The discovery of leptin has led to an understanding of the regulation of energy expenditure and food intake in a number of vertebrates. Leptin is also implicated in diverse physiological functions. In poultry, leptin cDNA was first cloned from chicken to assess the roles of leptin; however, this cDNA has not been confirmed by a number of researchers nor genomic DNA corresponding to the chicken leptin has been found. This controversy is one of the most important issues to be elucidated in avian endocrinology. Avian leptin receptor cDNA was first identified in chicken in 2000 and studies suggest that the receptor could mediate the leptin signal to exhibit its physiological functions. In this review, we summarize the recent findings in avian leptin research, including physiological roles and signal transduction.

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This study investigated the correlation between microsatellite DNA polymorphic loci and egg laying traits in Chinese Silkies (Gallus gallus) to find possible candidate loci for marker-assisted selection. 180 experimental birds were used, which were offspring of a dam line and a sire line of Silkies specialized for production and growth performances, respectively. Seventeen chicken-specific microsatellite markers were analyzed for polymorphism. Multiplex PCR and capillary electrophoresis were used to detect alleles and allele frequencies. All the 17 microsatellite markers were polymorphic. In all, 109 alleles were detected from these polymorphic loci, with a range of 4 to 10 alleles and an average of 6.41 alleles per locus. The frequencies of the 109 alleles ranged from 0.0090 to 0.7559. The average value of polymorphism information content (PIC) was 0.644, ranging from 0.357 to 0.859. The average observed heterozygosity of 17 markers was 0.335, and the average expected heterozygosity was 0.681, ranging from 0.370 to 0.876. Ten microsatellite loci were found to be correlated with four egg quality traits and two onsets of lay traits (P<0.01 or P<0.05). Within marker MCW0036, allele 164 had a positive correlation, while allele 174 had a negative correlation with shell proportion. In MCW0254, allele 114 had positive effect on albumen proportion trait, while alleles 108 and 110 had negative effect. Therefore, genotype 164/164 in MCW0036 and genotype 114/114 in MCW0254 are two potential candidate loci for egg quality traits in Chinese Silkies. Furthermore, genotypes 224/224 and 220/220 in MCW0036 are probably candidate loci for onset of lay traits in these birds. These findings would provide a valuable theoretical basis for marker-assisted selection for the improvement of production performances in Silkies.

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Microsatellite markers are tandem repeats of short nucleotides which are abundant, evenly distributed and highly polymorphic in eukaryotic genomes. As such, they are a useful tool in poultry breeding. Microsattelite markers have been identified in genomes of poultry such as chickens and quail. Exchange of marker information between chickens, quail and other avian species such as guinea fowl would be an important step towards the construction of a high-resolution comparative genetic map of these poultry species of agricultural importance. Using the polymerase chain reaction, chicken and quail microsatellite markers were tested to see if they would be suitable in amplifying guinea fowl loci. Eighty three percent (30/36) and 73 percent (19/26) of chicken and quail primers, respectively, amplified individual loci in guinea fowl. Fifty percent (15/30) and 47 percent (9/19) of the amplified loci using chicken and quail primers, respectively, were found to be polymorphic. These very few chicken and quail microsatellite markers that seem to reveal guinea fowl loci could be used as anchor points for comparative mapping. However, more effort should be committed to developing guinea fowl-specific markers since those of chickens and quail may not be sufficient for studies in guinea fowl.

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Experiments were conducted with male growing chicken (Cobb 500) to examine effects of added microbial phytase on growth performance and nutrient utilization in corn-soybean meal (CSM) and wheat-soybean meal (WSM) diets. Low P basal diets (CSM1: 0.15 / 0.11% NPP in DM of starter/grower diets; WSM1: 0.16/0.12% NPP in DM of starter/grower diets) were supplemented with 250 or 500U/kg of an experimental microbial phytase (CSM2, CSM3; WSM2, WSM3) or 1.5g/kg inorganic phosphorus (CSM4, WSM4). Growth studies were conducted (7-42d) to establish nutrient deposition (6 pens per diet, 10 birds per pen). Separate balance studies (n=8) yielded individual N and P balance data for the age period 21-25d. Additionally, studies with CSM diets also provided tibia composition data.
Phytase supplementation in CSM diets yielded significant effects on growth and deposition data. Additionally, the mortality rate declined significantly and tibia composition (ash, P, Ca) was improved. WSM diets provided more pronounced effects on deposition data, but growth responded only numerical. Balance studies delivered significant effects on P utilization due to phytase addition in both CSM and WSM diets, respectively. However, lower P utilization was observed in CSM diets. Significant effects of phytase addition on N utilization were established only in CSM diets. Consequently, generalized conclusions due to improved N utilization following phytase addition are not supported by the current study.

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The efficacy of ground marigold flower and orange skin was evaluated for egg yolk coloration. Two feeding trials were conducted. The first trial was carried out with 63 laying pullets (Shaver 579) that received 0, 40g marigold flower and 40g orange skin per kg of mixed feed in three dietary treatments. Each of the treatments comprised of 21 birds distributed to three replicate groups each of seven. The second trial was conducted with 84 laying pullets of the same genetic source that received 0, 40g marigold flower, 40g orange skin and 30mg synthetic pigment in four dietary treatments each having number of birds and replicates similar to trial 1. All birds received identical care and management including diets of more or less similar in composition. Yolk color scores were measured using Roche yolk color fan and other egg quality characteristics and production performance were recorded simultaneously. The noteworthy findings are i) egg yolk color significantly improved and reached to a level of consumers' standard by feeding 40g/kg marigold flower and ii) egg yolk color was slightly improved by feeding 40g/kg orange skin as compared to wheat-based control diet. It was concluded that yolk color in laying pullets may be improved by feeding both orange skin or marigold flower but the latter ingredient appeared to be most effective.

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The effect of feeding measured energy (ME) allowances during rearing and laying periods on body weight (BW) gain, production performance and hatchability were evaluated in a female broiler parent line. In grower period (5-20wk), ME required for maintenance, activity and growth was calculated targeting 100g increases in BW/week in control (C) group. In another group, ME was quantitatively reduced by 20% (R) over C. Both groups were offered measured quantity of grower diet to satisfy the scheduled energy inputs. At 21 weeks, C and R groups were individually sub-grouped into four each, to either restrict energy severely (S-20%), moderately (M-10%) or increase (E-10%) over control. Thus, 8 sub-groups were formed: CS, CM, CC, CE and RS, RM, RC, RR. The CC and RC sub-groups were offered calculated ME for 50g increase in BW/week and anticipated egg production. Measured amount of breeder diet was offered to each sub-group following energy schedule. At 20 weeks, significant increase in BW was observed in C-group with better conversion efficiency of feed, energy and protein compared to R-group. The R-group had lesser abdominal fat and liver weights, higher muscle protein and lower fat than C-group. Breeders in R-group matured late by 7.7 days, but produced significantly more eggs with better-feed efficiency up to 64 weeks than C-group. In laying phase, breeders maintained on 20 and 10% less energy (RM) during rearing and production periods, respectively matured late, but produced significantly more eggs with higher persistency than CC. At 68 weeks, maximum fertility and hatchability on total eggs set was recorded in RM sub-group. These results showed complimentary influence of grower and breeder energy restriction on egg and chick production and saved feed substantially in RM sub-group. It appeared that the energy requirement under energy restriction was lesser than that calculated.

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Deficiencies of single essential amino acids decreases food intake and this is likely to be involved in the central nervous system. Central mechanism underlying the decreased food intake induced by amino acid deficiency in chickens remains to be elucidated. We determined the hypothalamic interstitial monoamines (dopamine, norepinephrine and serotonin) with brain microdialysis technique to investigate whether hypothalamic monoaminergic system is associated with the reduction of food intake in growing chickens on a lysine devoid (LD) diet (a purified diet with a crystalline amino acid mixture not containing lysine as a sole source of nitrogen). Microdialysis probes had been inserted at the ventromedial (VMH) and lateral hypothalamus (LH) before presenting the diets. Perfusate was collected every 30min from two hours before feeding the LD diet to five hours later. Monoamines in the perfusate were determined using a high performance liquid chromatography. Chickens on the LD diets ate as much as the control chickens for early three hours, but the former ate less amount of food than the control one four and five hours after presenting the diet. Out of the ventromedial hypothalamic monoamines, dopamine level of the LD group started to decrease from the basal line one hour later and was lower than that of the control group 3.5 hours and afterward. Compared with the control group norepinephrine level of the LD group showed no change. Serotonin level was lower in the LD than control groups at one and four hours. The level of monoamines in the lateral hypothalamus did not differ between the dietary treatments. In conclusion, the present results demonstrate that feeding the lysine devoid diet decreased DA release in the VMH not in the LH before food intake started to decrease.

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A total of 180 day-old straight run Arbor Acre broiler chicks were fed ad libitum diets without or with growth promoters such as, flavomycin, surmax (avilamycin), genex and availa-Z/M at 65mg, 100mg, 2g and 1g per kg respectively, up to 42 days of age to evaluate the efficacy of different growth promoters and recommend a suitable growth promoter in broiler diet. The results indicated that live weight and feed conversion ratio differed significantly (P<0.01), and it was observed that surmax group was the best performer among the dietary groups. The study also reveals that antibiotic groups (flavomycin and surmax) were better in terms of growth and meat yield compared to the non-antibiotic groups (genex and availa-Z/M). Livability was apparently higher in surmax group (100%) compared to other groups. Profitability ($/kg broiler) was found 0.225 (Tk.15.21), 0.269 (Tk.18.28), 0.309 (Tk.21.01), 0.242 (Tk.16.44) and 0.231(Tk.15.68) in control, flavomycin, surmax, genex and availa-Z/M groups, respectively. Dressed yield and breast meat of broiler were increased in surmax groups. Abdominal fat in female was increased (P<0.05).

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Primordial germ cells (PGCs) are the progenitor cells of gametes. Avian PGCs are located in the central region of the area pellucida at the blastoderm stage. PGCs enter the circulation soon after the formation of blood vessels in incubating eggs and eventually settle in the gonadal primordium. We have now examined exposure of chicken embryos to soft (low-energy) x-rays as a means of depleting endogenous PGCs and thereby improving the efficiency of chimera production. The blastoderm of White Leghorn eggs was exposed to soft x-rays for 0, 20, 40 or 60s before incubation. The irradiated embryos manifested delayed development at 60h of incubation. They also showed reduced numbers of circulating PGCs at stages 14 and 15 and of gonadal PGCs at stage 30. The hatchability of irradiated embryos was lower than that of nonirradiated controls. Irradiation for 20s was found to provide the best outcome taking into consideration both the restriction of PGC proliferation and hatchability. Dispersed blastoderm cells of quail (black plumage) embryos were introduced into the blastoderm of chicken embryos irradiated for 20 s or of nonirradiated embryos. The number of donor-derived PGCs was higher in the irradiated embryos than in the nonirradiated controls at stage 30. These results suggest that soft x-irradiation of chicken embryos is a feasible approach to depletion of endogenous germ cells and consequent improvement in the efficiency of incorporation of donor PGCs.

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Japanese quail (Coturnix coturnix japonica) is widely used in avian reproduction tests and avian sex reversal screening tests for evaluating adverse effects of endocrine disrupting chemicals (EDCs). However, there are few reports on the molecular biological profiles during the development and sexual differentiation of the gonads in Japanese quail. In the present study, we investigated mRNA expression of cytochrome P450 17αhydroxylase (P450c17), cytochrome P450 aromatase (P450arom), anti-Müllerian hormone (AMH), estrogen receptor α (ERα) and androgen receptor (AR) in the embryonic and post-hatching gonads of Japanese quail by using real-time RT-PCR. The left gonads of male and female Japanese quail at 16 days of incubation and 3, 7 and 14 days after hatching were used in the study. P450c17 mRNA expression in females was significantly higher than that in males at 16 days of incubation, 3 and 7 days after hatching. P450arom mRNA expression in females was markedly higher than that in males and there were significant differences at 3, 7 and 14 days after hatching. AMH mRNA expression in males was apparently higher than that in females and there were significant differences at 16 days of incubation and 3 days after hatching. ERα mRNA was highly expressed not only in females but also in males at 16 days of incubation. There were no meaningful trends of AR mRNA expressions in male and female gonads during the observation periods. It is likely that the profiles of mRNA expression of P450c17, P450arom, AMH, ERα and AR in the embryonic and post-hatching gonads of normal Japanese quail in the present study provide basic and useful information.

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