Lean Genotype Research Articles

The interaction between ovulation rate and embryo survival in determining prolificacy of different strains of obese swine with gene polymorphisms for leptin receptors

The Mediterranean Iberian pigs show a clear predisposition to obesity, due to gene polymorphisms for leptin receptors, and a lower prolificacy when compared with lean breeds. Previous studies indicate a bimodal effect of obese genotypes on prolificacy; either by lowering ovulation rate or by increasing embryo losses when compared with lean genotypes. The present study aimed to discriminate the relative influence of both parameters by comparing strains of Iberian females with different prolificacy (14 original purebred Retinto, group R, and 20 Retinto × Torbiscal females selected for prolificacy, group RT). Examination of ovaries around Day 40 of pregnancy showed a higher ovulation rate in the RT than in the R sows (21.5 ± 1.4 versus 12.3 ± 1.0 corpora lutea, respectively; P < 0.0005). However, there was a higher incidence of implantation failures and early embryo losses in the RT females (42.9 versus 14% for the group R; P < 0.005). Thus, the number of viable embryos was higher in the RT line (10.8 ± 0.5 versus 7.6 ± 0.7 in the R sows, P < 0.0005), but also limited when compared with ovulation rate. Conversely, this effect was not found in the R sows; however, prolificacy of these females was limited by higher embryo mortality (24.1 versus 4.6% for RT females). In conclusion, the present study evidences dissimilar reproductive behaviour among strains of the Iberian pig differing in prolificacy and confirms previous evidences suggesting the existence of intrinsic factors avoiding excessively large litter sizes in Iberian females.

Prepuberal evolution of plasma leptin levels in gilts of thrifty genotype (Iberian pig) and lean commercial crosses (Large White × Landrace)

Current study aimed to determine possible differences in plasma leptin levels during the prepuberal period and their relationship with the onset of puberty in gilts of obese thrifty genotype (Iberian breed) and lean genotype (Large White×Landrace commercial crosses) reared under similar conditions. Plasma leptin concentration increased linearly during the 7weeks prior to the day of puberty attainment in both genotypes (P<0.005, r=0.707 for LW×L and P<0.0005, r=0.874 for Iberian gilts). However, leptin levels in the Iberian gilts was higher from the first sample of the experimental period, with females having 16weeks-old (2.7±0.3 vs 1.7±0.2ng/ml in LW×L; P<0.001), to the onset of puberty (8.5±0.7 vs 2.8±0.3ng/ml in LW×L; P<0.005). Thus, the current study reinforces previous data on changes in around puberty and evidences, for the first time, profound differences in prepuberal plasma leptin levels between gilts of obese (Iberian) and lean genotypes (LW×L).

Developmental competence of antral follicles and their oocytes after gonadotrophin treatment of sows with gene polymorphisms for leptin and melanocortin receptors (Iberian pig)

To evaluate possible differences in follicle and oocyte developmental competence after gonadotrophin treatment in sows of obese and lean genotypes. Follicle dynamics, ovulation rate and oocyte developmental competence to embryo were compared between females, of obese (n = 7) and lean genotypes (n = 10), treated with 1,250I.U. of eCG and 500I.U. of hCG. The obese genotype showed lower numbers of follicles growing to preovulatory stages (12.4 ± 1.8 vs 18.6 ± 1.0, P < 0.05), of corpora lutea (16.0 ± 0.9 vs 23.5 ± 0.9, P < 0.05), and of recovered oocytes/embryos (8.0 ± 1.3 vs 12.9 ± 0.9, P < 0.05). Thereafter, embryo viability rates also decreased when compared to lean genotypes (62.5 vs 77.6%, P < 0.05). To our knowledge, this is the first study analyzing the effect of obese genotypes on the ovarian response to exogenous gonadotrophins in a non-rodent animal model, the pig. A lower efficiency of gonadotrophin treatments for stimulation of follicle development and induction of ovulation was observed.

Dietary CLA supplementation and gender modify fatty acid composition of subcutaneous and intramuscular fat in Iberian × Duroc finishing heavy pigs

The objective of this research was to evaluate the effect of dietary conjugated linoleic acid (CLA) enrichment for finishing heavy fatty pigs on performance, carcass traits and fatty acid composition in subcutaneous and intramuscular fat (IMF), including CLA main isomers concentration. Forty castrated Iberian × Duroc pigs, half males and half females, with 120 (±2.83) kg live weight were used. Pigs were fed experimental diets containing two levels (0 and 1%) of CLA. No effect of CLA was observed on backfat thickness or IMF concentration. In subcutaneous backfat, dietary CLA increased the C16:0, C18:0, c9,t11-CLA , t10,c12-CLA and saturated fatty acids (SFA) proportion and decreased those C18:1 n-9, C18:2 n-6, monounsaturated fatty acids (MUFA), polyunsaturated fatty acids (PUFA) proportions and MUFA/SFA and C18:1 n-9/C18:0 and C16:1 n-7/C16:0 ratios. In the IMF, dietary CLA increased C16:0, SFA, c9,t11 and t10,c12 proportions and reduced C18:1 n-9 and MUFA, MUFA/SFA and C18:1 n-9/C18:0 ratios, but showed no effect on C18:2 n-6 and PUFA proportion. Subcutaneous backfat fatty acid profile was affected by gender, but no gender effect on intramuscular fatty acid profile was observed. CLA isomer accumulation was lower in heavy pigs compared to the lean genotype probably as a consequence of the higher carcass fat concentration in the former.

The Effects Of Chronic Exercise On Regulatory Mitochondrial Key Proteins And Gene Expression In Insulin Resistant Obese Rat Skeletal Muscles

PURPOSE: Recent emerging evidences suggested that regulatory key transcriptional factors, including myocyte enhancer factor 2C (MEF2C), peroxisome proliferator-activated receptor d(PPARd), and peroxisome proliferator-activated receptorγ coactivator 1a (PGC-1a), are involved in gene expression of glucose transporter 4 protein(GLUT4) and uncoupling protein 3(UCP3), and these factors exert their unique functions in molecular and genetic cascades. METHODS: Present study investigated regulatory effects of exercise training on expression of GLUT4, UCP3, MEF2C, PPARd, and PGC-1a in skeletal muscles (soleus, extensor digitorum logus (EDL)) of obese Zucker rats. After 8 weeks of experiment procedure, oral glucose tolerance test, blood analysis, enzyme activity, analyses of protein and mRNA were performed. RESULTS: Treadmill running exercise significantly improved the insulin sensitivity and increased in citrate synthase activity in soleus of obese Zucker rat. However, both exercise training and genotypically-induced obese condition did not alter the basal levels of gene expression in GLUT4, UCP3, MEF2C, PPARd, and PGC-1a in both muscle fibers. Unlike with gene expressions, protein expressions of these factors were selectively up-regulated or down-regulated by regular exercise training or by obese genotype. The protein expression of PPARd and PGC-1a was significantly higher in both muscles, but GLUT4 and MEF2C protein expression was only higher in soleus of obese genotype compared to lean genotype. Interestingly, UCP3 protein expression was significantly decreased in soleus muscle (but not in EDL). CONCLUSIONS: These findings indicate that adaptation of skeletal muscles to exercise training was occurred by enhancement of not only glucose metabolism (GLUT4 and MEF2C protein expression) but also fatty acid oxidation (PPARd and PGC-1a protein expression). The downregulation of UCP3 protein expression may be associated with decrease of thermogenesis and fatty acid oxidation.

Glucocorticoids and cyclic AMP selectively increase hepatic lipin-1 expression, and insulin acts antagonistically

Glucocorticoids (GCs) increase hepatic phosphatidate phosphatase (PAP1) activity. This is important in enhancing the liver's capacity for storing fatty acids as triacylglycerols (TAGs) that can be used subsequently for beta-oxidation or VLDL secretion. PAP1 catalyzes the conversion of phosphatidate to diacylglycerol, a key substrate for TAG and phospholipid biosynthesis. PAP1 enzymes in liver include lipin-1A and -1B (alternatively spliced isoforms) and two distinct gene products, lipin-2 and lipin-3. We determined the mechanisms by which the composite PAP1 activity is regulated using rat and mouse hepatocytes. Levels of lipin-1A and -1B mRNA were increased by dexamethasone (dex; a synthetic GC), and this resulted in increased lipin-1 synthesis, protein levels, and PAP1 activity. The stimulatory effect of dex on lipin-1 expression was enhanced by glucagon or cAMP and antagonized by insulin. Lipin-2 and lipin-3 mRNA were not increased by dex/cAMP, indicating that increased PAP1 activity is attributable specifically to enhanced lipin-1 expression. This work provides the first evidence for the differential regulation of lipin activities. Selective lipin-1 expression explains the GC and cAMP effects on increased hepatic PAP1 activity, which occurs in hepatic steatosis during starvation, diabetes, stress, and ethanol consumption.

Conjugated linoleic acid reduces hepatic steatosis, improves liver function, and favorably modifies lipid metabolism in obese insulin‐resistant rats

CLA has been shown to induce or suppress excess liver lipid accumulation in various animal models. Interestingly, the state of insulin resistance may be an important modulator of this effect. The objective of the current study was to determine how feeding a dietary CLA mixture would affect liver lipid accumulation in insulin-resistant/obese and lean rats in relation to liver function, lipidemia, liver TAG and phospholipid FA composition, and expression of hepatic markers of FA transport, oxidation, and synthesis. Six-week-old fa/fa and lean Zucker rats (n = 20/genotype) were fed either a 1.5% CLA mixture or a control diet for 8 wk. CLA supplementation reduced liver lipid concentration of fa/fa rats by 62% in concurrence with improved liver function (lower serum alanine aminotransferase and alkaline phosphatase) and favorable modification of the serum lipoprotein profile (reduced VLDL and LDL and elevated HDL) compared with controlfed fa/fa rats. The fa/fa genotype had two-thirds the amount of CLA (as % total FA) incorporated into liver TAG and phospholipids compared with the lean genotype. In both genotypes, CLA altered the hepatic FA profile (TAG greater than phospholipids) and these changes were explained by a desaturase enzyme index. Liver-FA-binding protein and acyl CoA oxidase, markers of FA transport and oxidation, respectively, were expressed at higher levels in CLA-fed fa/fa rats. In summary, these results illustrate a strong relationship between the state of insulin resistance and liver lipid metabolism and suggest that CLA acts to favorably modify lipid metabolism in fa/fa Zucker rats.

Consequences for body composition at farrowing and nutrient partitioning during lactation of a choice-feeding regime during rearing and pregnancy in gilts of different genotypes

The potential conflict between reproductive functions and the drive to deposit body protein may impair productive performance in modern gilts of lean genotype. To study the response of the gilt to this conflict, a choice-feeding experiment was carried out to measure the nutrient intake selected by breeding gilts and responses in reproductive and lactation performance. Using a 2 × 2 factorial design, gilts of two different genotypes (24 of NPD 402, expected higher body protein/lipid ratio (L) or 24 of Camborough 23, expected lower body protein/lipid ratio, (F)) were either choice-fed (C) by offering both a low (120 g crude protein (CP)/kg) and a high protein (218 g CP/kg) feed during rearing and pregnancy or fed conventionally (R) single feeds, ad libitum during rearing and restricted during pregnancy. Choice-fed gilts selected mainly the low protein feed (0.92 of total feed intake) regardless of genotype and had lower protein intakes than R gilts prior to puberty. However, in pregnancy, due to higher feed intakes, C gilts had higher dietary protein and energy intakes than R gilts. C gilts were heavier, and had greater back-fat and eye muscle depth at farrowing than R gilts, but had smaller litter sizes ( P < 0.01). During lactation, dietary treatments were reallocated so that gilts received either a low (LE, maintenance + 45 MJ/day) or a high (HE, maintenance + 67 MJ/day) digestible energy intake. Litter size was standardised within 2 days of farrowing. LE gilts had greater decreases in weight and back-fat and eye-muscle depth during lactation than HE gilts, but dietary lactation treatment had no effect on litter performance. The choice-feeding regime which resulted in heavier gilts with greater back-fat and eye-muscle depth at farrowing did not produce any advantage in terms of partitioning of nutrients towards milk production, as indicated by litter performance, irrespective of gilt genotype. F gilts had greater piglet growth rates than L gilts and also had a higher milk protein concentration. A greater number of L than F gilts failed to complete the experiment for health reasons. Treatment effects on glucose tolerance at day 13 of lactation were not significant. Choice-feeding was therefore not found to be suitable for determining nutrient requirements of modern lean-genotype gilts which would improve reproductive performance.

OPTIMISATION OF NUTRIENT USE TO MAXIMISE PROFITABILITY AND MINIMISE NITROGEN EXCRETION IN PIG MEAT PRODUCTION SYSTEMS

Reduction of environmental mineral pollution, while maintaining profitability, is one of the major challenges faced by the pig industry today. This paper describes a computer-based growth simulation study undertaken to demonstrate how economic profitability can be maintained whilst the environmental effects associated with nitrogen wastes are minimised. For this purpose, a computer program linking a linear program, a stochastic pig growth model and a genetic algorithm (GA) was developed. The objective function to be maximised by the GA is the weighted difference of gross margin and nitrogen excretion cost. Simulations were conducted to investigate how different pig genotypes (fat, normal, lean) and different relative economic weighting of gross margin (1) and nitrogen excretion (0, 1, 5, 10, 20, 40, 80 or 120) affect the nitrogen excretion and profitability under practical or GA optimised feeding strategies in Switzerland. In all the cases investigated, nitrogen excretion is reduced and profitability increased when the pigs are from a leaner genotype. Across all genotypes a 45% reduction in nitrogen excretion can be achieved with only a 3.5% drop in profitability when diets designed to maximize profitability and minimize nitrogen excretion are fed. The maximal nitrogen retentions observed were 44.9%, 52.6% and 57% for the fat, normal and lean genotypes respectively. It is concluded that a more sustainable pork meat production system can be achieved by using better genotypes and optimizing the diet composition.

Leptin receptor-deficient MMTV-TGF-alpha/Lepr(db)Lepr(db) female mice do not develop oncogene-induced mammary tumors.

Being overweight is a risk factor for postmenopausal breast cancer and is associated with an increased incidence and shortened latency of spontaneous and chemically induced mammary tumors in rodents. However, leptin-deficient obese Lep(ob)Lep(ob) female mice have reduced incidences of spontaneous and oncogene-induced mammary tumors. Of interest, leptin enhances the proliferation of human breast cancer cell lines in which leptin receptors are expressed, which suggests that leptin signaling plays a role in tumor development. We evaluated oncogene-induced mammary tumor development in obese MMTV-TGF-alpha/Lepr(db)Lepr(db) mice that exhibit a defect in OB-Rb, which is considered to be the major signaling isoform of the leptin receptor. Lepr and MMTV-TGF-alpha mice were crossed, and the offspring were genotyped for oncogene expression and the determination of Lepr status. Lean MMTV-TGF-alpha/Lepr(+)Lepr(+) (homozygous) and MMTV-TGF-alpha/Lepr(+)Lepr(db) (heterozygous) mice and obese MMTV-TGF-alpha/Lepr(db)Lepr(db) mice were monitored until age 104 weeks. Body weights of MMTV-TGF-alpha/ Lepr(db)Lepr(db) mice were significantly heavier than those of the lean groups. No mammary tumors were detected in MMTV-TGF-alpha/Lepr(db)Lepr(db) mice, whereas the incidence of mammary tumors in MMTV-TGF-alpha/Lepr(+)Lepr(+) and MMTV-TGF-alpha/ Lepr(+)Lepr(db) mice was 69% and 82%, respectively. Examination of mammary tissue whole mounts indicated an absence of duct formation and branching for MMTV-TGF-alpha/Lepr(db)Lepr(db) mice. Both age at mammary tumor detection and tumor burden (tumors/mouse and tumor weights) were similar for the lean genotypes. Serum leptin levels of MMTV-TGF-alpha/Lepr(db)Lepr(db) mice were 12-20-fold higher than levels of lean mice. Thus, despite elevated serum leptin levels, leptin receptor-deficient MMTV-TGF-alpha/Lepr(db)Lepr(db) mice do not develop mammary tumors. This study provides additional evidence that leptin and its cognate receptor may be involved in mammary tumorigenesis.

Hydrogenated dietary fat improves pork quality of pigs from two lean genotypes.

Pork quality is influenced by nutrition, genetics, management, and pork-processing procedures. Pigs of lean genotype fed diets high in unsaturated fat may have thinner, lower-quality bellies with a soft fat composition. Therefore, we investigated the effects of supplementing 5% choice white grease that had been chemically hydrogenated to iodine values of 80, 60, 40, or 20 on pork quality. Diets were fed to barrows and gilts of two genotypes (NPD [Ham-line x Manor hybrid] and PIC [406, 419, or 420 x C22]; n = 240) in a 4 x 2 x 2 factorial design. Pigs (76.8 kg of mean initial weight) were placed on test at a common age and were fed dietary treatments for 52 d. Pigs of PIC genotype were heavier at trial initiation, had higher feed intake and feed conversion ratio (F/G; P < 0.05), and greater backfat (26.3 vs. 24.0 mm; P < 0.001) and loin depth (59.0 vs. 55.3 mm; P < 0.001) compared with the NPD genotype pigs. As the iodine value of dietary fat was reduced, belly thickness increased (P < 0.05) and length decreased linearly (P < 0.05). Congruently, belly fat iodine value decreased from 73.9 to 67.4 (linear effect; P < 0.001) and belly fat C18:2 concentration declined from 20.6 to 16.3% (linear and quadratic effect; P < 0.001). The belly mono- and polyunsaturated fat ratio increased 29% as diet iodine value declined from 80 to 20 (linear and quadratic effect; P < 0.001). Further, there was a linear increase (P < 0.001) in saturated fatty acid concentration of belly fat (C14:0, C16:0, and C18:0) as dietary fat iodine value declined. Quadratic (P < 0.005) effects were detected in the level of C18:1trans as iodine value decreased from 80 to 20, paralleling dietary content. Dietary fat iodine value did not affect fat digestibility, ADFI, or F/G. Pork belly quality was improved as defined by reduced iodine value, C18:2 content, increased saturated fatty acid content, increased thickness, and decreased length as dietary iodine value decreased. Results indicate that reduction of dietary fat iodine value by chemical hydrogenation has the desirable effect of improving pork quality and does not alter growth performance.

Conjugated Linoleic Acid in Combination with Supplemental Dietary Fat Alters Pork Fat Quality

Interest in fortification of human foods, including pork, with conjugated linoleic acid (CLA) is growing and may provide benefits as a neutraceutical based on research evaluating CLA as an anticarcinogen, immune modulator, antiatherogenic agent and a body composition modulator. This study evaluated the combined effects of dietary CLA and supplemental fat source on growth, fatty acid composition and belly quality of lean genotype gilts (n = 144). Pigs (49.3 kg) were randomly assigned to six diets (3 x 2 factorial) varying in supplemental fat (none, 4 g/100 g yellow grease or 4 g/100 g tallow) and linoleic acid [1 g/100 g corn oil (CO) or 1 g/100 g CLA (CLA-60)] for 47 d. Both the cis-9, trans-11 and the trans-10, cis-12 isomers of CLA were increased in belly and longissimus fat depots from pigs fed CLA, and that increase was up to 92% greater when CLA was fed with 4 g/100 g supplemental fat (fat source x linoleic acid interaction, P < 0.05). Pigs fed CLA had a greater concentration of 18:0 and less 18:1 cis-9 (P < 0.01) in various fat depots, suggesting a reduction in Delta(9) desaturase activity. The iodine value of belly fat from pigs consuming tallow and CLA combined was reduced to 62.0 from an initial value of 70.4. CLA supplementation also increased belly weights (P < 0.05). CLA did not affect longissimus muscle area, backfat depth and the percentage of fat-free lean (P > 0.10), but it increased the subjective intramuscular fat score by 18.8% (P < 0.01). In conclusion, CLA enrichment of pork products may be enhanced when combined with additional supplemental dietary fat, and together with tallow can be used to increase the saturated fatty acid content of pork.

Effect of dietary methionine to lysine ratio on lactation performance of first and second parity Yorkshire and Hampshire lean genotype sows

A total of 196 Yorkshire (Y) sows, 137 of first and 59 of second parity, and 97 Hampshire (H) sows, 55 of first and 42 of second parity, were used to determine the effect of increased dietary amino acids and two methionine-to-lysine ratios on sow lactation performance. The three treatment diets were: (1) a barley-wheat-soybean meal diet containing lysine at 0.43 g MJ-1 DE with no supplemental amino acids, 2) the same as diet 1, except the lysine content was increased to 0.68 g MJ-1 DE with supplemental threonine and methionine providing threonine and methionine to lysine ratios of 0.60 and 0.26, respectively, and 3) the same as diet 2, except with an increased methionine-to-lysine ratio of 0.30. All diets were fed as pellets, ad libitum in self-feeders, with free access to drinking water during a 28-d lactation period. Nursing piglets were given creep feed after 14 d of age. The average daily feed intake increased during lactation, and it was higher (P &lt; 0.05) in the second than the first parity sows. Feeding diets 2 and 3 increased (P &lt; 0.05) sow lactation weight and backfat gains, compared to diet 1 for both breeds. Feeding diet 3 increased (P &lt; 0.05) the sow lactation weight and backfat gains and piglet weight gains in the second parity Y sows, but not H sows. Post-weaning sow weight loss and weaning to estrus interval were not different (P &gt; 0.10) among the diets in both breeds. Feeding diets 2 and 3 decreased (P &lt; 0.05) the serum urea nitrogen concentration in Y sows indicating less amino acid catabolism. The results indicated that a dietary methionine-to-lysine ratio higher than 0.27 was not beneficial in maximizing lactation performance of modern lean genotype sows. Key words: Sows, lactation, ideal amino acid, Yorkshire, Hampshire, piglet

Effect of supplemental phytase and ideal dietary amino acid ratios in covered and hulless-barley-based diets on pig performance and excretion of phosphorus and nitrogen in manure

A total of 144 (72 barrows + 72 gilts) crossbred pigs were used to determine the effect of feeding supplemental phytase and ideal dietary amino acid ratios in covered barley (CB) or hulless barley (HB)-based diets on growth performance, carcass quality, and excretion of phosphorus and nitrogen in manure during the grower and finisher periods. The three experimental grower and finisher diets were: 1) control diet (CB or HB) with Ca:P ratios according to National Research Counci l (NAS–NRC 1988), 2) the same as diet 1 but without added inorganic P, but supplemented with phytase (Novo Nordisk, Denmark) at 500 FTU kg–1, 3) the same as diet 2 with reduced dietary protein level, and supplemental amino acids lysine, threonine, and methionine to provide ideal dietary amino acid ratios of 0.70 for threonine to lysine and 0.30 for methionine to lysine. All diets were fed as pellets ad libitum in self-feeders with free access to drinking water. The ADG was not different (P &gt; 0.10) between CB and HB or among the treatment diets during the grower, finisher and combined grower-finisher periods. The gain-to-feed ratios were higher (P &lt; 0.01) for HB than for CB diets. They were also higher (P &lt; 0.05) for diet 3 than for diet 1 during the finisher and combined grower-finisher periods. Carcass index and dressing percent were not different (P &gt; 0.10) among the treatment diets. Supplemental phytase decreased (P &lt; 0.05) the excretion of P during both grower and finisher periods. The combination of phytase and dietary ideal amino acid ratios decreased (P &lt; 0.01) the excretion of both P and N. The ammonia and hydrogen sulphide production in stored liquid manure was not different among the diets 1, 2 and 3, and the urinary N excretion was closely related to ammonia production. These results indicate that replacing inorganic P with phytase and lowering the dietary protein level while supplementing amino acids in CB or HB diets can decrease the excretion of P up to 44.0% and N up to 28.0% in manure with no adverse effect on performanceof lean genotype pigs. Key words: Pigs, phytase, amino acids, phosphorus, nitrogen, excretion

The effect of restricted feeding on growth hormone (GH) secretory patterns in genetically lean and fat wether lambs

AbstractThe aim of this work was to determine whether developmental changes in growth hormone (GH) secretory patterns and carcass composition were influenced by nutrition and genotype in sheep. Four-month-old wether lambs from lean (low backfat), fat (high backfat) and control selection lines were nutritionally restricted to maintain a 28 kg live weight or given food ad libitum for 24 weeks. Plasma concentrations of GH and insulin-like growth factor 1 (IGF-1) were measured at predetermined times and carcass composition of the animals determined at the end of the trial.From week 3 on, restrictions in dry matter (DM) intake were observed as the ad libitum treatment group had a significantly greater intake than the restricted treatment group (7·70 v. 5·80 kg DM per week, s.e.d. = 0·81). Differences in live weight between the feeding treatments were significant (P &lt; 0·05) at week 9. The restricted feeding regime was associated with significant reductions in plasma levels of IGF-1 but had no effect (P &gt; 0·05) on carcass weight-adjusted carcass fat proportion at the close of the trial. The effect of food restriction on GH secretory patterns was variable. Although there was initially a suppression in mean plasma GH, there was subsequently significantly higher mean plasma GH in the restricted feeding treatment. Periodogram analysis indicated that both the absolute levels of GH and the GH secretory pattern were altered by restricted feeding. In all animals, mean and basal GH concentrations, as well as the frequency and amplitude of pulses, declined from February to March and then increased from May to July (P &lt; 0·001).DM intake and live weight did not differ (P &gt; 0·05) between genotypes, however the fat genotype had greater carcass fatness than lean or control genotypes (P &lt; 0·01). There were no consistent differences between genotypes in plasma IGF-1 concentrations. In the ad libitum treatment, the lean and control genotypes had higher plasma GH levels than the f at genotype but the pattern of GH release did not vary. Under restricted feeding, both the pattern and the level of plasma GH varied between genotypes.It is concluded that the developmental change in GH secretory patterns is affected by nutrition but not in a consistent manner. Although restricted feeding resulted in higher mean plasma GH concentrations later in the trial, this did not result in a change in carcass composition. The biological cues which lead to increased fat deposition in older lambs need further study but plasma GH levels may not he an important mechanism in this process.

Stochastic simulation of growth in pigs: relations between body composition and maintenance requirements as mediated through protein turn-over and thermoregulation

AbstractA dynamic model for simulation of growth in pigs, extended to describe thermoregulatory processes, was made stochastic to simulate groups of pigs with between-animal variation in mature body protein (Pα) and lipid mass (Lα), in the potential rate at which mature mass is attained (B⋆), and in the distribution of body protein and lipid over pools and depots. The resulting variation in body composition leads to variation in energy requirements for protein turn-over and thermoregulation, causing between-animal variation in maintenance requirements (MEmaint).Simulated population means for Pα, Lα/Pαand B⋆were varied in three steps each. Excluding unrealistic parameter combinations this led to 33 – 6 = 21 simulated genotypes. Simulated within-population coefficients of variation (CV) were 7, 15 and 3%. Random replicates of each genotype were simulated five times, in climatic conditions that were in turn severely cold, mildly cold (about 5 and 1ºC below lower critical temperature), thermoneutral, mildly hot and severely hot (about 1 and 5ºC above upper critical temperature), during the entire growth period of 23 to 100 kg live weight. Simulated food intake was ad libitum.Simulated thermoneutral within-population standard deviations of body protein and lipid content were 0·21 to 0·46 kg and 0·78 to 2·14 kg at 100 kg body weight. On average, the corresponding values in cold and hot conditions were slightly higher.MEmaintshowed a protein-turn-over-related within-population CV of 1·5% at thermoneutrality. Thermoregulatory action contributed about 4% extra variance in cold and hot conditions but CV values were not affected. A genetic increase in the maximum protein deposition rate from 100 to 250 g/day would increase MEmaintas related to protein turn-over and thermoregulation by 11% at thermoneutrality, and by 6 to 11% in cold or hot conditions. Two relevant groups of genotypes could be distinguished based on the within-population regression coefficients of MEmainton daily or cumulative protein deposition (bdailyPdep, bcumPdep). These ranged from 0·250 to 0·428 kJ/kg0·75 per day per g/day and from 2·77 to 5·45 kJ/kg0·75per day per kg, respectively, in 12 ‘conventional’ genotypes at thermoneutrality. On average, bdailyPdepwas increased by 48%, 20%, –11% and –36% in the other climatic conditions mentioned above, respectively. The corresponding increase of bcumPdepwas 32%, 14%, 8% and 48%. Three fast-growing lean genotypes showed similar bdailyPdepand bcumPdepat thermoneutrality, but much more pronounced increases in cold and hot conditions: 137%, 49%, –12% and + 88% for bdailyPdepand 248%, 108%, 17% and 196% for bcumPdep.It is concluded that differences in body composition traits between pig genotypes do not cause important between-genotype differences in thermoregulatory MEmaint, and that thermoregulatory processes contribute little body-composition-related variation to hot or cold MEmaintwithin most genotypes.The inferences to be made from this with regard to experimental design are discussed. The verification of the above predictions will require a very elaborate and large-scale experiment.

Differences in pituitary cell number but not cell type between genetically lean and fat Coopworth sheep☆

Coopworth sheep selected for low backfat (lean genotype) have been shown to have heavier pituitary glands than those selected for high backfat (fat genotype). This paper investigated whether this difference was due to an increase in pituitary cell number or cell size and whether the relative proportions of different pituitary cell types differed between the genotypes. In three separate trials, ram lambs aged 6 to 8 months were slaughtered and the pituitary glands were processed for stereological or immunocytochemical studies. The pituitary glands of lean genotype sheep were between 30 and 60% heavier than those of the fat sheep. Lean sheep had a significantly (P < 0.05) larger cross-sectional area of the pituitary fossa (96.6 vs. 81.7 mm 2) than fat genotype sheep. The pituitaries from lean sheep contained significantly more total cells than fat sheep (Trial 1: 290 vs. 183 million cells, P < 0.01; Trial 2: 353 vs. 239 million cells, P < 0.05). The volume of individual cells did not differ between the genotypes. Trial 3 showed that there was no difference between lean and fat sheep in the percentage of cells staining positive for the five pituitary hormones studied. It is concluded that the larger pituitary glands of lean compared to fat genotype sheep are a result of a nonspecific increase in the size of the whole gland through increased cell numbers, with no change in cell size or the relative proportion of different cell types.

The response of gilt body composition to low and high dietary protein during lactation

Lactating sows will respond to increasing dietary lysine during lactation providing that energy does not become limiting. In a recent experiment Sauber et al. (1998) demonstrated that fat genotypes readily mobilised fat to make up for inadequate nutrient intake in lactation whereas lean genotypes mobilised protein. The aim of this experiment was to investigate whether fat versus lean animals of similar genetic merit were equally able to utilise diets varying in lysine content. The animals used in this experiment were of a high lean genotype and had been allowed to express their natural variation for fatness during rearing and gestation.

Metabolic Differences between Genetically Lean and Fat Chickens Are Partly Attributed to the Alteration of Insulin Signaling in Liver

Insulin signaling [tyrosine phosphorylation of insulin receptor (IR), insulin receptor substrate-1 (IRS-1), Src homology and collagen protein (Shc) and phosphatidyl inositol 3′-kinase activity (PI 3′-kinase)] was studied in the liver and thigh muscles of fat (FL) and lean (LL) chickens. These lines result from a divergent selection on abdominal fat pad size. The divergence is of metabolic origin. Extreme nutritional states were studied (fed, 48-h starved and 30-min refed). Such conditions significantly altered insulin signaling in chicken liver, but surprisingly not in the muscle (except the phosphorylation of Shc in the refed state). No major differences that could account for this divergence were found in muscle. Liver IR number and Shc protein did not differ between genotypes. Liver IRS-1 (protein and messenger) was lower in the fed state and higher in the starved state in FL compared to that in LL chickens. In the fed state, tyrosine phosphorylation of liver IR, IRS-1 and Shc action was higher in FL than in LL chickens that in the absence of insulin resistance rely on higher plasma insulin levels. In the starved state, phosphorylation of liver IR was lower, but the phosphorylation of IR and IRS-1 were higher in LL than in FL chickens, most likely in response to higher plasma glucose and insulin in the lean genotype. In the refed state, the phosphorylation of liver IR and IRS-1 did not differ between genotypes despite significantly lower plasma insulin in FL chickens. Finally, PI 3′-kinase was not affected by the genotype. A significant activation of early steps of insulin signaling in liver of fed FL chickens may at least partly account for their increased liver lipogenesis and ultimately their fattening.

Neuropeptide Y Overexpression in the Preweanling Zucker ( fa/fa) Rat

Hypothalamic preproNPY overexpression in the Zucker fatty ( fa/fa) rat was examined. In situ hybridization was used to determine the relative level of preproNPY mRNA in the arcuate nucleus of +/+, +/ fa, and fa/fa pups aged postnatal day 2 (P2), 5, 9, 12, or 25. The relative optical density (ROD) of probe hybridization in the arcuate, the area of hybridization (A), and the product of ROD × A (a measure of total arcuate preproNPY mRNA hybridization) were measured. Values were normalized to the mean +/ fa value within each litter. Initial analysis showed that preproNPY mRNA hybridization (ROD × A) in fa/fa pups was significantly higher than +/ fa and +/+ pups on P9, 12, and 25, and significantly higher than +/ fa on P5. No significant difference between lean (+/+ and +/ fa) genotypes, however, were observed at any age tested. Values from the lean genotypes were, therefore, pooled, and data were normalized to the mean value of lean animals for analysis. This analysis revealed that preproNPY mRNA hybridization in fa/fa pups was higher than lean littermates as early as P2.