Considerable interest exists in the development of transgenic poultry as a means of improving commercial poultry stocks and for applications in the pharmaceutical industry. The development of transgenic poultry requires stable insertion of genes into the germline. Because of the unique aspects of reproduction in birds, new methods of embryo manipulation had to be developed that include the ex ovo culture of embryos and the formation of germline chimeras using blastodermal cells and primordial germ cells. Currently, transgenic poultry can be produced using retroviral vectors and through the microinjection of DNA into the germinal disk of the newly fertilized egg. However, other approaches such as the development of embryonic stem cells, the culture of primordial germ cells, and sperm-mediated transfection are being explored for their potential to produce transgenic poultry.

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The nutritional value of diets fed to chickens has traditionally been evaluated by growth performance and nutrient digestibility. In addition to nutritional physiological studies, research on intestinal structure is also important, as the intestine is the digestive and absorptive organ. In macroscopic anatomy, the guts of poultry differ relative to body weight (Thomas, 1984). Fowls produced for the meat purpose, such as broiler (BR) chickens and Peking ducks, have intestines of greater length, weight and area than those of egg-laying fowl, such as the White Leghorn (WL) chickens and wild ducks (Yamauchi et al., 1990b). Poultry innards are affected by diet (Moss, 1974; Miller, 1975; Langhout et al., 1999; Yasar and Forbes, 1999). Feeding habits rather than individual body weight difference account for gross anatomical differences in the intestine (Yamauchi and Zhou, 1988). These reports suggest that the nutritional value of diets may produce microscopic alterations in the intestinal mucosa. Although the general histological features of the intestine are well known, the relationship between the structure and function of the intestine has not been established. The reason that no information on the histological alterations related with intestinal function has been reported is related to the fact that studies on the interaction between them are limited to morphological observations, which is due to lack of an immunocytochemical procedure using antibodies. Confirmation that intestinal histological alterations are indeed induced by intestinal functions is currently impossible and can be established only by comparison of morphological characteristics with intestinal functions.
Consequently, over the past decade, there has been much interest in establishing how intestinal histological alterations are related to intestinal function. The intent of this interest is to assess the enteral nutrient absorption of feed ingredients histologically. This review highlights recent studies on histological alterations related to intestinal function, and adds new information to the assessment of the nutritional values of various kinds of chicken feed.

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Marrow cells were isolated from medullary bone of hens at two opposing phases, the bone formative and resorptive phases, of the egg-laying cycle. These cells were cultured for up to 14 days on cover slips. After culture, the osteoclast-like cells which were multinuclear, positive for tartrate-resistant acid phosphatase (TRAP) and formed bone-resorption pit, were observed on the cover slip. The number of them increased by 8 days of culture and decreased thereafter. Also, the osteoclast-like cell formation was prominent in culture of medullary bone marrow cells at the bone resorptive phase, compared with those at the bone formative phase. Additionally, before forming osteoclast-like cells, TRAP-positive mononuclear cells were adherent to the cover slip and later aggregated as clusters. In the clusters, the TRAP-positive mononuclear cells contacted each other and partially became multinucleated.
These results show that medullary bone marrow cells contain osteoclast progenitors or precursor, and these cells differentiate into TRAP-positive precursors and terminally fuse each other to form mature and functional osteoclast-like cells. Also, the medullary bone marrow cells at the bone resorptive phase contain many osteoclast progenitors or precursors, suggesting that medullary bone marrow cells at the bone resorptive phase have high potential to form osteoclasts.

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The aim of the current study was to determine whether administration of nonylphenol to laying quail causes disorder of female reproductive functions in F1 generation. Regularly laying Japanese quail were daily-injected i.m. with 50μl of corn oil or 10 μg of 4-nonylphenol for 5 days. Fertilized eggs from both groups were collected on 2 d, 4 d and 6 d after the first injection (C1, C3, C5 in oil treated group ; N1, N3 and N5 in nonylphenol treated group). The chicks hatched from these eggs were reared to maturity, and their reproductive functions and oviductal structures (including the distribution of calcium binding protein-D28K ; CaBP-D28K) were examined. The area showing immunopositive for CaBP-D28K in the tubular glands of shell gland was significantly greater in C1 than N1 and in C3 than in N3. Although the rate of egg-laying was significantly higher in C3 than in N3, no differences were observed in the other nonylphenol-treated groups compared with their corresponding control. The nonylphenol treatment did not affect the age of sexual maturity, periods of laying fertilized eggs, fertility and egg-shell quality. Histology of the oviductal magnum, isthmus and uterovaginal junction including sperm storage tubules showed no structural difference among each group. These results suggest that injection of maternal birds with nonylphenol may affect the shell gland development to reduce the density of tubular gland in F1 generation.

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It is important to know the limit of artificial selection for efficient animal production. The aim of this research was to examine whether the selection for small body weight in Japanese quail has reached to the limit after the long term selection over 65 generations. In this research, two lines, SS and RR were compared. RR line was produced by random mating in a closed population as the control, and SS line was selected for small body weight at 6 weeks of age until 65 generations. Additionally, the data of LL line selected for large body weight was used to evaluate a selection limit in SS line though the details were not shown. Each line was composed of about 30 pair-matings, and body weight measurement was performed every week until 6 weeks of age, but the body weights of candidate birds selected for production of next generation were measured until 15 weeks of age. In the first step of selection, 4 males and 4 females were selected as a general rule among the offspring from each pair-mating at about 4 weeks of age. In the second step of selection, one male and one female were chosen by body weight at 6 weeks of age from 8 individuals selected in the first step, and 30 pari-matings were arranged with the individuals having no consanguineous relation in the preceding 4 generations. Mean body weight of SS line during 60-65 generations was 59.5g and that of RR line was 106.5 g, and the difference was significant (P<0.01). Selection pressure (SP) in the two lines was constant throughout the generations. Selection intensity (SI) in SS line was in the negative direction, and that in RR line was near zero. Estimated heritability in the two lines was variable from generation to generation. Realized heritabilities in SS line increased in both males and females during two terms of 54 to 59 and 60 to 65 generations. The selection response increased in the negative direction in response to cumulative selection differential. The observed ratio of mean body weight at 6 weeks of age in SS line to that in LL line (ORM) and observed ratio of difference between mean body weight at the same age in SS line and that in LL line to the standard deviation of body weight in RR line (OR) suggested that selection limit may not have been reached in SS line after the long term selection for 65 generations and it may be possible to expect further genetic improvement.
Generally, artificial selection during a very long period would reach to a limit on account of decrease in genetic diversity. However, selection in the direction for small body weight was found to show the different tendency from the selection for large body weight. Miniaturization of body size is an interesting biological phenomenon from the evolutionary point of view. The SS line established in the present study would be useful for the research from molecular biologic and metabolic aspects to have an insight into evolutionary mechanism of miniaturization.

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It was examined whether dietary adenine has adverse effects on growth and feed intake in 2-month-old chickens as reported previously in younger chickens. The male chickens were fed ad libitum on control and adenine (0.96%) diets for 15 days. Dietary adenine retarded chicken growth, reduced feed intake and increased renal weight per body weight and water intake (P<0.05), without affecting feed conversion and nitrogen retention. This dietary treatment also caused five-fold or more excretory rates of uric acid and xanthine (P<0.05), and an appreciable excretion of adenine and hypoxanthine. However, no effects of dietary adenine on adenine, xanthine, hypoxanthine, uric acid and adenosine monophosphate concentrations were found in the blood, liver and kidney. Although 2,8-dihydroxyadenine (2,8-DHA) is usually not detectable in excreta, blood, kidney and liver in chickens, the substance appreciably appeared and accumulated in excreta and in the kidney when adenine was fed.
It is concluded that dietary adenine has similar adverse effects on feed intake, growth and renal weight in 2-month-old chickens to those in younger ones, and also that dietary adenine causes 2,8-DHA to appear in excreta and kidney.

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In order to introduce exogenous DNA into early chicken embryos by transfecting the stage X (EG&K) blastoderm, in vivo electroporation was applied to it. A pair of novel electrodes was devised for applying electric pulses vertically to the blastoderm layer. Fertilised eggs at stage X were broken and the blastoderm was placed on top of the yolk. One of the electrodes was placed on the blastoderm layer through the yolk membrane, and the other electrode was placed on the bottom of the yolk. DNA (GFP gene) was injected into the blastoderm, and electric square pulses were applied 5 times at 5-100V for loading periods of 50 msec per pulse at one-second intervals. The manipulated embryos were transferred into host eggshells and incubated for 4 days. The viability of the manipulated embryos was 67.0% (59/88) on day 3 of incubation. The expression pattern of GFP gene was mostly mosaic in the embryos, and the percentages of embryos that expressed the GFP gene were 97.7% (86/88), 93.2% (82/88) and 75.0% (66/88) on days 1, 2 and 3 of incubation. A high rate of GFP gene expression was observed in the embryonic and extra-embryonic tissues (54.2%, 32/59) and also in the extra-embryonic tissues only (27.1%, 16/59) on day 3 of incubation. The expression of the GFP gene throughout the embryonic tissues was also observed. These results suggest that the system for applying electric pulses vertically to the blastoderm layer is effective in introducing exogenous DNA into early chicken embryos.

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Effects of estradiol-17β (E2) and p-nonylphenol (NP) on mRNA expression of estrogen receptor α (ERα), estrogen receptor β (ERβ) and cytochrome P450 aromatase (P450arom) were examined in the early stage of chicken embryonic gonads. Fertilized eggs were treated with either E2 (1.0 mg/egg) or NP (0.01, 0.1 mg/egg) immediately before incubation (day 0 of incubation) and were incubated at 37.5°C. In the control group the eggs were treated with the vehicle (10% propanediol, PD, 50μl). On day 10 of incubation the gonad was collected and mRNA expression was determined for semi-quantitative assay by the reverse transcription-polymerase chain reaction (RT-PCR). In the control group, ERα and P450arom mRNA showed higher expression in females than in males while ERβ mRNA showed no sexual difference. In the E2 treated group, the expression of ERα and P450arom mRNA markedly increased in males (about 4- and 16-fold, respectively). NP increased mRNA expression of ERα and P450arom (about 2-fold each) in males. ERβ mRNA expression did not apparently change after the E2 or NP treatment in both sexes. These results suggest that NP induces some female-specific genes in the male gonads during the critical period of sex determination in chicken embryos.

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This study examined whether administration of ethynylestradiol to laying quail affects male reproductive function in the F1 generation. Regularly laying Japanese quail were daily-injected with 50 μl of corn oil or 1 μg of ethynylestradiol dissolved in 50 μl of corn oil for 5 days. Fertilized eggs were then collected 2, 4 and 6 d after the first injection (groups C1, C3 and C5 for oil treatment ; E1, E3 and E5 for ethynylestradiol treatment). The chicks that hatched from these eggs were raised and their reproductive functions (age at sexual maturity, copulation frequency, testicular weight, semen or sperm quality and fertility) were examined. Reproductive function did not differ significantly between ethynylestradiol-treated groups and corresponding controls (C1 to E1, C3 to E3, C5 to E5) and a among treatment days within control or treatment (C1—C5 or E1—E5). These results suggest that injection of ethynylestradiol in laying birds under the conditions used in this study does not significantly disrupt male reproductive function in the F1 generation.

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Octopamine, an important neurotransmitter in invertebrates, has noted several similarities with noradrenaline (NA) in mammals. To compare the effect of octopamine and NA in the central nervous system, food intake and categorized postures of fasted chicks were investigated after intracerebroventricular (ICV) injection. We found that ICV injection of NA significantly inhibited food intake of fasted chicks at 30 min postinjection, but not octopamine. Although chicks treated NA showed a tendency to be sleep-like behavior, octopamine significantly induced hyperactivity when compared with NA. The results presented here suggest that octopamine may also act on nervous system(s) without noradrenergic system in the brain of chicks.

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