Climate model projections indicate that the global surface temperature will probably rise a further 1.1 to 6.4°C during the twenty-first century, which is expected to have a significant impact on the efficiency, production, morbidity and mortality of domestic animals. Presently, high environmental temperature exposure is of major concern for the poultry industry especially in hot regions of the world because of the resulting poor performance, immuno-suppression and high mortality. There are different nutritional strategies for decreasing heat production to alleviate stress in high temperature-exposed chickens. The nutritional strategies are designed after considering factors such as the type of birds, age of birds, stage of production, duration of heat exposure, intensity of heat exposure and health of the birds. The nutritionists can base their strategy on less heat-production, increased nutrient intake, decreased energy wastage, and reduction in heat-induced oxidative stress and damage in birds to overcome the deleterious effects of high temperature on metabolism, physiology, feed efficiency, production performance and health. This can be accomplished by nutritional strategies to reduce heat stress by feeding good quality feed with high digestibility and nutrient density, adding fat as an energy source, balancing and provision of additional amino acids, and supplementing with vitamins, minerals and glucose. Recently, new concepts have been proposed for nutritional strategies that focus on the reactive oxygen species (ROS) production by the birds and decrease the oxidative stress and damage caused by exposure to high environmental temperature. None of these strategies are effective alone in terms of growth, feed efficiency, livability, product quality, stress tolerance or immune response, however, a combination of the nutritional strategies may help to alleviate the deleterious effects of heat stress and maintain the efficiency and production of chickens under high environmental temperature.

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It has been found that female progeny with the early feathering (EF) phenotype rarely emerge in late feathering (LF) strains of chickens. However, few detailed studies on the incidence of reversion have been reported. The present study was conducted to examine the incidence of reversion across three generations (G7-G9) in an LF line of the Nagoya breed and to investigate the characteristics of DNA structures of the revertant EF females. A total of five EF revertant females were observed (G7: 3 out of 376, G8: 1 out of 383, G9: 1 out of 411), and the incidences observed in G7, G8, and G9 were 0.80, 0.26, and 0.24%, respectively. Results of two PCR and one RFLP-PCR analyses indicated that there were two types of EF revertants in the Nagoya breed (3 birds were Type I and 2 birds were Type II), and that the reversion to the EF phenotype might be accompanied by the loss of either an OR (occupied repeat) or a UR-K region (unoccupied repeat on the K locus), which were homologous DNA regions produced by insertion of an avian endogenous virus gene (ev21) and duplication. Moreover, phenotypes of full-sib and half-sib sisters of the EF revertants confirmed that the sires of the EF revertants have never harbored excision of either OR or UR-K at the ev21-K complex locus on one of two Z chromosomes, suggesting that the reversion event occurred in spermatogenesis.

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Cellular retinol-binding protein 2 (CRBP2), a vitamin A binding protein that is expressed specifically in small intestinal villus absorptive cells, plays a pivotal role in the vitamin A absorption, transport, and metabolism. Considering the fact that egg weight and egg quality were largely affected by the vitamin A levels in chicken, we investigated the genetic polymorphism of CRBP2 gene and the association with egg production traits among 349 Erlang Mountainous Chickens in this study. In the coding sequence (408bp) of four exons, we only detected one nucleotide substitution (c.349T>C) in the third exon, which caused amino acid change (p.117Y>H). The frequencies of three genotypes were 52.43% (TT), 42.41% (TC), and 5.16% (CC), respectively. Among the six studied traits, the age at first egg (AFE), total number of eggs with 300 age (EN), and average egg-laying interval (AEI) differed significantly among genotypes. The CC genotype would be genetically advantageous to improve egg production traits in Erlang Mountainous Chicken. The evolutionary conservation analysis revealed that the p.117Y>H site was high conservative in mammals, which potentially confirm the important biological function of this mutation. To our knowledge, this is first report to study the genetic polymorphism of CRBP2 gene and association with egg production traits in chicken.

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Toll-like receptors (TLRs) play a crucial role in innate immune response of mammalian and avian species. The chicken TLR repertoire consists of ten genes. TLR15 is avian specific TLR with no mammalian homologue. The present study has characterized full-length coding sequence of TLR15 in Japanese quail and Indian indigenous chicken (Aseel and Kadaknath). Open reading frame of all three sequences were 2,607bp long encoding 868 amino acids similar to that of broiler chicken. Japanese quail, Aseel and Kadaknath sequences showed 95.1%, 99.7% and 99.8% similarity with broiler chicken TLR15 sequence at nucleotide level respectively. Domain architecture analysis revealed minor variations in number and position of leucine rich repeats (LRRs) in the ectodomain region of all three sequences. Phylogenetic analysis revealed TLR15 groups with high bootstrap support to avian TLR1 family members. TLR15 mRNA expression in a range of tissues as quantified by real time PCR was found significantly (P<0.01) higher in Aseel in comparison to Kadaknath and Japanese quail in most of the tissues investigated.

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The Silkie fowl (Gallus gallus var. domesticus) is distinct from other chicken breeds in terms of its appearance and behavioural characteristics. It is a Japanese native breed and has inhabited Japan since before the Edo era. Although the breed is considered to have originated in India and established in China and Japan, its evolutionary history and genetic relationship with other breeds are not clear. In this study, we determined the mitochondrial complete D-loop nucleotide sequences of 27 Silkie fowls and 3 other chicken breeds. In the Silkie fowls, we found 27 sites of single nucleotide polymorphism and 4 sites of single nucleotide insertion. Phylogenetic analysis revealed that the Silkie fowls, 9 other chicken breeds, 4 red jungle fowls and 42 haplotypes in Oka et al. (2007) were distributed in 5 clades. Silkie fowls belonged to 5 clades (A-E). These results suggest that Japanese Silkie fowls have high genetic divergence. However, all categories except SLSG (Saga Prefectural Livestock Experiment Station, white feathers) were distributed in only 1 or 2 clades, and 5 individuals with black feathers belonged to clade A. The Silkie fowl's wide distribution in the phylogenetic tree suggests that old Asian breeds crossed with several chicken breeds that had unusual traits to establish the Silkie fowl breed.

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The avian endogenous virus gene (ev21) and dominant sex-linked late feathering (LF) gene (K) are closely associated on the Z chromosome of LF chickens. The K gene is linked to two large repeats: ev21-unoccupied repeat region (URa) and ev21-occupied repeat region (OR). On the other hand, the recessive allele (early feathering, EF: k⁺) is linked to ev21-unoccupied region (URb). These three regions show high similarity but due to minor sequence differences, restriction enzyme treatment distinguishes URa and URb in White Leghorn. However, the applicability of the PCR-RFLP technique or the association between ev21 and K gene are not well investigated in the other breeds or strains. In this study, ev21 loci were detected in White Leghorn, Nagoya, Silky, Geline but not Gifujidori breeds of chickens, and the URa and URb from the various breeds were sequenced. Four types of sequence (URa-1 and URa-2 from LF or ev21 positive, URb-1 and URb-2 from EF or ev21 negative) were identified. At position 1072-1075, URa-2, URb-1 and URb-2 had “GGCC” whereas URa-1 had “AGCC”. The transition at 1072 clearly indicates that the PCR-RFLP technique used for White Leghorn is not applicable to Nagoya. Interestingly, both URa-1 and URa-2 were obtained from the ev21 positive sample of Geline. Presence of different sequence of URa in the Geline may explain that fixation of one of sequences to White Leghorn or Nagoya had occurred during breed establishment.

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Developmental changes in immune-related cells of the upper and lower gut during the first 2 weeks post-hatch were determined in broiler chickens fed a corn-soybean meal based diet with or without antibiotics (salinomycin and enramycin). In the upper gut, expressions of CD3, Bu-1, interferon (IFN)-γ, interleukin (IL)-10, toll like receptor (TLR)-2 and TLR-4 mRNA were greater in the antibiotics-fed group during 3 to 8 days of age. Similar effect of antibiotics on these expressions was observed in the lower gut with lesser extent. At 15 days of age, expression of most of immune related makers did not differ in the both groups, but some of makers (IFN-γ, Bu-1and TLR-4 mRNA) in the antibiotics-free group were greater. IL-18 mRNA expression was greater in the antibiotics-free group through the experimental periods in the lower gut. The findings suggest that functional maturation of some of immune-related cells in the gut is faster in the antibiotics fed group than that in the antibiotics-free group and effect of antibiotics feeding is much remarkable in the upper gut.

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A study was conducted to examine the effect of dietary oregano essential oil supplementation on the performance of broiler chickens challenged with Eimeria acervulina and Eimeria maxima at 14 days of age. A total of 375 day-old Cobb-500 male chicks separated into 5 equal groups with three replicates each, were used in this study. Two of the groups, one challenged with 1×10⁵ sporulated oocysts of E. acervulina along with 1×10⁵ sporulated oocysts of E. maxima and the other not, were given a basal diet and served as controls. The other three groups also challenged with combined E. acervulina and E. maxima were administered diets supplemented with oregano essential oil by adding the product OregoStim (containing 5% oregano essential oil) at the levels of 300 or 600mg/kg, and the last group the anticoccidial substance salinomycin at the dosage of 60mg/kg. Following the challenge, survival rate, bloody diarrhea and oocysts excretion, as well as intestinal lesion score were all determined. Throughout the experimental period that lasted 35 days, body weight gain and feed intake were weekly recorded, and feed conversion ratios were calculated. The results showed that dietary oregano oil supplementation in both oregano supplemented groups, attained body weight gains and feed conversion ratios not differing (p>0.05) to those of the non-challenged group or the salinomycin group. The challenged control presented lower (p>0.05) performance than those of the other groups for the consecutive three weeks after the challenge. These performance parameters along with lesion scoring indicated that oregano essential oil exerted an anticoccidial effect against E. acervulina and E. maxima, comparable to salinomycin.

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This study was conducted to show that dietary supplementation of fungi, Aspergillus awamori and Aspergillus niger so called Koji in Japan, improves growth performance and meat quality in broiler chickens. Total number of 42 chicks at 15 d of age with average weight (365±3) were divided into 7 treatments (n=6). First treatment as control was fed control diet and other chicks were fed diets supplemented with either A. awamori or A. niger at the levels of 0.01, 0.05 and 0.1%. The birds were raised for 12 d from 15 d of age to evaluate the effect on growth, organs weights, abdominal fat content, muscle fatty acids contents, muscle thiobarbituric acid reactive substance (TBARS) and plasma biochemical parameters etc. Body weight gain was increased, and feed intake and feed conversion ratio were decreased by the fungi. Plasma 3-methylhistidine as an index of skeletal muscle protein breakdown tended to be decreased by the fungi. Due to the fungi, abdominal fat and plasma cholesterol were decreased, while fat content in the breast muscle was increased. Interestingly, muscle α-tocopherol content was increased, and muscle TBARS as an index of lipid oxidation were decreased by the fungi, indicating anti-oxidative activities of the fungi. Furthermore, it was observed a decrease in saturated fatty acid and increases in unsaturated fatty acids due to the fungi in the muscle fat. In conclusion, feeding A. awamori and A. niger improved growth performance and meat quality in broiler chickens.

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The aim of this study was to establish which aspect of egg production, plasma lipoproteins and preovulatory follicle steroid hormones in laying hens is altered by thermal environment. In experiment 1, Single Comb White Leghorn hens (80-90wk of age) were exposed to three levels of environmental temperature by rotation (23, 27 and 31°C) for total 3 months, and feed intake, rectal temperature and egg production parameters were measured in each experimental period. In experiment 2, the hens (80wk of age) were exposed to two levels of environmental temperature (23 and 31°C) for 7 days, and concentration of plasma lipoproteins and follicle steroid hormones were determined. Feed intake in hens exposed to 31°C significantly decreased compared with that at 23 and 27°C, and rectal temperature at 31°C was significantly higher than that at 23°C. In the egg production parameter, egg yolk density was significantly smaller at 27 and 31 than at 23°C. Finally, the concentrations of very low density lipoprotein in serum, and of estradiol 17-β and progesterone in follicles were adversely affected by environmental temperature at 31°C. These results suggest that high environmental temperature negatively influences both the lipoprotein and steroid hormones and consequently reduces egg production, but the reduction in feed intake is not the only reason for a decline in egg quality in laying hens.

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The vertical transmission rate of Mycoplasma synoviae into primordial germ cells (PGCs) was evaluated. PGCs were collected from eggs (n=54) of M. synoviae positive chickens, with 10 to 214 PGCs obtained per egg. PGCs were mixed with Frey's medium (2ml) and incubated at 37°C for two weeks. After incubation, DNA was extracted from the medium and used as a polymerase chain reaction (PCR) template to detect M. synoviae. All samples tested PCR negative. Thus, potentially all isolated PGCs were not infected with M. synoviae. These results suggested that vertical transmission of M. synoviae into PGCs might be rare. Given that chickens are typically culled if this infection is confirmed, even among rare breeds, utilization of PGCs is a promising means of preserving chicken breeds that are infected with M. synoviae.

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