The development of the commercial broiler industry during the last half of the 20^th century has seen dramatic changes in growth, feed efficiency, and yield. In this paper we extracted results from three independent two-way (high-low) selection experiments to interface with what has occurred in commercial broiler breeding. Although the experiments differed in duration, specific traits, and focus, when viewed as a whole there was consistency with changes that have occurred in commercial broilers during the past half century. Other than to point-out consistencies among what is seen with commercial stocks, correlated responses of reproductive traits are discussed peripherally.

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A study was carried out to investigate nitrogen metabolism in response to cecal ligation and colostomy in chickens. We used colostomized plus ceca-ligated chickens fed a low protein diet or a low protein diet supplemented with urea. When both types of diets were fed, nitrogen balance and utilization tended to increase by cecal ligation while total nitrogen excretion tended to decrease. Colostomy increased total nitrogen excretion and decreased nitrogen balance and utilization in chickens fed both types of diets. Therefore, total nitrogen excretion, nitrogen balance and utilization were significantly different between the ceca-ligated and colostomized chicken fed both types of diets (P<0.05). Cecall ligation tended to decrease urinary nitrogen excretion in chickens fed a low protein diet and significantly decreased it in chickens fed the low protein diet supplemented with urea (P<0.05), but did not change fecal nitrogen excretion in chickens fed both types of diets. Total uric acid excretion and urinary uric acid excretion were decreased by cecal ligation (P<0.05) but increased by colostomy (P<0.05) in chickens fed both types of diets. When a low protein diet supplemented with urea was fed, total urea excretion was significantly higher in colostomized than in other three groups (P<0.05), and urinary urea excretion in colostomized chickens was significantly decreased by cecal ligation (P<0.05). Total ammonia excretion was significantly higher in ceca-ligated chickens than those of three other groups fed the low protein diet supplemented with urea (P<0.05), but was similar in the four groups when the low protein diet was given. This indicates that ceca in chickens fed protein-deficient diets may have two different roles in nitrogen utilization : the urine nitrogen retrograded from the cloaca into the ceca is beneficial, but ingesta nitrogen from the small intestine into the ceca is not so. Therefore, collectively chicken ceca could have a negative effect in nitrogen utilization in the chicken regardless of having a significant recovery of urinary nitrogen through ceca.

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Avian primordial germ cells (PGCs) arise from the epiblast and circulate temporarily via the blood vascular system in their migration route to the gonadal anlage. There are egg-to-egg variations in the number of circulating PGCs (cPGCs) at the same developmental stage, which are reportedly due to the individual differences among the females that produced the eggs (Tajima et al., 1999).
In the present study, 11 hens and 3 roosters of the Rhode Island Red variety were separated into 3 mating groups, and the hens were inseminated with the semen collected from certain roosters. The resulting fertilized eggs were incubated to reach stages 13 to 16 (staging of Hamburger and Hamilton, 1951), and blood samples collected from individual embryos were analyzed for the number of cPGCs.
In Group 3, the total number of cPGCs was higher in the eggs laid by two of the females than in those laid by the other two. Moreover, the total cPGC number contained in the eggs laid by hens in Group 1 increased after the mating rooster was changed. The hens that laid eggs with a high total cPGC number in the embryonic blood often had a low egg-laying ability, and the blood volume in eggs laid by these hens reached a plateau between stages 14 and 15. Three variation patterns of total cPGC number in different individuals could be determined, with peaks at stages 13, 14 and 15, respectively.
The results indicate that not only the females that produced the eggs but also the males that provided the sperm influenced the total cPGC number in different individuals.

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In the purpose to reducing excretion of nitrogen (N) and phosphorus (P) without the influence of the growth performances and abdominal fat in broilers, a feeding trial and balance test were conducted. Four diets were prepared. The control diets (C) contained 23% crude protein (CP) for 0 to 21 days of age and 19% CP for 22 to 49 days of age, respectively. In the second diets (L), CP were reduced to 19 and 16% for both phases and crystal amino acids were added to be 110% of requirements at both phases. In the third diets (LE), an enzyme mixture (cellulase, xylanase and pectinase) was added to L. In the fourth diets (LEP), non-phytate P were reduced to 0.32% and 0.28% for both phases, and phytase was added. Eight hundred one-day-old broiler chicks, equal number of male and female, were divided into 4 treatments and given free access to one of the diets for 49 days of age, and body weight (BW), feed intake and mortality were recorded. At the end of experiment, 50 chicks per each treatment were slaughtered by bleeding through a jugular vein and eviscerated for the determination of abdominal fat. Using another 10 male broiler chicks per each treatment, excretion of dry matter (DM), N and P were determined by the balance test. There were no significant differences in BW gain, feed intake, feed conversion ratio and mortality among four treatments. Abdominal fat of broilers fed L was significantly heavier than that of other three treatments, and no significant differences were found in abdominal fat among other three treatments. Excretion of DM and N in L, LE and LEP decreased to 91, 84 and 82%, and 73, 70 and 70% of C, respectively. Excretion of P of broilers fed LEP decreased to a half of other three treatments, and there were no differences in P excretion among other three treatments.

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The biological actions of estrogen are mediated via estrogen receptors (ER). Although chicken ER cDNA for subtypes α and β have been identified, only the β form of ER cDNA was cloned in quail. Hence, in this study the cDNA of ERα subtype was cloned and levels of mRNA expression were studied in different tissues in quail. Quail ERα cDNA containing the sequence containing the open reading frame (1770bp) encodes the predicted 589 amino acid residues and had high homology to chicken ERα (98.8%). Both RT-PCR and northern blot analyses indicate that relatively higher expression was observed in the liver, ovary, oviduct and testes. Relatively lower expression was detected in adrenal, cerebrum, hypothalamus, gizzard, heart, kidney and intestine by RT-PCR analysis. Conversely, low levels of expression of quail ERβ mRNA was detected in all the examined tissues. The results indicate that ERα subtype plays a predominant role for estrogenic actions in reproduction in quail.

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Bursal epithelial cells derived from 14-day-old chick embryos were cultured under a serum-free condition and the recovered culture supernatant was analyzed for surface immunoglobulin M (sIgM)-inducing activity on the bursacytes of 12-day-old chick embryos. Surface IgM positive rate of bursacytes incubated with the culture supernatant increased significantly, thus indicating the presence of sIgM-inducing factor(s) in the culture supernatant. The sIgM-inducing factor(s) in the supernatant was analyzed by gel filtration chromatography and HPLC. Results from these analyses indicated that the factor may be a polypeptide with a molecular weight of about 1300. This substance which is different from already known factors, such as Bursin, may be a newly discovered B cell differentiating factor in the bursa of Fabricius that promotes chicken B cell differentiation.

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Time course changes in ¹³C enrichment of respiratory CO₂ in young chickens intravenously injected with [1-¹³C] sodium acetate were examined to clarify the rapidity of oxidation of intravenous acetate to CO₂ in chicken body. The ¹³C enrichment reached the peak level within 20-30 minutes after single intravenous injection with 1 ml of 1% [1-¹³C] sodium acetate and returned to the initial level by 180 minutes. On the other hand, no change in ¹³C enrichment of respiratory CO₂ was observed in control chicks injected with saline throughout the experimental period. The recovery of the injected [1-¹³C] sodium acetate was estimated to be 47.0%.
These results indicate that intravenously injected acetate into young chickens is rapidly metabolized to CO₂ and suggest a rapid use of cecal acetate as an energy source in chickens.

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