Dwarf Chickens Research Articles

Abnormal growth hormone receptor gene expression in the sex-linked dwarf chicken

Sex-finked dwarfism is a recessive mutation that causes a reduction in body weight gain and long bone growth of chickens. We examined the effect of the dwarfing gene on body weight, hepatic GH-binding activity, and the structure and expression of the growth hormone receptor (GHR) gene in two different lines of sex-linked dwarf (SLD) broiler chickens. Liver samples from one line of dwarf chicken were obtained from Arbor Acres Farm, Inc. (Glastonbury, CT) and fertile eggs from the second line of SLD were obtained from the University of Georgia. In the GA line, the average body weight of homozygous ( dwdw) males at 1 1 weeks of age was 43% lower than that of normal ( DwDw) males, while heterozygous ( Dwdw) males were only 9% below normal. In the CT fine, hepatic GH-binding activity of 35-week-old chickens was high (20% specific binding) in normal ( DwDw) males and undetectable in liver membranes prepared from dwdw males. At 11 weeks of age, hepatic GH-binding activity of Dwdw males (3.9% specific binding) in the GA line was reduced by 44% and that of dwdw males was almost undetectable (0.34% specific binding) when compared to the average of normal GA males (7.l%-specific binding). Southern and Northern blot analyses revealed different abnormalities in the GHR.. gene from the two separate lines of SLD. A restriction fragment length polymorphism in DNA and an aberrantly sized transcript (mRNA) were detected in the CT line of SLD chickens. In the GA line, the DNA restriction pattern of dwdw males was identical to that found in normal GA chickens; however, there was no expression of the GHR gene in dwdw chickens since we did not detect an mRNA that corresponds to the GHR. These data suggest that the molecular defect of SLD chickens resides within the gene for the GHR and the dwdw phenotype results from a lack of synthesis of a functional GHR protein.

Characteristics of chicken serum transferrin and immunological determination of its serum levels in dwarf chickens

1. 1. The molecular mass of serum transferrin (Tf), purified from blood of immature Rhode Island Red (RIR) chickens was 74,000 by both gel filtration and SDS-gel electrophoresis. 2. 2. The chicken serum Tf bound two iron atoms per molecule and iron-saturated Tf showed maximum absorbance at 465 nm. The Tf had one sialic acid residue per molecule. 3. 3. The amino acid composition of the Tf was similar to that of turtle serum Tf. 4. 4. Serum Tf levels in normal and dwarf RIR chickens gradually declined after hatch and then rose steadily with their sexual maturation, but no distinct differences between sexes or strains were noted.

Effects of insulin-like growth factor-I (IGF-I) infusion and dietary tri-iodothyronine (T3) supplementation on growth, body composition and plasma hormone levels in sex-linked dwarf mutant and normal chickens.

This study used a sex-linked dwarf mutant (SLD) chicken to evaluate growth-promoting and metabolic effects of recombinant human insulin-like growth factor-I (rhIGF-I) treatment. The SLD chicken is characterized by a 30% reduction in body weight and by high plasma GH levels, low plasma IGF-I and triodothyronine (T3) levels and very low GH binding on liver membranes, suggesting reduced functional GH receptors compared with normal chickens. The effects of a continuous s.c. infusion by osmotic mini-pump of 0.1 mg rhIGF-I/kg per day from 4 to 8 weeks of age on body weight, bone growth and body composition were investigated in female SLD and normal chicks. In addition, half of the birds received a dietary supplement of T3 (0.1 parts per million). Plasma levels of IGF-I, GH, T3, thyroxine and insulin were followed during the treatment. In normal chicks, rhIGF-I infusion had no effect on growth and little effect on plasma hormone levels except for a decrease in plasma insulin. In dwarf chicks, rhIGF-I infusion slightly increased body weight but had no effect on longitudinal bone growth. In addition, plasma GH levels were decreased and T3 levels remained lower than in normal chicks. Normal and dwarf chicks showed a decrease in abdominal fat after both IGF-I administration and T3 supplementation, the treatments having additive effects in dwarf chicks only. The combined rhIGF-I and T3 treatment restored a quasi-normal hormonal pattern in dwarf chicks, except for insulin which remained lower than in normal chicks. These results suggest that IGF-I in the chicken has no direct endocrine effect on statural growth.

Effect of triiodothyronine supplementation on thyrotropin-releasing hormone-induced growth hormone secretion in sex-linked dwarf and normal chicks

The effect of a dietary triiodothyronine (T 3) supplement, of either 0.1 or 0.5 μg/g of feed, was studied on the thyrotropin-releasing hormone (TRH)-induced growth hormone (GH) secretion in sex-linked dwarf ( dw) or normal ( Dw) chicks of both sexes. In normal chicks, 0.1 μg/g T 3 decreased plasma GH levels before TRH as well as the GH increase after TRH, and 0.5 μg/g T3 totally suppressed any response to TRH, either at 4 or at 7 weeks of age. Dwarf chicks were more sensitive to TRH than normals when receiving either 0 or 0.1 μg/g T 3; 0.5 μg/g T 3 abolished the difference between genotypes at 4 weeks of age but not so clearly at 7 weeks of age, where dwarf females showed a slight but still significant GH increase after TRH. Interactions between genotype, TRH injection, and T 3 treatments were often significant at 4 weeks of age and even more at 7 weeks of age. Dwarf chicks receiving 0.1 μg/g T 3, expected to have normal plasma T 3 levels, showed a higher GH response after TRH. This suggests that other hormones may be involved in the regulation of this response, particularly IGF-I, which is known to remain at a low level in T 3-treated dwarf chicks.

Molecular Cloning of the Chicken Growth Hormone Receptor Complementary Deoxyribonucleic Acid: Mutation of the Gene in Sex-Linked Dwarf Chickens*

A novel complementary DNA (cDNA) encoding the chicken GH receptor was isolated from a chicken liver cDNA library, using polymerase chain reaction with primers derived from highly conserved sequences of the mammalian GH receptor. The nucleotide sequence predicts a mature protein of 592 amino acids and a 16 amino acid signal peptide that are partially homologous to the sequence reported for the rabbit (53%), rat (58%), and human (50%) GH receptors. Despite this low level of homology, a number of structural features of the GH receptor are conserved, including 7 cysteine residues in the extracellular domain and 5 in the intracellular region. Three transcripts of approximately 4.7, 4.0, and 1.0 kilobases are present on Northern blots of total RNA prepared from the livers of 35-week-old male chickens. Expression of the GH receptor was also detected in a wide range of tissues. The chicken GH receptor cDNA was then used as a probe in Southern and Northern blot analyses of DNA and RNA prepared from livers of sex-linked dwarf chickens, which have undetectable levels of hepatic GH-binding activity, in addition to other endocrine abnormalities. A restriction fragment length polymorphism was found in DNA, and an aberrantly-sized transcript was found in hepatic RNA of the dwarf chicken. These results indicate that a mutation in the GH receptor gene is responsible for the phenotype of the sex-linked dwarf chicken. This type of dwarfism resembles Laron-type dwarfism in humans, where a defect in the GH receptor gene has recently been identified. These receptor-deficient chickens should serve as a unique model system for studying the role of the GH receptor in growth and development.

Central somatostatinergic regulation of growth hormone secretion in dwarf chickens

1. 1. Basal circulating growth hormone (GH) concentrations in sex-linked-dwarf (SLD) chickens were unaffected by the intracerebroventricular (icv) injection of 10, 50 or 100 μg somatostatin (SRIF). 2. 2. The GH response to systemic thyrotropin-releasing hormone (TRH; 10μg/kg, iv) was, however, ‘paradoxically’ enhanced 20 min after icv SRIF administration. 3. 3. A lower dose (1.0μg) of SRIF had no effect on basal or TRH-induced GH release. 4. 4. High-litre SRIF antisera (4μl) also had no acute effect on basal plasma GH concentrations, but augmented the GH response to TRH challenge. 5. 5. SRIF would appear to act at central sites to modulate stimulated GH secretion in SLD chickens.

Differences in hepatic growth hormone receptor binding during development of normal and dwarf chickens

The aim of this study was to compare the growth hormone (GH) receptor in liver microsomal fractions of normal chickens (Dw) and chickens carrying the dwarf gene (dw). Specific binding of GH to its hepatic receptor was significantly higher for Dw embryos from d 14 till d 20 of incubation than for dw embryos. The difference in binding was due to a decreased binding capacity but not affinity in the livers of the dwarf embryos. The same binding pattern was found in livers of adult chickens: lower binding was again caused by a lower number of GH receptors and at this stage the difference was even clearer than during embryonic development. Binding studies on livers of growing chicks demonstrated that binding was low for both genotypes, but a small though significant difference between them remained. The cause of this decrease in number of GH receptors in dwarf birds has yet to be determined but may be due to the primary action of the dwarf gene.

Effects of dietary T 3 on growth parameters and hormone levels in normal and sex-linked dwarf chickens

Tri-iodothyronine (T 3) has been administered in the diet, from day of hatch until 8 weeks of age, to sex-linked dwarf and normal chicks of both sexes from a brown-egg slow-growing strain. Feed was supplemented with either 0.1 ppm or 0.5 ppm T 3. A significant genotype by treatment interaction was observed on body weight: the effect of T 3 in males was significantly positive for dwarfs and null for normals, the effect in females was null for dwarfs and significantly negative for normals. Feed efficiency was rather decreased by the treatment in both genotypes. Abdominal fatness was decreased in a dose-dependent manner in both genotypes, while rectal temperature was raised in dwarf chicks only. Plasma T 3 was raised to normal levels in dwarfs receiving 0.1 ppm exogenous T 3, while the 0.5 ppm dose yielded hyperthyroid levels. Plasma GH levels were decreased in a dose-dependent manner by the T 3 treatment, the effect being larger in dwarfs. Surprisingly, plasma IGF-I was unchanged in spite of the GH decrease, whatever the genotype or the sex. It was concluded that exogenous T 3 alone can have a stimulatory effect on growth in dwarfs but can not fully restore a normal growth rate. Both T 3 and IGF-I are important for a normal growth and the relationships between T 3 and IGF-I production should be further investigated in order to better understand the physiological modifications due to the sex-linked dwarf gene.

Research Note: Composition of Eggs from Dwarf and Normal Chickens Before Incubation and at Hatching in Lines Selected for 56-Day Body Weight

Comparisons of egg composition prior to incubation and when the chick had pipped through the shell were made for dwarf (D) and normal (N) chickens from lines selected for high (H) or low (L) body weight. Weight of moisture, ash, and fat decreased and nonlipid organic matter increased during incubation. The pattern for these components was the same on a percentage of egg weight basis except that there was no change in ash. Genotype by line interactions were significant for egg weight, moisture, ash, fat, and nonlipid organic matter before incubation and for all of these characteristics except fat at pipping. The interactions were due to values being lower for D than N in Line L, and D and N were similar in Line H. When egg component weights were expressed relative to egg weight, interactions were not significant prior to incubation but were present for moisture and fat at hatch. These data show that characteristics influenced by the sex-linked dwarfing gene are modified by the background genome.

Increased in-vivo insulin sensitivity but normal liver insulin receptor kinase activity in dwarf chickens

The effects of the recessive and sex-linked dw gene on insulin sensitivity and liver insulin receptors were compared in normal (Dw-dw) and dwarf (dw-dw) brother or half-brother chickens. At 3.5 weeks of age, following an overnight fast, exogenous insulin (0-6.9 nmol/kg body weight) was slightly but significantly more hypoglycaemic in dwarf chickens. At 4 weeks of age, following an oral glucose load (2 g/kg), glucose tolerance was the same in both genotypes, whereas plasma insulin levels were greatly decreased in dwarf chickens. At 5 weeks of age, plasma concentrations of glucose and insulin were the same in both genotypes in the fasting state and decreased in the fed state in dwarf chickens. In liver membranes prepared from fasted chickens, insulin binding was increased in dwarf chickens, while the affinity of insulin receptors and the insulin-degrading activity of the membranes were the same in both genotypes. Following solubilization with Triton X-100, liver receptors were successively purified on lentil then wheat germ lectins. Autophosphorylation of the beta-subunit did not differ between either the genotype or the nutritional (fed or fasted) state. In the basal state (in the absence of insulin) the tyrosine kinase activity of the receptor towards artificial substrate poly(Glu, Tyr)4:1 was significantly decreased in dwarf chickens by fasting. However, the change in tyrosine kinase activity of the receptor in response to insulin was similar, irrespective of the genotype and the nutritional state.(ABSTRACT TRUNCATED AT 250 WORDS)

Thyroid function in dex-linked and autosomal dwarf chickens

Thyrotropin-releasing hormone (TRH) and thyrotropin (TSH) elevated plasma thyroxine (T 4) and triiodothyronine (T 3) concentrations in a (euthyroid) control line of chickens and in an autosomal dwarf strain. These agents were ineffective in sex-linked dwarf (SLD) chickens. Similarly, while somatostatin (SRIF) lowered plasma T 4 and T 3 concentrations in autosomal dwarf (ADW) chickens and controls, it had no inhibitory effect in the SLD strain. These results suggest that an impairment in the hypothalamus-pituitary-thyroid axis is at least partly responsible for hypothyroidism in the SLD strain.

Effects of thyroid hormones on cartilage sulphation in sex-linked dwarf chickens.

The present investigation was undertaken to see if exogenous thyroid hormome could stimulate cartilage sulphation in vivo and in vitro in sex-linked dwaft chickens B-thyroxine or 1-3,5,5-triiodothyronine injection for 7 consecutive days stimulated in vivo 35SO2-4 incorporation into trachea cartilages of the dwarf chicken. Both thyroid hormones added to the incubation medium with or without 2.5% dwarf chicken serum also stimulated in vitro 35SO2-4 incorporation into pelvic rudiment from 11-day chick embryos. These data demonstrate that thyroid hormones, like insulin-like growth factor 1, might be responsible for the reduced growth rate of dwarf chickens.

Composition of Eggs from Dwarf and Normal Chickens in Lines Selected for 56-Day Body Weight

Egg weight and egg components were measured at two ages in random samples of 30 nondwarf and 30 dwarf chickens from lines selected for high and low body weight at 56 days of age. Egg, dry shell, dry albumen, total moisture, relative moisture, and dry albumen weights as well as albumen and yolk percentage dry matter were similar at 300 and 360 days of age. Absolute and relative dry yolk weights increased with age, whereas relative shell weight and wet and dry albumen to yolk (A:Y) ratios decreased.Pullets from the high weight line laid larger eggs with more dry yolk, but less relative dry yolk and shell dry matter than those from the low weight line. Nondwarf pullets produced larger eggs with more absolute and relative dry yolk and shell dry matter than dwarf pullets. Line × genotype interactions were present for egg traits other than absolute and relative dry yolk and shell dry matter, providing evidence of differential effects of the dwarfing allele in different genotypic backgrounds.

Serum lipids in the sex-linked dwarf chicken.

The concentration and fatty acid composition of serum lipids from thesex-linked dwarf chickens were compared with those from the nondwarf chickensbetween 7 and 28 weeks of age. Concentrations of free fatty acids, triglycerides, phospholipids and free or total cholesterol were higher in the dwarfs than in thenondwarfs. This trend was more evident in mature birds. Differences in fattyacid composition between genotypes or sexes were not great in growing birds.

Cartilage response to thyroid hormones in the sex-linked dwarf chicken

1. 1. Trachea cartilages were dissected from normal and dwarf chickens which had been injected with thyroxine (T4, 200 μg/kg) or triiodothyronine (T3, 200 μg/kg) for seven consecutive days, and were analysed for nucleic acids, proteins and polyamines. 2. 2. In saline-injected control chickens, RNA, but not DNA and protein, concentration of the cartilage was higher in dwarfs than in normals. The concentration of putrescine was lower in dwarfs than in normals, while that of spermine was the reverse. 3. 3. Thyroid hormones, especially T3, tended to increase concentrations of RNA, spermidine and spermine, and to decrease that of putrescine. However, there were no clear differences in the response to hormones between breeds.

Thyroid hormone and growth : relationships with growth hormone effects and regulation

For some years, research in the field of growth endocrinology has been mainly focused on growth hormone (GH). However, it appears that GH does not always control growth rate. For instance, it does not clearly influence intra-uterine growth: moreover, although the results of GRF or GH administration appear convincing in rats, pigs or heifers, this is not the case in chickens and lambs. In addition, GH does not always clearly stimulate somatomedin production, particularly diring food restriction and fetal life, and in hypothyroid animals or sex-linked dwarf chickens. In such situations, this phenomenon is associated with a reduced T3 production, suggesting a significant influence of thyroid function on GH action, and more generally, on body growth. In fact, numerous data demonstrate that thyroid hormone is strongly involved in the regulation of body growth. In species with low maturity at birth, such as the rat. T4 and T3 affect postnatal growth eleven days earlier than the appearance of GH influence. In contrast to GH, thyroid hormone significantly influences fetal growth in sheep. Moreover, the body growth rate is clearly stimulated by T3 in dwarf animals. In addition to its complex metabolic effects involved in the general mechanisms of body growth, thyroid hormone stimulates the production of growth factors, particularly EGF and NGF. Moreover, it affects GH and somatomedin production and also their tissue activity. All these results strongly suggest that it would be difficult to study GH regulation and physiological effects without taking thyroid function into account.

Selection for 8-Week Body Weight in Normal and Dwarf Chickens Under Different Water/Feed Environments

Normal and dwarf chickens fed either regular (.4%) or high (1.6%) salt diets were selected for four generations for high 8-wk body weight. Selection gains in body weight were greater in dwarf than in normal genotypes. Selection differentials, gains, and heritabilities were greater in lines selected under the .4% salt environment. When tested females were fed .4% salt diets, normal females from lines selected after being fed 1.6% salt diets had less fat than those from lines selected after being fed .4% salt diets. However, no differences were observed in dwarf females from the two selection environments.

Plasma concentrations of growth hormone and somatomedin C in dwarf and normal chickens.

Sex-linked dwarf chicks, offspring from the mating of heterozygous sires with dwarf females, were used in this study. On days 18 and 20 of incubation, plasma concentrations of growth hormone (GH) and somatomedin C (Sm-C) did not differ between normal chicks and those of the dw-dwdw genotype. After hatching, Sm-C concentrations in normal chicks remained comparable to the embryo values for up to 1 week, but those in dwarf chicks were lower. After 3 weeks Sm-C increased greatly in the controls, whereas in dwarf birds it was far less pronounced up to 18 weeks of age and only increased to control levels on week 12. GH was low during incubation and increased sharply after hatching in normal and dwarf chicks. After 3 weeks and up to 18 weeks, GH levels were higher in dwarf chicks, except at week 12 when they decreased to control concentrations.

Influence of triiodothyronine and growth hormone on growth of dwarf and normal chickens: Interactions of hormones and genotype

1. 1. The effects of dietary triiodothyronine (T 3), injections of a preparation of growth hormone (GH) (purified from chicken pituitary tissue) and their combination on growth were investigated in three lines of chickens. The three lines were the Cornell K strain (K) (a Single Comb White Leghorn strain), the Cornell K strain hemizygous for the sex-linked dwarfing gene (SLD), and the Cornell K strain homozygous recessive for the autosomal dwarfing gene (ADW). 2. 2. A dietary T 3 treatment by genotype interaction was observed. Dietary T 3 (0.1 ppm) decreased growth in the K line, tended to decrease growth in the ADW line while it tended to increase growth in the SLD line. 3. 3. Chicken growth hormone (100 μg/kg body wt) alone did not affect growth in any of the lines studied. There was, however, a GH treatment by T 3 treatment interaction. Chicken GH overcame the growth-depressing effects of T 3 in the K and ADW lines while it tended to promote growth in T 3 treated SLD birds. 4. 4. Dwarf (SLD) chickens had higher basal circulating GH concentrations, lower circulating immunoreactive somatomedin C concentrations, and lower circulating T 3 concentrations than the K or ADW chickens.

Muscle Protein Turnover in Sex-Linked Dwarf and Normal Broiler Chickens ,

Dietary infusion of L-[U-14 C]tyrosine was used to estimate the fractional protein synthesis rates (FSR) in normal and dwarf female broiler chicks. Five 2-week-old and five 3-week-old birds of each genotype were placed in individual metabolism cages and given a purified diet in agar-gel containing 2 μCi L-[U-14 C]tyrosine for 6 hr. Birds were killed and the pectoralis major (PM) and combined gastrocnemius and peroneous longus muscles (LM) were removed for analyses. Additional groups of 4 to 5 chickens were killed 3 days before and 3 days after each infusion to determine fractional protein accretion rate (FAR) over the 6-day period. Fractional degradation rate (FDR) was obtained by difference (FDR = FSR – FAR). Protein, ribonucleic acid (RNA), and deoxyribonucleic acid (DNA) concentrations were determined to observe possible relationships between these cellular constituents and FSR. Activities of RNA and DNA were determined as units of protein synthesized per unit RNA or DNA per day. Two-week-old chicks, dwarf chicks, and the PM muscles had higher (P<.05) FSR than 3-week-old chicks, normal chicks, and the LM, respectively. Two-week-old chicks and dwarf chicks had higher FDR than 3-week-old chicks, respectively. There was a significant decrease in RNA concentration and RNA activity from 2 to 3 weeks. The RNA activity tended to be higher in dwarf than normal birds. Concentration of RNA was higher (P<.05) in the PM than LM. However, DNA concentration was higher (P<.05) in the LM than PM. Results indicate that protein turnover was greater in dwarf chickens than in normal chickens and this turnover decreased with increasing age.