Feathered dinosaurs from China and the evolution of major avian characters

Recent discoveries of feathered dinosaurs from Early Cretaceous deposits in Liaoning, China, have not only lent strongest support for the dinosaurian hypothesis of bird origins, but have also provided much‐needed information about the origins of feathers and avian flight. Preliminary analysis of character evolution suggests that the major avian osteological characters were acquired during the early evolution of maniraptoran dinosaurs. The available evidence also suggests that the first feathers with a filamentous morphology probably evolved in basal coelurosaurs and pennaceous feathers (including those with aerodynamic features) were developed in non‐avian maniraptorans, indicating that feathers evolved before the origin of birds and their flight. An evolutionary model is proposed here to describe the major stages of feather evolution, a process characterized by a combination of both transformational and innovative modifications. This model is different from some recent developmental models, which suggest that feathers are evolutionary novelties without a homologous relationship to reptilian scales. Although non‐avian theropods are traditionally regarded as distinctly cursorial animals, recent discoveries suggest that the closest relatives of birds might be arboreal theropods. Many bird features, such as the furcula and pennaceous feathers, evolved in a terrestrial context, whereas others, such as some pedal modifications, may have evolved in an arboreal context. Consequently, arboreality may have also contributed to the origin of avian flight.     

A description of the growth and moulting of feathers in commercial broilers

ABSTRACT

1. Changes in feather length and weight and daily losses of down, contour feathers, remiges and retrices were studied in two commercial broiler strains to determine feather growth and moult in broilers up to 112 d of age.

2. Ten pens of 20 chicks for each sex x strain were fed adequate amounts of dietary protein in a four-phase feeding programme. Ten birds were sampled per genotype at 14, 28, 42, 56, 70, 84, 98 and 112 d. Feather loss was determined for individual birds caged within a nylon net.

3. All feathers were dry-plucked from each of seven tracts, with representative feathers from the capital-cervical, dorsopelvic and interscapular, pectoral and femoral tracts being randomly selected. Three rectrices of the dorsocaudal tract and three primaries and secondaries of the humeral-alar tract of the right wing were evaluated.

4. The length of the selected feathers was measured, and the feathers from each tract and from the whole bird were weighed.

5. A wide range of rates of maturing (0.0250–0.0907/d) and mature weights (9.62–52.9 g) were evident between sampled tracts.

6. Feather weight failed to predict some moults which were detected by the measurement of feather losses. From the weight data, moulting was evident only in the humeral-alar and dorsocaudal tracts, whereas, when daily losses were measured, contour feathers accounted for over 0.7 proportion of feather losses. Logistic equations adequately described the cumulative losses of down, contour feathers and remiges.

7. Feather loss needs to be considered when feather growth is determined from feather weight at different ages.

8. The rate of maturing (B) of feathers was numerically higher in Ross males and females than in the Cobb strain. In females, B was higher than in males (0.0483 vs. 0335/d) but the mature weight was lower (162 vs. 230 g).     

Describing the growth and molt of modern domestic turkey (Meleagris gallopavo) primary wing feathers

The use of feathers as noninvasive physiological measurements of biomarkers in poultry research is expanding. Feather molting patterns and growth rates, however, are not well described in domestic poultry. These parameters could influence the measurement of these biomarkers. Therefore, the objective of this study was to describe the juvenile primary feather molting patterns and feather growth rates for domestic turkeys. The 10 primary wing feathers of 48 female turkeys were measured weekly from week 1 (0 d of age) to week 20. Feathers were manually measured, and the presence or absence of each primary feather was recorded weekly. Generalized linear mixed models were used to investigate if feather growth differed between the primary feathers. The molting of the juvenile primary feathers followed a typical descending pattern starting with P1 (5 wk of age), while P9 and P10 had not molted by the end of the study (20 wk of age). The average feather growth rate was 2.4 cm/wk, although there was a significant difference between the 10 primary feathers (P < 0.0001, 2.1 to 2.8 cm/wk). Over time, feather growth followed a pattern where the growth rate reaches a peak and then declines until the feather is molted. The results of this study provide a critical update of patterns of molting and feather growth in primary wing feathers of modern turkeys. This can have implications for the interpretation of physiological biomarkers, such as the longitudinal deposition of corticosterone, in the feathers of domestic turkeys.     

Proteolytic system of Bacillus sp. CL18 is capable of extensive feather degradation and hydrolysis of diverse protein substrates

1. Feathers are recalcitrant protein-rich wastes produced in huge amounts by poultry processing for meat production. Hence, feather bioconversion and protease production by Bacillus sp. CL18 were investigated.

2. Bacillus sp. CL18 demonstrated a remarkable feather-degrading potential. Through cultivations on feather broth (10 g l^?1 feathers), 94.5% ± 3% of whole feathers were degraded after 4 d. Increases in soluble protein contents were observed and protease production was maximal also at d 4. This strain produced diverse proteolytic enzymes during growth.

3. Crude protease displayed optimal activity at 55°C (50–62°C), pH 8.0 (7.0–9.0) and a low thermal stability. Proteolytic activity increased in the presence of Ca²⁺, Mg²⁺, Triton X-100, Tween 20 and dimethyl sulphoxide. Inhibition profile indicated that crude protease contains, mainly, serine proteases. Enzyme preparation hydrolysed mainly casein and soy protein isolate.

4. The keratinolytic capacity of Bacillus sp. CL18 at moderate temperatures (30°C) might be appropriate for feather conversion, resulting in protein hydrolysates and proteolytic enzymes. Proteases are postulated to be added-value products that can be obtained from such a bioprocess.     

Heavy metals in horse blood, serum, and feed in Minas Gerais, Brazil

Pollution is a subject of worldwide concern and discussion and various areas of science are seeking to integrate their knowledge in an attempt to improve understanding of the harmful effects of modern human activities. Thus, the objective of the current study was to assess the potential for using the horse as a bio-indicator of environmental pollution. Blood and serum samples from 120 horses from locations with different degrees of urbanization and industrialization and the feeds used for these animals were analyzed to determine their heavy metal (Cd, Pb, Ni, Cu, and Zn) content. The data obtained were compared. The results did not show increases in heavy metal concentration in the blood and serum of the horses with the intensification of urbanization and industrialization around the farms. Only Cd, as determined in the blood of the animals, showed a certain potential for using horses as bio-indicators of environmental pollution. The data for sex, age, and chemical composition of the foodstuffs supplied to the animals were not determinants in explaining the variation in the concentrations of heavy metals observed.     

Effects of dietary protein concentration and specific amino acids on body weight,body composition and feather growth in young turkeys

1. Two randomised block factorial experiments were conducted to investigate the relationships between the effects of dietary crude protein and specific amino acid concentrations on the relative growth of the body and feathers of young turkeys. 2. Decreasing dietary crude protein concentration from 300 to 180 g/kg in experiment 1 reduced the body and breast muscle weights of a large male line of turkeys proportionally by 0.44 and 0.52 compared with 0.19 and 0.24 in a small traditional line. 3. Decreasing dietary crude protein concentration was associated with a maximum reduction in feather weight of 0.18 and 0.24 respectively in male line and traditional turkeys. The length of the feathers in the cranial region of the breast decreased from 26 to 19mm in the traditional line compared with an increase from 14 to 25 mm in male line turkeys. 4. Decreasing dietary crude protein concentration was associated with an increase in the fat content of the feather-free carcase. Male line turkeys had a higher carcase fat and lower feather dry matter content than the traditional turkeys. 5. It was concluded that dietary crude protein was preferentially partitioned to feather rather than muscle growth in the male line in contrast to a traditional line of turkeys in which the growth of feathers and muscle were affected equally. 6. In experiment 2, the amino acids arginine, valine, methionine and tyrosine were added separately to a common basal ration (180g CP/kg) to raise their concentration to that of the control ration (260 g CP/kg). Each ration was fed ad libitum to male line turkeys from 2 to 6 weeks of age. 7. Amino acid supplementation increased body and breast muscle weights. 8. Compared with the basal ration, tyrosine was associated with a reduction in feather weight whereas valine had no effect. Supplementation with arginine and methionine resulted in increased feather weights that were similar to that of the controls. 9. It was concluded that arginine and methionine were used preferentially and are essential for feather growth. Excess amino acids that are not required for feather growth such as tyrosine and valine were used for increased body growth and resulted in relatively poor feather cover. 10. The results suggest that feather growth was maintained as much as possible at the expense of body growth when the amino acid concentration of the ration was less than that required to maximise body and muscle weight gain in large male line turkeys.     

Vimentin-and Desmin-Positive Cells in the Moulting Budgerigar (Melopsittacus undulatus) Skin

The distribution of vimentin- and desmin-positive cells in the budgerigar (Melopsittacus undulatus) dermis was investigated by means of immunohistochemical reactivity with the commercially available (Euro-Diagnostics) polyclonal antibodies. The staining pattern for vimentin in the paraffin sections was generally comparable to that in other animal species with regard to endothelial cells, vascular wall cells, muscle cells and fibroblasts. The modified Schwann cells in the inner core of the Herbst corpuscles reacted distinctly with anti-vimentin and anti-desmin. Some connective tissue cells in the superficial dermal layer, in the feather papilla and along the pulp core inside of the regenerating feathers were particularly well stained with anti-vimentin. Fibroblast-like cells of the regenerating feathers, particularly at the base of the pulp, also reacted strongly with anti-desmin. The findings were discussed with regard to references.     

Depletion study of three formulations of flumequine in edible tissues and drug transfer into chicken feathers

Cornejo, J., Lapierre, L., Iragüen, D., Pizarro, N., Hidalgo, H., San Martín, B. Depletion study of three formulations of flumequine in edible tissues and drug transfer into chicken feathers. J. vet. Pharmacol. Therap. 34 , 168–175. To ensure the delivery of safe animal products to consumers, withdrawal times (WDT) of drugs must be respected. Drugs administered in therapies can also reach nonedible tissues (for humans) such as feathers; this transfer is of concern as feather meal is used in diets of food producing animals, being this a possible source of residue contamination of final products for human consumption. WDTs of three flumequine formulations (10%, 80% premix powder and 20% solution) as well as the transfer of this drug into feathers were determined. One hundred and twenty broiler chickens were allocated into four experimental groups (36 birds each). Three of them were treated with 24 mg/kg bw orally for five consecutive days of each flumequine formulation, whereas one group remained untreated (12 birds as control group). After the treatment ended, six chickens of each experimental group and two controls were slaughtered daily for 6 days. Samples of muscle, liver and feathers were collected and analyzed by liquid chromatography tandem mass spectrometry (LC MS/MS). The WDTs showed differences between formulations. Flumequine concentrations found in feathers remained high during WDT and after this period, thus suggesting that the WDTs estimated for the pharmaceutical formulation of flumequine do not guarantee the absence of this drug in chicken nonedible tissues such as feathers.     

Prevalence and Risk Factors of Feather Plucking in African Grey Parrots (Psittacus erithacus erithacus and Psittacus erithacus timneh) and Cockatoos (Cacatua spp.)

Feather plucking, or the removal by a parrot of its own feathers, is thought to be one of the most common behaviour presentations in veterinary practices that treat avian patients. However, its aetiology is poorly understood. The aims of this study were to estimate the prevalence of feather plucking within the population of African grey parrots (Psittacus erithacus erithacus and Psittacus erithacus timneh) and cockatoos (Cacatua spp.) registered with 9 veterinary practices in the United Kingdom (UK) and to explore the association between frequently hypothesised risk factors and feather plucking in these species. A questionnaire was sent to the owners of 400 African grey parrots and 310 cockatoos registered with 9 UK veterinary practices. Returned questionnaires from 137 African grey parrots and 92 cockatoos were analysed, of which 39.4% of African grey parrots and 42.4% of cockatoos had exhibited feather-plucking behaviour at some point in their lifetime. Multivariable logistic regression modelling demonstrated that increasing hours of sleep and length of ownership were significantly associated (P < 0.05) with feather plucking in African grey parrots. Pet shop origin, cage location against ≥1 wall and ≥1 vacation taken by owners each year were significantly associated (P < 0.05) with feather plucking in cockatoos. The high prevalence of feather plucking in these commonly kept pets highlights this problem as a welfare concern, whereas the risk factor analysis challenges many frequently cited hypotheses regarding its aetiology. Further research is required to explore whether there is a causal relationship between the significant risk factors identified in this study and feather-plucking behaviour.     

Seroprevalence of psittacine beak and feather disease in wild psittacine birds in New South Wales

SUMMARY A haemagglutination inhibition assay was used to detect antibody to psittacine beak and feather disease virus in sera from wild sulphur crested cockatoos (Cacatua galerita), galahs (Eolophus roseicapillus), short-billed corellas (Cacatua sanguinea), eastern long-billed corellas (Cacatua tenuirostris) and other psittacine birds in New South Wales. The seroprevalence of psittacine beak and feather disease ranged from 41% to 94% in different flocks, indicating infection with the virus is widespread in wild populations.     

The role of waterbirds in the dispersal of freshwater cladocera and bryozoa in southern Africa

It has long been presumed that waterbirds disperse the propagules of aquatic organisms. However, it is only in recent years that this claim has been empirically explored and little is still known about waterbird-mediated dispersal in southern Africa. Aquatic invertebrates are thought to be well adapted to dispersal by waterbirds because of their ability to produce hardy resting eggs. We explored the capacity of waterbirds to disperse the eggs of both cladocera and bryozoans via endo- and ectozoochory. We examined 283 faecal samples and 394 feather brushings from six waterbird species and two wetland sites in South Africa for the presence of diapausing eggs. A total of 108 intact diaspores were recovered, with intact eggs present in 16% and 7% of the faecal samples and feather brushings, respectively. Our results indicate that southern African waterbirds do take up the resting eggs of aquatic invertebrates and that these eggs can survive intact through the gut or remain attached to the feathers. These results provide evidence that waterbirds may be important vectors for aquatic invertebrates in southern Africa and imply that waterbirds may play a vital role in maintaining connectivity between invertebrate populations in isolated wetland patches.     

Influence of dietary feathers on the fecal microbiota in captive Arctic fox: Do dietary hair or feathers play a role in the evolution of carnivorous mammals?

Hair and feathers are composed of keratin and are indigestible, inalimental and unpalatable for carnivores. However, carnivores often ingest hair and feathers during feeding or when grooming. We hypothesized that ingestion of hair and feathers changes species diversity and relative abundance of bacteria in the gut of carnivores. To test this hypothesis, we added disinfected poultry down feathers to the normal diet of captive Arctic foxes (Alopex lagopus). We then used fluorescently labeled terminal restriction fragments (T‐RFs) to examine changes in fecal bacterial diversity and abundance. The results showed that the number of bacterial species increased significantly after feather ingestion, but that total abundance was unchanged. This demonstrated that addition of disinfected feathers to the diet stimulated increased production among less abundant bacteria, resulting in a balancing of relative abundance of different bacterial species, or that some newly‐ingested microbial species would colonize the gut because a suitable microhabitat had become available. This implies that the overall production of bacterial metabolites would be made up of a greater range of substances after feather ingestion. On one hand, the host's immune response would be more diverse, increasing the capacity of the immune system to regulate gut microflora. On the other hand, the animal's physiological performance would also be affected. For wild animals, such altered physiological traits would be subjected to natural selection, and, hence, persistent geographic differences in the character of ingested feathers or fur would drive speciation.     

Laboratory diagnosis of psittacine beak and feather disease by haemagglutination and haemagglutination inhibition

SUMMARY Simple and sensitive haemagglutination and haemagglutination Inhibition assays were developed for psittacine beak and feather disease (PBFD) virus and serum antibody, respectively. The assays were used in the examination of samples from 73 birds clinically affected with PBFD. High antigen titres (log₂ 9 to log₂ 12) were detected In feathers, faeces and cloacal contents of PBFD-affected birds. Antigen was not detected In either faecal or feather samples from 20 normal galahs (Eolophus roselcapillus) and 9 normal sulphur crested cockatoos (Cacatua galerita). After kaolin treatment and haemadsorption of serum, haemagglutination inhibition (HI) antibody titres could not be detected in serum from 42 PBFD-affected birds, whereas serum HI titres from 64 normal psittacine birds ranged from less than log₂ 1 to log₂ 8. Serum and yolk HI antibody responses of 6 PBFD virus-inoculated layer hens were measured. Pre-inoculation chicken sera contained high concentrations of non-specific haemagglutination inhibitors (not detected in chloroform-extracted yolk), which were removed by kaolin treatment and haemadsorption.     

Variations in heavy metal concentrations among trophic levels of the food webs in two agroecosystems

Excessive accumulation of trace metal in soil represents a growing environmental problem posing severe risks to biota, humans and ecosystems. Concentrations of Cd, Pb, Cu and Zn were determined in soil, as well as in representatives of some trophic levels in the terrestrial food webs in two Egyptian agroecosystems; El-Manzala (a rural area located in the northeast of the River Nile Delta) and El-Tebbin (an industrial area located in South Cairo). Representatives of trophic levels included arthropods, amphibians, reptiles, birds and small mammals. Metal concentrations were determined in the leaves of wild plants, bodies of arthropods and livers of vertebrates. Levels of metals in the soil, plants and most animal species were higher in El-Tebbin than El-Manzala. Minimal concentrations of metals were detected more often in plants and in the cattle egret, whereas maximum values were common in the soil, amphibians and a mantid. Accumulation of metals was more frequent in arthropods and other taxa at lower trophic levels of food webs, suggesting that the transfer of metals along the vertebrate food web may be of relatively minor importance. However, of all the metals examined, only Pb was bioaccumulated to any appreciable extent in some of the higher trophic levels. A significant increase in liver mass and relative liver mass of the Norway rat from the polluted site was observed.     

Bioprocess enhancement of feather degradation using alkaliphilic microbial mixture

1. The main aim of this work is to develop a robust method to generate a microbial mixture which can successfully degrade poultry feathers to overcome environmental problems.

2. Four different alkaliphilic microbes were isolated and shown to degrade poultry feathers.

3. Two of the isolates were phylogenetically identified as Lysinibacillus and the others were identified as Nocardiopsis and Micrococcus.

4. The best microbial co-culture for white and black feather degradation was optimised for pH, temperature and relative population of the isolates to achieve almost 96% of degradation compared with a maximum of 31% when applying each isolate individually.

5. The maximum activity of keratinase was estimated to be 1.5 U/ml after 3 d for white feathers and 0.6 U/ml after 4 d for black feathers in a basal medium containing feather as the main carbon source. Additionally, non-denaturing polyacrylamide gel electrophoresis showed 4 and 3 protease activity bands for white and black feather, respectively.

6. This study provides a robust method to develop potential new mixtures of microorganisms that are able to degrade both white and black feathers by applying a Central Composite Design.     

镉、汞、铅污染及其微生物修复研究进展

随着人类活动的增强,重金属的应用越来越广,同时造成的环境污染问题愈发严重,特别是重金属镉、汞、铅。利用微生物技术修复环境污染中的重金属,以其成本低、效率高等特点,已经成为环境污染修复领域的研究热点。作者综述镉、汞、铅污染及其微生物修复的研究进展,并提出利用微生物细胞表面展示技术构建高效吸附重金属的基因工程菌,在微生物修复方面应用的重要价值。     

A description of the potential growth and body composition of two commercial broiler strains

ABSTRACT

1. The potential growth of feathers and feather-free body and their chemical components was measured in two commercial broiler strains.

2. A total of 200 chicks of each sex x strain were fed adequate amounts of dietary protein using a four-phase feeding programme. Ten birds per genotype were sampled at 14, 28, 42, 56, 70, 84, 98 and 112 d of age. They were weighed before and after being dry-plucked to determine the weight of feathers, and the feather-free body was then minced and analysed for water, protein and lipid.

3. Body weights and chemical composition of males of the two strains were similar throughout the trial. Females of the two strains differed only in their body lipid contents, with mature Cobb females being higher than Ross (1371 vs. 1210 g).

4. Mature body weights of males and females from both strains averaged 8420 g and 6650 g; mature body protein weights averaged 1555 g and 1030 g; and mature body lipid contents averaged 908 and 1290 g, respectively.

5. Rates of maturing per day of body weights of males and females of both strains averaged 0.0385 and 0.0368; feather-free body protein was 0.0316 and 0.0348 and body lipid was 0.0503 and 0.0375, respectively. The rates for body lipid differed between Cobb and Ross females (0.0352 vs. 0.0397/d). Separate equations were required for males and females to describe the allometric relationship between lipid and protein in the feather-free body.

6. The rate of maturing of feathers in females was higher than in males (0.0526 vs. 0398/d) and the mature weight was lower (205 vs. 266 g), respectively. Mature body weights of broilers in this trial were considerably higher than those measured using the same protocol 24 years ago, whereas rates of maturing remained the same.     

Monitoring the effects of land transformation on African clawless otters (Aonyx capensis) using fecal glucocorticoid metabolite concentrations as a measure of stress

In a time of increasing environmental change caused by anthropogenic disturbance, there is a greater need to understand animal adaptations to manmade environments. In this regard, the measurement of stress‐related endocrine markers provides a useful tool to examine the impact of environmental challenges and the physiological consequences for wildlife occupying such space. The aims of the present study were to validate fecal glucocorticoid metabolite (fGCM) concentrations as a measure of stress using samples from a male African clawless otter (Aonyx capensis; n = 1) and to compare fGCM concentrations of otters occurring in a transformed and in 2 natural areas in South Africa. From the 5 different enzyme‐immunoassays (EIA) tested, a cortisol and oxoetiocholanolone (measuring 11,17 dioxoandrostanes) EIA revealed the highest response (74% and 48% increase, respectively) 30 and 24 hours after a stress event (translocation of a captive individual as part of its rehabilitation prior to release), respectively. For both EIAs, fGCM concentrations were comparable for samples collected up to 3 h post‐defecation. Using the cortisol EIA for subsequent analyses, fGCM concentrations of animals from the transformed area (n = 20; mean [± SD]: 0.468 [± 0.539] µg/g dry weight [DW]) were significantly higher (P = 0.013) than those from otters in the natural areas (n = 17; 0.242 [± 0.226] µg/g DW). These preliminary results suggest that African clawless otters may have increased adrenocortical activity that could be due to conditions linked to living in a transformed environment.     

Further investigation of lead exposure as a potential threatening process for a scavenging marsupial species

There is a growing recognition of the harmful effects of lead exposure on avian and mammalian scavengers. This can lead to both lethal and non-lethal effects which may negatively impact wildlife populations. Our objective was to assess medium-term lead exposure in wild Tasmanian devils (Sarcophilus harrisii). Frozen liver samples (n = 41), opportunistically collected in 2017–2022, were analysed using inductively coupled plasma mass spectrometry (ICP-MS) to determine liver lead concentrations. These results were then used to calculate the proportion of animals with elevated lead levels (>5 mg/kg dry weight) and examine the role of explanatory variables that may have influenced the results. The majority of samples analysed were from the south-east corner of Tasmania, within 50 km of Hobart. No Tasmanian devil samples were found to have elevated lead levels. The median liver lead concentration was 0.17 mg/kg (range 0.05–1.32 mg/kg). Female devils were found to have significantly higher liver lead concentrations than males (P = 0.013), which was likely related to lactation, but other variables (age, location, body mass) were not significant. These results suggest that wild Tasmanian devil populations currently show minimal medium-term evidence of exposure to lead pollution, although samples were concentrated in peri-urban areas. The results provide a baseline level which can be used to assess the impact of any future changes in lead use in Tasmania. Furthermore, these data can be used as a comparison for lead exposure studies in other mammalian scavengers, including other carnivorous marsupial species.     

A gene co‐expression network analysis of the candidate genes and molecular pathways associated with feather follicle traits of chicken skin

Back and thigh skin of chickens showed significant differences in the thickness and the feather follicle density and size, which are important traits for slaughtered chickens' appearance. In the present study, global gene expression profiling was conducted in the back and thigh skin of chickens using Microarray technology. The results showed that 676 genes were differentially expressed between back and thigh skin. The expression of the differentially expressed genes (DEGs), including PPP1R3C, IGF1, PTCHD1, HOXB6, FGF9, CAMK4, SHH, BMP8B, FOXN1 and PTGER2, was validated by real‐time quantitative polymerase chain reaction (RT‐qPCR), and the results were consistent with microarray results. Functional analysis revealed that the DEGs were significantly involved in cell proliferation, differentiation, apoptosis, adhesion and transport process, and the pathways were significantly mapped into the ECM‐receptor interaction, peroxisome, focal adhesion, Hedgehog and PPAR signalling pathways. Protein–protein interaction network analysis suggested that signalling pathways related to feathers morphogenesis and development, such as Wnt, FGF, MAPK, SHH and BMP signalling pathways, occupied important positions in the network. Genes involved in these signalling pathways and adhesion molecules might play a vital role in skin and feather follicle development. Further single nucleotide polymorphism (SNP) association analysis of Wnt3A showed that the AC genotype of SNP g.255361 C>A significantly increased the feather follicle density of thigh skin. Our findings may provide new insights on candidate genes and pathways related to skin and feather follicle formation of chickens.