Ontogeny of growth hormone (GH), insulin-like growth factors (IGF-I and IGF-II) and IGF binding protein-2 (IGFBP-2) in genetically lean and obese swine

Role of Akt and mammalian target of rapamycin signalling in insulin-like growth factor 1-mediated cell proliferation in porcine Sertoli cells

The critical role of insulin-like growth factor (IGF) 1 in promoting Sertoli cell proliferation invivo and invitro has been established, but its downstream signalling mechanisms remain unknown. In addition to mitogenic effects, a role for IGF1 in mediating cholesterol biosynthesis within testes has been implied. The aims of this study were to investigate the roles of: (1) phosphatidylinositol 3-kinase/Akt/mammalian target of rapamycin (mTOR) signalling in IGF1-mediated Sertoli cell proliferation; and (2) IGF1 in mediating cholesterol biosynthesis in Sertoli cells. Primary cultures of Sertoli cells were prepared from 1-week-old porcine testes. On Day 3 of culture, Sertoli cells were treated with 300ng mL-1 IGF1, alone or in combination with inhibitors of IGF1 receptor (2μM picropodophyllotoxin), Akt (1μM wortmannin) or mTOR (200nM rapamycin). Cells were cultured for 30min and phosphorylation levels of Akt, mTOR and p70 ribosomal protein S6 kinase (p70S6K) were determined by immunoblotting. Cell proliferation and quantitative polymerase chain reaction assays were conducted using cells cultured for 24h. IGF1 increased phosphorylation of Akt, mTOR and p70S6K and cell proliferation, and these effects were inhibited by inhibitors of IGF1R, Akt and mTOR. Furthermore, IGF1 upregulated the expression of cholesterol biosynthetic genes (3-hydroxy-3-methylglutaryl-CoA reductase (HMGCR), 3-hydroxy-3-methylglutaryl-CoA synthase (HMGCS1) and cytochrome P450, family 5, subfamily A, polypeptide 1 (CYP5A1)), but not sterol regulatory element-binding transcription factor 1 (SREBF1). Increased phosphorylation of p70S6K, a major downstream target of mTOR, and upregulated expression of genes involved in cholesterol biosynthesis are indicative of the key role played by IGF1 in regulating the synthesis of cholesterol, the precursor for steroid hormones.

Growth Hormone Secretion Patterns in German Landrace (DL) Fetuses and Piglets Compared to DL Piglets with Inherited 1,25-Dihydroxyvitamin D3 Deficiency

The regulation of growth hormone (GH) release during prenatal development and during early postnatal life is not entirely clarified. In this study plasma GH concentrations in pigs with inherited pseudo vitamin D deficiency type I (PDDR-I), which regularly show growth retardation, were compared during ontogeny with unaffected pigs of the same breed (German Landrace, DL) as control. Plasma GH concentrations were measured in plasma of chronically catheterized fetuses (beginning on day 101 after mating or after artificial insemination) and in piglets (day 37 postpartum (p.p.)—day 42 p.p.) of both lines. A growth curve beginning at day 7 p.p. was recorded for both lines. The relative amount of GH receptor (GHR) mRNA in liver was quantified by competitive reverse transcription polymerase chain reaction in piglets at day 42 p.p. A trend for higher GH concentrations was observed in PDDR-I fetuses (p < 0.1). In PDDR-I piglets compared to DL piglets higher plasma GH values (p < 0.01), were observed despite lower body weight. The relative quantity of GHR mRNA in liver was not significantly different between the two lines. Piglets with an inherited defect of vitamin D synthesis showed higher GH concentrations. A hormonal imprinting by low 1,25(OH)₂D₃ could be one reason for our observations and should be analysed in detail in future.

Number of Secretory Vesicles in Growth Hormone Cells of the Pituitary Remains Unchanged After Secretion

Immunogold-labeled transmission electron microscopy (TEM) was used to determine the total number of secretory vesicles in resting and in growth hormone (GH)-stimulated porcine pituitary cells. We identified three categories of vesicles: filled, empty, and partly empty. Resting GH cells contained more than twice as many filled vesicles than did the stimulated ones. Stimulated cells, however, contained nearly twice as many empty vesicles and 2.5 times more partly empty vesicles than did resting cells. Secretory vesicles in GH cells further revealed the localization of GH only in electron-dense vesicles in both resting and stimulated cells. The total number of secretory vesicles did not change after secretion. These results are consistent with a mechanism that, after stimulation of secretion, vesicles transiently dock and fuse at the fusion pore to release vesicular contents.

Differences in the somatotropic axis, in blood cortisol, insulin and thyroid hormone concentrations between two pig genotypes with markedly divergent growth rates and the effects of growth hormone treatment

The intention of the current study was to gain more insight into the endocrine and molecular control mechanisms of growth in the pig. For this purpose various growth related parameters were determined in 4-month-old barrows of two extreme pig genotyes, the small, obese Göttingen Miniature (GM) and the large and lean German Landrace (DL). Mean growth hormone (GH) concentration, GH pulse frequency and GH pulse amplitude did not differ between breeds. Likewise, plasma IGF-1, thyroxine, tri-iodothyronine (T3) concentrations were similar in both breeds. However the plasma GH response (maximum level and area under curve) to a single i.v. injection of GHRH in DL was higher than in GM (P < 0·05). Furthermore, basal plasma insulin and in particular plasma cortisol concentrations were higher in GM compared with DL pigs (P 0·05 and 0·01 respectively). Analysis of cortisol during 4-h frequent blood sampling indicated higher cortisol amplitudes in GM compared with DL (P ≤ 0·01). Specific bGH-binding to hepatic membrane preparations was not different between breeds and IGF-1 m RNA concentrations determined by reverse transcription-polymerase chain reaction in liver, m. semimenbranosus and m. longissimus dorsi were similar in both breeds. I.m. treatment with recombinant porcine somatotropin (rpST; 70 µg/kg live weight) over an 8-day period in contemporary barrows increased without any breed difference, plasma IGF-1, T3 and insulin concentrations and hepatic specific bGH-binding, but did not affect thyroxine or cortisol concentrations in plasma. IGF-1 gene expression was also elevated in liver and muscle tissues in rpST-treated animals without obvious breed effects. The observations underline the complexity of the hormonal and molecular control of growth and support the notion that differences in growth potential are the consequence of differences at various levels of the somatotropic axis and apparently relate to differences in other control systems of energy metabolism such as the pituitary adrenal axis or the endocrine pancreas as well.

Selection for high or low backfat depth in Coopworth sheep: breeding-ewe traits

A breeding experiment in Coopworth sheep where selection was applied to backfat depth was evaluated after 14 years (1981-94). There were three self-replacing lines, two selected for increased or decreased subcutaneous fat depth, and an unselected control (average size = 51 ewes per line per year). Reproductive traits, ewe body weight and ewe fleece weight were monitored in each line as potential correlated responses. In the last 4 years studied, the fat (F), control (C) and lean (L) lines differed significantly in the proportion of ewes lambing (0·87, 0·93, 0·94 respectively), litter size at birth (1·64, 1·83 and 1·89), and lamb survival up to weaning, unadjusted for birth rank and sex (0·88, 0·81 and 0·74). The overall reproductive trait, lambs weaned per ewe joined (1·22, 1·33 and 1·26), did not differ significantly among lines. From pre-mating weights of ewes present in 1993 or 1994, means for mature ewes by line were 60·1, 62·4 and 63·3 kg, respectively (P < 0·01). Means for weight at scanning time (7 months of age) by line, as a proportion of mature weight were: 0·533, 0·561 and 0·559, respectively (P < 0·05). There were also significant line differences in ewe fleece weights, with the 1993 and 1994 data averaging 3·93, 4·05 and 4·27 kg respectively (P < 0·01). For weight of lamb weaned per ewe weaning at least one lamb, the L line had a 0·09 higher mean proportionally than the F line (P < 0·05), but for a composite trait which was a weighted combination of weight of lambs weaned and ewe fleece weight per ewe joined (with or without allowance for different ewe live weights), the L line was no longer significantly different from the F line. Repeatabilities and single-record heritabilities were also estimated for various ewe traits. The implications are that lean-lamb selection would be associated with only small changes in net reproduction, ewe fleece weight and live weight, but larger differences would be expected from selection in the opposite direction.

Expression of insulin-like growth factor-1 (IGF-1) and growth hormone-receptor (GHR) mRNA in liver, skeletal muscle and adipose tissue of different breeds of pig

The work described was carried out to study the expression of insulin-like growth factor 1 (IGF-1) and growth hormone-receptor (GHR) mRNA in liver, skeletal muscle and adipose tissue from three breeds of pig with varying growth characteristics. The three breeds studied were the Large Wlrite, noted for its lean tissue; the Duroc, characterized by its high intramuscular fat content; and the Meishan × Landrace (0·5 Meishan), noted for its fat, poorly conformed carcass and slower growth rate. The probes used were designed to monitor promoter usage for IGF-1 expression and also expression of the extra-cellular domain of the GHR. Eighteen gilts, six of each breed, were given a barley/wheat diet (158 g crude protein, 10·7 g lysine and 13·9 MJ energy per kg), to appetite, for 1 to 2 weeks until they reached about 85 kg. Samples of liver, longissimu s dorsi (LD) muscle and three adipose tissue depots (subcutaneous (SC), perirenal (PR) and omental (OM)) were collected immediately after slaughter and frozen in liquid nitrogen (total time of sample collection to plunging of sample into liquid nitrogen was <3 min), prior to extraction of total RNA and ribonuclease protection assays. Individual serum samples collected at exsanguination were frozen prior to IGF-1 radioimmunoassay. There were no breed differences in the serum IGF-1 concentrations (range 49 to 134 μg/l), or in expression of the GHR gene or either class of IGF-1 transcript in the liver. However, there was a significant difference between the breeds in expression of IGF-1 mRNA in the LD muscle (P < 0·001), the order being Duroc > Wliite > Meishan, with only class 1 transcripts of IGF-1 being found. GHR expression in LD muscle was lower in White than in the other tivo breeds (P = 0·022). There was a significant difference between the breeds in expression of IGF-1 mRNA (only class 1 transcripts present) in the adipose tissue (P = 0-006), the order being Wliite · Duroc · Meishan, and also a significant depot difference, with expression being highest in the SC depot (P < 0·001). There were no differences between the breeds or depots in expression of GHR mRNA in adipose tissue. The observed differences in muscle and adipose tissue IGF-1 expression may relate to the overall growth of the animal.

Ontogenic study of insulin-like growth factor-1 and growth hormone receptor mRNA expression in porcine liver and skeletal muscle

The growth hormone-insulin-like growth factor (GH-IGF) axis is involved in the control of postnatal growth in all animals studied to date. At birth, blood levels of IGF-1 are low, although levels of GH are high. Thus a switching occurs during the postnatal period, which involves an increase in liver GH-receptors (GHR). This study investigates the changes in serum IGF-1 and IGF-1 and GHR mRNA in liver and skeletal muscle of growing pigs. The period from birth to 20 days of age showed a gradual increase in both IGF-1 and GHR mRNA expression by the liver, thus accounting for the gradual increase in serum IGF-1. The IGF-1 mRNA expressed was found to be predominantly class 1 transcripts with very few class 2 transcripts. There was a plateau of liver IGF-1 mRNA levels after 20 days and up to 140 days, even though the expression of GHR mRNA continued to increase. The levels of expression of the two genes were found to correlate in the first 20-day period (r = 0·76, P < 0·005), but not in the later period (r = 0·44, P > 0·05).

Levels of expression of both genes in the LD muscle were highly variable, with no age related changes being observed. However, a significant negative correlation of expression of the two genes was observed (R = 0·60, P < 0·001), with the correlation still being significant in the two age periods.

The data are consistent with a likely initial dependence for postnatal growth upon GH-stimulated IGF-1 mRNA expression by the liver, up to 20 days of age. After this time, hepatic expression of IGF-1 mRNA reaches a plateau, even though the serum IGF-1 and hepatic GHR mRNA levels continue to rise. A possible explanation for this could be an increase in either turn-over or stability of IGF-1 mRNA, giving rise to increased levels of peptide with no apparent change in mRNA level. Another possibility is that an increased expression/production of the IGF-binding proteins leads to an increase in the half-life of the peptide in the circulation.

Patterns of gene expression in pig adipose tissue: insulin-like growth factor system proteins, neuropeptide Y (NPY), NPY receptors, neurotrophic factors and other secreted factors

Although cDNA microarray studies have examined gene expression in human and rodent adipose tissue, only one microarray study of adipose tissue from growing pigs has been reported. Total RNA was collected at slaughter from outer subcutaneous adipose tissue (OSQ) and middle subcutaneous adipose tissue (MSQ) from gilts at 90, 150, and 210 d (n=5 age(-1)). Dye labeled cDNA probes were hybridized to custom porcine microarrays (70-mer oligonucleotides). Gene expression of insulin-like growth factor binding proteins (IGFBPs), hormones, growth factors, neuropeptide Y (NPY) receptors (NPYRs) and other receptors in OSQ and MSQ changed little with age in growing pigs. Distinct patterns of relative gene expression were evident within NPYR and IGFBP family members in adipose tissue from growing pigs. Relative gene expression levels of NPY2R, NPY4R and angiopoietin 2 (ANG-2) distinguished OSQ and MSQ depots in growing pigs. We demonstrated, for the first time, the expression of IGFBP-7, IGFBP-5, NPY1R, NPY2R, NPY, connective tissue growth factor (CTGF), brain-derived neurotrophic factor (BDNF) and ciliary neurotrophic factor (CNTF) genes in pig adipose tissue with microarray and RT-PCR assays. Furthermore, adipose tissue CTGF gene expression was upregulated while NPY and NPY2R gene expression were significantly down regulated by age. These studies demonstrate that expression of neuropeptides and neurotrophic factors in pig adipose tissue may be involved in regulation of leptin secretion. Many other regulatory factors were not influenced by age in growing pigs but may be influenced by location or depot.

Association of CA repeat polymorphism at intron 1 of insulin-like growth factor (IGF-I) gene with circulating IGF-I concentration, growth, and fatness in swine

Evidence is accumulating that intronic polymorphic cytosine-adenosine (CA) repeats may play a role in gene expression. In this work, we investigated whether a polymorphic CA short tandem repeat (STR) located at the first intron of the pig insulin-like growth factor I (IGF-I) gene influences plasma IGF-I concentration in pigs as well as phenotypic variation in growth and fatness traits. We measured plasma IGF-I levels at one to four time points from 35 to 215 days of age in 340 performance-tested Landrace and Duroc pigs previously genotyped for the IGF-I STR. Data were analyzed within breed with a linear mixed model with the number of CA repeats as a covariate. At least five alleles were segregating in each breed, differing in one to seven repeats. The results showed that in each breed, circulating IGF-I at 160 days of age increased with the length of the shortest allele, accounting for an average trend of 4.38 +/- 1.28 ng/ml of IGF-I per additional repeat (P = 0.001). Longer repeats were associated with early growth in Landrace boars (1.92 +/- 0.92 kg per CA at 160 days; P = 0.038) and with back fat thickness (-0.57 +/- 0.20 mm per CA; P = 0.005) and lean content (7.52 +/- 3.00 g/kg per CA at 105 kg; P = 0.013) adjusted for carcass weight in Duroc barrows, as expected from the effect of circulating IGF-I on these traits. The consistency of the results across populations supports the hypothesis that the length of the CA repeats at intron 1 of the IGF-I gene is associated with circulating IGF-I levels, and that this effect is not neutral with respect to growth and fatness.

Insulin-like growth factor-I and analogues increase growth in artificially-reared neonatal pigs

Exogenous insulin-like growth factor (IGF)-I has been shown to increase growth rate in neonatal pigs while an analogue of IGF-I, long arginine (LR3) IGF-I, has been shown to be more potent than IGF-I in the rat. Therefore, two studies were conducted to determine whether IGF-I and LR3IGF-I increase growth in the artificially-reared neonatal pig. Expt 1 involved forty-two (2 kg initial weight) pigs infused with either control, IGF-I (2, 4 or 8 μg/h) or LR3IGF-I (2, 4 or 8 μg/h) infusions for 8 d. Pigs were weighed and then offered 1·7 MJ (gross energy) milk replacer/kg0·75 per d. Expt 2 involved eighteen pigs (2 kg initial weight) treated with control saline, IGF-I (8 μg/h) or LR3IGF-I (8 μg/h) infusions. After 9 d an additional pump was inserted to increase the infusion rates of each of the growth factors (16 μg/h) for a further 9 d. Cows' milk was provided ad libitum. In Expt 1 there was no overall effect of growth factors on daily weight gain or slaughter weight. However, milk intake was greater in pigs infused with growth factors (909 v. 867 g/d, P=0·027), with an apparently greater milk intake by the pigs infused with IGF-I compared with LR3IGF-I (920 v. 898 g/d, P=0·12). Infusion of LR3IGF-I decreased plasma IGF-I concentrations, but had no effect on plasma IGF-II concentrations. In Expt 2, neither IGF-I nor LR3IGF-I infusion had any effect upon daily weight gain over the first 9 d of the study. However, over the second 9 d of the study, daily weight gain was increased in LR3IGF-I-infused pigs (457 v. 386 g/d, P<0·01), but not in pigs infused with IGF-I (413 v. 386 g/d, P=0·15). Milk intake was not different during the first 9 d of the study but was significantly greater in pigs infused with growth factors over the second half of the study (3407 v. 2905 g/d, P<0·01). Plasma IGF-binding protein-3 concentrations were highly correlated (R=0·85) with average daily gain over the 3 d preceding blood sampling. In conclusion, exogenous IGF-I and particularly LR3IGF-I can increase growth rate and milk intake in artificially-reared pigs fed ad libitum but not in limit-fed piglets.

Genetic correlation between serum insulin-like growth factor-1 concentration and performance and meat quality traits in Duroc pigs1

This study was intended to examine whether serum IGF-I concentration is appropriate for use as a physiological predictor for genetic improvement of meat production and meat quality traits in pigs. Heritabilities and genetic correlations were estimated for these traits. The Duroc breed used in this study was selected for seven generations for average daily BW gain (DG) from 30 to 105 kg of BW, loin-eye muscle area (EM), backfat thickness (BF), and intramuscular fat (IMF) content. Serum IGF-I concentration of boars and gilts at the fourth generation of selection and that of boars, gilts, and barrows from the fifth to seventh generations of selection were measured at 8 wk (IGFI-8W) for 832 animals and again at the time they reached 105 kg of BW (IGFI-105KG) for 834 animals. A multivariate REML procedure was used to estimate genetic parameters with a model incorporating generation of selection, sex, common environmental effect of litter, and individual additive genetic effects. Heritability estimates for IGFI-8W and IGFI-105KG were 0.23 +/- 0.02 and 0.26 +/- 0.03, respectively. The estimates of common environmental effect for IGFI-8W and IGFI-105KG were 0.20 +/- 0.02 and 0.03 +/- 0.01, respectively. Positive genetic correlations were estimated between IGFI-8W and DG (0.26 +/- 0.08), EM (0.22 +/- 0.10), and IMF (0.32 +/- 0.10). Moreover, the positive genetic correlation between IGFI-105KG and EM was 0.42 +/- 0.08. These results indicate that serum IGF-I concentration at an early stage of growth was effective for prediction of IMF, but it was not a reliable physiological predictor of genetic merit of meat production traits.

Exogenous porcine somatotropin administered to neonatal pigs at high doses can alter lifetime fat but not lean tissue deposition

The growth rate of the young pig is generally much less than its potential and may be constrained by endocrine status as well as nutrient intake. The aim of the present study was to determine whether porcine (p) somatotropin (ST) treatment of the sucking pig could alter subsequent body composition. Twelve mixed-parity cross-bred sows with an average litter size of ten piglets were used to nurse pigs for the present study. On day 1 of lactation, the median two male pigs (by weight) from each litter were randomly allocated to one of two doses of pST (0 or 1 mg/kg per d) until weaning on day 21. Pigs were weaned and offered feed ad libitum until slaughter at 134 d of age. Body composition was measured using dual-energy X-ray absorptiometry (DXA) at 21, 49, 77, 105 and 133 d of age. There was no significant difference in growth rates between day 1 and 21 of lactation in pigs injected with either saline (9 g/l NaCl/l) or pST (258 v. 246 g/d for control and pST-treated pigs respectively, P=0.61), and as a consequence there was no significant difference in liveweight at weaning (7.13 v. 6.84 kg, P=0.59). However, fat mass at weaning tended to be decreased (1.18 v. 0.96 kg, P=0.064), while the % fat in the body at weaning was significantly (16.7 v. 13.9 %, P=0.008) decreased by exogenous pST treatment. In the immediate post-weaning period there was a reduction in lean tissue deposition (347 v. 300 g/d, P=0.021) but no effect on fat deposition (35 v. 33 g/d, P=0.72). Over the entire weaning-to-slaughter period, pST treatment of neonatal pigs decreased the rate of fat deposition (130 v. 112 g/d, P=0.033), but had no effect on lean tissue deposition (550 v. 538 g/d, P=0.49). Therefore, treatment of nursing pigs with high doses of pST for a short period before weaning may provide a means of reducing the fat content of pork and pork products.

Growth performance, dry matter and nitrogen digestibilities, serum profile, and carcass and meat quality of pigs with distinct genotypes

We investigated the effect of distinct genotypes on growth performance, DM and N digestibilities, serum metabolite and hormonal profiles, and carcass and meat quality of pigs. Eight control-line and eight select-line pigs with an equal number of gilts and castrated males per genotype were chosen from the group of pigs subjected to selection for lean growth efficiency. Pigs were housed individually and allowed ad libitum access to common grower, finisher 1, and finisher 2 diets when they reached approximately 20, 50, and 80 kg, respectively, and water throughout the study. Although genotype had no effect on growth performance during the finisher 2 phase and overall, select-line pigs grew faster and more efficiently (P < 0.05) during the grower and finisher 1 phases than did control-line pigs. Dry matter and N digestibilities during the grower phase were lower (P < 0.05) in select-line pigs compared with control-line pigs. Select-line pigs had less ultrasound backfat (P < 0.05) at the end of the grower and finisher 2 phases. Serum urea N (P < 0.05) and leptin concentrations were lower in select-line pigs than in control-line pigs, but the effect of genotype on serum glucose, triglyceride, or insulin concentration was rather inconsistent. Select-line pigs had heavier heart (P < 0.05), liver (P = 0.08), and kidneys (P < 0.01), implying a higher metabolic activity. Less 10th-rib carcass backfat (P < 0.01) and a trend for larger carcass longissimus muscle area (P = 0.10) were reflected in the greater (P < 0.01) rate and efficiency of lean accretion in select-line pigs. Select-line pigs had lower subjective meat color (P < 0.01), marbling (P < 0.05), and firmness (P < 0.01) scores. Final serum leptin concentration was correlated positively with carcass backfat thickness (r = 0.73; P < 0.01) and negatively with overall feed intake (r = -0.77; P < 0.01). These results indicate that pigs with distinct genotypes exhibited differences in the growth rate, metabolite and hormonal profiles, and body composition. Further research is necessary to determine whether pigs with distinct genotypes respond differently to dietary manipulations, which would have an effect on developing optimal feeding strategies for efficient and sustainable pig production.

Neuroendocrine regulation of growth hormone and luteinizing hormone in fetal and neonatal pig

Ontogeny of the production and the regulation of growth hormone and Luteinizing hormone is studied in a series of experiments utilizing male and female pigs at different fetal and neonatal stages. Growth hormone mRNA is detectable in both sexes as early as d. 50 p.c. The mRNA levels increase to reach the maximum levels at d. 95-110 p.c. Plasma levels of GH follow the developmental patterns of GH mRNA. A sex difference is evident around d. 80-90 p.c. with males having higher GH levels than females. The stimulatory but not the inhibitory mechanisms of GH secretion are fully functioning in the pig fetus. LHbeta mRNA is detectable earlier in females (d. 50 p.c.) than in males (d. 65 p.c.). Plasma concentrations of LH increase with fetal age in female fetuses, but in male fetuses there is no distinct developmental pattern evident. Basal LH secretion achieves maximum levels in both sexes after birth. Opioids do modulate fetal LH secretion, however, the mode of their action is age-dependent.

Moderate doses of porcine somatotropin do not increase plasma insulin-like growth factor-I (IGF-I) or IGF binding protein-3

The growth rate of the young pig is generally much less than its potential and may be constrained by endocrine status as well as by nutrient intake. The aim of this study was to determine whether porcine somatotropin (pST) could increase growth in the nursing pig. Fourteen sows nursing litters of 6 (n = 7) or 12 (n = 7) piglets were utilized to establish a high and low plane of nutrition for sucking pigs. On Day 4 of lactation, the median two male pigs from each litter were randomly allocated to one of two doses of pST (0 or 60 micrograms/kg/d) until weaning on Day 31. Pigs were bled on Days 4, 13, 22, and 31 of lactation and the plasma was analyzed for insulin-like growth factor (IGF)-I, IGF-II, and IGF binding protein-3 (IGFBP-3). Pigs were weaned into conventional accommodation and further weighed on Days 63, 91, and 119. Pigs from litters of 6 grew more quickly and weighed 2.2 kg (P = 0.01) and 3.5 kg (P = 0.04) more than pigs from litters of 12 at 31 and 63 d of age, respectively. There was no effect of pST on preweaning growth of sucking pigs (261 vs. 258 g/d, P = 0.68), although growth rate increased in the final 3 d before weaning at 31 d (241 vs. 294 g/d, P = 0.01). IGFBP-3 was greater (1.09 vs. 0.78 micrograms/ml, P < 0.001), whereas IGF-I tended to be greater (206 vs. 176 ng/ml, P = 0.14), in pigs from the small litters. There was no effect of pST on plasma IGF-I (182 vs. 195 ng/ml, P = 0.454) or IGFBP-3 (0.93 vs. 0.94 microgram/ml, P = 0.85) concentrations. Plasma IGF-I and IGFBP-3 were highly correlated with the growth rate of nursing pigs (R = 0.638 and 0.756, respectively). There were no effects of pST (340 vs. 328 ng/ml, P = 0.48) or litter size (336 vs. 333 ng/ml, P = 0.88) on IGF-II. In conclusion, pST had no little or no effect on growth performance or plasma IGF-I, IGF-II, or IGFBP-3 in sucking pigs on either a high or low plane of nutrition.

Interactions between environmental temperature and porcine growth hormone (pGH) treatment in neonatal pigs

Age-dependent interactions between environmental temperature and porcine growth hormone (pGH) treatment on the function of the somatotrophic axis were evaluated in the neonatal pig. At 3 d of age, 40 Landrace x Yorkshire x Duroc piglets received intraperitoneal implants containing either recombinant pGH (0.5 mg/d; n = 20) or vehicle (control; n = 20). Piglets were maintained at either a low (21 degrees C, 50% relative humidity; n = 20) or high (32 degrees C, 50% relative humidity; n = 20) temperature. At 4 and 6 wk of age, 5 pGH-treated and 5 control piglets from each thermal group were sacrificed for tissue collection. Blood samples were collected at the time of sacrifice and analyzed for serum concentrations of GH, insulin-like growth factor 1 (IGF-1), and IGF-2. Liver RNA was analyzed for mRNAs specific for the GH receptor, IGF-1, IGF-2, and IGF binding protein 3. There was no effect of pGH treatment (P = 0.4) on average daily gain; however, both age (P = 0.002) and temperature (P = 0.001) had an effect on average daily gain such that those animals maintained at a low temperature and those sacrificed at 6 wk had greater average daily gains. Serum concentration of GH was elevated (P = 0.003) by pGH treatment and was lowest in the 6-wk-old group (P = 0.008). Serum concentration of IGF-1 was elevated (P = 0.007) by pGH treatment and increased with age (P = 0.01). Liver GH receptor mRNA was unaffected (P > 0.5) by pGH treatment, but was greater in the 6-wk-old group (P < 0.0001) and in piglets maintained at the high temperature (P = 0.04). IGF-1 mRNA was enhanced by pGH treatment (P = 0.0003) and by exposure to the high temperature (P = 0.04), but did not differ (P > 0.5) between age groups. IGF-2 mRNA was greater (P = 0.0009) in the 4-wk-old group and in piglets maintained at the high temperature (P = 0.007), but was unaffected (P = 0.5) by pGH treatment. IGF binding protein 3 mRNA increased with age (P = 0.0004) and was stimulated by pGH treatment in the 6-wk-old group (P = 0.034). The relatively lower level of GH receptor and IGF mRNAs in conjunction with greater growth in the cold environment suggests that somatotrophic gene expression in the liver is not rate limiting for growth in the neonatal pig.

Somatotropin regulates adipose tissue metabolism in neonatal swine

Somatotropin (ST) reduces lipid deposition in growing and adult animals, but its effect in neonatal pigs is not clear. In this study, we tested the hypothesis that ST inhibits lipid deposition in neonatal pig adipose tissue. Four neonatal (2.9 +/- 0.1 kg, 7 d of age) and four growing (17.0 +/- 1.4 kg, 60 +/- 3 d of age) crossbred pigs were used. Subscapular adipose tissue fragments were cultured with or without ST (4.5 nmol/L) for 24 h in the absence or presence of insulin (7 nmol/L). After culture for 24 h with insulin alone, adipocytes from neonatal and growing pig adipose tissue maintained the capacity to incorporate glucose into total lipid at rates comparable to those in fresh tissue. Culture for 24 h with ST in the presence or absence of insulin decreased adipocyte glucose incorporation into fatty acids. Addition of ST, in the absence or presence of insulin, also increased the accumulation of glycerol in the medium during culture of neonatal and growing pig adipose tissue. Furthermore, culture for 24 h with ST resulted in higher basal lipolysis measured during incubation of isolated adipocytes in the presence of adenosine deaminase. In addition, culture with ST decreased adipose tissue lipoprotein lipase (LPL) activity and completely blocked the stimulatory effect of insulin on activity of this enzyme. The present study is the first to demonstrate in neonatal pigs that, as in growing pigs, ST regulates adipose tissue metabolism through decreasing lipid synthesis and LPL activity and increasing lipolysis. Thus, ST may play an important role in nutrient partitioning during the neonatal period.

Redefining body composition: nutrients hormones, and genes in meat production

Growth rate and body composition of livestock can be optimized to meet consumer needs for a leaner product and to improve the efficiency of meat-animal production. Optimization strategies have traditionally focused on genetic selection and cost-effective ration formulation to achieve the genetic potential. Advances in understanding the mechanisms of growth and its control have led to additional opportunities for its manipulation. These include nutritional manipulation,the use of growth promotants, and, more recently, the ability to change the genetic potential through genetic engineering. Selection of appropriate candidate genes for manipulation depends on understanding the mechanisms underlying differentiation and growth of embryonic muscle cells. Recent advances in genetic engineering techniques, including gene therapy and germline transgenesis, will likely hasten the genetic progress toward a leaner carcass in domestic livestock. Such strategies may prove to be more beneficial then the controlled enhancement of somatotropin expression.

Endocrine responses to weaning and changes in post-weaning diet in the young pig

The effects of weaning and changing post-weaning diet composition on growth patterns and growth-related hormonal profiles were evaluated in neonatal pigs. Forty-eight crossbred piglets were assigned to two groups (n = 24/group) based on weaning at 2 or 3 wk of age (2W and 3W groups. respectively). At weaning, piglets were removed from the sow and placed on a commercial starter ration for the first 11 d post-weaning (Phase I diet). At Day 12 post-weaning, pigs were placed on a growing ration for the remainder of the study (Phase II diet). Body weights and blood samples were collected twice weekly from birth until 42 d of age. Serum insulin-like growth factor (IGF)-1, IGF-2, and average daily gain (ADG) were reduced (P < 0.05) in both groups as a result of weaning, whereas serum growth hormone (GH) was elevated (P < 0.05). Earlier weaning resulted in a greater reduction in growth rate and serum IGF-2 values (P < 0.05). Mild reductions in ADG occurred after the Phase I to II dietary change in both weaning groups (P < 0.05), but serum IGF-1 decreased only in the 2W group (P < 0.05). Growth hormone concentrations tended to increase after the change in post-weaning diets (P = 0.07 and 0.16 in 2W and 3W, respectively). Serum thyroxine (T4) and triiodothyronine (T3) levels were unaltered by weaning but declined in both groups after the change in starter diets (P < 0.05). Changes in cortisol concentrations were not associated with weaning or the change in post-weaning diets. With the exception of serum IGF-1 concentrations, which were elevated in the 2W group, growth and endocrine endpoints were equivalent between experimental groups at the end of the study (42 d of age). These results indicate that earlier weaning and changing solid diets can more severely affect patterns of early growth and related hormone secretion, but effective compensatory mechanisms restore normal physiological and physical development.

Somatotroph function in the neonatal pig

The objective of this study was to evaluate developmental changes in somatotroph function and related gene expression in neonatal pigs. Male piglets were sacrificed at 1, 7, 14, 21, 28, 35, and 42 d of age (8/age group) for the collection of tissue and blood. Serum concentrations of GH were determined. Quantitations of mRNA were performed for pituitary Pit-1, GH, and GHRH receptor. Cultures of pituitary cells from each pig were stimulated with 0, 0.1, 1, or 10 nM GHRH; 2 mM 8-Br-cAMP; or 100 nM phorbol myristate acetate. Elevated serum concentrations of GH were observed at 1 d of age, followed by a pronounced decrease to basal levels thereafter (P < 0.0001). A mild transient increase in circulating GH occurred at Day 28. In vitro GH secretion was significantly stimulated by secretagogue treatments (P < 0.0001). Age-related declines in in vitro GH secretion were observed regardless of if the cells were stimulated by GHRH or by secretagogues that bypass the GHRH receptor (P < 0.001). Similarly, cellular GH content varied with age (P = 0.01). Levels of pituitary GH mRNA (P = 0.01) and GHRH receptor mRNA (P = 0.0002) decreased with age. The quantity of GHRH receptor mRNA was correlated with GH mRNA levels (r = 0.55, P = 0.02), serum GH concentrations (r = 0.55, P = 0.02), and in vitro GH secretion (r = 0.66, P = 0.001). Pituitary Pit-1 mRNA levels at 7 and 14 d of age were significantly elevated relative to all other sampling times (P = 0.0002). Levels of Pit-1 and GH mRNAs were significantly correlated (r = 0.64, P = 0.003). These results demonstrate a strong developmental regulation of somatotrophic function and related gene expression during the early neonatal period of the pig. Age-related decreases in secretory function may be mediated by concurrent mechanisms relating to the expression of the GHRH receptor and of GH.

Developmental changes in serum IGF-1 and IGFBP levels and liver IGFBP-3 mRNA expression in intrauterine growth-retarded and control swine

The 29 M(r) x 10(-3) IGFBP was significantly elevated (P < 0.01) in IUGR piglets at 90 days fetally and at birth. Developmentally, 29 M(r) x 10(-3) IGFBP levels were higher fetally and at birth than at 21 and 49 days of age (P < 0.05). At 90 days fetally, hepatic IGFBP-3 mRNA levels were very high, while circulating levels of IGFBP-3 were extremely low whereas postnatally, hepatic IGFBP-3 mRNA and serum IGFBP-3 levels were parallel. This study provides new information concerning the developmental expression of IGFBP-3 and the relationship between serum levels of the 29 M(r) x 10(-3) IGFBP and IUGR in swine.