Effect of pullet body weight and hen dietary amino acid treatments on their progeny fed high and low amino acid diets

Four studies were conducted on Cobb 700 broilers to evaluate the dietary protein and any maternal effects on live production and processing parameters. Day-old Cobb 700 broiler breeder pullets were reared to conform to 2 different BW curves (control BW and increased BW) with 8 replicate pens per treatment. Birds were fed common diets from 1 d of age until first egg (24 wk). At 24 wk, 12 pens of each pullet treatment were given different amino acid (AA) diets (low = 14% CP, high = 15% CP). The performance of female and male progeny from 32 and 45 wk hens were evaluated on low AA and high AA density diets. The 4 progeny trial designs were identical factorial 2 × 2 × 2 designs, with 2 pullet BW curves (control BW and increased BW), 2 dam CP diet levels (low and high), and 2 progeny CP diets (low and high), with 6 replicates each containing 18 birds, for a total of 108 broiler progeny per treatment. Broiler chickens on the higher AA density feed exhibited consistent improvement in mid-growth BW and FCR and white meat yield percentage. Some maternal effects were noted, including increased carcass yield in female broilers from 32 wk old hens. There were 3-way interactions of pullet BW × hen dietary AA × progeny dietary AA treatments for female progeny carcass yield (from 32-week-old hens) and male tender yield (from 45-week-old hens). There were 2-way interactions of pullet BW x hen dietary AA treatments effect on female and male progeny drumstick yield from 32-week-old hens, pullet BW × progeny dietary AA treatments effect on male 27 d BW from 32-week-old hens, and hen dietary AA × progeny dietary AA treatments effect on male thigh yield from 45-week-old hen. The epigenetic effects of maternal pullet BW and dietary AA treatments were seen in processing yields suggesting, the need of dietary CP changes of the progeny.

Metabolic and hormonal responses of growing modern meat-type chickens to fasting

1. The present study compared the effects of fasting on circulating concentrations of glucose, insulin and glucagon in male and female modern meat-type chickens (Ross 708) at three ages (19 d, 33 d and 47 d). 2. Plasma concentrations of glucose were reduced by fasting with reductions of 24.9% (19-d-old), 22.6% (33-d-old) and 17.9% (47-d-old) in broiler chickens fasted for 12 h. 3. Plasma concentrations of insulin decreased with fasting. For instance, circulating concentrations of insulin declined after 6 h of fasting by 45.7%, 54.7% and 50.0%, respectively, in 19-d-old, 33-d-old and 47-d-old broiler chickens. 4. Plasma concentrations of glucagon were increased by fasting. Plasma concentrations of glucagon were elevated by 3.79% (19-d-old), 3.51% (33-d-old) and 3.79% (47-d-old) with 6 h of fasting and remained elevated with 12 h, 18 h and 24 h of fasting.

Changes in body temperature during growth and in response to fasting in growing modern meat type chickens

1. Rectal or core body temperature was determined in a study to examine the effects of fasting in modern meat type broilers at three stages of growth, namely d 19, 33 and 47. 2. There were two treatment groups: fed with feed available ad libitum and fasted. Rectal temperatures were determined at noon (1200 h). At that time, feed was removed from the fasted group. The body temperatures were then determined again after 6, 12, 18 and 24 h. 3. Core body temperatures decreased with fasting. The decrease was evident after as little as 6 h of fasting with a further decline evident by 12 h. 4. Accompanying the decrease in body temperature with fasting there were decreases in the venous concentrations of carbon dioxide in the blood and sodium in the plasma. 5. The decrease in both body temperature and carbon dioxide presumably reflects depressed metabolic rate. 6. Unexpectedly, the core body temperature increased progressively with age in the control fed group (d 19 = 41·04 ± 0·02°C, d 33 = 41·65 ± 0·05°C, d 47 = 42·21 ± 0·12°C). 7. In the fed control group, core body temperatures were reduced at night, when feeding activity would be anticipated to be greatly reduced.

Effects ofLactobacilliand lactose onSalmonella typhimuriumcolonisation and microbial fermentation in the crop of the young turkey

1. Three experiments were performed to examine the effects of Lactobacilli and lactose on microbial fermentation and Salmonella enterica serovar Typhimurium colonisation in the crop of the young turkey. 2. The following carboxylic acids were detected in the crop ingesta: formic, acetic, butyric, lactic, valeric, caproic, oxalic, phenyl acetic, succinic and fumaric; propionic, isobutyric and isovaleric acids were not detectable. 3. At the beginning of the night, there were considerable quantities of ingesta in the crop of young turkeys. During the scotophase, there were progressive reductions in the contents and pH. Moreover, there were linear increases in the concentration of lactic, valeric and caproic acids (by approximately 7-fold over 8 h). Much smaller changes in crop pH were observed in the study where dietary treatments of Lactobacilli were not included. 4. Chronic addition of lactose or Lactobacilli to the diet exerted modest effects on the carboxylic acid concentration in the crop contents but did not consistently influence colonisation of the crop by Salmonella enterica serovar Typhimurium. 5. Young turkeys confine eating to the hours of illumination (photophase) with a peak in consumption prior to the subjective dusk.

Lack of Estrogenic or Antiestrogenic Actions of Soy Isoflavones in an Avian Model: The Japanese Quail

Isoflavones are soy compounds that possess weak estrogenic and antiestrogenic activities. In addition, phytochemicals, including isoflavones, may play a role in regulating seasonal reproductive cycles. As soy is a common constituent in poultry diets, the effect of these compounds on the reproductive system of production birds may be of concern. The present study examined the putative effects of soy isoflavones supplemented into the diet at 1 and 5% using endpoints of growth and reproduction in the Japanese quail. Isoflavones did not exert an effect on growth, feed intake, growth:feed, or the weight of the estrogen-sensitive immature oviduct in female quail. Furthermore, isoflavones did not influence the growth of the oviduct stimulated by exogenous estradiol. Similarly, isoflavones did not influence growth, feed intake, or growth:feed in male quail. However, isoflavones at 1%, but not 5%, in the diet reduced photoperiod-induced testis development 40% vs. control. In contrast, isoflavones did not influence testis regression stimulated by exogenous estradiol in sexually maturing male quail. The present results suggest that isoflavones may exert modest endocrine disruptor-like effects on reproduction in male, but not female, quail.

Evaluation of corn furan fatty acid putative endocrine disruptors on reproductive performance in adult female chickens

Based on evidence from rodent models, it was hypothesized that furan fatty acids found in corn would inhibit reproduction in the laying hen. An isomeric mixture of furan fatty acids [9, (12)-oxy-10,13-dihydroxystearic acid and 10, (13)-oxy-9,12-dihydroxystearic acid] was administered for a period of 3 wk via the diet (1 and 3 ppm) at levels greater than those in corn to 20-wk-old pullets. There were no overt indications of acute or chronic toxicity (no effects on mortality, feed intake, or average daily gain). Similarly, there was no dose-dependent effect on reproductive parameters [egg production, egg weight, shell thickness, ovarian weight, number or weight of large yolky preovulatory follicles, and number of small yellow follicles (4-8 mm in diameter)]. The present data do not suggest that furan fatty acids are a cause of concern to the poultry industry.

Lack of effects of atrazine on estrogen-responsive organs and circulating hormone concentrations in sexually immature female Japanese quail (Coturnix coturnix japonica)

The widely used herbicide, atrazine, has been reported to exhibit reproductive toxicity in rats and amphibians. The present studies investigate toxicity of atrazine in Japanese quail and its ability to influence reproduction in sexually immature females. Atrazine was administered in the diet at concentrations from 0.001 to 1000 ppm (approximately 109 mg kg-1 per day) or systemically via daily subcutaneous injections (1 and 10 mg kg-1) or Silastic implants. Atrazine did not cause overt toxicity in sexually immature female quail (no effects on change in body weight, feed intake, mortality or on circulating concentrations of the stress hormone, corticosterone). It was hypothesized that if atrazine were to have estrogenic activity or to enhance endogenous estrogen production, there would be marked increases in the weights of estrogen sensitive tissues including the oviduct, the liver and the ovary together with changes in gonadotropin secretion. However, atrazine had no effect on either liver or ovary weights. Atrazine in the diet increased oviduct weights at 0.1 and 1 ppm in some studies. These effects were not consistently observed and were not significant when data from studies were combined. Systemic administration of atrazine had no effect on oviduct weights. Dietary (concentrations from 0.001 to 1000 ppm) and systemically administered atrazine had no effect on circulating concentrations of luteinizing hormone (LH). The present studies provide evidence for a lack of general or reproductive toxicity of atrazine in birds.

In ovo exposure to a triazine herbicide: effects of atrazine on circulating reproductive hormones and gonadal histology in young Japanese quail

The triazine herbicide, atrazine, has come under scrutiny for its reported feminizing effects in amphibians. To date, there is little information concerning the effects of atrazine on reproduction in avian species. The current study examined the putative reproductive toxicity of atrazine after exposure in ovo. Atrazine at 504, 246, and 123 microg/kg was administered to Japanese quail eggs before incubation. The eggs were hatched and the birds raised to 14 days of age. Indices of hatchability, sex ratios, and growth were determined. Furthermore, circulating concentrations of reproductive hormones (estradiol, progesterone, and testosterone) and gonadal histology were examined. Atrazine at 504 microg/kg decreased 14-day hatchling weight by 13.1% versus controls. However, no detrimental effects on hatchability or sex ratios were observed. In female birds, atrazine at 504 microg/kg decreased ovarian weights and circulating concentrations of progesterone to 48.3% and 73.3%, respectively, versus control. However, concentrations of estradiol and testosterone did not differ from controls. In male quail, at all doses tested, atrazine had no effect on gonadal weights or circulating concentrations of estradiol, testosterone, or progesterone. Moreover, no incidences of left ovotestis formation were observed. In contrast, 10 ng/kg ethinylestradiol (a positive control) induced the formation of a left ovotestis in four of eight birds analyzed. The current results may suggest that exposure to atrazine in ovo at concentrations above ecologic relevance exerts effects on the reproductive system of young Japanese quail. However, no evidence is presented that atrazine induces feminization of the testis in male quail.

Changes in Tissue Nitrite Concentration in the Crop of the Turkey Poult in Response to Salmonella Typhimurium Challenge

The present study examines whether Salmonella typhimurium colonization of the crop of young turkeys influences nitrite concentration in the component tissues of the crop. Nitric oxide (NO) is the principal compound in biological samples that is converted into nitrites and NO is known to be a component of the early host response to infection. Challenge with S. typhimurium increased the concentration of nitrite in the crop wall of 3-wk-old turkey poults. The magnitude of the response was reduced at 8 h and absent at 48 h after challenge. As would be expected, S. typhimurium concentrations in the crop were markedly increased following challenge, and were nondetectable in control poults.

Physiology of ghrelin and related peptides

Growth hormone (GH) released from pituitary under direct control of hypothalamic releasing (i.e., GHRH) and inhibiting (i.e., sst or SRIF) hormones is an anabolic hormone that regulates metabolism of proteins, fats, sugars and minerals in mammals. Cyril Bowers' discovery of GH-releasing peptide (GHRP-6) was followed by a search for synthetic peptide and nonpeptide GH-secretagogues (GHSs) that stimulate GH release, as well as a receptor(s) unique from GHRH receptor. GHRH and GHSs operate through distinct G protein-coupled receptors to release GH. Signal transduction pathways activated by GHS increase intracellular Ca2+ concentration in somatotrophs, whereas GHRH increases cAMP. Isolation and characterization of ghrelin, the natural ligand for GHS receptor, has opened a new era of understanding to physiology of anabolism, feeding behavior, and nutritional homeostasis for GH secretion and gastrointestinal motility through gut-brain interactions. Other peptide hormones (i.e., motilin, TRH, PACAP, GnRH, leptin, FMRF amide, galanin, NPY, NPW) from gut, brain and other tissues also play a role in modulating GH secretion in livestock and lower vertebrate species. Physiological processes, such as neurotransmission, and secretion of hormones or enzymes, require fusion of secretory vesicles at the cell plasma membrane and expulsion of vesicular contents. This process for GH release from porcine somatotrophs was revealed by atomic force microscopy (AFM), transmission electron microscopy (TEM) and immunohistochemical distribution of the cells in pituitary during stages of development.

The anterior pituitary gland: lessons from livestock

There has been extensive research of the anterior pituitary gland of livestock and poultry due to the economic (agricultural) importance of physiological processes controlled by it including reproduction, growth, lactation and stress. Moreover, farm animals can be biomedical models or useful in evolutionary/ecological research. There are for multiple sites of control of the secretion of anterior pituitary hormones. These include the potential for independent control of proliferation, differentiation, de-differentiation and/or inter-conversion cell death, expression and translation, post-translational modification (potentially generating multiple isoforms with potentially different biological activities), release with or without a specific binding protein and intra-cellular catabolism (proteolysis) of pituitary hormones. Multiple hypothalamic hypophysiotropic peptides (which may also be produced peripherally, e.g. ghrelin) influence the secretion of the anterior pituitary hormones. There is also feedback for hormones from the target endocrine glands. These control mechanisms show broadly a consistency across species and life stages; however, there are some marked differences. Examples from growth hormone, prolactin, follicle stimulating hormone and luteinizing hormone will be considered. In addition, attention will be focused on areas that have been neglected including the role of stellate cells, multiple sub-types of the major adenohypophyseal cells, functional zonation within the anterior pituitary and the role of multiple secretagogues for single hormones.

Characterization of a bioactive 15 kDa fragment produced by proteolytic cleavage of chicken growth hormone

There is evidence for a cleaved form of GH in the chicken pituitary gland. A 25 kDa band of immunoreactive-(ir-)GH, as well as the 22 kDa monomeric form and some oligomeric forms were observed when purified GH or fresh pituitary extract were subjected to SDS-PAGE under nonreducing conditions. Under reducing conditions, the 25 kDa ir-GH was no longer observed, being replaced by a 15 kDa band, consistent with reduction of the disulfide bridges of the cleaved form. The type of protease involved was investigated using exogenous proteases and monomeric cGH. Cleaved forms of chicken GH were generated by thrombin or collagenase. The site of cleavage was found in position Arg133-Gly134 as revealed by sequencing the fragments produced. The NH2-terminal sequence of 40 amino acid residues in the 15 kDa form was identical to that of the rcGH and analysis of the remaining 7 kDa fragment showed an exact identity with positions 134-140 of cGH structure. The thrombin cleaved GH and the 15 kDa form showed reduced activity (0.8% and 0.5% of GH, respectively) in a radioreceptor assay employing a chicken liver membrane preparation. However, this fragment had a clear bioactivity in an angiogenic bioassay and was capable to inhibit the activity of deiodinase type III in the chicken liver.

Growth hormone size variants: changes in the pituitary during development of the chicken

There is considerable evidence for the existence of structural variants of growth hormone (GH). The chicken is a useful model for investigating GH heterogeneity as both size and charge immunoreactive-(ir) variants have been observed in the pituitary and plasma. The present study examined the size distribution of ir-GH in the pituitary gland of chicken, from late embryogenesis through adulthood. Pituitaries were homogenized in the presence of protease inhibitor, and the GH size variants were separated by SDS-PAGE, transferred by Western blotting, immunostained with a specific antiserum to chicken GH, and quantitated by chemiluminescence followed by laser densitometry (chemiluminescent assay). Under nonreducing conditions ir-GH bands of 15, 22, 25, 44, 50, 66, 80, 98, 105 and >110 kDa were observed. Both the relative proportion of the GH size variants and the total pituitary content varied with developmental stage and age. The proportion of the 15-kDa fragment was greatest in the embryonic stage, and then it decreased. The proportion of the monomeric 22-kDa form was lowest at 18 days of embryogenesis (dE) and highest at 20 dE. In contrast, the high MW forms (>/=66 kDa) were lowest in embryos, and they increased (P < 0.05) after hatching. The 22-, 44-, 66-, and 80-kDa forms were assayed for activity by radioreceptor assay following isolation by semipreparative SDS-PAGE. Only the 22-kDa GH variant showed radioreceptor activity. Under reducing conditions for SDS-PAGE, ir-GH bands of 13, 15, 18, 23, 26, 36, 39, 44, 48, 59 and 72 kDa were oberved, but most of the high MW form disappeared. There was a concomitant increase in the proportion of the monomeric band and of several submonomeric forms. The present data indicate that the expression, processing, and/or release of some if not all size variants are under some differential control during growth and development of the chicken.

Corticosterone and growth hormone levels in shorebirds during spring and fall migration stopover

Large numbers of shorebirds stop over at Delaware Bay during spring migration and undergo major mass increases within a two- to three-week period. We studied plasma levels of corticosterone and growth hormone in three species of migrants that use this site, sanderlings, Calidris alba, semipalmated plovers, Charadrius semipalmatus, and semipalmated sandpipers, Calidris pusilla. Semipalmated sandpipers were also studied at a fall migration stopover in Manomet, Massachusetts. These two hormones were chosen because they modulate the physiological processes of lipogenesis/lipolysis and promote increased feeding in birds. The stress response was not suppressed in the shorebirds studied, and plasma levels of corticosterone were elevated compared to other studies. We believe that the high levels of corticosterone relate to the rapid fat deposition that takes place at this stop-over site. There was a significant negative correlation between plasma growth hormone and body mass, indicating the lipolytic effects of the growth hormone. Because the lighter birds are recent arrivals to Delaware Bay they may have elevated plasma growth because of fat breakdown during flight to this stop-over site. High levels of growth hormone may also result in protein synthesis, replenishing tissues broken down during the previous migratory bout. J. Exp. Zool. 284:645-651, 1999.

Effects of polychlorinated biphenyls on thyroid hormones and liver type I monodeiodinase in the chick embryo

Polychlorinated biphenyls (PCBs) are widespread environmental contaminants which can biomagnify to higher tropic level organisms including birds. Circulating thyroid hormones (TH) and growth are decreased by PCB exposure. The first set of studies investigated the effects of PCBs on an enzyme responsible for TH homeostasis, hepatic type I monodeiodinase (MDI) in chicken embryos. Fertile chicken eggs were injected with Aroclor 1242, Aroclor 1254, 2,2',6, 6'-tetrachlorobiphenyl (TCB), 3,3',4,4'-TCB, or 3,3',5,5'-TCB on Day 0 and studies were terminated on Incubation Day 21. Hepatic MDI activity was reduced in embryos treated with the Aroclor mixtures. No effects on MDI activities were observed after PCB isomer treatment. Liver weights from embryos treated with Aroclor 1242 were decreased. In the second study, chick embryos were exposed to these same PCBs in order to evaluate their effect on circulating THs and growth. Treatment with PCBs had no effect on body weight. Femur length were decreased with Arcolor 1242 treatment. A decrease in plasma concentration of thyroxine was observed after treatment with Aroclor 1242 and Aroclor 1254. Based on these findings, it is evident that PCBs alter the thyroid axis. Bird circulating TH levels, which are generally reported, may not be a good biomarker for low-dose exposure to PCBs. However, the reduction in MDI activity was more sensitive to PCB mixture exposure and may be a useful biomarker.

Influence of continuous growth hormone or insulin-like growth factor I administration in adult female chickens

A series of studies was conducted to determine whether growth hormone (GH) exerts effects on adult female chickens. Recombinant chicken GH (rcGH) was administered continuously via osmotic minipumps. No consistent effects of rcGH treatment were observed on reproductive indices. Hens receiving rcGH treatment for 10 days exhibited hepatomegaly and showed a tendency (P < 0.1) for increased spleen and thymus weights. Moreover, there were increases in the circulating concentrations of insulin-like growth factor-I (IGF-I) and IGF-binding proteins (IGF-BPs) (22-kDa IGF-BP after 2, 5, and 10 days; 28-kDa IGF-BP after 5 and 10 days; and 36-kDa IGF-BP after 10 days) with rcGH treatment. To determine whether the changes in IGF-BPs were due directly to GH or indirectly via IGF-I, the effects of the continuous administration of rcGH or recombinant human IGF-I (rhIGF-I) were compared. While rcGH again elevated the circulating levels of 28- and 36-kDa IGF-BPs, no such effect was observed with rhIGF-I treatment. However, both treatments exerted similar effects in depressing pituitary GH mRNA levels and elevating plasma concentrations of IGF-I. It is concluded that GH directly elevates circulating concentrations of IGF-I and IGF-BPs, but the negative feedback effect on GH synthesis is mediated via IGF-I.

The effects of protein restriction on insulin-like growth factor-I and IGF-binding proteins in chickens

The effect of dietary protein restriction (5% and 10% compared to control 20%) on circulating concentrations of insulin-like growth factor (IGF)-1 and IGF binding proteins (IGFBPs) was examined in young (18-day-old) chickens during a 2-week period. Reductions in dietary protein caused progressive growth retardation as evidenced by decreased body-weight gain and reduced bone growth. The decrease in plasma concentrations of IGF-I appeared to be directly related to dietary protein levels (i.e., the lower the amount of dietary protein, the greater the reduction in the circulating concentrations of this growth factor). Three IGFBPs with MWs of 30, 36, and 40 kDa were detected by radioligand assay following separation by SDS-electrophoresis. Binding activity of the 30-kDa IGFBP was transiently increased on Day 3 by protein restriction (both 5% and 10%). The 36-kDa IGFBP was also affected by protein restriction with binding activity of this IGFBP decreased throughout the study. The binding activity of the 40-kDa IGFBP was transiently increased on Days 3 and 7 but subsequently decreased on Days 10 and 14 in the 10% protein group. In the 5% protein group, binding activity of the 40-kDa IGFBP was decreased throughout the study. The decrease in circulating concentrations of IGF-I appeared to be inversely related to the initial increase in the binding activity of the 30-kDa IGFBP on Day 3 (5% and 10% protein) and to the increased binding activity of the 40-kDa IGFBP on Days 3 and 7 (10% protein). This may suggest that bioavailability of plasma IGF-I is decreased initially due to increased binding with these IGFBPs. However, binding activity of all three IGFBPs then decreased in a manner directly related to the decreasing IGF-I plasma concentrations for the remainder of the experiment. The initial increase in binding activity observed with the 30-kDa IGFBP is similar to that observed with IGFBP-1 in mammals in that both of these IGFBPs respond rapidly to nutritional deprivation. Decreased protein intake would certainly have an impact on the amount of available proteins required for the synthesis of these growth factors.

The effects of glucocorticoids (dexamethasone) on insulin-like growth factor-I, IGF-binding proteins, and growth in chickens

The effect of glucocorticoids (dexamethasone) on circulating concentrations of insulin-like growth factor (IGF)-I and IGF binding proteins (IGFBPs) was examined in young (2-week-old) chickens. Increasing dosages (6, 60, and 600 microg/kg) of dexamethasone resulted in progressive growth retardation as evidenced by decreased body-weight gain, reduced bone growth, and breast muscle weights, together with immunosuppression as indicated by decreased thymus and bursa weights. Plasma concentrations of IGF-I were progressively reduced with increased doses of dexamethasone. There were no changes in circulating IGFBPs except on Day 7 when binding activity of the 36-kDa IGFBP was increased by dexamethasone (6 microg/kg). It is speculated that similarities exist between the 36-kDa IGFBP and the mammalian IGFBP-1 based on the response to dexamethasone treatment.

Aluminum and acid effects on calcium and phosphorus metabolism in young growing chickens (Gallus gallus domesticus) and mallard ducks (Anas platyrhynchos)

Acidification is associated with increased mortality, reduced growth, and bone abnormalities in birds. Associated with acid deposition is an increase in aluminum availability due to solubilization from soil and other sources. (Conversely, experimental diets containing aluminum sulfate have much reduced pHs.) The present studies compare the effects of two levels of dietary acid (sulfuric acid) (0.122 and 0.56 mol H+ per kg feed; 0.056 and 0.277 mol sulfate per kg feed) and dietary aluminum (aluminum sulfate at 0.1 and 0.5%; sulfate at 0. 056 and 0.277 mol sulfate per kg feed) on bone growth, mineralization, and phosphorous/calcium homeostasis in growing birds (chickens and mallard ducks). Growth was reduced by the high acid (chicken) and aluminum (ducks and chickens) diets. A reduction in bone mineralization was observed in birds receiving aluminum-containing diets [low aluminum diet: decreased tibia ash, calcium, and phosphorus (chickens); high aluminum diet: decreased tibia dry weight, % of ash and mg; ash, calcium (chickens, ducks as % of ash), and phosphorus (chickens mg/duck, % of ash)]. Moreover, plasma concentrations of inorganic phosphate were reduced in chicks on the high aluminum diet. There were also marked decreases in bone growth and mineralization [tibia weight, ash (mg), calcium (mg), phosphorus (mg)] and plasma concentrations of 1,25-dihydroxy vitamin D3 in chicks on the high acid diet compared to those on a control diet. These changes were probably due to reduced feed intake; changes in bone indices being of a greater or similar magnitude in pairfed control. There was little change in bone indices, growth rate or feed consumption in ducklings receiving either the low or high acid diets. It is concluded that aluminum directly adversely affected bone mineralization whereas acid effects are mediated in part by changes in feed consumption.

Pulsatile release of somatotropin related to meal feeding and somatotropin response to secretagogues in horses

Our goal was to establish a time of day and(or) interval from feeding that would avoid the refractory period after a somatotropin (ST) surge and optimize the responsiveness of horses to ST secretagogues. Two experiments were conducted with eight geldings conditioned to consume grain at 0800 and 1600 daily. In Exp. 1, during a 24-h period, these geldings averaged 3.2 +/- .3 pulses of ST with peak amplitude of 4.2 +/- .4 ng/mL, pulse duration of 55 +/- 6 min, and interpeak interval of 400 +/- 57 min. No ST peaks occurred within 2 h after either grain feeding. In Exp. 2, eight geldings were given 50 micrograms of ST-releasing factor (STRF) at 0800. Two geldings that had a pulse of ST between 0700 and 0800 failed to respond to STRF, but the other six responded with a pulse of ST at 37 +/- 3 min; peak amplitude was 4.6 +/- 2.2 ng/mL and duration was 123 +/- 25 min. Experiments 3 and 4 were with mares aged 20 to 26 yr and conditioned to be fed grain at 0800 daily. In Exp. 3, blood was sampled for 8 h beginning at 0500. Seven of the eight mares had a ST pulse in progress at 0500. Five additional pulses were detected, all from 0740 to 0940, but none from 0600 to 0700 or from 1000 to 1300. In Exp. 4, four of the same eight mares were given 50 micrograms of STRF at 0700 and the other four at 1300. Three of the four treated at 0700 and all four treated at 1300 responded to STRF with ST peaks at 20 +/- 5 min; peak amplitude was 12.7 +/- 9.5 ng/mL and duration was 69 +/- 6 min. In Exp. 5, nine mares aged 20 to 26 yr were fed grain at 0800 and 1600 as in Exp. 1 and 2 and given a nonpeptidal ST secretagogue (STS, Merck L-163,255) i.v. at 0, 1, or 5 mg/kg (n = 3 mares/dose) at 1300. No mare had a pulse of ST during the 1 h before treatment. All six mares given STS responded with ST pulses. The ST responses to STS at 1 and 5 mg/kg did not differ (P > .05); time to ST peak was 35 +/- 4 min, pulse amplitude was 24.0 +/- 6.3 ng/mL, and pulse duration was 100 +/- 9 min. We conclude that mares and geldings fed grain once or twice daily usually have a period of 2 to 5 h after feeding with no ST pulses. When horses are fed grain at 0800, one may give a ST secretagogue at 1300 to avoid a refractory period and improve the probability of an ST response.

Quantitative studies of chicken somatotrophs during growth and development by morphometry, immunocytochemistry, and flow cytometry

Changes in the male chicken somatotroph during growth and maturation have been examined by morphometric and immunocytochemical (ICC) analysis of serial sections of the anterior pituitary gland and by flow cytometry of dispersed anterior pituitary cells. ICC showed that somatotrophs are confined to the middle and caudal thirds of the anterior pituitary gland at all ages from 5 to 26 weeks. At a given age somatotrophs are of equal size at all positions along the cephalocaudal axis of the anterior pituitary gland. However, there are age-related changes: from 5 to 11 weeks rises occur in both the mean total somatotroph volume per gland (64%) and the mean number of somatotrophs (78%), while the mean volume of the single somatotroph is unchanged. From 11 to 18 weeks the mean volume of the single somatotroph decreases 41%. From 18 to 26 weeks the mean volume of the somatotroph, the mean total somatotroph volume, and the mean number per gland do not change. Flow cytometry studies suggested that somatotrophs from adults have less growth hormone (GH) than somatotrophs from young birds. The increases in total somatotroph volume and number from 5 to 11 weeks are consistent with the rise in anterior pituitary GH reported previously. Basic quantitative morphological information about age-related changes in somatotrophs is reported here. When combined with additional facts from future work, they may explain the well-documented sharp decline in circulating GH from 5 to 11 weeks.

The effects of dietary restriction on insulin-like growth factor (IGF)-I and II, and IGF-binding proteins in chickens

The effect of feed (energy/protein) restriction on circulating concentrations of insulin-like growth factor (IGF)-I and II, and IGF-binding proteins (IGFBPs) was examined in young (4-week-old) chickens. Increasing levels of feed restriction caused progressive growth retardation, as evidenced by decreased body-weight gain and reduced bone growth. Plasma concentrations of both IGF-I and IGF-II were decreased, and the degree of reduction in the plasma concentrations of these growth factors appeared to be related to the magnitude of feed restriction. A tendency for greater decreases in these growth factors appeared to be associated with greater feed restriction at the majority of time points evaluated. However, nutritional restriction had a greater effect on plasma concentrations of IGF-I than on those of IGF-II. The reductions in plasma concentrations of IGF-I were observed earlier in the experiment and at a lower degree of nutritional deprivation than for plasma concentrations of IGF-II, possibly suggesting greater sensitivity of IGF-I plasma concentrations to feed restriction. Three IGFBPs with molecular weights of 30, 36, and 40 kDa were detected by radioligand assay following separation by SDS-electrophoresis. The 30-kDa IGFBP was most affected by feed restriction with binding activity of this IGFBP increased by 2 days of feed restriction irrespective of the degree of feed deprivation. The binding activity of the 36-kDa IGFBP was increased, albeit transiently, on the second day of feed restriction. Nutritional restriction had no discernible effect on the binding activity of the 40-kDa IGFBP. Increases in the binding activity of the 30-kDa IGFBP appeared to correspond with the observed decreases in IGF-I plasma concentrations. This suggests decreased bioavailability of IGF-I, and possibly IGF-II, attributed to the formation of a complex between IGF-I and the 30-kDa IGFBP during feed restriction. The initial increase in binding activity of the 36-kDa IGFBP may suggest that this binding protein also plays a role in the regulation and availability of circulating concentrations of IGF-I and IGF-II. Although the binding activity of the 40-kDa IGFBP was unaffected by feed restriction, we can not exclude its importance in the regulation of IGF-I. The substantial binding activity of the 40-kDa IGFBP observed in this experiment suggests that it is one of the major chicken IGFBPs, and that its role in IGF-I regulation warrants further study.

The thyroid hormone, 3,5,3'-triiodothyronine, is a negative modulator of domestic fowl (Gallus gallus domesticus) adrenal steroidogenic function

Previous work with chickens (Gallus gallus domesticus) suggests a relationship between depressed thyroid hormone status and enhanced adrenal steroidogenic function. In addition, in hypophysectomized chickens, replacement of the thyroid hormone, 3,5,3'-triiodothyronine (T3), maintains chicken adrenal steroidogenic cell sensitivity to adrenocorticotropin (ACTH) but decreases steroidogenic capacity further than that due to hypophysectomy alone. The present in vivo and in vitro studies were conducted to determine the influence of thyroid status and T3 per se on avian adrenal steroidogenic function. Chicks (1 day old) were thyroidectomized using combined surgical and chemical (6-propyl-2-thiouracil) treatments and were administered a replacement dose of T3 (0, 1.5, 4.5, 15, and 45 microg/kg body wt/day) for 5 weeks. Whereas thyroidectomy (TX) decreased adrenal weight (-20%), it increased relative adrenal weight (mg/100 g body weight) (+171%), trunk plasma corticosterone (+880%), and aldosterone (+124%). In addition, TX increased basal, maximal ACTH-induced, maximal 8-bromo-cyclic AMP-induced, and maximal 25-hydroxycholesterol-supported corticosterone production (+520, +93, +124, and +195%, respectively) and aldosterone production (+578, +288, +280, and +275%, respectively) by isolated adrenal steroidogenic cells. T3, in a dose-dependent manner, reversed the effects of TX on these in vivo and in vitro parameters of adrenal steroidogenic function. Restoration of most of these parameters to those in the sham-treated control was attained with 4.5-15 microg/kg body wt/day. Although some of the effects of TX and T3 replacement on adrenal steroidogenic function may have been mediated through changes in circulating levels of ACTH, other data suggest a direct effect on adrenal steroidogenic cell function. Adrenal steroidogenic cells from sham-treated and TX birds were preincubated (0, 4, and 12 hr) with various concentrations of T3 (0, 0.3, 3, and 30 nM), washed, and then incubated for an additional 2 hr in medium containing the same respective concentrations of T3, with or without a maximal steroidogenic concentration of ACTH (100 nM). T3 had no acute effects on TX-dependent enhancement of adrenal steroidogenic cell function (2-hr incubation). However, with preincubation (4 and 12 hr), T3 inhibited basal and maximal ACTH-induced corticosterone production in a dose-dependent manner. This concentration-dependent, direct effect of T3 was not observed with cells from sham-treated birds. In addition, the ostensibly inactive thyroid hormone metabolite, 3,3',5'-triiodothyronine [reverse T3; 30 nM], was without effect. Taken collectively, these studies indicate that T3 is a direct negative modulator of avian adrenal steroidogenic function.

Ontogeny of insulin-like growth factors (IGF-I and IGF-II) and IGF-binding proteins in the chicken following hatching

The present study examined plasma concentrations of insulin-like growth factor (IGF)-I, IGF-II and IGF-binding proteins (IGFBPs) during posthatch growth and development in chickens. Three distinct proteins which bound 125I-IGF-I were observed irrespective of age or sex, these having apparent molecular weights of 22, 28, and 36 kDa. The major IGFBP present during much of the growth and development period was the 28-kDa form followed by the 36-kDa form. Plasma concentrations of IGF-II and of the 22-kDa IGFBP showed little ontogenic variation with the exception of elevated levels of the 22 kDa IGFBP in 1-day-old chicks. The circulating concentrations of IGF-I and of the 28-kDa IGFBP increased progressively between the time of hatching to reach a maximum at 6 weeks of age and subsequently declined to lower levels in adults. Somewhat similarly, the 36-kDa IGFBP increased during early pre- and posthatching growth to a maximum at 6 weeks of age. There were marked sex differences in circulating concentrations of IGF-I in young (4 week) and adult chickens and in the 36-kDa IGFBP in the adult, both being lower in females. Estrogen treatment of adult male chickens decreased the circulating concentrations of IGF-I together with the level of both the 28- and 36-kDa IGFBPs. Testosterone treatment had no effect on the circulating concentrations of either IGF-I or IGFBPs in adult female chickens. We conclude that the relative levels of IGF-I, IGF-II, and the IGFBPs change with age. In addition, circulating concentrations of estrogen may play a role in the regulation of IGF-I and IGFBPs.

Acute effects of short-term feed deprivation and refeeding on circulating concentrations of metabolites, insulin-like growth factor I, insulin-like growth factor binding proteins, somatotropin, and thyroid hormones in adult geldings

Two studies were performed with Standardbred geldings 7 to 21 yr of age to determine the sequence of changes in blood plasma concentrations of some hormones and metabolites during feed deprivation for 48 h and for 12 h after refeeding. Plasma hormone and metabolite concentrations were determined with methods validated for horse plasma. Insulin-like growth factor binding proteins (IGFBP) were determined with radioligand analysis following SDS-PAGE electrophoresis. In both experiments, plasma concentrations of triiodothyronine and thyroxine decreased (P < .01) during feed deprivation and increased (P < .01) during refeeding. Plasma glucose and IGF-I either decreased or were not altered during feed deprivation. In contrast, plasma concentrations of NEFA and urea nitrogen increased (P < .01) during feed deprivation and decreased (P < .01) during the refeeding period. Plasma somatotropin (ST) increased (P < .01) approximately 80% at 24 to 36 h of feed deprivation, declined (P < .01) to control values at 48 h of feed deprivation, increased (P < .01) nearly three fold at 3 h after refeeding, and returned to control values by 6 h after refeeding. We identified five IGFBP, and their plasma concentrations were not significantly altered during feed deprivation or following refeeding. We conclude that metabolite availability during feed deprivation and following refeeding alters the secretion of thyroid hormones, ST, and possibly IGF-I, thereby maintaining homeostasis in horses.

Effects of polychlorinated biphenyl mixtures and three specific congeners on growth and circulating growth-related hormones

Polychlorinated biphenyls (PCB) are ubiquitous environmental contaminants that bioaccumulate in avian species. Exposure to PCBs can result in decreased growth. Thyroid hormones and growth hormone (GH) are important for normal growth. The present studies employed the chicken embryo to investigate effects of Aroclor 1242, Aroclor 1254, 2,2',6,6'-tetrachlorobiphenyl (TCB), 3,3',4,4'-TCB, and 3,3',5,5'-TCB on growth and growth-related hormones. The following indices were measured: embryo mortality, body weights, bone length, pituitary GH content, and plasma concentrations of triiodothyronine (T3), thyroxine (T4), GH, and insulin-like growth factor-1 (IGF-1). Fertile eggs were injected with PCBs on Day 0 and indices determined on Day 17 of incubation. Unexpectedly, 3,3',5,5'-TCB or low-dose Aroclor 1242 treatment increased body weight and bone length (P < 0.05), whereas Aroclor 1242 (high dose), 3,3,4,4'-TCB, or Aroclor 1254 treatment reduced body weights and/or bone length (P < 0.05). Aroclor 1242 or 3,3',4,4'-TCB (low-dose treatment) elevated plasma T4 concentrations (P < 0.05). Both growth and pituitary GH content were increased (P < 0.05) by 3,3',5,5'-TCB (low dose) or Aroclor 1242 treatment. Despite marked differences in growth rates, plasma T3, GH, and IGF-I concentrations were unaffected by PCB treatment. Growth-related hormones may not be responsible for the growth depression observed after PCB treatment. Possibly the decrease in growth occurred because of general toxicity. The importance of chlorine position in causing thyroid hormone axis alterations was not clearly established.

Ontogenic changes in the circulating concentrations of insulin-like growth factor (IGF)-I, IGF-II, and IGF-binding proteins in the chicken embryo

The ontogeny of circulating concentrations of insulin-like growth factor (IGF-)-I, IGF-II, and IGF-binding proteins (IGF-BPs) was examined in the chick embryo. Distinct ontogenic changes in the circulating concentrations of IGF-I and IGF-II were observed. The present study confirms the overall profile for circulating concentrations of IGF-I. During middevelopment, plasma concentrations of IGF-I increased to a maximum which was attained on Day 14.5 of incubation. Thereafter, plasma concentrations of IGF-I declined with decreases (P < 0.05) between Days 14.5 and 15.5 and between Days 16.5 and 17.5 of incubation. In contrast to the monophasic profile for IGF-I, plasma concentrations of IGF-II were maximal on Day 10.5 of incubation and declined to a nadir on Day 17.5 of incubation. In late developmental stages (17.5 or 18.5 days of incubation), three IGF-BPs, having molecular weights of 22, 28, and 36 kDa, were detected in the plasma of chick embryos. No significant ontogenic changes in the circulating levels of the 28- and 36-kDa IGF-BPs were observed. However, it should be noted that prior to Day 17.5 of incubation, the 22-kDa IGF-BP was nondetectable in the circulation. The role of these changes in the functioning of IGF in embryonic development is discussed.

Chronic administration of growth hormone (GH) to adult chickens exerts marked effects on circulating concentrations of insulin-like growth factor-I (IGF-I), IGF binding proteins, hepatic GH regulated gene I, and hepatic GH receptor mRNA

In young birds, growth hormone (GH) administration has been found to have only a small or even no effect on circulating concentrations of insulin-like growth factor-I (IGF-I). This is in obvious contrast to the situation in mammals. The present study examines the effect of continuous administration of GH in adult male chickens. Plasma concentrations of IGF-I were markedly elevated (2.5-3.0-fold, p < 0.001) in GH-treated chickens. There were also some transient increases in the circulating levels of IGF binding proteins. Adult chickens showed other manifestations of increased responsiveness to GH, including elevated hepatic expression of GH-regulated gene-I (mRNA) with GH treatment (p < 0.05), and a tendency (p < 0.08) for decreased GH-receptor mRNA. In contrast to the changes in circulating concentrations of GH and IGF-I with GH treatment, no changes in plasma concentrations of thyroid hormones, reproductive hormones, glucose, or nonesterified fatty acids were evident.

Feed intake, body weight, body condition score, musculation, and immunocompetence in aged mares given equine somatotropin

Sixteen 20- to 26-yr-old mares were given 0, 6.25, or 12.5 mg/d equine somatotropin (eST) to determine whether aged mares respond to ST with changes in feed intake, body weight, body condition score (based mostly on fat cover), or immunocompetence. Neither dry matter intake, body weight, nor body condition scores were altered during the 6 wk of eST injection. However, based on photographs taken to evaluate musculation before and after treatment (scores 0 to 4), mares given eST developed greater (P < .07) muscle definition (1.8 +/- .6 and 2.5 +/- .6 for 6.25 and 12.5 mg eST/d, respectively) than control mares (.7 +/- .4). Total circulating leukocytes increased (P < .05) in both of the eST-treated groups during the 6-wk injection period, caused by an increase (P < .05) in granulocytes. Lymphocyte numbers were not altered. Granulocyte oxidative burst activity was not altered by eST treatment. Although lymphocyte proliferative responses to phytohemagglutinin, pokeweed mitogen, or lipopolysaccharide were not altered during the treatment period, lymphocyte proliferation in response to phytohemagglutinin and pokeweed mitogen increased twofold in eST-treated horses at 2 wk after eST treatment. In overview, the increased musculation and the increase in granulocyte numbers in mares given eST suggest that eST supplementation may improve the health and well-being of aged mares.

Age and breed differences in thyroid hormones, insulin-like growth factor (IGF)-I and IGF binding proteins in female horses

A survey with horses was conducted to determine whether plasma concentrations of triiodothyronine (T3), thyroxine (T4), insulin-like growth factor (IGF)-I and IGF binding proteins (IGFBP) change as horses grow, mature sexually, and age. Jugular blood was sampled from Standardbred fillies and mares at ages 0, 1, 7, and 14 d, at 1, 2, 4, 5, 6, and 9 mo, and at 5 to 8 and 16 to 22 yr (n = 5 to 18). In a second survey, we measured the same variables in eight breeds of horses with markedly different adult body sizes, from Miniatures to Friesians. Plasma T3, T4, and IGF-I were determined by radioimmunoassays validated for horses, and IGFBP were estimated from radioligand assay following separation of the IGFBP by SDS-PAGE electrophoresis. Plasma T3 decreased (P < .01) nearly continuously from 7.9 ng/mL on the day of birth to .9 ng/mL at 6 mo, and then changed little from .7 ng/mL at 9 mo to .5 ng/mL in mares 16 to 22 yr old. Similarly, T4 declined (P < .01) from 233 ng/mL on the day of birth to 49 ng/mL at 14 d and varied from 35 to 9 ng/mL among all of the older age groups. Plasma concentrations of IGF-I increased (P < .01) from 285 ng/mL on the day of birth to 572 ng/mL at 14 d, remained relatively constant until 9 mo of age (530 ng/mL), and then declined (P < .01) to low levels (295 ng/mL) in the oldest mares. We detected six IGFBP. The two smallest IGFBP (26 and 39 kDa) were highest during the first 14 d after birth and lowest (P < .01) in aged mares. The four larger IGFBP were lowest at birth and increased to the highest values during the most rapid growth period, but these changes were not significant (P > .20). In agreement with data for other species, our data suggest that IGF-I and IGFBP modulate growth in horses. Although there were impressive interbreed differences in circulating concentrations of T3, T4, IGF-I, and IGFBP, these were not related to differences in adult body size.

Effect of acid or aluminum on growth and adrenal function in young chickens

Acid precipitation can have a harmful effect on aquatic birds, due in part to increases in aluminum availability. Young rapidly growing (broiler strain) chickens were used as a model to examine the effects of aluminum and acid on growth and circulating concentrations of adrenocorticol hormones. Two concentrations of acid (sulfuric acid) or aluminum (aluminum sulfate) or sodium sulfate were administered to a heavy (broiler) strain of chickens for 10 days (Days 4 to 14 of age). Additional treatment groups included a control diet either fed ad libitum or pair-fed relative to the chicks on the acid or aluminum diets. Compared with the chicks receiving the control diet ad libitum, growth (body weight) was reduced in chicks on the aluminum (high and low level), acid (high level), and sodium sulfate (high level) treatments and the respective pair-fed groups. Circulating concentrations of corticosterone (B) were elevated in the chicks receiving the high dose of aluminum and the respective pair-fed control when compared with the chicks which had free access to the control diet. Thus, the increase in plasma B appears to be linked to the low food intake and not to the A1 per se. Circulating concentrations of aldosterone were increased in the chicks receiving either the high dose of aluminum or the acid relative to chicks fed the control diet (both ad libitum or pair-fed controls). However, circulating concentrations of aldosterone were unaffected by either dose of sodium sulfate employed. Thus, the increase in plasma aldosterone appears to be specific to the metabolic acidosis created by A1 or acid. It is concluded that environmental acid may either directly or indirectly influence adrenocortical function. Moreover, the present study provides evidence for the independent control of circulating concentrations of corticosterone and aldosterone in the chicken.

The suppressive effects of testosterone on growth in young chickens appears to be mediated via a peripheral androgen receptor; studies of the anti-androgen ICI 176,334

ICI 176,334 is a nonsteroidal anti-androgen that has been shown to selectively block peripheral androgen receptors in rats and is presumed to do so in chickens. In chickens, androgens stimulate secondary sexual characteristics (e.g., comb), but inhibit growth and the immune tissues. The present study examined the effect of dietary ICI 176,334 (5 or 25 mg/kg body weight) on growth in chickens in the presence or absence of testosterone treatment (as 1-cm long silastic implants). Treatments began at 2 wk of age and continued through 6 wk of age. Testosterone alone reduced body growth (average daily gain and shank-toe length, together with weights of the body, skeletal muscle, and the bursa of Fabricius, an immune tissue), and stimulated comb development. At the low dose (5 mg/kg), ICI 176,334 alone had no effect on body growth or organ weight with the exception that comb weight was reduced. At the high dose (25 mg/kg), ICI 176,334 decreased growth (body weight, average daily gain, and shank-toe length) and organ weights (breast muscle, bursa of Fabricius, testis, and comb weights). This effect may represent a toxicity. As might be expected with an anti-androgen, ICI 176,334 (at either 5 or 25 mg/kg) completely suppressed the stimulation of comb growth evoked by testosterone. Similarly, ICI 176,334 (5 mg/kg) overcame, albeit partially, the growth-suppressive effects of testosterone (on body weight, average daily gain, shank-toe length, and breast muscle weight) and also had inhibitory effects on the weights of the testis and bursa of Fabricius. The anti-androgen, ICI 176,334, did not influence the reduction in circulating concentrations of luteinizing hormone occurring after testosterone treatment. The present data are consistent with the growth-suppressive effects of testosterone in chickens being mediated via a peripheral androgen receptor. No effects of either testosterone or ICI 176,334 were observed on circulating concentrations of insulin-like growth factor-I despite the marked changes in growth rate.

Differential and tissue-specific regulation of (pro)insulin and insulin-like growth factor-I mRNAs and levels of thyroid hormones in growth-retarded embryos

The control of embryonic growth in vertebrates appears to rely on the orchestrated action of several families of growth factors and hormones. The contribution of insulin-like growth factor (IGF-I) to prenatal growth regulation is better established in mammals than in other vertebrate species. The status of (pro)insulin gene product(s) in the pancreas and non-pancreatic tissues may be another important contribution to embryonic growth signals. We have characterized tissue sources of IGF-I gene and (pro)insulin gene mRNAs in normal chicken embryogenesis and their changes in a model of avian growth retardation. We studied, by a highly sensitive reverse-transcription coupled to polymerase chain reaction (RT-PCR), the expression of IGF-I and (pro)insulin genes in brain, pancreas, liver and eye in embryos from late organogenesis (E8) to late development (E17); hatching is at E20-21, a period of fast embryonic growth. In brain, pancreas and eye, growth-retarded embryos had lower IGF-I mRNA expression. In contrast, in the liver, little IGF-I mRNA was found during normal embryogenesis, but some early induction occurred in E17 growth-retarded embryos. (pro)insulin gene expression was much lower in absolute levels in non-pancreatic tissues than in pancreas. However, it was developmentally regulated in brain, liver and eye. The growth-retarded, IGF-I-deficient embryos had an increased expression of (pro)insulin mRNA in the brain. While IGF-I treatment of growth-retarded embryos increased their serum IGF-I values, only partial recovery of embryonic weight was obtained. Since abnormalities in other hormones may contribute to the failure of systemic IGF-I to reverse the retarded phenotype, thyroid hormones (T3 and T4) levels were determined in liver, brain and eye. They were markedly altered only in the liver of growth-retarded embryos, where an increase in thyroid hormone content was observed. We conclude that, in chicken embryos and possibly other vertebrates, normal growth may implicate multiple hormones, including the concerted action, endocrine/paracrine, of IGF-I and (pro)insulin gene products.

Comparison of the ontogenesis of thyroid hormones, growth hormone, and insulin-like growth factor-I in ad libitum and food-restricted (altricial) European starlings and (precocial) Japanese quail

In this study, we compare the ontogenic patterns for thyroid hormones, growth hormone (GH), and insulin-like growth factor-I (IGF-I) in altricial European starlings and precocial Japanese quail and examine the effects of feed restriction on these species. The most marked difference in development between the altricial and precocial birds was with respect to plasma thyroid hormone patterns. In the starling, circulating concentrations of triiodothyronine (T3) and thyroxine (T4) were very low in embryos, then increased progressively after hatching to peak at 10-11 days of age. In contrast, in quail, in which other studies have shown that most thyroid maturation occurs during the embryonic and peri-hatch periods, the circulating concentrations of T3 and T4 showed little posthatch ontogenic change. Plasma concentrations of both GH and IGF-I showed similar patterns in both species with a posthatch rise (peak at 3 days in starlings and 8 days in quail), followed by a decline. Food restriction to maintain body weight resulted in decreased plasma concentrations of T3 and IGF-I in both species. After return to ad libitum feeding, plasma T3 and IGF-I increased in both early and late restricted starlings and in late restricted quail. Although both species responded to food restriction with similar patterns of endocrine change, age-related differences in the magnitude of hormonal responses were observed.

Effect of dietary acid or aluminum on growth and growth-related hormones in young chickens

The effect of two concentrations of dietary acid (sulfuric acid) or aluminum (aluminum sulfate) on growth and growth-related hormones was examined in a heavy (broiler) strain of chicken between 4 and 18 days old. Growth (body weight, average daily gain, and tibial length) in chicks receiving either dietary acid or aluminum-containing diets were compared to chicks fed a control diet and to chicks fed diets containing sodium sulfate. Despite the reduced growth in acid-fed chicks, there were no changes in the plasma concentrations of growth hormone, insulin-like growth factor-I (IGF-I) and insulin-like growth factor-binding proteins (IGF-BP). However, in chicks receiving the high aluminum diet where growth was markedly depressed (by 57%), plasma concentrations of IGF-I were depressed, while those of the 36-kDa IGF-BP were elevated. The effects of acid and aluminum on growth were mediated at least partially by reductions in feed intake. Pair feeding depressed growth and tended to decrease plasma concentrations of IGF-I. Some differences were observed between acid or aluminum groups and their respective pair-fed controls. For the groups receiving the low-aluminum and both the high- and low-acid diets, values were increased compared to corresponding pair-fed controls for average daily gain, the level of the 36-kDa IGF-BP, and skeletal growth. On the other hand, high aluminum had a toxic effect in addition to reducing feed intake, with skeletal growth being reduced more in chicks receiving the aluminum diet than in the pair-fed controls.

Evidence for functionally distinct subpopulations of steroidogenic cells in the domestic turkey (Meleagris gallopavo) adrenal gland

A body of histological and functional evidence supports the hypothesis that there are functionally distinct subpopulations of steroidogenic cells comprising the avian adrenal gland. In the present study, we tested this hypothesis by evaluating the steroidogenic responses of density-dependent subpopulations of adrenal steroidogenic cells isolated from domestic turkeys fed either a high-normal (control) sodium diet (0.4% Na+) or a Na(+)-restricted diet (0.04% Na+) for 8 days, the latter to stimulate the activity or appearance of possible zona glomerulosa-like cells. Subpopulations were visually yet reproducibly determined by their density-dependent separation on a continuous density gradient of Percoll (45%). The subpopulations were arbitrarily ascribed as being either low-density or high-density adrenal steroidogenic cells [LDAC (p = 1.0350-1.0585 g/ml) and HDAC (p = 1.0590-1.0720 g/ml), respectively]. LDAC and HDAC comprised 95.2 and 4.8%, respectively, of the total number of adrenal steroidogenic cells isolated. The LDAC was further subdivided into three visually distinct subpopulations. The functional differences between the LDAC subpopulations is discussed but was less dramatic than the functional distinction between the HDAC subpopulation and the pooled LDAC subpopulations. Basal aldosterone production values between control LDAC and HDAC were equivalent. In addition, there were no differences in maximal aldosterone production between control LDAC and HDAC in response to [Ile5]angiotensin II (AII), the avian equivalent, [Val5]AII, K+ (as KCl), and that supported by exogenous corticosterone. However, maximal aldosterone production in response to human ACTH-(1-39) (ACTH) of the LDAC was 32% greater than that of the HDAC. Na+ restriction enhanced basal aldosterone production of the LDAC by 84% over the control LDAC. In addition, it enhanced maximal aldosterone production of the LDAC in response to AII peptides, K+, ACTH and that supported by corticosterone by 54, 164, 83, and 74%, respectively, over that of the control LDAC. However, Na+ restriction disproportionately enhanced basal aldosterone production of the HDAC by 348% over that of the control HDAC. In addition, with Na+ restriction, maximal aldosterone production of the HDAC in response to AII, K+, and ACTH and that supported by exogenous corticosterone was consistently greater than that of the LDAC. Moreover, with Na+ restriction, maximal aldosterone production of the HDAC in response to AII peptides and K+ was increased over that of the control HDAC to a greater extent than was maximal aldosterone production in response to ACTH and that supported by corticosterone (% enhancement over control was as follows: AII peptides, 502%; K+, 668%; ACTH, 273%; corticosterone, 183%).(ABSTRACT TRUNCATED AT 400 WORDS)

Hypoglycemia, enteritis, and spiking mortality in Georgia broiler chickens: experimental reproduction in broiler breeder chicks

The clinical signs, hypoglycemia, and mortality of "spiking mortality syndrome" were experimentally reproduced. Seven groups of day-old male primary broiler breeder chicks were orally inoculated with tissue and/or fecal-urate homogenates taken from field broilers with spiking mortality syndrome and from field broilers with enteritis and/or runting-stunting syndrome. All homogenates used as inocula were shown by transmission electron microscopy and negative staining to contain arenavirus-like particles. Inocula produced from field broilers with spiking mortality syndrome contained the highest numbers of the arena-virus-like particles and produced the highest percentage of hypoglycemic chicks 13-15 days postinoculation after a 5-to-9-hour fast. These homogenates also produced the most significant differences in mean plasma growth hormone and insulin-like growth factor-1 levels. The significance of the arenavirus-like particles is unknown but is currently being investigated.