Sex-linked Dwarf Gene Research Articles

The impact of sex-linked dwarf gene on hormonal reproductive profiles and biochemical traits in Iraqi dwarf roosters

The current experiment was aimed to explore the influencing of the sex-linked dwarf gene on some fertility hormones and biochemical profile in normal local and dwarf roosters. Thirty normal local and dwarf roosters at age 28 weeks were housed at opened system for 6 weeks. At end of 6th week, blood samples collected from all roosters and centrifuged to obtained sera for measuring the concentrations of Interstitial cell stimulating hormone ‘ICSH’, Follicle stimulating hormone ‘FSH’ and testosterone hormone, total protein, albumen, globulin, glutamic oxaloacetic transaminase ‘GOT’, Alkaline phosphatase ‘ALP’, and glutamic pyruvic transaminase ‘GPT’. The statistical analysis documented significant (P<0.05) decline in FSH and testosterone hormone in dwarf group roosters compared with normal local roosters. As well as, the level of total protein and globulin registered significant decline (P<0.05) in dwarf group roosters in comparison with normal local group roosters. On the other hand, the level of hepatic enzymes, GOT, GPT and ALK, recorded a significant (P<0.05) elevation in dwarf group roosters when compared with normal local group roosters. Concluded, that the sex-linked dwarf gene could be affected on hormonal fecundity profile and some biochemical traits in dwarf roosters.

Effect of sex-linked dwarf gene on exterior appearance, productive performance and egg characteristics in a colored broiler dam line

The effect of sex-linked dwarf gene was investigated through comparison of dwarf hens with their full-sib normal sisters obtained by mating heterozygous males (DW/dw) to normal females (DW/_) from line F (used as maternal form for production of slow-growing colored chickens) with respect to the following traits: body weight, shank and keel length at 40 weeks of age, age of sexual maturity (at 50 % production), egg production, egg weight, feed intake, feed utilization, livability, fertility, hatchability and egg quality characteristics. The results demonstrated that the dw gene caused statistically significant reduction of body weight by 29.15 %, shank length by 20.17 %, keel length by 7 % and egg weight by 5.72 % (p&lt;0.001). The hens with normal genotype attained sexual maturity 7 days earlier (p&lt;0.001), but nevertheless, rate of lay was similar to that of mini forms. There were no considerable differences between both genetic groups with respect to livability percentage over the production cycle. Dwarf hens consumed by 23.38 % less feed (p&lt;0.01) than normal sized hens and converted nutrients more efficiently by 12.69 % (p&lt;0.05). The presence of dw gene in hen genotype increased the eggshell percentage, reduced egg yolk and albumen weights and had no effect on their quality. The positive effect of the sex-linked dwarf gene on economically important traits - feed intake and feed conversion, hatchability of eggs set, is a prerequisite for the development of more efficient broiler breeder hens for production of slow-growing chickens.

Assessing the thermo-tolerance potentials of five commercial layer chicken genotypes under long-term heat stress environment as measured by their performance traits

This study was conducted to test the thermo-tolerance ability of five commercial chicken genotypes (Lohmann Brown, LB; Lohmann White, LW; New Hampshire, NH; White Leghorn selected for low feed expenditure, WL-FE and White Leghorn with sex-linked dwarf gene, WL-dw) under long-term heat exposure. Two-hundred forty female chickens were assigned to a completely randomized design in a 5 × 2 factorial arrangements (five genetic groups and two ambient temperatures [thermo-neutral, 18–20 °C; heat stress, 30–32 °C]). Individual eggs were collected on daily basis while egg weight and feed intake were determined on individual and group basis at 28-days intervals, respectively. Shell quality traits were determined at 25, 40 and 56 weeks age. No Genotype × ambient temperature interactions were found except for body weight and egg deformation. Chickens at thermo-neutral temperature produced significantly heavier eggs than those of heat-exposed (60 g vs. 54 g). Hen-housed egg production of chickens in thermo-neutral temperature was significantly higher than those of heat-stressed (76.8 % vs. 66.2 %). Daily egg mass production at thermo-neutral and heat stressed chickens was 46 g and 35.8 g, respectively. Feed consumption in heat-stressed and thermo-neutral chickens was 109 and 80.8 g, respectively. Shell thickness, breaking strength and Haugh unit values were significantly reduced in heat-stressed chickens. Among heat-exposed chickens, the NH had the highest body weight while the LW produced 10 % more eggs than the group average. The heat-induced effect on shell quality traits was lowest in LW chickens. The results indicated that the magnitude of heat stress was breed dependent in which the LB showed poor adaptability to heat stress while both NH and LW genotypes demonstrated better thermo-tolerance ability.

Effects of the Chicken Sex-linked Dwarf Gene on rowth and Muscle Development

The aim of this study was to analyze the effects on growth and muscle development during the growing period of the sex-linked dwarf gene in the background of a Taiwan Country chicken strain, L2, selected for egg production. Eight crossbred males, heterozygous for the DW*DW mutation, were each backcrossed to six females of the L2 strain to produce two genotypes of BC females, either normal (DW*N + /-) or dwarf (DW*DW/-). The experiment included 251 normal and 207 dwarf pullets. The effect of the dwarf gene on body weight and shank length was highly significant from 2 weeks of age. The reduction of body weight by the dwarf gene reached 34.8% and 37.4% as compared to normal sibs at 16 and 20 weeks of age, respectively. Parameters of the growth curve were estimated: the age at inflection (TI) was higher in normal pullets (66.9 days) than in dwarf pullets (61.2 days). A significant effect of the dwarf gene on single muscle fiber cross-section area was found from 12 weeks of age onwards, whereas the dwarf gene had no effect on the total number of muscle fibers. Comparing the effect of the dwarf gene on shank length at different ages revealed an earlier effect on skeleton growth, observed from 2 weeks of age, than on muscle development, which was affected from 8 to 12 weeks of age. (Key Words : Growth Curve, Muscle Development, Sex-linked Dwarf Gene, Chicken)

Influence of Naked Neck Gene on Laying Performance and Some Hematological Parameters of Dwarfing Hens

2 Abstract: Dwarfing gene is of interest among scientist, because of its numerous pleiotropic effects in physiology, nutrition and pathology. Also, the naked neck (Na) gene has received great attention for poultry production, because of their association with heat tolerance. From this view, An experiment was conducted to evaluate the effect of sex-linked dwarf (dw), autosomal naked neck (Na) and double segregation genes on laying performance and some hematological parameters of egg-type chicken under prevailing condition of Egypt. Three hundred brown Dahlem (Germany strain) hens from four genotypes {normal body size- normally feathered (Dw-nana), dwarf size-normally feathered (dw-nana), normal body size-naked neck (Dw- Nana) and dwarf size-naked neck (dw-Nana)} were reared under the same environmental, managerial and hygienic conditions from 20 to 40 weeks of age. The results obtained showed that the sex-linked dwarf (dw) gene significantly reduced body weight, egg mass and egg number compared to normal body size sibs. On the other hand, the dwarf birds had significantly consumed less feed and better feed conversion ratio. With respect to internal and eggshell quality, it could speculate that the presence of dw gene associated with higher yolk percentage, higher haugh units and thicker eggshell thickness than that of normal body size counterparts. Concerning hematological parameters, the presence of dw gene significantly reduced plasma T3, plasma cholesterol and liver enzymes compared to normal body size hens. The opposite trend was noticed for both total lipids and triglycerides. In contrary to dw gene, the Na gene had a better effect on laying performance parameters of egg-type chicken. With respect to double segregation genes, it could be noted that the introducing Na gene could compensate the reducing effect associated with dwarfing (dw) gene on laying performance measurements and some hematological parameters. In conclusion, the loss of revenue due to reduction in egg production associated with sex-linked dwarf gene may be exceeded by revenu e saved from lower feed intake and better feed efficiency. Moreover, incorporating the Na gene into dwarfed birds could compensate the reduction effects associated with dwarfing (dw) gene.

Deficiency of Growth Hormone Receptor Does Not Affect Male Reproduction in Dwarf Chickens

Sex-linked dwarf chickens caused by the mutation of the growth hormone receptor gene are characterized by normal growth hormone (GH), very low insulin-like growth factor I (IGF-I) level in the blood, and reduced growth. It has been demonstrated that the sex-linked dwarfing gene has negative effects on female reproduction. In the current study, dwarf cocks and their phenotypic normal siblings were used to investigate the effects of dwarf gene on male reproduction. Dwarf cocks grew slower than the normal cocks did, and at 20 wk of age, their BW were 36.4% smaller. However, all parameters for semen quality, including volume, sperm concentration, viability, mobility, pH, and percentage of abnormal sperms, examined at 30 wk of age showed no significant difference between normal and dwarf cocks. The fertility of dwarf cocks was 95.2%, and the normal was 92.4%. The concentrations of GH and IGF-I in serum and seminal plasma were measured with RIA and ELISA, respectively. The serum GH in the dwarf cocks was significantly higher than their normal siblings (P < 0.05), whereas the serum IGF-I in the dwarf cocks was very low. However, the concentration of seminal IGF-I in dwarf cocks was similar to that of their normal siblings, indicating that IGF-I might be produced and acted independently in testis. In conclusion, the deficiency in GH receptor did not affect the male reproduction in dwarf chickens, and the fertility of dwarf cocks could be satisfactory for production when artificial insemination was adopted.

Sex-linked Dwarf Gene for Broiler Production in Hot-humid Climates

This review has been done to examine sex-linked dwarf gene in broiler production in hot-humid climates. Introduction of sex-linked dwarf gene especially in hot harsh tropical environments brings a great advantage for broiler production. The heavy broiler parent suffers due to the stress of these adverse climates. Sex-linked dwarf genes reduce body weight, egg weight, but are superior for adaptability under harsh tropical environments, with a lower requirement for housing and feed, better survivability and reproductive fitness giving fewer defective eggs, more hatching eggs, better fertility, hatchability, feed conversion efficiency and resistance to disease. Overall the cost of chick production from dwarf hens is lower than from their normal siblings. Market weights of broilers from sex-linked dwarf dams is almost similar to those of broilers from normal dams with normal sires. But the net benefit of broiler production from sex-linked dwarf dams is found to be greater than that of broilers from normal dams. This will be the most important to the rural communities in Bangladesh and in other countries where the similar environment and socio-economic conditions exist. Therefore, sex-linked dwarf hens might be used in broiler breeding plan as well as broiler production in the tropics.

Comparison of Feed Intake, Blood Metabolic Parameters, Body and Organ Weights of Growing Broilers Originating from Dwarf and Standard Broiler

Growing broilers from three female breeder lines were compared to determine the relationship between feed intake, body weights, relative growth (RG), blood triiodothyronine (T ) and carbon dioxide partial 3 pressure (pCO ) levels, heart and liver ratio to body weights in order to establish the dynamics of growth at 2 different periods during rearing. The lines included a standard heavy S line, an experimental (E) line and a Label-type line (L). The E and L lines breeders carry the sex-linked dwarfing gene and are being used to assess the potential for the gene to reduce feed intake or lower feed restriction to improv e reproductive performance in heavy female broiler parent stock. Four incubation settings, each of 2 replications of 150 eggs /line (total of 3,600 eggs) were incubated. At the end of each incubation setting, samples of chicks were reared in order to record broiler body, heart and liver weights, and to measure thyroid hormone levels and gas pressure in blood during specific periods of growth namely at d 14, 28 or 41 of age. The results showed that although broiler body weights at 14, 28 and 41 d were different between lines (S > E > L) at these times, only the RG during the periods 1-14 d and 15-28 d were different between lines. The RG decreased sharply with increasing age of broilers depending on the lines but become similar during the period of 28 to 41 d. On the contrary, feed intake increased with the age of broilers. Feed conversion ratio (FCR) decreased with age but not different between lines. Heart and liver ratios to body weights as well as pCO levels followed the same trend as RG in relation to the age of broilers and the lines. The levels of T 2 3 also decreased with increasing age of broilers but at each age these levels were similar between lines. These data suggest a logical positive correlation between T , pCO , FCR, heart and liver ratios to RG at 3 2 different stages of growth depending on the lines. It is concluded that selection for fast growth improved broilers growth mainly during the first 4 weeks of rearing in the S line; the dwarf lines also showed high growth during the same period with a higher rate in the E line. The results suggest that heavy broiler production may benefit from the use of the dw E line from the viewpoint of lower feed consumption in both the parent stock and the broilers combined with the higher reproductive performance of the parent stock.

Oviposition and egg quality traits of dwarf and naked neck layers

Oviposition and egg quality traits were studied in dwarf and naked neck layers in Maputo (Mozambique) during a 28-d period at 35 weeks of age. Birds were caged individually in a laying house with natural light and ventilation. Average daylight length during the study was 11.2 hr and minimum and maximum temperature was 19.6 °C and 30.1 °C, respectively. The main results show that the sex-linked dwarfing gene (dw) increased the mean interval and time of oviposition, and reduced the sequence length and rate of lay. A bimodal distribution of oviposition intervals was observed in the dwarf population. No meaningful effect of the naked neck (Na) gene could be seen on oviposition traits. The dw gene also reduced the egg and components weight as well as the height of the albumen. The Na gene was associated with increased yolk weight and reduced albumen height. Keywords: Naked neck, Dwarf, Oviposition, Egg quality, Laying hens South African Journal of Animal Science Vol.33(2) 2003: 105-111

Comparison of outbred lines of chickens for resistance to experimental infection with coccidiosis (Eimeria tenella)

Coccidiosis causes dramatic economic losses in the poultry industry. Next to the extensive use of anticoccidial drugs, improving genetic resistance of birds to this parasitic disease represents an attractive alternative. An experiment was run in order to identify lines of chickens resistant and susceptible to coccidiosis as a tool to search for genetic markers of resistance. Five outbred lines were used: two Egyptian lines (Mandarah and Fayoumi), a Rhode Island Red line, and two White Leghorn lines (WLB21 and WLDW). The WLDW line segregated for three MHC haplotypes, B15, B19, and B21, and for the sex-linked dwarf gene, DW. Chicks were challenged at 4 wk of age with a high dose of Eimeria tenella (150,000 oocysts) and slaughtered 8 d postinoculation. Innate resistance was assessed individually by measures of lesion score, mortality, and body weight gain at slaughter, and plasma coloration 4 d postinoculation. Large differences in resistance to E. tenella were observed between lines. The Fayoumi line appeared clearly as the most resistant line, showing no mortality, less severe lesions than other lines, and a 30% reduction of growth as compared to control birds. The WLDW line was the most susceptible, with 27% mortality and a 85% reduction in growth. No major effect of MHC or dwarfism on resistance to E. tenella was found.

Tissue-Specific Alterations in Insulin-like Growth Factor-I Concentrations in Response to 3,3′,5-Triiodo-l-thyronine Supplementation in the Growth Hormone Receptor-Deficient Sex-Linked Dwarf Chicken

Insulin-like growth factor-I (IGF-I) mediates many of the effects of growth hormone (GH). The regulation of IGF-I, independent of GH, is methodologically difficult to assessin vivo,as hypophysectomy results in derangement of many pituitary hormone axes in addition to GH, and a gene knockout model is not available. The recessive sex-linked dwarfing (SLD) gene (dw) in chickens results in a lack of functional target tissue GH receptors due to a variety of molecular defects, which provides a unique model for evaluating GH-independent regulation of IGF-I. In the present study, the impact of 3,3′,5-triiodo-l-thyronine (T3) on circulating and tissue IGF-I was determined in normal versus SLD birds. Adult, nonovulatory female normal and SLD chickens were restrict-fed 40 g of feed/kg bw/day containing 0, 0.5, or 1.0 ppm T3, resulting in supplementation levels of 0 (control), 20 (low dose), or 40 (high dose) μg T3/kg bw/day for 10 days. Samples of GH target tissues including liver, abdominal fat pad, skeletal muscle (pectoralis major), and spleen were extracted and assayed for IGF-I. Plasma T3, T4, GH, and IGF-I were determined by homologous RIA. Tissue GH binding was determined for hepatic membranes by radioreceptor assay. Under control conditions, dwarf chickens were markedly hypersomatotropic (33.3±4.1 ng GH/ml plasma; mean±SEM) compared to normals (2.4±3.9 ng/ml), and T3supplementation reduced this to normal levels. Despite the high circulating level of GH in dwarfs, plasma IGF-I was low compared to normal controls (dwarfs 1.5±.9 ng/ml; normals 5.3±.9 ng/ml;P=0.004), but this difference was eliminated with low-dose T3. In this study, tissue IGF-I was undetectable in liver and pectoralis muscle in adults (55 weeks of age) of both genotypes, under all treatments. In contrast, adipose tissue IGF-I was relatively high and did not differ (P=0.84) between genotypes under control conditions (normals 776.5±236.7; dwarfs 844.6±236.7 pg/mg protein), but was increased in normals and decreased in dwarfs, resulting in higher levels (P=0.02) in the normal (1249.9±200.0 pg/mg protein) than in the dwarf genotype (558.4±200.0 pg/mg protein) at the higher level of T3supplementation. This relationship was somewhat reversed in spleen, where T3tended to decrease tissue IGF-I concentration in normals and increase it in dwarfs. The low level of plasma IGF-I despite nonmeasureable hepatic IGF-I tissue concentrations suggests that IGF-I synthesis by extrahepatic tissues contributes to the circulating pool of IGF-I. The relatively high control levels of adipose tissue IGF-I in the dwarf genotype further suggest that considerable IGF-I synthesis exists that is GH-independent in this extrahepatic tissue. The presence of GH action, however, may mediate the effects of other hormones that can influence local IGF-I production in this tissue, as reflected by the differential response to T3supplementation between genotypes. The tissue-specific nature of the effect of T3on IGF-I production supports an additional point of regulation of hormone action at the target tissue level.

Effects of the Sex-linked Dwarf Gene (dw) on the Expression of the Muscular Dystrophy Gene (am) in Chicken

The sex-linked dwarf gene (dw) was introduced into companion muscular dystrophic (am) and nondystrophic (Am+) New Hampshire chicken lines to investigate influences of the dwarf gene on breast muscle weights, muscle fiber area, and the histological expression of muscular dystrophy. Dystrophic and nondystrophic chickens within dwarf or nondwarf genotypes were similar in body and carcass weights. Pectoralis and supracoracoideus muscle weights (as a percentage of adjusted carcass weight) were similar in nondystrophic dwarf and nondwarf males and females. In addition, pectoralis weight was similar in dystrophic dwarf males and dystrophic nondwarf males and females. However, pectoralis weight was significantly smaller in dystrophic dwarf females than in dystrophic nondwarf females, whereas supracoracoideus weight was significantly larger in dystrophic dwarf males than in dystrophic nondwarf males. Supracoracoideus weight was similar in dystrophic dwarf males and females and dystrophic nondwarf females. Pectoralis muscle fiber area was influenced by sex and by dwarf and dystrophy genotype. Muscle fiber area was larger in females than in males, smaller in dwarfs than in nondwarfs, and smaller in dystrophic than in nondystrophic muscles. Muscle fiber degeneration and adipose infiltration was more extensive in dystrophic than in nondystrophic females and males, and it was more advanced in dwarfs than in nondwarfs. Excessive acetylcholinesterase staining patterns were characteristic of dystrophic muscle in both dwarf and nondwarf genotypes. Nondystrophic and dystrophic dwarf male and female chickens are comparable substitutes for nondwarfs as biomedical models with respect to pectoralis histology, acetylcholinesterase staining pattern, and pectoralis muscle hypertrophy.

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.

Effect of the Sex-Linked Dwarfing Gene (dw) upon Skeletal Development of Young Broiler Chicks

The influence of the sex-linked dwarfing gene (dw) on growth and skeletal development in young male broiler chicks was investigated. Chickens that were homozygous (dw/dw) for the dwarfing gene had significantly lower BW and tibiotarsus lengths when compared with the heterozygous (Dw/dw) or normal (Dw/Dw) genotypes. All genotypes exhibited similar incidences of tibial dyschondroplasia. In contrast to several other types of dwarfism, there was no effect of the dw gene on the width of the epiphyseal growth plate or the proteoglycan content of this tissue.

Effect of the sex‐linked dwarf gene on circulating levels of 17/β‐estradiol, progesterone and luteinising hormone in the laying hen

1. The sex-linked dwarf gene did not appear to affect the LH, progesterone (P4) and oestradiol 17-beta (E2) levels around the onset of lay in a sample of White Leghorn hens. 2. A longer interval between oviposition and subsequent ovulation was suggested in dwarf layers by a slower decrease in the P4 plasma concentration after the preovulatory peak and is consistent with the increased oviposition interval already described. 3. A higher ratio of E2/P4 basal levels was found in dwarf layers; this is consistent with their lower number of fast-growing follicles and with their reduced laying rate. 4. Lipid mobilisation was modified in dwarf layers (as shown by their reduced abdominal fattiness); although plasma concentrations of triglycerides were normal, unusual correlations between plasma triglycerides, E2 basal concentrations and body weight were recorded.

Influence of the sex‐linked dwarfing gene (dw) on the contribution of dietary lipid to yolk lipid synthesis

1. The efficiency and time course of dietary fatty acid incorporation into lipids of egg yolk and abdominal adipose tissue was compared in "White Leghorn", normal (Dw) and dwarf (dw) laying hens at 56 weeks of age, using 14C labelled linoleic acid. 2. The sex-linked dwarfing gene, dw, was shown to reduce not only body weight and abdominal fat pad deposition, but also yolk production and the average clutch size. 3. Higher peak incorporation and total recovery of the linoleic acid radioactivity into yolk lipids, but lower label recovery into adipose tissue triglycerides were found in dwarf hens. 4. The higher esterification of the dietary linoleic acid in its native form into dwarf yolk triglycerides indicates that dwarf hens use more dietary lipids to synthesise yolk lipids but these results also suggest that the dw allele might reduce the lipogenic capacities of the liver and adipose tissue in laying hens.

Strain differences in whole‐body protein turnover in the chicken embryo

1. Whether or not there is a strain difference in embryonic whole-body protein turnover rates was tested using the chicken embryos of Rhode Island Red carrying a sex-linked dwarf gene (dwarf), White Leghorn (layer), and White Cornish X White Plymouth Rock (broiler) strains on day 12 of incubation. 2. Whole-body protein synthesis was estimated by injecting L-[15N]-phenylalanine either intraperitoneally or intravenously on day 12 of incubation in order to investigate the effect of the route of isotope administration. The results showed that the values for fractional and absolute synthesis rates were approximately 13% higher by intravenous injection than by intraperitoneal injection. 3. Whole-body protein turnover, both in terms of fractional and absolute rates, was significantly faster in dwarf than in broiler embryos, with intermediate values in layer embryos, although no growth differences were observed on day 12. 4. Difference in egg weight, measured before incubation, did not affect protein turnover. 5. It was concluded that the strain difference manifested in whole-body protein turnover of the chicken embryo would probably be a reflection of differences in genetic background.

Influence of the Sex-Linked Dwarfing Gene (dw) on the Lipid Composition of Plasma, Egg Yolk and Abdominal Fat Pad in White Leghorn Laying Hens: Effect of Dietary Fat

The levels and fatty acid composition of lipids were determined in very low density lipoproteins (VLDL, d less than 1.006), yolk and abdominal adipose tissue of normal (Dw) and sex-linked dwarf (dw) White Leghorn laying hens. Effects of adding 4% tallow to the diet were also examined. In 40-wk-old hens, neither plasma lipids (triglycerides, phospholipids and cholesterol), VLDL levels, nor the chemical composition of VLDL was altered by the dw gene or dietary fat. Dwarfism reduced egg and yolk weights. Though the yolk lipid content was similar in normal and dwarf hens, yolk from dwarfs had slightly more phospholipids and less triglycerides than yolk from normal hens. Higher linoleic acid [18:2(n-6)] and lower oleic acid [18:1(n-9)] levels were observed in triglycerides of VLDL, yolk and adipose tissue from dwarf hens. In addition, the dietary fatty acid pattern had a greater influence on the fatty acid composition of the yolk lipid major precursors (VLDL triglycerides) in dwarf laying hens than in normal hens. These results suggest that the dwarfing gene might reduce the hepatic de novo fatty acid synthesis and/or dwarf hens might incorporate more dietary lipids into yolk than do normal hens.

Effect of the sex-linked dwarf gene on thyrotrophic and somatotrophic axes in the chick embryo.

Plasma concentrations of thyroxine (T4), triiodothyronine (T3), reversed triiodothyronine (rT3), and insulin-like growth factors I and II (IGF-I, IGF-II) together with peripheral 5'-monodeiodination activity were measured in both normal and sex-linked dwarf embryos between day 14 of incubation and day 1 posthatch. Plasma T4 levels increased gradually during embryonic development while T3 concentrations remained low until day 20, when a sharp increase was observed. rT3 levels also increased from day 14 and dropped on day 20 when T3 levels started to increase. 5'-monodeiodination activity was high on day 14 of incubation, decreased thereafter, and showed an increase at the time of air sac penetration together with increased T3 levels. At this stage, differences between normal and dwarf embryos were observed; the latter had lower nonsignificant 5'-Monodeiodination activity and lower (P less than 0.01) plasma T3 levels. Plasma IGF-II levels were high during the whole embryonic period studied. Dwarf embryos had lower (P less than 0.05) IGF-II levels at the time of hatching. IGF-I levels were high on days 14 and 16, declined afterwards, and started to increase again around hatching. With the exception of T3 and IGF-II levels, introduction of the dwarf gene did not cause major changes in the hormonal parameters studied. This may explain the identical body weight at hatching.