs, respectively. Overall, lean pigs tended to possess fewer fibers (-16%) per unit of area than obese pigs, indicating that total muscle fiber hypertrophy was partially responsible for the increased longissimus muscle area of the lean strain. Sensory properties of longissimus meat samples from lean and obese strains were not different. However, the shear force requirement of the longissimus samples from the lean strain were slightly, but significantly (P less than .10), higher than those from the obese strain. No differences were observed in meat color.     

Fetal hypophysectomy causes a decrease in preadipocyte growth and insulin like growth factor-1 in pigs

Fetal pigs in one uterine horn of each of five gilts were hypophysectomized (HX) in utero by electrical cauterization at 72-74 days of gestation and sera collected at 110 days of gestation. Sera from HX fetuses had lower levels of insulin-like growth factor-1 compared to control littermates (P less than .05). Sera were tested for their effects on primary cultures of stromal-vascular cells from adipose tissue. The soluble protein concentration/dish was lower when pig cells were cultured in sera from HX fetuses compared to sera from control fetuses (P less than .01). Sera from HX fetuses inadequately supported growth of stromal-vascular cells so subsequent experiments utilized pooled sera from normal and HX adult pigs. Sera from HX and control fetuses were mixed with sera from the two adult pools and tested for incorporation of tritiated thymidine into rat preadipocytes and the appearance of adipocytes (determined histochemically) in pig stromal-vascular cultures. In cultures fed sera from HX fetuses there was a lower (P less than .05) number of pig fat cells/culture and a lower level (P less than .06) of preadipocyte proliferation in rat cell cultures when compared to control fetal sera. Fetal pig serum contains factors (adipogenic) which promote the proliferation and differentiation of adipocytes in culture. Serum from HX fetuses has a lower level of adipogenic factors.     

Plasma thyroid hormones, growth and carcass measurements of genetically obese and lean pigs as influenced by thyroprotein supplementation

A 2 X 2 factorial arrangement with two genotypes of pigs (genetically obese and lean) and two dietary treatments (basal, a 16% protein corn-soybean meal standard grower diet, and basal +220 ppm thyroprotein as iodinated casein) was used. The 28 gilts were housed individually and fed ad libitum from 121 d of age until slaughtered at 99 kg body weight. Compared with lean pigs, genetically obese pigs had significantly lower average daily gain and gain/feed, greater backfat thickness, smaller loin eye area, shorter carcass length and lower circulating plasma triiodothyronine (T3) concentration. However, both total plasma and free thyroxine (T4) concentrations were similar comparing obese and lean pigs. Supplementation with thyroprotein increased circulating plasma concentration of both total and free T4 and produced interactions with genotype in affecting daily gain and gain/feed of pigs. Thyroprotein reduced both daily gain and gain/feed in obese pigs, but increased daily gain and gain/feed in lean pigs. It is suggested, similar to the case with obese mice, that heat production of our genetically obese pigs may be more sensitive to thyroprotein administration compared with similar treatment of lean animals.     

Evaluation of strategies for selection for lean growth rate in pigs

Lean growth rate (LGR) in pigs is a nonlinear biological function of growth rate and lean quantity. According to animal breeding theory, genetic progress for LGR is maximized with selection on a linear index of its component traits, but selection on direct EBV for LGR is also common. In this study, the performance of five criteria for selection on estimated LGR in pigs was evaluated through simulation over five generations: linear indexes of multiple-trait EBV of component traits with or without updating index weights in each generation; a nonlinear index of multiple-trait EBV of component traits; and direct selection on EBV for LGR from a single-trait model or a multiple-trait model that included LGR and component traits. The nonlinear index yielded the highest response in LGR in Generation 5, but the linear index with updating performed almost as well. Not updating weights for the linear index reduced response in LGR by 1.1% in Generation 5 (P < 0.05). Direct selection on single-trait EBV for LGR yielded the lowest responses in Generation 5. Direct selection on EBV for LGR from a multiple-trait animal model yielded a 3.1% greater response in LGR in Generation 5 than direct selection on EBV for LGR based on a single-trait animal model (P < 0.05), but yielded a 1.9% lower response than the nonlinear index. Although differences in response in LGR were limited, alternative selection criteria resulted in substantially different responses in component traits. Linear index selection for LGR placed more emphasis on lean quantity, whereas direct selection for LGR emphasized growth rate. Based on the relative changes in the responses in LGR, selection for estimated LGR based on a nonlinear index or a linear index with updating is recommended for use in the swine industry.     

Selection for lean growth efficiency in Duroc pigs influences pork quality

A unique line of Duroc pigs was established by intensive selection for increased lean growth efficiency. The objective of this study was to determine the influence of this selection strategy on fresh pork quality traits. Two lines of Duroc pigs originating from the same foundation herd were evaluated. One line was selected for lean growth efficiency over five generations (Select line), and the other was a contemporary line maintained from the foundation herd (Control line). All pigs in the trial tested negative for the halothane gene. Selection for lean growth efficiency resulted in improved lean gain, carcass lean, increased loin eye area, and less overall carcass fat. The Select line had significantly lower subjective firmness scores in longissimus and significantly greater amounts of moisture and protein lost as measurable drip in longissimus, semimembranosus, and semitendinosus. There were no differences in subjective color scores or in Hunter L, a, and b values between lines. No selection line differences were observed in glycolytic potential or ultimate pH. The longissimus and the semitendinosus exhibited significantly lower early postmortem pH values in Select line pigs. Warner-Bratzler shear values were higher for Select line longissimus chops. Degradation of troponin-T was decreased in the Select line longissimus samples. This result suggests that reduced degradation of myofibrillar proteins may be associated with increased moisture and protein lost during storage. This research points out that elimination of the halothane gene will solve some but not all of the genetically influenced pork quality problems faced by the industry. The Select line of pigs appears to be more prone to producing pork that is soft and exudative, indicating a link between soft and exudative pork and some genetic selection strategies may exist. Therefore, it appears that selection for some economically important traits, such as feed efficiency or increased lean growth in the absence of the halothane gene, may compromise pork quality.     

Dietary B vitamin needs of strains of pigs with high and moderate lean growth

Ten sets of 5 littermate pigs from each of 2 genetic strains were utilized to determine the impact of the dietary concentration of 5 B vitamins (riboflavin, niacin, pantothenic acid, cobalamin, and folacin) on growth from 9 to 28 kg of BW in pigs with high or moderate capacity for lean growth. All pigs (penned individually) were reared via a segregated, early weaning scheme, so that the lean growth potential of each strain could be expressed. The basal diet provided the 5 test vitamins at concentrations of total and estimated bioavailability equivalent to a minimum of 100 and 70%, respectively, of their estimated requirements (NRC, 1998) for 5- to 10-kg pigs. At a BW of 9 +/- 0.9 kg, pigs within each litter were allotted to the basal diet supplemented with sources of the 5 test vitamins equivalent to an additional 0, 100, 200, 300, or 400% (bioavailable) of the NRC requirements. Pigs from the high lean strain consumed less feed (P < 0.05) and gained BW faster (P < 0.02) and more efficiently (P < 0.01) than pigs of the moderate lean strain. In both lean strains, the rate and efficiency of growth were improved (P < 0.01) as dietary B vitamin concentrations were increased. However, the dietary B vitamin concentrations needed to optimize G:F were greater (P < 0.03) in the high (>470% of NRC, 1998) vs. moderate (270%) lean strain. Based on these data, the dietary needs for 1 or more of the 5 B vitamins are greater than current NRC (1998) estimates, particularly in pigs expressing a high rate of lean tissue growth. The greater need for these vitamins is not associated with greater dietary energy intake or body energy accretion rate but is potentially due to shifts in the predominant metabolic pathways.     

快速和中等生长速度猪种的日粮维生素B需求

本研究利用来自2个猪品系的10组（每组5头同窝仔猪）试验猪,测定5种B族维生素（核黄素、烟酸、泛酸、维生素B12和叶酸）的日粮水平对体重9～28kg的高和中等瘦肉系仔猪生长的影响。所有试验仔猪均采用单只圈养,并进行早期隔离断奶,以便能够使其发挥出瘦肉生长潜力。基因日粮所提供的5种测试维生素生物的总体和估测生物可利用率分别相当于体重5～10kg仔猪的NRC（1998）估测需求量的100%和70%。当体重为9±0.9kg时,给每窝内的各头仔猪分别喂给添加了生物可利用率相当于NRC（1998）需求量的0%、100%、200%、300%或400%的5种测试维生素的基础日粮。结果表明,与中等瘦肉系猪相比,高瘦肉系猪消耗的饲料少（P〈0.05）、体重增长快（P〈0.02）和饲料利用率高（P〈0.01）。当日粮B族维生素添加水平提高时,两个瘦肉品系的试验猪生长速度和生长效率均得到提高（P〈0.01）。然而,高瘦肉系试验猪获得最佳增重/耗料比所需的日粮B族维生素水平（为NRC需求量的470%以上）显著高于中等瘦肉率试验猪（270%）（P〈0.03）。根据这些研究结果,表明现代猪种对5种B族维生素中的1种或多种维生素的需求量要高于目前NRC（1998）的估测值,尤其是高瘦肉系的猪种。对这些维生素较高的需求与较高的日粮能量摄入量或较高的机体能量沉积量无关,但很可能是由于主要的代谢通路发生改变所致。     

Stearoyl-coenzyme A desaturase gene expression during growth in adipose tissue from obese and crossbred pigs.

This investigation addressed the hypothesis that, as a marker of adipocyte differentiation, stearoyl-coenzyme A desaturase (SCD) gene expression would be greater during growth in obese pigs than in crossbred, contemporary pigs. Suckled pigs from a single litter were removed from the sow for sampling at 0, 3, 10, and 17 d. The number of litters at 0, 3, 10, and 17 d of age was zero, two, three, and three (obese sows) and four, two, three, and three (crossbred sows), respectively. Postweaning pigs were removed from the sow at 14 d of age. One set of postweaning pigs was fed a high-fat, milk-based diet from d 28 to 49; pigs were killed on d 28 and 49 for sampling. The grain-fed pigs were switched to a pelleted, grain-based grower diet at d 28, and samples were obtained at 31, 35, or 49 d of age. Adipose tissue from all pigs in a litter for preweaning and postweaning pigs was pooled for the measurement of cellularity and SCD mRNA. There were significant genetic and age effects for adipocyte diameter and volume; overall, adipocytes from obese pigs were larger than those from crossbred pigs. Stearoyl-coenzyme A desaturase mRNA was barely detectable at 0 d of age and increased (P < .01) by 20-fold by 49 d of age. There was a significant genetic x age interaction (P = .026); there was more SCD mRNA in adipose tissue from obese pigs than in that from crossbred pigs during the suckling period, whereas crossbred pigs exhibited greater SCD gene expression than obese pigs during the postweaning period. The lesser SCD gene expression in postweaning obese pigs was caused by a strong depression in SCD gene expression in the grain-fed obese pigs. The data indicate that SCD gene expression provides a marker for terminal differentiation, especially in preweaning pigs. Furthermore, these results provide additional evidence that SCD gene expression is up-regulated by diets high in saturated fatty acids.     

Encephalomyocarditis virus antibodies in sera from apparently normal pigs.

Antibodies which neutralise and precipitate encephalomyocarditis virus habe been found in the serum of more than 28 per cent of normal pigs in Britain. Neutralising activity was found in association with several size classes of antibody.     

Degree of amino acid restrictions during the grower phase and compensatory growth in pigs selected for lean growth efficiency

A total of 32 select line (SL) and 32 control line (CL) Duroc pigs were used in two trials to determine the effect of dietary amino acid contents during the grower (G) phase and selection for lean growth efficiency on growth performance, carcass traits, and meat quality. In each trial, pigs weighing 20 kg were assigned to 16 pens with two gilts or two castrated males per pen, and pens were randomly assigned within the genetic line to corn-soybean meal G diets formulated to contain 5.0, 7.0, 9.0, or 11.0 g lysine/kg. After 50 kg, all pigs were fed common finisher 1 (F1) and finisher 2 (F2) diets. Pigs were allowed ad libitum access to feed and water. After the initial statistical analyses, the data sets from the two trials were combined. During the G phase, pigs consumed less feed [linear (Ln), P < 0.001] and more lysine (Ln, P < 0.001), grew faster (Ln, P < 0.05) but utilized feed more and lysine less efficiently (Ln, P < 0.001) for weight gain as the amino acid content of G diets increased. Increasing dietary amino acids resulted in less ultrasound backfat (Ln, P < 0.001) and more serum urea nitrogen [Ln, P < 0.001; quadratic (Qd), P < 0.01] at the end of the G phase. Pigs grew more slowly during the F1 (Ln, P < 0.01 and Qd, P = 0.05) and F2 (Ln, P = 0.07) phases and utilized feed and lysine less efficiently (Ln, P < 0.05) for weight gain during the F1 phase as the amino acid content of G diets increased. The grower diet had no effect on overall weight gain and feed efficiency, carcass traits, or meat quality scores. The efficiency of lysine utilization for overall weight gain (Ln, P < 0.001) and lean accretion (Ln, P < 0.05) improved as the amino acid content of G diets decreased. The SL pigs grew faster (P < 0.05) and had less (P < 0.001) ultrasound backfat throughout the study compared with the CL pigs. The SL pigs had less 10th rib backfat (P < 0.001) and tended to have larger longissimus muscle area (P = 0.09) than the CL pigs, which were reflected in greater rate (P < 0.001) and efficiency (P < 0.05) of lean accretion. Marbling (P < 0.05) and meat color (P = 0.07) scores were lower in the SL pigs. No grower diet x genotype interactions were observed in response criteria of interest. The results indicate that pigs subjected to dietary amino acid restrictions during the G phase (as low as 5.0 g lysine/kg) compensated completely in terms of growth rate and body composition regardless of the genotype. Compensatory growth can have a positive impact not only on the overall efficiency of pig production but also on the environment by reducing excretion of unused nutrients.     

Administration of porcine somatotropin by sustained-release implant: growth and endocrine responses in genetically lean and obese barrows and gilts.

Previous studies have documented the effectiveness of porcine somatotropin (pST) administered by daily injection in promoting lean tissue growth in lean and obese pigs and the influence of sex and genotype. The present study examined the accretive responses in pigs of different lines and sexes to a slow release formulation of pST (pST-SR). Implants that deliver 2.0 mg of pST/d were implanted in genetically lean and obese barrows and gilts at 65 +/- .7 kg BW (mean +/- SE). Pigs received no, one, or two implants (i.e., doses of 0, 2.0, and 4.0 mg of pST/d). Pigs (four per line x sex x dose) were housed individually and continuously supplied with fresh water and a 19% CP diet containing 1.08% lysine. Pigs were slaughtered on d 0 (four per line x sex) and at the end of the trial (approximately 42 d after implantation) for estimation of initial composition and calculation of accretion rates. Blood samples were collected at d 0, 7, 14, 28, and 42 to measure endocrine and metabolite responses to pST-SR. Sustained-release pST elevated (P < .05) circulating pST throughout the trial with peak concentrations at d 7. On d 7, serum pST concentrations in the pigs given 2.0 mg of pST-SR per day were 16-fold greater than those in control pigs, and in pigs given 4.0 mg of pST-SR per day pST concentrations were 33-fold greater than in controls. Elevated serum pST resulted in increased (P < .05) serum concentrations of insulin-like growth factor (IGF)-I, IGF-II, insulin, and glucose and in reduced (P < .05) concentrations of urea nitrogen and IGF binding protein (IGFBP)-2. Gain was not influenced by pST-SR dose; however, feed consumption was reduced (P < .05) and efficiency of gain was increased (P < .05). Accretion of all body components except cold carcass weight, cecum, and untrimmed Boston butt and ham were changed (P < .05) with pST-SR administration. Heart and stomach were the only components of the carcass and offal whose accretion was not affected by line or sex. Increases in accretion of carcass components (< 75%) induced by sustained-release pST were considerably less than those measured in the organs (liver, 157%; lungs, 748%). The pST-SR treatment resulted in elevated serum concentrations of pST and its mediators and improved efficiency and composition of gain.(ABSTRACT TRUNCATED AT 400 WORDS)