Effect of feed restriction on serum somatotropin, insulin-like growth factor-I-(IGF-I) and IGF binding proteins in cyclic heifers actively immunized against growth hormone releasing factor

Feed restriction often increases serum somatotropin (ST) and decreases insulin-like growth factor-I (IGF-I) in ruminants; however, the mechanisms responsible for this change in ST and IGF-I are not well defined. We investigated the effects of feed restriction on serum ST, IGF-I, IGF binding proteins (IGFBP), insulin and nonesterified fatty acids (NEFA) in cyclic Angus and Charolais heifers (n=15) previously immunized against growth hormone releasing factor (GRFi) or human serum albumin (HSAi). Cows were fed a concentrate diet ad libitum (AL) or were restricted to 2 kg cotton seed hulls (R) for 4 d. Each heifer received each dietary treatment in a single reversal design. As anticipated, GRFi decreased ST, IGF-I and insulin (P<.05). In addition, GRFi decreased serum IGFBP-3 (P<.01), but increased IGFBP-2 (P<.01). Feed restriction resulted in an increase in serum ST in HSAi, but not in GRFi heifers. Regardless of immunization treatment, feed restriction decreased serum IGF-I and insulin, and increased NEFA (P<.01). In conclusion, the increase in serum ST levels observed during feed restriction was blocked by active immunization against GRF. However, feed restriction resulted in decreased serum IGF-I in GRFi heifers in spite of initial low levels of IGF-I (due to GRFi). Although GRFi decreased levels of IGFBP-3 and increased levels of IGFBP-2, feed restriction for 4 d did not alter serum IGFBP.     

营养限制与补偿对蒙古羔羊体重和血液中生长相关激素的影响

试验研究不同能氮水平的营养限制与补偿对蒙古羔羊体重和血液生长相关的激素影响。选用内蒙古草原上健康的、平均体重15 kg左右的蒙古羔羊64只,随机分为对照组(CG)、限制1组(RG1)和限制2组(RG2)三个组,营养限制期(60 d)分别饲喂ME 10.88 MJ/kg、CP 13.0%(CG),ME10.88 MJ/kg、CP 8.9%(RG1),ME 8.62 MJ/kg、CP 5.7%(RG2)三个营养水平的日粮;营养补偿期(90 d)各组饲喂同一能氮水平饲粮(ME 9.75 MJ/kg,CP 12%)。结果表明:①随着营养水平的逐步降低,在限制末期,RG1组和RG2组羔羊的平均体重显著低于CG组(P<0.05),在补偿期,RG2组平均日增重显著高于CG组(P<0.05)。②在限制末期RG2组血液中GHRH及RG1、RG2组血液中GH浓度显著高于CG组(P<0.05),而RG2组血液中SS、IGF-I浓度显著低于CG组(P<0.05)。在补偿期,RG1、RG2组血液中IGF-I浓度有升高的趋势(P>0.05)。结果提示,营养限制所导致的羔羊血液中GHRH浓度升高和SS浓度降低可能是其在限制期血液中GH浓度升高及其在补偿期快速生长的原因之一。     

Alterations of serum insulin-like growth factor-I (IGF-I) and IGF-binding proteins (IGFBPs) in swine infected with the protozoan parasite Sarcocystis miescheriana.

The effects of a Sarcocystis miescheriana infection on insulin-like growth factor-I (IGF-I) and insulin-like growth factor binding proteins (IGFBPs) were investigated to determine possible mechanisms of growth retardation in growing pigs. Sixteen pigs averaging 14 kg body weight were divided into 4 groups of 4 pigs each and infected either with 0.5, 1.0, or 3.0 × 10⁶ sporocysts of S. miescheriana. Four pigs were retained as non-infected controls; however, they became serologically positive during the course of the infection. Effects also were investigated in 2 groups of 3 pregnant sows. One group was infected with 0.5 × 10⁶ sporocysts and the other group was retained as uninfected controls. Body weights of infected growing pigs were depressed as compared to controls following the acute phase 15 d after infection (dai). Serum concentrations of IGF-I dropped significantly (p < 0.05) during the acute phase of infection in all infected groups of growing pigs. Conversely, the amounts of unsaturated serum IGFBPs were elevated significantly (p < 0.05) during the acute phase of infection. Specifically, serum concentrations of IGFBP-1, IGFBP-2, and IGFBP-4 were elevated at this time, as determined by ligand blot analysis. There was no association between growth factor alterations and tissue damage as measured by serum creatinine kinase and aspartate aminotransferase levels. The extent of effects in growing pigs was related to the amount of the original parasite inoculum.

During the acute phase of infection 2 of 3 pregnant sows aborted. The third sow went to term, but piglets were stillborn or died within 24 hr. Compared to uninfected controls, serum concentrations of IGF-I in infected pregnant sows were depressed during and after the acute phase of the infection. Levels of unsaturated serum IGFBPs in pregnant sows were not affected.

These data suggest that decreased IGF-I levels and/or elevated levels of specific forms of IGFBPs may be a mechanism by which growth is affected in feeder pigs infected with S. miescheriana.     

营养限制及补偿对羔羊肉品质的影响

试验旨在研究营养限制期不同能氮水平和补偿期对羔羊肉品质的影响。选用80只蒙古羔羊,随机分为4组,分别为对照组(CG)、中等限制Ⅰ组(RG1)、中等限制Ⅱ组(RG2)和严重限制组(RG3)。营养限制期(60 d)4组羔羊日粮能量(ME)和蛋白质(CP)水平分别为10.88、10.88、9.41、8.62 MJ/kg和15.0%、10.0%、10.0%、5.7%。营养补偿期(90 d)4组羔羊日粮能量水平一致(ME 9.75 MJ/kg、CP 12%)。营养限制期结束和补偿期结束时,每组分别屠宰4只羔羊,测定背最长肌pH、失水率和剪切力值及胴体营养水平。结果表明,限制期结束时,RG3组羔羊背最长肌pH₁和胴体粗蛋白质、粗灰分含量显著高于CG组(P<0.05),背最长肌剪切力值显著低于CG组(P<0.05),胴体干物质含量极显著低于CG组(P<0.01);补偿期结束时,RG2组羔羊背最长肌pH₁显著高于CG组(P<0.05);RG1和RG2组羔羊背最长肌剪切力值和胴体粗蛋白质含量显著高于CG组(P<0.05);RG3组羔羊胴体粗灰分含量显著高于CG组(P<0.05)。因此,背最长肌pH、嫩度及胴体化学组成均受到营养限制的影响,经补偿后除嫩度外均能恢复到对照组水平,且随着受限程度的加剧,恢复速度越慢。     

Insulin-like growth factor (IGF)-I and IGF binding proteins-2, -3, -4, -5 in porcine corpora lutea during the estrous cycle; evidence for inhibitory actions of IGFBP-3

In this study we measured protein concentrations of insulin-like growth factor (IGF)-I and IGF binding proteins (IGFBPs) 2-5 in porcine corpora lutea (CLs) throughout the estrous cycle (Experiment 1), and examined the effects of IGFBP-3 and IGFBP-3 antibody (AB) on luteal progesterone (P4) secretion in vitro (Experiment 2). For Experiment 1, (CLs) and serum were collected on days (D) 4, 7, 10, 13, 15 and 16 of the estrous cycle (n = 5 animals per day). IGF-I was extracted from CLs and sera, and measured by radioimmunoassay (RIA). IGFBPs were measured in CLs by ligand blots. For Experiment 2, CLs (from Experiment 1) were enzyme dissociated and luteal cells cultured (24 h) in Medium 199 (M199) containing (0-500 ng/ml) IGFBP-3 (+/-IGF-I; 100 ng/ml), or (0-10 microg/ml) IGFBP-3 AB. P4 in media was measured by RIA. In Experiment 1, luteal IGF-I concentrations (ng/g tissue) were maximal on day 4 and gradually decreased thereafter. Serum IGF-I concentrations (ng/ml) were highest on days 4 and 7, compared with days 10-15. Peak levels of luteal IGFBP-3 were also seen on days 4 and 7 of the cycle. Luteal IGFBP-2 concentrations showed a tendency to increase on day 16 (P < 0.05 versus day 10), but no significant changes in IGFBP-4 or -5 were seen. In Experiment 2, IGFBP-3 (w IGF) inhibited the steroidogenic actions of IGF-I, but had no significant actions alone (IGFBP-3 w/o IGF). Finally, IGFBP-3 AB stimulated P4 secretion on days 4 and 7, but not on days 10-16. We conclude that IGFBP-3 inhibits IGF-I actions in the porcine CL.     

The effect of growth hormone-releasing peptide-2 (KP102) administration on plasma insulin-like growth factor (IGF)-1 and IGF-binding proteins in Holstein steers on different planes of nutrition

This study was conducted to investigate the nutrition-dependent changes in insulin-like growth factor (IGF)-1 and IGF-binding proteins (IGFBPs) with growth hormone releasing peptide-2 (D-Ala-D-betaNal-Ala-Trp-D-Phe-Lys-NH(2); GHRP-2 or KP102) treatment in growing Holstein steers. Eight 13 month-old Holstein steers were grouped on two levels of feed intake (high intake (HI); 2.43% body weight or low intake (LI); 1.22%) and each group was daily injected with KP102 (12.5 microg/kg body weight/day) or saline solution into the jugular vein during 6-day period. The concentration of plasma GH showed an increase after an i.v. bolus injection of KP102 on Day 1 and Day 6 in both the LI and HI groups. Plasma IGF-1 began to increase 10 hr following an i.v. bolus injection of KP102, but this was only observed in the HI group (P < 0.05). Also, the plasma IGF-1 in the HI group with daily injections was significantly greater than the LI group from Day 1 of KP102 administration (P < 0.05). It reached maximum values of 125.1 +/- 7.6 ng/ml after Day 2, and returned to pre-injection levels after Day 4, however, no change in plasma IGF-1 was observed in LI with administration of KP102. During 6 days of treatment, plasma 38-43 kDa IGFBP-3 and 24 kDa IGFBP-4 were significantly higher in KP102 treated steers but only in the HI group (P < 0.05). Plasma 34 kDa IGFBP-2 decreased in the HI group and did not show any change following an injection of KP102. In conclusion, the effect of stimulated endogenous GH with KP102 administration increased plasma IGF-1, 38-43 kDa IGFBP-3 and 24 kDa IGFBP-4 levels in the HI group of growing Holstein steers, but not in the LI one. Thus, we strongly believe that the plasma IGF-1 and IGFBPs response to KP102 treatment is modulated by the nutritional status of growing Holstein steers and the increased plasma IGF-1 concentration with KP102 treatment may be regulated by plasma 38-43 kDa IGFBP-3 and 24 kDa IGFBP-4 in Holstein steers.     

Predicting growth in angus bulls: the use of GHRH challenge, insulin-like growth factor-I, and insulin-like growth factor binding proteins

Plasma IGF-I, IGF binding protein-2 (IGFBP-2), and IGFBP-3 were quantified in growing Angus bulls (n = 56) to determine their relationship with postweaning growth and carcass ultrasound measurements. In addition, GH response to GHRH challenge (area-under-the-curve GH [AUC-GH) was determined for each bull as part of a previous study. Blood was collected by jugular venipuncture at the start of a 140-d postweaning growth performance test and at 28 d intervals for plasma IGF-I determination by RIA. Plasma IGFBP-2 and -3 content was measured at the start of the study, on d 70, and d 140 by Western ligand blotting. Individual weights and hip heights were measured every 28 d during the study and carcass longissimus muscle area, intramuscular fat percentage, and carcass backfat were estimated by ultrasound on d 140. Greater plasma IGF-I at the start of the performance test was associated with reduced postweaning ADG and increased longissimus area. Throughout the performance test period, the correlations between plasma IGF-I and hip height were consistently positive, ranging from 0.10 to 0.38, but the correlations between ADG and IGF-I varied from -0.32 to 0.31. Age-adjusted d-1 plasma IGFBP-2 was related to ADG during the performance test, explaining nearly 30% of the variation in ADG. A model combining weaning age, IGFBP-2, and AUC-GH showed a strong relationship with ADG (R2 = 0.40). Plasma IGFBP-2 and -3 were not related to carcass characteristics, and IGFBP-3 was not related to growth rates. This study provides additional evidence for the variable relationship between plasma IGF-I and growth rates in cattle. A significant positive relationship between plasma IGFBP-2, AUC-GH, and postweaning ADG warrants further investigation.     

Insulin-like growth factors and IGF-binding proteins in bovine seminal plasma.

Insulin-like growth factor-I (IGF-I) is an important factor for germ cell development and maturation of spermatozoa. Actions of IGFs are modulated by IGF-binding proteins (IGFBPs) that may, depending on their concentration and site of expression, inhibit or enhance effects of IGF-I. We characterized IGFs and IGFBPs in seminal plasma from bulls routinely used for artificial insemination (AI) and from bulls producing poor-quality semen (low mass and individual motility of spermatozoa). IGFs were measured by specific radioimmunoassay in 22 samples of seminal plasma from nine different AI bulls with high (> 76.8%), average (72.8-73.4%), or low (< 69.5%) nonreturn rate (NRR). IGF-I and IGF-II levels were 144 +/- 9 ng/ml (mean +/- SE; range, 79-238 ng/ml) and 144 +/- 10 ng/ml (range, 55-221 ng/ml), respectively, and did not correlate with NRRs. IGF-I concentrations in seminal plasma from bulls producing poor-quality semen (n = 10) were significantly (P < 0.05) greater (194 +/- 26 ng/ml; range, 94-370 ng/ml), whereas IGF-II levels were significantly (P < 0.05) lower (93 +/- 17 ng/ml; range, 38-183 ng/ml) than in AI bulls. Ligand blot analysis of seminal plasma for IGFBPs revealed the presence of a 38-/45-kDa doublet band and a 30-kDa IGFBP. These IGFBPs were identified as IGFBP-3 and IGFBP-5, respectively, by immunoprecipitation using specific antibodies. In addition, a low amount of IGFBP-4 was detected in bovine seminal plasma by immunoprecipitation. There was a marked difference in the activity of IGFBPs between individual bulls, with a relatively small within-bull variance. The differences in IGFBP activities did not correlate with the fertilization capacity of the bulls in vivo or in vitro nor with immunoreactive IGF-I and IGF-II levels in seminal plasma. Our results demonstrate the presence of IGFBPs in bovine seminal plasma. In contrast to human seminal plasma, high activity of IGFBP-3 was detected in seminal plasma of some bulls, suggesting species-specific regulation of IGFBP activity by proteases.     

The relationship between endogenous insulin-like growth factors and growth in pigs.

Previous studies have reported conflicting data on gender differences in plasma IGF-I in postnatal pigs. There is also debate over the role of IGF-II in regulation of postnatal growth. We have, therefore, determined the concentrations of plasma IGF-I, IGF-II, and IGF-binding protein-3 (IGFBP-3) in boars, barrows, and gilts and related these to postnatal growth characteristics. Plasma concentrations of IGF-I were higher in boars than in gilts or barrows from 13 wk. of age, and plasma IGF-II levels were generally higher in barrows than in boars or gilts. Plasma IGFBP-3 levels were higher in boars than in gilts or barrows at most ages. Between 15 and 23 wk. of age, IGF-I and IGFBP-3, but not IGF-II, were positively associated with growth rate, voluntary feed intake, and gain:feed ratio. Plasma IGF-II, but not IGF-I or IGFBP-3, was positively associated with backfat depth during this period. These results support the hypothesis that circulating IGF-I and IGF-II are regulators of lean and adipose tissue growth, respectively.     

Effects of restricted feeding, low-energy diet, and implantation of trenbolone acetate plus estradiol on growth, carcass traits, and circulating concentrations of insulin-like growth factor (IGF)-I and IGF-binding protein-3 in finishing barrows

Effects of restricted feeding (80% ad libitum), feeding a low-energy diet containing 84% DE (2.95 Mcal/kg) of the control diet, and implantation of Revalor H (140 mg trenbolone acetate plus 14 mg estradiol-17beta) on growth, carcass traits, and serum concentrations of insulin-like growth factor (IGF)-I and IGFbinding protein-3 (IGFBP-3) were studied in crossbred finishing barrows beginning from 59 +/- 0.9 kg of body weight. Blood samples were taken every 3 wk and the animals were slaughtered at approximately 105 kg body weight. Restricted feeding caused a decrease (P < 0.01) in ADG; feeding the low-energy diet was effective in reducing backfat thickness but decreased gain:feed; the implantation caused a decrease in ADG, feed intake, and backfat thickness and increased gain:feed. Overall pork quality based on pH, drip loss, and the lightness in color of longissimus muscle was not affected by any of the treatments. Serum IGF-I concentration increased following the implantation but did not change (P > 0.05) due to other treatments. Immunoreactive IGFBP-3 concentration was not changed by any of the treatments. Overall ADG was positively correlated with early-stage (d 21) IGF-I and IGFBP-3 concentrations only in unimplanted barrows, whereas backfat thickness was negatively correlated with d-42 IGF-I concentration in all but unimplanted barrows with ad libitum intake. A strong positive correlation (P < 0.01) between IGF-I and IGFBP-3 concentrations was apparent with increasing age of the animals. Results suggest that growth rate and backfat thickness are decreased by a moderate restriction of feed or energy intake with no accompanying changes in circulating IGF-I and IGFBP-3 concentrations and that the beneficial effect of Revalor H implantation on feed efficiency may be mediated, in part, by IGF-I. Moreover, both IGF-I and IGFBP-3 concentrations may be useful as growth indices in pigs.     

Cloning and expression of equine insulin-like growth factor binding proteins in normal equine tendon

OBJECTIVES: To define a portion of the nucleotide sequences of each of the 6 insulin-like growth factor (IGF) binding proteins (IGFBPs) in horses and describe patterns of messenger RNA (mRNA) and protein expression for IGFBPs in normal equine tendons. ANIMALS: 7 horses. PROCEDURE: Total RNA was extracted from the tensile region of normal superficial digital flexor tendons and reverse transcribed into complimentary DNA (cDNA). The cDNA was amplified via PCR, and products representing portions of each IGFBP were cloned and sequenced. Nucleotide sequences were used to deduce the amino acid sequences, and both nucleotide and predicted amino acid sequences were compared with those published for bovine, human, mouse, and ovine IGFBPs. Gene expression was quantitated by real-time PCR assay, and protein expression was evaluated by western ligand blot (WLB). RESULTS: Clones ranged in size from 262 to 522 bp and had high degrees of sequence homology with other mammalian species. Sequence homology was highest between bovine and equine IGFBPs (86% to 95%) and amongst the IGFBP-5 sequences from the various species (92% to 95%). Message for IGFBP-2 to -6, but not IGFBP-1, was expressed in normal tendon. Protein expression for IGFBP-2, -3, and -4 was detected byWLB in normal tendon and markedly increased in damaged tendons. CONCLUSIONS AND CLINICAL RELEVANCE: Results provide basic information and tools needed for further characterization of the role of the IGF system in tendon healing and may lead to the ability to potentiate the response of healing tendon to exogenous IGF-I via concurrent manipulation of IGFBPs.     

Increased degradation of insulin-like growth factor-I in serum from feed-deprived steers

Severe feed restriction decreases serum insulin-like growth factor I (IGF-I) concentration in animals, and this decrease is thought to be due to reduced IGF-I production in the liver. The objective of this study was to determine whether feed deprivation also increases degradation of serum IGF-I and serum levels of IGF binding protein 3 (IGFBP-3) and acid-labile subunit (ALS), which inhibit IGF-I degradation and increase IGF-I retention in the blood by forming a ternary complex with IGF-I, in cattle. Five steers had free access to pasture, and another five were deprived of feed for 60 h. Serum concentration of IGF-I and liver abundance of IGF-I mRNA at the end of the 60-h period were 50% and 80% lower, respectively, in feed-deprived steers than in fed steers. Less ¹²⁵I-labeled IGF-I remained intact after a 45-h incubation in sera of feed-deprived steers than in sera of fed steers, suggesting that serum IGF-I is more quickly degraded in feed-deprived animals. Serum levels of IGFBP-3 and ALS were decreased by 40% and 30%, respectively, in feed-deprived steers compared with fed steers. These decreases were associated with more than 50% reductions in IGFBP-3 and ALS mRNA in the liver, the major source of serum IGFBP-3 and ALS. Taken together, these results suggest that feed deprivation reduces serum concentration of IGF-I in cattle not only by decreasing IGF-I gene expression in the liver, but also by increasing IGF-I degradation and reducing IGF-I retention in the blood through decreasing IGFBP-3 and ALS production in the liver.     

Effects of dietary protein and growth hormone-releasing peptide (GHRP-2) on plasma IGF-1 and IGFBPs in Holstein steers

This study was conduct to determine the influence of dietary protein on the response of plasma insulin-like growth factor-1 (IGF-1) and insulin-like growth factor binding proteins (IGFBPs) to exogenous growth hormone releasing peptide-2 (GHRP-2 or KP 102) in Holstein steers. Eight 16-month-old Holstein steers were grouped by liveweight to two feeding treatments; high protein (HP; CP 1.38 kg/day and TDN 4.5 kg/day DM intake, n=4) or low protein (LP; CP 0.66 kg/day and TDN 4.42 kg/day DM intake, n=4). The experiment was a single reverse design whereby each group was injected twice daily with GHRP-2 (12.5 microg/kg body weight (BW)/day) or saline solution into the jugular vein for a 6-day period. Plasma IGF-1 in the HP group were higher than in the LP group (P<0.05), but plasma 34 kDa IGFBP-2 was lower in the HP than the LP group (P<0.05). The amplitude of the maximum growth hormone (GH) peaks responding to GHRP-2 injection were higher at day 1 than at day 6 of saline or GHRP-2 treatment in both LP and HP steers (P<0.05). The area under the GH response curve for 180 min after the GHRP-2 injection was not significantly different between the LP and the HP groups at days 1 and 6. A response in plasma IGF-1 concentration to GHRP-2 treatment in the HP group was observed at day 1 (198.9+/-18.1 ng/ml), day 2 (195.2+/-21.1 ng/ml) and day 6 (201.3+/-14.8 ng/ml) (P<0.05). No increase in plasma IGF-1 was observed from GHRP-2 administration in the LP group. Although the response of plasma IGF-1 concentration to GHRP-2 administration was increased in the HP group (P<0.05), there was no apparent effect of GHRP-2 treatment on plasma 38-43 kDa IGFBP-3 and 34 kDa IGFBP-2 at days 2 and 6 of treatment. In conclusion, it is proposed that the 34 kDa IGFBP-2 is sensitive to dietary protein level and may play an important role in the regulation of circulating IGF-1 in ruminant. In addition, increased plasma IGF-1 concentration observed in the HP group in response to the GHRP-2 treatment did not appear to affect plasma IGFBPs.     

The influence of level of feeding on growth and serum insulin-like growth factor I and insulin-like growth factor-binding proteins in growing beef cattle supplemented with somatotropin

The objective of this study was to determine the effects of level of feeding on growth, feed efficiency (gain:feed; G:F), body composition (BC), and serum concentrations of somatotropin (ST), IGF-I, and IGF-binding proteins (BP) in growing beef cattle supplemented with bovine (b) ST. In each of two consecutive years, 40 growing beef cattle were blocked by weight (average BW: yr 1 = 316 kg, yr 2 = 305 kg) and used in a 2 x 2 factorial arrangement with main effects of bST (0 or 33 microg x kg BW(-1) x d(-1)) and level of feed intake (ad libitum [AL] or 0.75 AL). Relative to uninjected cattle, treatment with bST increased ADG 9.6% (1.14 vs 1.25 kg/d; P < 0.05) and increased G:F 8.1% (12.3 vs 13.3 gain [g]:feed [kg]; P < 0.05), whereas ADG in AL animals was 39% greater than that in 0.75 AL animals (1.39 vs 1.00 kg/d; P < 0.05). There was a tendency (P = 0.10) for a bST x level of feeding interaction, such that the increase in ADG with bST was greater in AL cattle than in 0.75 AL cattle (10.6 vs 7.8%; P = 0.10). Serum concentrations of ST were greater in 0.75 AL cattle than in AL cattle (13.0 vs 8.6 ng/mL; P < 0.05) and in bST-treated cattle than in uninjected cattle (16.3 vs 5.2 ng/mL; P < 0.05). Due to a bST x level of feeding interaction (P < 0.01), the magnitude of the increase in serum ST to exogenous bST was greater (P < 0.01) in 0.75 AL cattle than in AL cattle. Relative to uninjected cattle, treatment with bST increased (P < 0.05) serum concentrations of IGF-I and IGFBP-3 and reduced (P < 0.05) concentrations of IGFBP-2. Similarly, AL cattle had greater (P < 0.05) serum concentrations of IGF-I and IGFBP-3 and reduced (P < 0.05) IGFBP-2 compared with 0.75 AL cattle. In summary, treatment with bST increased growth rate and G:F and stimulated serum IGF-I and IGFBP-3 while reducing IGFBP-2. Feeding at 0.75 ad libitum intake reduced the magnitude of response for each of these variables. Thus, limit-feeding may reduce the effect of exogenous bST on growth rate by blunting bST-induced increases in IGF-I and IGFBP-3 and bST-induced decreases in IGFBP-2.     

Effect of recombinant porcine somatotropin on energy and protein utilization by growing pigs: interaction with capacity for lean tissue growth.

Three litters of four pigs from each of four different groups were used to evaluate the effect of porcine somatotropin (pST) on growth performance, body gain composition, energy and N metabolism, and in vitro cytochrome oxydase (final enzyme of the respiratory chain) activity of tissues. The four groups included boars from a synthetic line (SG1) or the Large White breed (SG2) and barrows from the Large White breed (SG3) or crossbred between Large White and Meishan breeds (SG4). Inherent capacity for daily lean tissue growth (LTG) decreased from SG1 to SG4. Within a litter, one pig was slaughtered and dissected at the beginning of the experiment (55 kg BW) and the three others were fed the same daily supply of protein and amino acids (26 g of lysine/d) but relative daily energy levels were either 113 (without pST: E1/0), 100 (3 mg of pST/d: E2/pST) or 87 (3 mg of pST/d: E3/pST). The 100 energy level corresponded to the ad libitum intake of E2/pST pigs. Two energy and N balances were carried out in respiration chambers during the experimental period. Pigs were slaughtered and dissected at approximately 95 kg BW and composition of gain was estimated using the comparative slaughter technique. In E1/0 pigs, daily BW, lean, and N gain were affected (P less than .01) by group; 566, 471, 374, and 315 g/d of lean tissue gain in SG1, SG2, SG3, and SG4 pigs, respectively. At high ME intake (E2/pST vs E1/0), pST increased daily BW (+14%), lean (+27%), or N (+26%) gain and reduced adipose tissue (-50%) gain, but the pST effect was inversely related to LTG: for N, the improvement was 2.8, 7.1, 7.0, and 11.1 g/d in SG1, SG2, SG3, and SG4 groups, respectively. Energy restriction (E3/pST vs E2/pST) reduced (P less than .001) adipose tissue gain in all groups but did not affect lean tissue or N gains in SG1, SG2, and SG3 pigs. In the pST-treated pigs of the SG4 group, the lean tissue or N gains were reduced (P less than .01) by energy restriction. Energy restriction combined with pST treatment (E3/pST) led to negligible amounts of fat deposited (40 g/d for SG1 + SG2 + SG3 pigs) and a gain:feed ratio higher than 500 g/kg (580 in SG1 pigs). The increased heat production measured in pST-treated pigs was due to its maintenance component: 275 vs 257 kcal of ME.kg BW-.60.d-1 (P less than .01).(ABSTRACT TRUNCATED AT 400 WORDS)     

Effects of antimicrobials and weaning on porcine serum insulin-like growth factor binding protein levels

The effects of subtherapeutic antimicrobial supplementation and weaning on serum levels of IGF-I and insulin-like growth factor binding proteins (IGFBP)-2, -3 and -4 were determined in crossbred weanling pigs. At weaning, pigs were allotted to a diet containing 21.8% crude protein and 1.15% lysine with or without Aureozol (110 mg/kg of Aureomycin chlortetracycline, 110 mg/kg of sulfathiazole, and 55 mg/kg of penicillin) for 4 wk. Insulin-like growth factor-binding proteins and IGF-I analyses were performed on blood samples that were drawn weekly. Weaning decreased serum IGFBP-3 levels in both control and Aureozol-treated groups on d 6 and d 14 (P < 0.05) relative to preweaning levels. The IGFBP-3 values returned to preweaning levels by d 21. Although the circulating levels of both the 43-kDa and the 39-kDa glycosylation variants of IGFBP-3 were affected by weaning, the level of the 39-kDa IGFBP-3 was affected relatively more than that of the 43-kDa IGFBP-3 (P < 0.05). Compared with circulating IGFBP-3 levels in control pigs, Aureozol-treated pigs had higher circulating IGFBP-3 levels on d 21 (43%, P < 0.05) and d 27 (46%, P < 0.05). In direct contrast to the effect of weaning on serum IGFBP-3 level, serum IGFBP-2 levels increased on d 6 and d 14 after weaning (P < 0.05) and decreased to preweaning levels by d 21. The IGFBP-2 levels continued to decline and were less than preweaning levels by d 27 (P < 0.05). Aureozol treatment had no effect on serum IGFBP-2 levels at any time. Serum levels of nonglycosylated IGFBP-4 were not affected by either weaning or Aureozol supplementation. Weaning decreased circulating IGF-I concentration on d 6 in both control and Aureozol-treated pigs (76 and 73%, respectively, P < 0.05) and on d 14 (62%, P < 0.05) and d 21 (32%, P < 0.05) in control pigs. Aureozol-supplemented pigs had higher serum IGF-I concentrations than control pigs on d 14 (82%, P < 0.05), d 21 (55%, P < 0.05), and d 27 (36%, P < 0.05). The Aureozol-fed pigs had a 14.2% increase in BW gain (P < 0.05) and a 59.6% increase in ADG (P < 0.05) compared with pigs fed the control diet. Both Aureozol-supplementation and weaning cause changes in serum IGFBP levels and IGF-I concentrations that might be involved in regulating rate and efficiency of growth.     

Effects of fasting on IGF-I,IGF-II,and IGF-binding protein mRNA concentrations in channel catfish (Ictalurus punctatus)

The effects of fasting on insulin-like growth factor (IGF)-I, IGF-II, and IGF-binding protein (IGFBPs) mRNA in channel catfish were examined. Fed control fish (Fed) were compared to fish that had been fasted for 30 d followed by 15 d of additional feeding (Restricted). Sequence alignment and similarity to orthologous proteins in other vertebrates provided structural evidence that the 3 catfish sequences identified in the present research were IGFBP-1, -2, and -3. Prolonged fasting (30 d) reduced body weight approximately 60% (P < 0.001) and decreased IGF-I mRNA in the liver and muscle (P < 0.01). Fifteen days of re-feeding restored concentrations of hepatic and muscle IGF-I mRNA. Liver IGF-II mRNA was not affected by fasting but was increased 2.2-fold after 15 d of re-feeding (P < 0.05). Abundance of muscle IGF-II mRNA was similar between the fed control group and the restricted group throughout the experimental period. Fasting also increased liver IGFBP-1 mRNA (P < 0.05) and decreased IGFBP-3 mRNA (P < 0.01), whereas abundance of IGFBP-2 mRNA was not significantly affected. Interestingly, re-feeding for 15 d did not restore concentrations of IGFBP-1 and IGFBP-3 mRNA relative to fed control concentrations. The IGF results suggest that IGF-I and IGF-II are differently regulated by nutritional status and probably have a differential effect in promoting muscle growth during recovery from fasting. Similar to mammals, IGFBP-1 mRNA in catfish is increased during catabolism, whereas IGFBP-3 mRNA is decreased during inhibited somatic growth. The IGFBP results provide additional evidence of the conserved nature of the IGF-IGFBP-growth axis in catfish.     

Insulin administration suppresses an increase in insulin-like growth factor binding protein-2 gene expression stimulated by fasting in the chicken

1. We examined the changes in plasma IGF-I concentration and tissue IGFBP-2 gene expression of young fasted chickens refed a commercial diet or administered bovine insulin intravenously. 2. Plasma IGF-I concentration was decreased by fasting for 2 d. Although plasma IGF-I concentration was increased by refeeding, it didn't recover to the level of chickens fed a commercial diet ad libitum. 3. Insulin administration lowered plasma IGF-I concentration compared to other groups. 4. Hepatic IGFBP-2 mRNA was increased by fasting for 2 d and decreased by refeeding for 6 h. Insulin administration also decreased hepatic IGFBP-2 gene expression stimulated by fasting to the level of refed chickens. 5. IGFBP-2 mRNA in the gizzard was increased by fasting for 2 d and tended to decrease after refeeding for 6 h. Insulin administration decreased gizzard IGFBP-2 gene expression to less than that in refed chickens. 6. There was no between-treatment difference in IGFBP-2 mRNA in the brain and kidney. 7. These results suggest that the changes in IGFBP-2 gene expression in the liver and gizzard by fasting and refeeding might be partly regulated by the alteration in plasma insulin concentration.     

Ontogenic maturation of the somatotropin/insulin-like growth factor axis

The ontogeny of the somatotropin/insulin-like growth factor system was examined in well-fed pigs under basal conditions and during a short-term challenge of porcine ST (pST). The study was conducted with two replicates of eight castrate male pigs from 3.8 kg BW (10 d of age) to 92 kg BW (129 d of age). Pigs were reared individually with ad libitum access to milk replacer through 23 d of age. Thereafter, pigs were fed a corn, soybean meal, and dry skim milk diet formulated to exceed nutrient requirements by approximately 30%. Pigs were randomly assigned to receive daily i.m. injections of either 0 (buffer) or 120 microg/kg BW of pST for a duration of 4 d starting at 10, 19, 33, 43, 63, 83, and 125 d of age. Blood was collected via jugular venipuncture on d 0 and 4 of the challenge. Circulating levels of IGF-I were not dramatically affected by age, but levels of IGF-II were low from 10 to 19 d of age and then increased through later stages of growth. Circulating concentrations of IGF binding protein (BP)-3 increased with age (P < .05), but levels of IGFBP-2, a 30-kDa IGFBP, and IGFBP-4 were unchanged (P > .10). The pST challenge reduced plasma urea nitrogen at all ages, but the magnitude of the response was less in younger pigs compared with the maximum response in pigs greater than 30 kg BW (63 d of age). The IGF-I response to the pST challenge also increased from approximately 30% in young pigs to a threefold increase in older pigs. Regardless of age, concentrations of IGF-II were minimally affected by the pST challenge. Circulating levels of IGFBP-3 increased and IGFBP-2 levels decreased in response to the pST challenge, and the magnitude increased with age. The high nutritional status of pigs in the early phases of growth diminished the postnatal changes in IGF-I and IGFBP-2, but not IGF-II or IGFBP-3. Overall, data demonstrate a developmental regulation of the ST/IGF system, with pST challenges altering circulating concentrations of IGF-I, IGFBP-3, and IGFBP-2 coincident with changes in amino acid metabolism.     

Influence of nutritional deprivation on insulin-like growth factor I, somatotropin, and metabolic hormones in swine

Although growth hormone (GH) is a primary stimulus for the synthesis of insulin-like growth factor I (IGF-I), other factors such as nutritional status, insulin, and thyroid hormones are important modulators of circulating IGF-I levels. Thus, the effects of feed restriction and subsequent refeeding on plasma levels of IGF-I, GH, insulin, and thyroid hormones were studied in swine. Despite an elevation in plasma GH levels after 48 h of feed restriction, circulating IGF-I levels were decreased by 53% (P less than .05). Plasma triiodothyronine (T3) and insulin were lower (P less than .05) within 24 h after the feed restriction began, whereas thyroxine (T4) did not decrease until 48 h after removal of feed. Blood glucose levels remained unchanged throughout the experiment. Refeeding after the 48-h fast was associated with a decline (P less than .05) in circulating GH levels within 2 h, concomitant with an elevation (P less than .05) in plasma insulin and T3. Refeeding fasted pigs was associated with an increase (P less than .05) in plasma IGF-I; however, levels still had not returned to prefast concentrations within 24 h after refeeding. These data indicate that the GH-IGF-I axis becomes uncoupled during nutritional restriction in swine and that inadequate nutrient supply may limit the expression of the anabolic effects of GH.