An examination of the role of feeding regimens in regulating metabolism during the broiler breeder grower period. 2. Plasma hormones and metabolites.

A trial was conducted to determine the effects of different feeding regimens on plasma hormone and metabolite levels in 16-wk-old broiler breeder pullets. A flock of 350 Cobb 500 breeder pullets was divided in 2 at 28 d of age and fed either every day (ED, 5 pens of 35 birds) or skip-a-day (SKIP, 5 pens of 35 birds) from 28 to 112 d of age. Total feed intake did not differ between the 2 groups. At 112 d, 52 randomly selected pullets from the larger flock of ED-fed pullets, and 76 from the SKIP-fed pullets were individually caged and fed a meal of 74 g (ED) or 148 g (SKIP). Blood samples were collected from 4 pullets in each group by cardiac puncture at intervals after feeding. Plasma was analyzed for insulin, glucagon, insulin-like growth factor-I and insulin-like growth factor-II, triiodothyronine and thyroxine, corticosterone, leptin, glucose, nonesterified fatty acids, triglycerides, and uric acid. Feed retention in the crop was also noted at each interval. In ED birds, the crop was empty by 12 h and in SKIP birds, the crop was empty by 24 h after feeding. The physiological responses to fasting, such as increased glucagon and corticosterone and reduced plasma triglyceride, occurred at times coincidental with crop emptying in both ED and SKIP birds. Overall, mean insulin-like growth factor-I levels were higher (P < 0.05) in ED birds. Triiodothyronine was higher (P = 0.09) in SKIP birds. Overall mean plasma corticosterone was 2-fold higher in SKIP-fed birds, which may be related to the increased length of fasting periods, hunger, and stress. Plasma leptin was consistently higher in ED-fed birds, which was indicative of their more consistent food supply and more stable energy status. In summary, the experiment reported here shows that different feeding regimens can alter hormone and metabolite profiles, in spite of total feed intakes being equal.

Developmental changes in chicken and turkey insulin-like growth factor-I (IGF-I) studied with a homologous radioimmunoassay for chicken IGF-I.

The development of a homologous radioimmunoassay (RIA) for chicken insulin-like growth factor-I (cIGF-I) and its use to investigate the developmental changes in IGF-I in the chicken and turkey is described. A double-antibody RIA has been developed using recombinantly derived cIGF-I as antigen, radiolabelled tracer and standard. The resulting immunoassay has a minimum detection limit of 0.035 ng and effective dose of 2.5 ng. Dose-response curves of chicken and turkey plasma and tissue extracts were parallel with cIGF-I standard. The antiserum is specific for IGF-I as no cross-reactivity with chicken IGF-II, insulin, glucagon, gastrin or avian pancreatic polypeptide was observed. We have also established that acid/ethanol extraction of chicken and turkey plasma reduced possible interference of IGF-binding proteins (IGFBPs) in the RIA. Comparison of IGF-I immunoactivity in unextracted and acid/ethanol-extracted samples following gel filtration under acidic and neutral conditions indicates that the cIGFBPs may be acid-labile. Analyses of samples from growing chickens and turkeys using the homologous avian reagents revealed higher IGF-I concentrations than if the IGF were quantified using heterologous mammalian-derived reagents. A similar pattern was observed when tissue extracts were assayed for IGF-I content. The application of the homologous RIA to monitor blood and tissue IGF-I levels during embryonic development and posthatch growth in avian species will provide more accurate comparisons of results from studies on the role of IGF-I in growth and metabolism of domestic birds.

Assessment of developmental changes in chicken and turkey insulin-like growth factor-II by homologous radioimmunoassay.

The development of a homologous RIA for chicken insulin-like growth factor-II (cIGF-II) and its application to investigate the developmental changes in IGF-II in the chicken and turkey are described. A double-antibody RIA has been developed using recombinantly derived cIGF-II as antigen, radiolabelled tracer and standard. Serial dilutions of chicken and turkey plasma were parallel to serial dilutions of cIGF-II standard. We have also established that acid/ethanol extraction of chicken and turkey plasma reduced possible interference of insulin-like growth factor-binding proteins in the RIA. Consumption of a low-protein diet by male chickens lowered plasma IGF-I twofold, whereas IGF-II levels were unchanged. Food withdrawal evoked an increase in circulating IGF-II, while IGF-I levels were reduced. Refeeding returned both growth factors to normal circulating concentrations. During chick embryo incubation, plasma IGF-II levels were tenfold higher than those of IGF-I. In the turkey embryo, plasma IGF-II concentrations were higher than those of IGF-I. During the post-hatch period. IGF-II levels declined with age in chickens. In the growing turkey, IGF-II levels were consistently higher than IGF-I levels. The application of the homologous RIA to monitor plasma levels during embryonic development and post-hatch growth in avian species will provide more accurate comparisons of results from studies on the role of IGF-II in growth and metabolism of domestic birds.

Plasma clearance and tissue distribution of labelled chicken and human IGF-I and IGF-II in the chicken.

The metabolic clearance of chicken IGF-I (cIGF-I), cIGF-II, human IGF-I (hIGF-I), and hIGF-II was examined in the chicken using 125I-labelled growth factors. Superose-12 chromatography of plasma collected at 7.5 min post-infusion revealed peaks of radioactivity corresponding to 150 and 43 kDa and unbound tracer. Statistical analysis of trichloroacetic acid (TCA)-precipitable radioactivity in sequential plasma samples as well as following chromatography of the same samples revealed that clearance of the radiolabelled peptides followed an apparent triphasic pattern. The close similarity of the individual chromatographically defined pools in their clearance rate compared with the three components described by TCA precipitation strongly suggested their identity. Both free 125I-labelled cIGF-II (3.11 min) and hIGF-II (3.01 min) were cleared at a greater rate than their IGF-I counterparts. Unbound hIGF-I was cleared at a greater rate than cIGF-I (4.45 vs 5.66 min respectively). A similar pattern for clearance was evident in the radio-labelled growth factors associated with the 43 kDa component, although at a longer half-life. There was no difference in the apparent clearance of the radiolabelled growth factors associated with the 150 kDa component between IGF-I or -II or between species. Analysis of the chromatographic profiles of radioactive IGF-I peptides complexed to serum proteins versus those bound to labelled IGF-II peptides revealed the presence of a large molecular mass binding protein in vivo. Ligand blotting of chicken serum determined that a binding protein with a mass of 70 kDa was detectable with 125I-IGF-II probes only, and was not present in pig serum. In addition, tissue uptake of 125I-cIGF-I and -II was evaluated. Similar patterns of tissue distribution and uptake were observed for 125I-cIGF-I and -II, except that cIGF-II uptake by the liver exceeded that of 125I-cIGF-I at 15 min post-infusion. The rank order of tissue distribution was as follows: kidney > testis > heart > liver > pancreas > small intestine > cartilage > bursa > gizzard > leg muscle > breast muscle > brain. We conclude from these studies that the clearance of IGFs from the compartments identified in blood and the potential target tissues is dependent on their interactions with IGF-binding proteins and receptors.

The effect of insulin-like growth factor-I (IGF-I) on protein turnover in the meat-type chicken (Gallus domesticus).

Insulin-like growth factor-I (IGF-I) effects on chicken growth and development are poorly understood. This study examined the effect of IGF-I on protein synthesis rates in various tissues in the male broiler chicken. At three weeks of age, osmotic minipumps were subcutaneously implanted in the scapular area. Chickens were infused with either chicken IGF-I (450 micrograms/kg BW/day) or saline. After treatment for 5 days, the chickens received a flooding dose of [3H]-phenylalanine, and were sacrificed 20 min later. Wing vein blood samples were taken at 0, 5, 10 and 20 min post-injection. The following tissues were removed and frozen for analysis: pectoralis muscle, gastrocnemius muscle, heart, liver, and small intestine. In vivo total protein synthesis measurements were made using the double-label technique. Contractile protein degradation was evaluated using intracellular free 3-methylhistidine concentrations in skeletal muscle. There were no significant differences in absolute or relative body growth rates over the treatment period. Skeletal muscle (pectoralis and gastrocnemius) weights were significantly decreased with IGF-I treatment, while heart weight was significantly increased. Plasma insulin levels were significantly lower in IGF-treated chickens compared to that in control birds. There was no effect of IGF-I on protein synthesis rates in any of the tissues examined. Intracellular free 3-methylhistidine concentrations were higher in both the gastrocnemius (17%) and pectoralis muscles (25%) of chickens treated with IGF-I. This data demonstrates that IGF-I may have an indirect effect to regulate muscle protein turnover rates.

Developmental changes in embryonic and extra-embryonic insulin-like growth factor-I tissue concentrations in the turkey embryo.

The ontogeny of insulin-like growth factor-I (IGF-I) embryonic and extra-embryonic tissue concentrations were determined in the developing turkey embryo. At 2-d intervals, starting on Day 6 of incubation, individual tissues (n = 8 for each stage of incubation) were removed, weighed, pulverized, and extracted in 1 M acetic acid for IGF-I determination. Amniotic and allantoic fluid were collected starting on Day 8, serum on Day 12, and analyzed for IGF-I levels. Serum IGF-I levels were the lowest on Days 12 and 28 of incubation (5.9 and 9.5 ng/mL), respectively, and the highest on Day 20 (16.2 ng/mL). Allantoic and amniotic fluid IGF-I concentrations were essentially unchanged during incubation. Extra-embryonic tissue IGF-I levels increased in both the yolk sac and chorioallantoic membranes as incubation advanced with concentrations being 8- to 10-fold greater in the chorioallantois. Embryo tissue IGF-I concentrations varied greatly with regard to tissue and stage of development. Brain IGF-I levels were the highest on Day 8 and lowest on Day 26 (423 vs 35 pg/mg protein, respectively). Tissue IGF-I pattern in the heart mirrored that of brain. Liver IGF-I was low (< 40 pg/mg protein) from Day 10 to 20 and undetectable on Days 22 to 28. Muscle IGF-I levels were similar in the final days of development to those observed in early incubation. Bone IGF-I levels were highest in mid-incubation and lowest on Day 26. Peptide levels in the gastrointestinal tract (GI) tract and gizzard were dissimilar in that IGF-I was elevated in the GI tract in early incubation and declined with advancing incubation, whereas gizzard IGF-I levels peaked in late incubation. It is apparent that tissue synthesis of IGF-I is differentially regulated within a given tissue and stage of incubation during embryogenesis in the turkey embryo.

A surgical technique for serial blood sampling or continuous infusion of adult turkey hens.

A technique for cannulating the jugular vein of turkey hens is described. The procedure is relatively easy to perform with no deleterious effects elicited by the procedure. Cannulae have remained patent for up to 1 month.

Developmental changes in serum insulin-like growth factor-I and insulin-like growth factor binding proteins in the turkey embryo.

The ontogeny of insulin-like growth factor-I (IGF-I) and ontogeny as well as the molecular nature of the insulin-like growth factor binding proteins (IGFBP) as they relate to embryogenesis and posthatch growth in the turkey have not been reported. In this study, serum samples were harvested from turkey embryos incubated under shell-less and shelled conditions from Day 12 to 28 of incubation. Samples from 3, 6, and 8 wk posthatch were also evaluated. Significant changes in serum IGF-I in shelled embryos were observed in that IGF-I was low in early incubation, peaked at mid-incubation, and returned to levels equivalent to early incubation at hatching. No mid-embryogenesis (Days 14 to 18) increase in serum IGF-I was noted in the shell-less cultures. Embryo weights diverge at Day 18 of incubation, with shell-less embryos being significantly lighter than their age-matched shelled embryos, suggesting a possible relationship between total circulating IGF-I and body weight gain. Three distinct IGFBP were identified in serum from turkey embryos, exhibiting molecular weights of 27, 29, and 69 kDa. During embryonic development, the 29 kDa IGFBP appeared to be the predominant species, with levels peaking on Day 24 of incubation, and being minimally detectable at hatching. Ontogeny of the 29 kDa IGFBP was similar in the shelled and shell-less embryos. The 69-kDa IGFBP-like protein did not appear in the circulation until late in embryogenesis, Day 22 in shell-less and Day 26 in shelled embryos. The 27-kDa IGFBP appeared in late incubation. Similar IGFBP (28, 30, and 69 kDa) were observed in the growing male turkey. The 69-kDa protein did not vary across ages studied, whereas the 28-kDa IGFBP appeared to increase with age. This is the first report describing serum IGF-I and IGFBP in the developing turkey. Turkey IGFBP appear to be regulated by independent events during incubation and posthatch growth.

Hormonal regulation of leptin expression in broiler chickens.

Leptin, the polypeptide hormone encoded by the obese gene, is secreted by adipose tissue and has been shown to induce satiety and increase energy expenditure in mammals. In this study, we confirmed the presence of a leptin homolog in liver and adipose tissues of broiler chickens. Leptin expression was also detected in chicken embryonic liver and yolk sac. The effects of hormone treatment on leptin expression in chickens were also investigated. Leptin expression in the liver is increased by insulin and dexamethasone and decreased by glucagon and estrogen. There was no induction of leptin expression in adipose tissue by any treatment, whereas only estrogen decreased adipose expression. The differential effect on liver and adipose tissue suggests that adipocytes in chickens may be expressing leptin at a maximal rate or that its mechanism of expression regulation differs from liver. The localization of leptin expression and tissue-specific effects of hormone treatments on leptin expression observed in chickens may indicate a relationship between leptin and avian lipid metabolism.

Control of luteal relaxin release by prostaglandin F2 alpha: differences in the sow cycle and pregnancy.

The effect of an in vivo prostaglandin F2 alpha (PGF2 alpha) challenge in pregnant and cyclic sows was compared to determine whether PGF2 alpha-induced release of relaxin (RLX) from the corpus luteum (CL) in late pregnancy is also effective during the cycle. Ovarian venous RLX and progesterone were monitored by radioimmunoassay and RLX localized in the CL by immunohistochemistry. In Day 108 pregnant sows, infusion of PGF2 alpha (100 micrograms) into the ovarian artery resulted in an immediate and sustained rise in ovarian venous RLX with an initial decline in progesterone levels by 30 min which then returned to pretreatment levels. In Day 13 or 15 cyclic sows with functional corpora lutea (i.e., elevated progesterone), RLX was undetectable in ovarian venous blood after 100 micrograms of PGF2 alpha. Administration of PGF2 alpha via either the jugular vein or intramuscular route was also ineffective in releasing RLX from the CL of the cycle. The intensity of RLX immunostaining of the CL was similar in saline and PGF2 alpha-treated sows. These studies indicate that the control of RLX release from the sow CL differs in the estrous cycle and pregnancy.