Single fluff-spray application of mother hen uropygial secretion analogue positively influences bursa of Fabricius development and the heterophil-to-lymphocyte ratio in ROSS 308 chicks.

Stress is an important cause of illness and mortality in chick production. Stressors such as manipulation, absence of maternal care, transport, and housing can lead to welfare issues, immunodepression, and decreased productivity. The mother hen uropygial secretion analogue (MHUSA), a synthetic analog of a maternal semiochemical secretion, has been proven to protect chicks and broilers against stress, significantly reducing the heterophil-to-lymphocyte ratio. The aim of the present study was to test the effects of the MHUSA on chicks' stress when single-sprayed on their fluff at the age of 1 d. Two-hundred eighty ROSS 308 chicks were included in the study. At day 1, each chick received a spray of 200 µL of a 2% MHUSA aqueous solution (140 chicks) or the same amount of the excipient (control group, 140 chicks), and then chicks were housed in 2 separate rooms. To assess the persistence of the MHUSA after this single application, fluff was sampled from 10 chicks every day for 7 d and at day 13 and 19, weighed, placed in dichloromethane, and analyzed by gas chromatography. Blood smears and the bursa of Fabricius were collected every 3 d from 10 chicks of each group for 36 d to assess the heterophil-to-lymphocyte ratio and the bursa weight-to-BW ratio, respectively. Gas chromatography analysis showed that the MHUSA was present on chick fluff until day 5. The statistical analysis revealed that the heterophil-to-lymphocyte ratio was lower in the MHUSA group at day 4, 7, and 9 (P < 0.0001 for day 4 and 7; P = 0.0377 for day 9). The bursa weight-to-BW ratio was significantly higher in the MHUSA group than in the control group from day 4 until day 29. These results confirm the beneficial effects of the MHUSA on chicks' adaptation to the new environment and on bursa of Fabricius development, suggesting its potential role in improving chicks' immune response.

Research Note: Circular RNA expressing in different developmental stages of the chicken bursa of Fabricius.

The bursa of Fabricius plays an essential role in B lymphocyte development, which is controlled not only by proteins but by noncoding RNA. Circular RNA (circRNA) are expressed in diverse tissues in eukaryotes. To acquire a deeper perception of the molecular mechanism of bursal development, RNA sequencing was used to identify the circRNA during varied evolving stages of the chicken bursa of Fabricius. We identified 13,689 circRNA. All these circRNA were originated from 4565 chicken genes. Among them, only 1 circRNA was yielded from those 4131 parental genes, and 2 or more circular isoforms were generated from the remaining genes. There were 27 circRNA found to be differentially expressed between the embryonic day 20 and day 2 developmental stages. The 5 isoforms of immunoglobulin lambda-like polypeptide 1 circRNA were tested to validate the RNA sequencing data, and their targeted genes were also analyzed with quantitative reverse transcription PCR. These data indicate that cirRNA are abundant and essential during bursal development and may play essential roles in the development of bursa of Fabricius.

Effects of broiler genetic strain and dietary amino acid reduction on (part I) growth performance and internal organ development.

Genetic selection in broilers has resulted in improved growth performance, meat yield, and feed conversion efficiency. However, consumers have become increasingly concerned about modern broiler welfare that is related to their rapid growth rate, which may be alleviated by nutrient dilution. This study was conducted to investigate the effects of dietary amino acid (AA) reduction on the growth performance and internal organ development of different genetic strains of broilers. A randomized completed block design with a factorial arrangement of 10 treatments (5 strains × 2 AA levels) was used. The 5 different strains of broilers were fed either a control diet, with digestible AA (lysine, total sulfur AA, and threonine) at the highest recommended levels for the 5 strains, or an AA-reduced diet, with the digestible AA being 20% lower than the control diet. Feed conversion ratio was increased by AA reduction in all 5 strains during day 0-14, 14-28, and 28-41 but was not affected from day 41-55. Body weight and feed intake responses to AA reduction varied in the different strains and ages of birds. Liver weight relative to BW on day 40, and weights of the duodenum and jejunum relative to BW on day 60 were increased by decreasing the dietary AA concentration. These results indicate that the birds had adjusted their organ growth and metabolism in response to increases in digestion, absorption, and utilization efficiency to accommodate a decrease in dietary AA content. Surprisingly, the cost of feed required to produce the same BW was decreased in 4 of 5 strains on both day 41 and 55, which was largely because of the lower price of the diets containing reduced AA levels and the later compensatory growth experienced by the birds fed AA-reduced diets. In the future, when dietary AA levels need to be adjusted to control growth rate and improve welfare status, the genetic strain, age of the birds, and targeted goals need to be taken into consideration.

Transcriptomic analysis of early B-cell development in the chicken embryo.

The chicken bursa of Fabricius is a primary lymphoid tissue important for B-cell development. Our long-term goal is to understand the role of bursal microenvironment in an early B-cell differentiation event initiating repertoire development through immunoglobulin gene conversion in the chick embryo. We hypothesize that early bursal B-cell differentiation is guided by signals through cytokine receptors. Our theory is based on previous evidence for expression of the receptor tyrosine kinase superfamily members and interleukin receptors in unseparated populations of bursal B-cells and bursal tissue. Knowledge of the expressed genes that are responsible for B-cell differentiation is a prerequisite for understanding the bursal microenvironment's function. This project uses transcriptomic analysis to evaluate gene expression across early B-cell development. RNA-seq was performed with total RNA isolated from bursal B-cells at embryonic day (ED) 16 and ED 19 (n = 3). Approximately 90 million high-quality clean reads were obtained from the cDNA libraries. The analysis revealed differentially expressed genes involved in the Jak-STAT pathway, Wnt signaling pathway, MAPK signaling pathway, metabolic pathways including tyrosine metabolism, Toll-like receptor signaling pathway, and cell-adhesion molecules. The genes predicted to encode surface receptors, signal transduction proteins, and transcription factors identified in this study represent gene candidates for controlling B-cell development in response to differentiation factors in the bursal microenvironment.

Effects of the stems and leaves of Astragalus membranaceus on growth performance, immunological parameters, antioxidant status, and intestinal bacteria of quail.

This study was designed to evaluate the potential application of the stems and leaves of Astragalus membranaceus (AMSL) in the poultry industry. Quails were divided into four groups and fed daily with an AMSL-free diet (control) or with 1%, 3%, or 5% (w/w) AMSL-incorporated diets for 35 days. The results showed that supplementing AMSL in the diet, especially at a concentration of 3%, increased daily gain and feed intake during the entire experiment (p < 0.05). The immune organ development of the thymus and bursa of Fabricius was promoted, and the immune system was enhanced by increasing the quantities of IgA and complements C3 and C4 (p < 0.05). The total antioxidant capacity and the activities of glutathione peroxidase and catalase were increased (p < 0.05). Moreover, the 3%-5% AMSL groups regulated the intestinal flora by promoting the proliferation of lactic acid bacteria and inhibiting the growth of coliform bacteria (p < 0.05). In conclusion, feeding incorporated diets with appropriate AMSL levels significantly increased growth performance, strengthened the immune system, improved antioxidative status, and regulated the intestinal microflora of quails, suggesting that AMSL has the potential to serve as a feed additive in the poultry industry.

Modified Palygorskite Improves Immunity, Antioxidant Ability, Intestinal Morphology, and Barrier Function in Broiler Chickens Fed Naturally Contaminated Diet with Permitted Feed Concentrations of Fusarium Mycotoxins.

This study investigated effects of modified palygorskite (MPal) on immunity, antioxidant capacity, and intestinal barrier integrity in broiler chickens challenged with permitted feed Fusarium mycotoxin concentrations. One-day-old chicks were allocated into three treatments with eight replicates. Chickens in three groups were fed a basal diet with normal corn (control), contaminated diet containing moldy corn, with Fusarium mycotoxins contents in the diets lower than permitted feed mycotoxin concentrations, and the contaminated diet supplemented with 1 g/kg MPal for 42 days, respectively. Compared with control, moldy corn decreased bursa of Fabricius weight, jejunal secreted immunoglobulin A concentration, ileal superoxide dismutase (SOD) activity, jejunal and ileal villus height (VH) and VH/crypt depth (CD) ratio, and jejunal zonula occludens-1 and mucin 2 mRNA abundances at 42 days as well as ileal VH/CD ratio at 21 days; while they increased jejunal malondialdehyde accumulation at 21 and 42 days, jejunal SOD activity at 21 days, and serum diamine oxidase activity at 42 days, which were almost recovered by MPal. Moreover, dietary MPal upregulated ileal claudin-2 mRNA abundance compared with other two groups. The results indicated that MPal addition exerted protective effects on immunity, oxidative status, and intestinal barrier integrity in chickens challenged with permitted feed Fusarium mycotoxins levels.

Chitooligosaccharide promotes immune organ development in broiler chickens and reduces serum lipid levels.

This study investigated the effects of chitooligosaccharide on lipid metabolism, immune organ development, and lymphocyte apoptosis in broiler chickens. A total of 480 one-day-old broiler chickens (Arbor Acres) were randomly and evenly assigned to control group and experimental groups I, II, and III. The control group was given a basic diet, while experimental groups I, II, and III were given basic diets for 42 days, supplemented with 50 mg/kg chlortetracycline, 20, and 40 mg/kg chitooligosaccharide, respectively. We found levels of serum triglycerides (TG) and low density lipoprotein cholesterol (LDL-C) to be significantly reduced in experimental group II after 21 days, while the periarterial lymphatic sheath area of the spleens and the average number of bursa of Fabricius nodes were markedly increased. The serum total protein (TP) and high density lipoprotein cholesterol (HDL-C) levels, bursa of Fabricius index, and bursa of Fabricius lobule areas were additionally increased in experimental group III. After 42 days, the serum TP content had also increased and the bursa of Fabricius lobule area was augmented as well in experimental group II. Moreover, the splenic periarterial lymphatic sheat areas and the average numbers of bursa of Fabricius nodes were significantly increased in experimental group III. At both 21 and 42 days, numbers of Caspase 3-positive cells in spleen and bursa of Fabricius were significantly decreased in experimental groups II and III. Our results show that appropriate supplementation of chitooligosaccharide may improve lipid metabolism, promote immune organ development, and inhibit lymphocyte apoptosis in broilers.

Influence of the structural development of bursa on the susceptibility of chickens to infectious bursal disease virus.

Infectious bursal disease (IBD), caused by IBD virus (IBDV), is an acute, highly contagious immunosuppressive avian disease. Although age-dependent changes in susceptibility of chickens to IBDV have been established, the relationship between age-dependent structural changes in bursa of Fabricius and susceptibility of chickens to IBDV is still unclear. In the present study, we examined the bursa anatomical structure and pathological changes in specific-pathogen-free (SPF) white leghorn chickens 0 to 8 weeks post hatch (w.p.h.) and IBDV BC6/85-infected SPF chickens 2 to 6 w.p.h. respectively, by histology, histopathology, immunohistochemistry, and transmission electron microscopy. Almost all IBDV-exposed chickens (2 to 6 w.p.h.) were infected, with the severest bursal inflammation and complication in chickens at 3 w.p.h. Furthermore, the bursae of healthy chickens at 3 to 6 w.p.h. had decreased laminin immunoreactivities, lots of splits, and irregular shapes in basement membrane (BM) of cortico-medullary epithelium (CME), irregularly arranged CME, and large numbers of immunoglobulin M-bearing (IgM+) B lymphocytes in the medulla. The decreased barrier function of corticomedullary border and large amount of IgM+ B lymphocytes provide a chance for IBDV to easily contact and infect target cells at 3 to 6 w.p.h. By contrast, regular BM, neatly arranged CME, and few IgM+ B lymphocytes in healthy chickens younger than 2 w.p.h., as well as reduced IgM+ B lymphocytes and high immunoglobulin A (IgA) content in healthy chickens older than 8 w.p.h., were observed, suggesting that the integrity of corticomedullary border barrier, a small amount of target cells and high IgA content of the bursa could be the reasons for these chickens being less susceptible to IBDV. Although studies have shown how IBDV affects bursa, we focus first on the age-dependent changes of CME, BM of CME and IgA content, and our findings are the first to elucidate the structural development of bursa in relation to IBDV susceptibility from a morphological perspective.

mRNA expression in different developmental stages of the chicken bursa of Fabricius.

The bursa of Fabricius, the central humoral immune organ unique to birds, plays an important role in B-lymphocyte differentiation. In order to gain a better understanding of the molecular mechanism of critical biological processes like B-cell immigration, differentiation, and final emigration, the transcriptional changes during embryonic and posthatch development of this organ were investigated. We generated a cDNA library from total RNA isolated from 3 representative developmental stages (embryonic day [ED] 10, posthatch d 2 and d 21). We generated over 70 million high-quality reads from the cDNA library by using deep sequencing. The uniquely mapped sequences of ED 10, d 2 and d 21 were 71087280, 59167491 and 70263675 respectively. All of the differential expressed genes were involved in Vitamin A metabolism, regulation of actin cytoskeleton, Wnt signaling pathway, MAPK signaling pathway, Jak-STAT signaling pathway, Notch signaling pathway, Toll-like receptor signaling pathway. The RNA-seq analysis provides a powerful method for analyzing the transcriptome and investigating the transcriptional changes of different development stages of bursa of Fabricius. The assembled bursa transcriptome provides an essential resource for future investigations about chicken Bursa development.

Toxic effect of NiCl2 on development of the bursa of Fabricius in broiler chickens.

This study was conducted with objective of evaluating the toxic effects of nickel chloride (NiCl2) on development of bursa of Fabricius in broilers fed on diets supplemented with 0, 300, 600 and 900 mg/kg of NiCl2 for 42 days by using the methods of experimental pathology, flow cytometry (FCM), and quantitative real-time polymerase chain reaction (qRT-PCR). The results showed that dietary NiCl2 in 300 mg/kg and over induced toxic suppression in the bursal development, which was characterized by decreasing lymphocytes histopathologically and relative weight, increasing G0/G1 phase (a prolonged nondividing state), reducing S phase (DNA replication) and proliferating index, and increasing percentages of apoptotic cells. Concurrently, the mRNA expression levels of bax, cytochrome c (cyt c), apoptotic peptidase activating factor 1 (Apaf-1), caspase-3, caspase-6, caspase-7 and caspase-9 were increased and the bcl-2 mRNA expression levels were decreased. The toxic suppression of bursal development finally impaired humoral immunity duo to the reduction of B lymphocyte population and B lymphocyte activity in the broiler chicken. This study provides new evidences for further studying the effect mechanism of Ni and Ni compoundson B-cell or bursa of Fabricius.

Effect of in ovo-delivered prebiotics and synbiotics on the morphology and specific immune cell composition in the gut-associated lymphoid tissue.

The purpose of this study was to examine how pre- and synbiotic administration in ovo into the air chamber at d 12 of egg incubation influenced the specific immune cell composition and distribution in the ileum, cecal tonsils (CT) and bursa of Fabricius of broilers. The experiment was performed on 800 hatching eggs of the meat-type chickens (Ross 308). Hatching eggs were treated with: prebiotic, consisting of inulin (Pre1) or Bi(2)tos(®) (Pre2); symbiotic, composed of inulin and Lactococcus lactis subsp. lactis IBB SL1 (Syn1) or Bi(2)tos and Lactococcus lactis subsp. cremoris IBB SC1 (Syn2); or physiological saline as a control group. Seven chickens from each treatment group were randomly selected on , 1, 7, and 21 after hatch for tissue collection. Ileum, cecal tonsil and bursa of Fabricius samples were immunohistochemically stained and the proportions of Bu-1(+), CD3(+), CD4(+), CD8α(+) and TCRγδ(+) cells were estimated. It was indicated that the pre- and synbiotics do not adversely affect the development of the GALT of the chicken. The temporary decrease in B-cell number in bursa on d 7 after hatch suggested an increased colonization rate of the peripheral lymphoid organs by these cells after Pre1, Pre2, and Syn2 treatment. In CT at d 7 after hatch more potent colonization of the GALT by T cells was observed in all pre- and synbiotic treated groups and by B cells in both synbiotic-treated groups than those in respective controls. Then, on d 21 in both synbiotic-treated groups, an increase in T-cell number in ileum was also noticed with faster colonization of the CT by B cells. In 21-day-old chickens, both synbiotics exerted stronger stimulatory effect on the GALT colonization by T cells then prebiotics respectively. Similarly, the colonization by B cells was more pronounced in the Syn2 than in the Pre2 group. The data obtained in this study indicated that prebiotics and particularly synbiotics administrated in ovo stimulated GALT development after hatch.

Proposed bursa of Fabricius weight to body weight ratio standard in commercial broilers.

Several causes may induce change and atrophy in the bursa of Fabricius (BF). Databases on BF standards are available from published studies, however, updated references are needed to adjust the BF standards to present changes in highly specialized broiler genetic lines. The aim of this study was to evaluate BF-related measurements (weight and dimensions) under controlled conditions that would mimic field situations. Chickens were kept in isolation, thus avoiding exposure to disease agents by vaccination or field infections. This study was conducted using male Cobb 500 commercial broilers from the same hatch and source. Absence of disease was confirmed throughout the study. Despite the presence of individual variations, a minimum bursa-to-body weight ratio standard of 0.11 is proposed in broilers from 7 to 42 days of age.

Developmental changes in cell proliferation and apoptosis in the normal duck bursa of Fabricius.

The aim of this work was to investigate developmental changes in cell proliferation and apoptosis in normal duck bursa of Fabricius using flow cytometry and immunohistochemistry. Studies were carried out on Tianfu ducks on days 24 and 27 of embryogenesis (E24 and E27) along with days 20, 70, and 200 of postnatal development (P20, P70, and P200). Results showed that the percentage of G0/G1 bursa cells significantly increased between E24 and P200 while the percentage of cells in the S phase or G2 + M phase as well as the proliferating index obviously decreased during the same period. Proliferation cell nuclear antigen was detected in lymphocyte and interfollicular epithelium. The proliferative lymphocyte density tended to decrease from E24 to P200. Apoptotic bodies in macrophages, free apoptotic bodies, or nuclei with condensed chromatin in lymphocytes in follicles were identified by transferase-mediated dUTP nick-end labeling. Both flow cytometry and microscopic analysis reveal that the proportion of apoptotic cells and apoptotic lymphocyte density increased from E24 to P20, fell on P70, then rose again on P200. Our foundings demonstrate that cell proliferation decreases and apoptosis increases with age. These changes may account for duck bursa development and involution.

Performance traits and immune response of broiler chicks treated with zinc and ascorbic acid supplementation during cyclic heat stress.

This research was conducted to investigate the effect of supplementation of zinc (Zn) and ascorbic acid (AA) in heat-stressed broilers. A total of 160-day-old broiler chicks of approximately the same weight and appearance were divided into four treatment groups (control, T1, T2, and T3). Control group was fed a standard diet without any supplementation. T1 was supplemented with Zn at the rate of 60 mg/kg of feed, T2 was supplemented with 300 mg/kg of feed AA, and T3 was supplemented with combination of Zn and AA. From week 3 to 5, heat stress environment was provided at the rate of 12 h at 25 °C, 3 h at 25 to 34 °C, 6 h at 34 °C, and 3 h at 34 to 25 °C daily. The results revealed that feed intake, body weight and feed conversion ratio (FCR), and weight of thymus, spleen, and bursa of Fabricius improved significantly (P < 0.05) in T3 compared to the other treatments. Antibody titer against Newcastle disease (ND), infectious bursal disease (IBD), and infectious bronchitis (IB) increased significantly (P < 0.05) in T2 and T3 groups. However, total leucocytes count, lymphocytes, and monocytes increased (P < 0.05) in all treated groups compared to control. The results indicated that the supplementation of Zn or AA alone or in combination improved the performance and immune status of broilers reared under heat stress.

Effect of corticosterone on growth and welfare of broiler chickens showing long or short tonic immobility.

Tonic immobility (TI) test is commonly used to assess fear. Animals showing different TI durations demonstrate distinct behavior and biochemical responses to stress. However, less is known about how TI phenotype affects growth and welfare of domestic fowl. In this study, broiler chickens (Gallus gallus) were classified into short and long TI duration (STI and LTI) phenotypes and treated chronically with vehicle (CON) or corticosterone (CORT). STI broilers demonstrated significantly higher growth rate with higher breast muscle yield (P<0.05) and liver weight relative to BW tended to be lower (P=0.053), which was accompanied by higher serum concentration of CORT (P<0.05) and uric acid (P<0.01), but lower serum level of T4 (P=0.01). CORT severely reduced body weight, as well as the relative weight of muscle, bursa of Fabricius and spleen (P<0.001), but relative liver weight was increased (P<0.001). CORT-treated chickens had reduced serum CORT, elevated heterophile/lymphocyte ratio, and increased serum levels of total and free T3. STI broilers displayed more preening behavior (P<0.05), yet CORT elicited more walking behavior (P<0.05). No difference was observed in the welfare assessment scores between STI and LTI phenotypes under basal situation, while LTI chickens showed significantly increased incidence of pad dermatitis compared to STI under CORT exposure. The results suggest that STI broilers demonstrate better growth performance and higher adaptability to stress compared to LTI chickens.

Effects of yeast cell walls on performance and immune responses of cyclosporine A-treated, immunosuppressed broiler chickens.

The present study was conducted to investigate the effects of dietary yeast (Saccharomyces cerevisiae) cell walls (YCW) from the yeast extract industry on performance and immune function of cyclosporine A (CSA)-treated, immunosuppressed broiler chickens. A total of 240 day-old male broilers were allocated randomly into four treatments: (1) non-challenged control; (2) non-challenged control+0·3 % YCW; (3) CSA-challenged group; (4) CSA-challenged+0·3 % YCW. On days 1-4 and 22-25 of age, broilers were subcutaneously injected with CSA or sterile saline. The results showed that supplementation of YCW significantly improved daily weight gain (DWG) during the starter (days 1-21, P < 0·01), finisher (days 22-42, P < 0·01) and overall (days 1-42, P < 0·05) periods compared with the control birds, but had no effect on feed conversion ratio (FCR, P>0·05). Compared with the CSA-treated birds, YCW alleviated the decrease of DWG (P < 0·01) and increase of FCR (P < 0·05) caused by CSA challenge at different periods and cumulatively. On days 21 and 42, YCW mitigated the CSA-induced decrease of peripheral blood lymphocyte blastogenic response (P < 0·01). In addition, YCW improved the relative weights of the bursa of Fabricius (P < 0·01) and thymus (P < 0·01) and up-regulated the splenic expression of pro-inflammatory cytokines IL-1ß (P < 0·01) and IL-6 (P < 0·01) on day 42 compared with the CSA-treated birds. These results indicate that YCW supplementation has beneficial effects in attenuating the immunosuppressive effects of CSA challenge, therefore improving growth performance of broiler chickens.

Effect of n-3 fatty acids on immune function in broiler chickens.

There is interest in the enrichment of poultry meat with long-chain n-3 polyunsaturated fatty acids in order to increase the consumption of these fatty acids by humans. However, there is concern that high levels of n-3 polyunsaturated fatty acids may have detrimental effects on immune function in chickens. The effect of feeding increasing levels of fish oil (FO) on immune function was investigated in broiler chickens. Three-week-old broilers were fed 1 of 4 wheat-soybean basal diets that contained 0, 30, 50, or 60 g/kg of FO until slaughter. At slaughter, samples of blood, bursa of Fabricius, spleen, and thymus were collected from each bird. A range of immune parameters, including immune tissue weight, immuno-phenotyping, phagocytosis, and cell proliferation, were assessed. The pattern of fatty acid incorporation reflected the fatty acid composition of the diet. The FO did not affect the weight of the spleen, but it did increase thymus weight when fed at 50 g/kg (P < 0.001). Fish oil also lowered bursal weights when fed at 50 or 60 g/kg (P < 0.001). There was no significant effect of FO on immune cell phenotypes in the spleen, thymus, bursa, or blood. Feeding 60 g/kg of FO significantly decreased the percentage of monocytes engaged in phagocytosis, but it increased their mean fluorescence intensity relative to that of broilers fed 50 g/kg of FO. Lymphocyte proliferation was significantly decreased after feeding broiler chickens diets rich in FO when expressed as division index or proliferation index, although there was no significant effect of FO on the percentage of divided cells. In conclusion, dietary n-3 polyunsaturated fatty acids decrease phagocytosis and lymphocyte proliferation in broiler chickens, highlighting the need for the poultry industry to consider the health status of poultry when poultry meat is being enriched with FO.

Comparative studies on the secondary lymphoid tissue areas in the chicken bursa of Fabricius and calf ileal Peyer's patch.

The chicken bursa of Fabricius and calf ileal Peyer's patch are thought to be the primary lymphoid organs of B cell development. In the bursa, the existence of secondary lymphoid tissue, called the diffusely infiltrated area, has been recognized. Recently, we have found the presence of a region of secondary lymphoid tissue in the ileal Peyer's patch at the period of the most rapid growth of this organ. In this study, we compared the development of these secondary lymphoid tissue regions in the bursa and ileal Peyer's patch histologically. Before hatching, lymphatic follicle formation occurred in the bursa, but not in the diffusely infiltrated area, where only a small number of lymphoid cells were found. However, during fetal calf development, lymphatic follicle formation occurred not only in the primary lymphoid organ but also in the secondary lymphoid tissue regions. Therefore, the prenatal development of the secondary lymphoid tissue regions of the bursa and ileal Peyer's patch were distinct. After hatching, formation of the germinal center, which contained many CD4+ cells, was observed in the diffusely infiltrated area of the bursa. After birth, many CD4+ cells and IgG mRNA expression were observed in the lymphatic follicle of the secondary lymphoid tissue regions in the ileal Peyer's patch, but rarely in the ileal Peyer's patch lymphatic follicles. The change of character of these secondary lymphoid tissue regions at the postnatal stage might be dependent on external antigens.

Reduced serologic response to avian influenza vaccine in specific-pathogen-free chicks inoculated with Cryptosporidium baileyi.

Immunosuppression in chickens as a consequence of Cryptosporidium baileyi infection may compromise the effectiveness of vaccination for control of avian influenza (AI) H5N1. In a 13-wk study using 260 specific-pathogen-free chicks, immunological response and bursa weight:body weight ratios following vaccination against AI strain H5N1 were compared between uninfected and C baileyi-infected birds. The four experimental treatments were the following: infection with C. baileyi (5 x 10(5) oocysts dosed orally on day 0); C baileyi infection + vaccination against H5N1 (0.3 ml inactivated vaccine administered subcutaneously on day 7 and day 21; CB+VAC); vaccination only (VAC); and sham infection/vaccinations using sterile distilled water (control). At weekly intervals serum samples were analyzed by hemagglutination inhibition assay (HI), and five chicks/group were euthanatized for determination of bursa weights. In all but week 8, proportional bursa weights (bursa weight/body weight) were lower for CB+VAC chicks than for VAC chicks (i.e., the bursa index was below 1.0; average 0.81). Throughout the 13 wk, HI titres were lower (P < 0.01) in CB+VAC than in the VAC group, and compared with VAC, chicks in CB+VAC had a slightly shorter period of negative seroconversion. These data indicate bursal atrophy and immunosuppressive effects of C. baileyi infection on day-old chicks vaccinated against AI strain H5N1 and suggest that C. baileyi infection in chicks may increase the host susceptibility to AI virus.