Yolk-free Body Weight Research Articles

Temperature manipulation during incubation: effect on embryo development and incidence of white striping and expression of related genes in broiler chickens from two commercial breeds

ABSTRACT 1. This study evaluated the effects of cyclic eggshell temperature between 10 and 14 d of embryogenesis on traits viz. the expression of MYOZ2, PPARγ and GPx7 in breast muscle, meat quality and incidence of white striping at slaughter age. 2. Eggs were obtained from Cobb and Ross broiler breeders to investigate the response of breeds to eggshell temperature, which regulated air temperature. A total of 784 eggs were incubated at either the control eggshell temperature (37.8°C) from 0 to 18 d or exposed to cyclic high eggshell temperature (CHT) at 38.8°C for 6 h/d between 10 and 14 d of incubation. The temperature was 36.8°C between 18 and 21 d. Hatched chicks were reared under optimum rearing conditions. The birds were sampled at 19 d of incubation, at hatch and at 42 d post-hatch. 3. There was no effect of eggshell temperature on yolk-free body weight and residual yolk sac weight. The CHT chicks had wider breasts on the day of hatching. 4. At hatch and 42d post-hatch, PPARγ expression in Cobb-CHT was upregulated 4.78-fold and downregulated 3.28-fold, respectively, compared to the Cobb-control. At slaughter age, chickens from Ross-CHT had 1.98- and 2.33-fold upregulated PPARγ and GPX7 expressions, respectively, compared to Ross-control. The CHT increased GPx7 expression in the Cobb-CHT day-old chicks compared to the Cobb-control. On ED19, MYOZ2 expression was upregulated in Cobb and downregulated in Ross by CHT. 5. The effects of breed and eggshell temperature on pH15, L*, a*, expressible juice and cooking loss were not significant. The CHT increased the incidence of severe white striping lesions in Ross chickens. 6. It was concluded eggshell temperature modulated embryo development, incidence of white striping and expression of related genes differently in the two commercial breeds.

Breeder age and hatching egg storage duration: effects on post-hatch performance of FUNAAB- α broiler chickens.

This trial was designed to evaluate the influence of hatching egg storage length and broiler breeder hens' age on post-hatch growth performance and physiological responses of FUNAAB-α chickens. Five hundred fertile eggs from each of 60 and 32-wk-old FUNAAB-α breeder hens were collected and assigned to five storage durations (0, 3, 7, 11, and 15 d). The hatching eggs were incubated using the conventional protocol. Data were collected on the growth performance and physiological responses. A 2 × 5 factorial design was used for the experiment. The results revealed that there was a decline in the final body weight in chickens from eggs of 15 and 11 d storage compared to the chickens from 7, 3, and 0 egg storage days. Chickens of 32-week-old breeder hens had higher (P < 0.05) mean corpuscular volume, white blood cell, heterophil, and pack cell volume values compared to 60-week-old breeder hens. Hatchlings from 60-week-old breeders had a higher liver percentage (3.0% yolk-free body weight [YFBW]) than those from 32-week-old breeders (2.8% YFBW). It was concluded that an extended storage duration of 15 d adversely affected the carcass traits and growth performance of chickens from egg storage above seven days.

Providing colored photoperiodic light stimulation during incubation: 1. Effects on embryo development and hatching performance in broiler hatching eggs

Providing lighting schedule during incubation has been shown to improve chick quality and reduce stress posthatch. This study was conducted to evaluate the effects of providing light of different colors during incubation on embryo development, air cell temperature, the spread of hatch, and hatching performance. Four batches of eggs (n = 2,176, 1,664, 1,696 and 1,600) from Ross 308 broiler breeders were used in the experiment. In each trial, eggs were randomly distributed into 4 lighting treatments. The incubation lighting treatments included: incubated under dark as control, illuminated with white, red or blue lights for 12 h daily. There were no incubation lighting treatment differences in embryo development, the spread of hatch, hatchability, embryo mortality, hatch weight, chick length, navel closure quality, yolk-free body weight, or relative spleen weight. However, embryos incubated under red light had lower average air cell temperature than those in dark, white or blue light treatments. This finding may suggest higher melatonin secretion during the scotophase when illuminated with red light. Male chicks incubated under dark had a higher bursa of Fabricius weight than males illuminated with blue light. In conclusion, these results suggest that the red, white and blue light stimulation during incubation had no negative effects on hatchability, embryo mortality, spread of hatch or day-old chick quality, but may have potential impacts on immunity and energy metabolism in broiler embryos.

Fumigating broiler hatching eggs with lysozyme product (Inovapure) to reduce eggshell microbial load

Experiments were conducted to evaluate the effectiveness of a lysozyme product (InovapureTM) (LP) against E. coli penetrating eggshells. In the first microbiological experiment, 60 agar-filled eggs were inoculated with E. coli suspension, then fumigated with distilled water, 1.5% or 3.0% LP or a quaternary ammonium product (QA) at 0.125% for 10 min. In the second microbiological experiment, another 60 agar-filled eggs were fumigated with the same sanitizer treatments first, then inoculated with the E. coli suspension. Eggshells were candled and visual colonies were counted after 48 h incubation. An animal experiment was conducted to evaluate LP applied to the surface of 2080 broiler hatching eggs on hatching and growth performance. Hatching eggs were submerged in an E. coli suspension. After drip drying, eggs were randomly divided into four fumigation treatments, each with four subsets of 150 eggs. Fumigation treatments were the same as in the microbiological experiments. Eggs were incubated in 8 incubators (2 replicate incubators per treatment) and the broilers were grown to 33 d of age. In the microbiological experiments, inoculated eggs fumigated with 3.0% LP and 0.125% QA reduced (P < 0.05) the total amount of E. coli to 11 cfu/egg and 10 cfu/egg, respectively. When eggs were sanitized prior to inoculation, 3.0% LP demonstrated (P < 0.05) ongoing bactericidal action to prevent E. coli penetration. No differences in hatchability, fertility rate or egg weight loss percent were found among sanitation treatments. At hatch, body weight or the ratio of yolk sac weight to yolk-free body weight were not affected by the sanitation treatments. However, the application of sanitizers decreased (P < 0.05) the presence of E. coli in the yolk sac of newly hatched chicks. Feed consumption, body weight and feed conversion ratio were not affected by sanitation treatments. However, average daily body weight gain was lower (P < 0.05) following QA. Overall, 3.0% LP demonstrated acceptable activity against E. coli on eggshells, and provided ongoing bactericidal action to prevent E. coli penetration without negatively affecting growth performance.

The expression and role of CD59 in human extravillous trophoblast

The objective of the study was to investigate the effects of an in ovo injection of CuNano and the timing of injection on metabolic rate (O2 consumption and heat production, HP) and development of layer hatchlings. On day 1 of incubation, 192 fertile eggs from 29-week-old Lohmann breeder strain chickens were distributed into four groups that were administered colloidal CuNano on: day 1 and/or 10. Gaseous exchange was measured in an open-air-circuit respiration unit, and HP was calculated for 16- and 19-day-old embryos. Yolk free body weight (YFBW) at 24 h after hatching and the relative organ weights were used as a measure of hatchling development. In ovo injection of CuNano on different days during incubation significantly decreased O2 consumption and HP compared with the control group. The residual yolk sac weight in the treated groups was significantly higher than in the control group (P<0.0001), indicating that CuNano injection reduced lipid oxidation, which could be associated with the lower O2 consumption (P=0.001). Accordingly, the organ weights (intestine, heart, liver) relative to YFBW were also lower in embryos injected with CuNano (all; P<0.05). Interestingly, the difference in metabolic rate and organ weights between treatments was not reflected in YFBW (P>0.05). Furthermore, the plasma concentrations of IgM and IgG and the mRNA expression of NF-kB and TNF-α were not affected (both; P>0.05), indicating the absence of inflammatory modulation by CuNano. These preliminary results demonstrated that CuNano, regardless of the day of injection, altered the metabolic rate of embryos and depressed the development of organs; however, it did not affect YFBW, immunoglobulin concentrations and the expression of immuno-related genes.

Effect of copper nanoparticles and copper sulphate on metabolic rate and development of broiler embryos

Copper (Cu) is regularly used as a growth promoter in poultry production. However, it has been demonstrated that the content of Cu inside eggs might not be sufficient to support the embryonic development. It is possible to supply the embryo with extra nutrients by in-ovo administration. Recently, it has been shown that in-ovo administration of copper nanoparticles (Cu-NP) and copper sulphate (CuSO4) remarkably improved the body weights of growing chickens. Thus, the objective of the present experiment was to elucidate the potential effects of Cu-NP and CuSO4 on the metabolic rate (oxygen consumption — O2 and energy expenditure — EE) and development during embryogenesis.Fertilised broiler eggs were divided into six groups: a non-injected control, a placebo injected with demineralised water, two groups injected, at day one of incubation, with CuSO4 (50 and 100mg/kg) and two groups injected with Cu-NP (50 and 100mg/kg). Gaseous exchange was measured in an open-air-circuit respiration unit, and EE was estimated from day 10 to day 19 of embryogenesis. Body weight at 24h after hatching and the relative organ weights were used as a measure of hatching development. In-ovo injection of 50mg/kg Cu-NP and CuSO4 significantly increased O2 consumption and EE on the 16th and 19th day of incubation compared with the control group; Cu-NP had the largest effect on the metabolic rate. However, organ weights (intestine, heart, liver, and breast) relative to the yolk-free body weight were not affected in the injected groups. In addition, blood parameters did not show any changes among the groups. This result demonstrates that in-ovo injection of Cu-NP affects the metabolic rate of embryos, which might explain their improved performance after hatching.

Effects of in ovo injection of threonine on hatchability, intestinal morphology, and somatic attributes in Japanese quail (Coturnix japonica)

ABSTRACTA total of 540 Japanese quail eggs were in ovo injected threonine (THR) at day 11 of embryonic development to evaluate the effects of in ovo feeding of THR on the hatchability, somatic attributes, and gut morphology of hatchlings. A completely randomized experimental design with 9 treatments and 4 replicates of 15 eggs per replicate was used. The treatments were non-injected (control) eggs and those receiving in ovo injections of 0.05 or 0.1 ml of saline (diluent) with or without THR (5 mg/ml) in the air sac (IAS) or under the air sac (UAS). Although the number of hatched eggs injected with 0.05 ml diluent both with and without THR under the air sac was not significant in comparison to the control group, it was higher than that of the other injected treatments. Interestingly, the under air sac injection of 0.05 ml THR showed enhanced gut morphology in comparison with the other treatments. The dried yolk-free body weight of all chicks was not statistically significant. Overall, the present results suggest that the injection of 0.05 ml THR under the air sac may improve the intestinal morphology in newly hatched quail while having no negative effects on final yolk-free body weight.

The Effects of Different Eggshell Temperatures Between Embryonic Day 10 and 18 on Broiler Performance and Susceptibility to Ascites

The aim of the current study was to determine the effects of low (33.3-36.7 ˚C), control (37.8-38.2 ˚C) and high (38.9-40.0 ˚C) eggshell temperatures (ESTs) between days 10-18 of incubation on broiler performance and susceptibility to ascites. The effects of different ESTs on hatchling weight were significant. The highest residual yolk sac weight (7.7 g) and relative yolk sac weight (18.7%) were observed in high EST group, whereas the highest yolk-free body weight (36.22 g) was obtained in the control group. Relative post-hatch heart weight was lower in the high EST group (0.64%) compared with the control (0.84%) and low (0.88%) EST groups. At 6 weeks of age, body weights of broilers of the low, control, and high EST groups were 2172.6, 2543.9, 2282.6 g respectively. During the 6-week life span, the feed conversion ratio of broilers in the low (1.86) and high (1.83) EST groups was significantly worse than of those in the control EST group (1.68). Higher packed cell volume (PCV) and red blood cell (RBC) values were obtained in the high EST group relative to the other groups, whereas hemoglobin (Hb) level was lower in the control group than in the others. The relative heart weights and right ventricular to total ventricular (RV:TV) ratio for low, control, and high EST group were 0.46, 0.40, 0.37 g and 0.27, 0.28, 0.33% respectively. In conclusion, incubation length, yolk sac absorption, residual yolk sac weight, yolk-free BW, post-hatch performance, and heart, blood parameters, abdominal fluid accumulation at slaughter age are affected by changes in EST between incubation days 10 to 18.

Effects of broiler breeder-feeding programme and feeder space change at photostimulation using maize- or wheat-based diets on eggshell properties and progeny bone development

1. The effects of diet type, feeding programme and fast- or slow-feed allocation in fast-feathering Cobb 500 broiler breeder hens on eggshell properties and broiler progeny bone development were investigated in a 2 × 2 × 2 factorial experiment.2. The birds were fed on either maize- or wheat-based diets during rearing and production and on a fast- or slow-feed allocation programme from 14 to 29 weeks of age. At 22 weeks, 69 females from each pen were placed in a layer house where feeder space (FS) either remained similar or was increased.3. Eggs produced at 33 weeks were incubated, eggshell conductance (G) was determined and a sample of 14 chicks from each treatment combination was taken to obtain bone traits at hatching.4. Diet type did not influence G, yolk-free body weight (BW), residual yolk weight or relative asymmetry (RA) of any bilateral traits of leg bones of hatchlings. However, breeder diet type was involved on two-way and three-way interaction effects on progeny leg bone traits.5. Breeders feed restricted according to the slow-feeding programme laid eggs with greater G compared to those managed with the fast-feeding programme, but there was no effect of feeding programme on progeny bone traits at hatching.6. Eggs from breeders given more FS at photostimulation had greater G than those from breeders provided with similar FS. Maternal FS change did not influence hatchling yolk-free BW; however, breeders given more FS produced progeny with heavier tibias and shanks and longer femurs compared with those provided with similar FS, but only when breeders were fed on maize. Moreover, increased maternal FS at photostimulation was associated with an increased RA of femur length in the progeny.7. It was concluded that breeder FS change at photostimulation influenced eggshell conductance and consistently affected bone development of the broiler progeny.

Embryonic protein undernutrition by albumen removal programs the hepatic amino acid and glucose metabolism during the perinatal period in an avian model.

Different animal models have been used to study the effects of prenatal protein undernutrition and the mechanisms by which these occur. In mammals, the maternal diet is manipulated, exerting both direct nutritional and indirect hormonal effects. Chicken embryos develop independent from the hen in the egg. Therefore, in the chicken, the direct effects of protein deficiency by albumen removal early during incubation can be examined. Prenatal protein undernutrition was established in layer-type eggs by the partial replacement of albumen by saline at embryonic day 1 (albumen-deprived group), compared to a mock-treated sham and a non-treated control group. At hatch, survival of the albumen-deprived group was lower compared to the control and sham group due to increased early mortality by the manipulation. No treatment differences in yolk-free body weight or yolk weight could be detected. The water content of the yolk was reduced, whereas the water content of the carcass was increased in the albumen-deprived group, compared to the control group, indicating less uptake of nutrients from the yolk. At embryonic day 16, 20 and at hatch, plasma triiodothyronine (T3), corticosterone, lactate or glucose concentrations and hepatic glycogen content were not affected by treatment. At embryonic day 20, the plasma thyroxine (T4) concentrations of the albumen-deprived embryos was reduced compared to the control group, indicating a decreased metabolic rate. Screening for differential protein expression in the liver at hatch using two-dimensional difference gel electrophoresis revealed not only changed abundance of proteins important for amino acid metabolism, but also of enzymes related to energy and glucose metabolism. Interestingly, GLUT1, a glucose transporter, and PCK2 and FBP1, two out of three regulatory enzymes of the gluconeogenesis were dysregulated. No parallel differences in gene expressions causing the differences in protein abundance could be detected pointing to post-transcriptional or post-translational regulation of the observed differences.

Effect of copper nanoparticles on metabolic rate and development of chicken embryos

The objective of the study was to investigate the effects of an in ovo injection of CuNano and the timing of injection on metabolic rate (O2 consumption and heat production, HP) and development of layer hatchlings. On day 1 of incubation, 192 fertile eggs from 29-week-old Lohmann breeder strain chickens were distributed into four groups that were administered colloidal CuNano on: day 1 and/or 10. Gaseous exchange was measured in an open-air-circuit respiration unit, and HP was calculated for 16- and 19-day-old embryos. Yolk free body weight (YFBW) at 24h after hatching and the relative organ weights were used as a measure of hatchling development. In ovo injection of CuNano on different days during incubation significantly decreased O2 consumption and HP compared with the control group. The residual yolk sac weight in the treated groups was significantly higher than in the control group (P<0.0001), indicating that CuNano injection reduced lipid oxidation, which could be associated with the lower O2 consumption (P=0.001). Accordingly, the organ weights (intestine, heart, liver) relative to YFBW were also lower in embryos injected with CuNano (all; P<0.05). Interestingly, the difference in metabolic rate and organ weights between treatments was not reflected in YFBW (P>0.05). Furthermore, the plasma concentrations of IgM and IgG and the mRNA expression of NF-kB and TNF-α were not affected (both; P>0.05), indicating the absence of inflammatory modulation by CuNano. These preliminary results demonstrated that CuNano, regardless of the day of injection, altered the metabolic rate of embryos and depressed the development of organs; however, it did not affect YFBW, immunoglobulin concentrations and the expression of immuno-related genes.

Energy utilization and heat production of embryos from eggs originating from young and old broiler breeder flocks

Two experiments were conducted to study the interaction between breeder age and egg size on the energy utilization (experiment 1) and heat production (experiment 2) of broiler embryos. In experiment 1, a total of 4,800 Ross-308 hatching eggs from 2 breeder ages (29 and 53 wk of age, or young and old) and, within each age, 2 egg sizes (57 to 61 g and 66 to 70 g, or small and large) were used. In experiment 2, a total of 240 Ross-308 hatching eggs from 2 breeder flocks at 29 (young) and 53 (old) wk of age, and which were selected from the same egg weight range (58 to 61 g), were tested in 2 replicate chambers. In experiment 1, it was shown that the amount of yolk relative to albumen was higher in the old flock eggs, and this effect was more pronounced in the large eggs. The old flock eggs, especially the larger egg size, contained more energy as a result of a greater yolk size. Energy utilization of the embryos was positively related to yolk size and the amount of energy transferred to yolk-free body (YFB) was largely determined by the available egg energy. The efficiency of converting egg energy into chick body energy (E(YFB)) was equal for both egg sizes and both breeder age groups. Chick YFB weight of young and old flock eggs was equal. However, dry YFB weight of chicks from old flock eggs was higher than in chicks from young flock eggs, which was associated with more protein and fat content and thus more energy accumulated into YFB. As a consequence, embryos derived from old flock eggs produced more heat from d 16 of incubation onward than those of the young flock eggs. In conclusion, the higher energy deposition into chick YFB of old flock eggs, leading to higher embryonic heat production, is the result of a higher amount of available energy in the egg and is not due to changes in E(YFB).

Yolk absorption and embryo development of small and large eggs originating from young and old breeder hens

To evaluate the effect of breeder age and egg size on yolk absorption and embryo development, a total of 4,800 Ross 308 hatching eggs were subjected to 4 treatments arranged in a 2 × 2 factorial randomized complete block design using 2 breeder ages (29 and 53 wk of age, or young and old) and 2 egg sizes (57-61 g and 66-70 g, or small and large). A significant interaction between breeder age and egg size was found for egg composition. Yolk weight increased with flock age, whereas a larger egg size resulted in higher albumen content. A significant interaction between breeder age and egg size was found for yolk-free body (YFB) weight only at d 7. Until the fourteenth day of incubation, eggs from the old flock yielded greater YFB weight than did eggs from the young flock. At hatch, chicks of both age groups had comparable wet YFB weight, chick weight, wet and dry residual yolk weight, and chick length. Dry YFB weight of chicks from the old flock was higher than that of chicks from the young flock. Compared with the small eggs, embryos and chicks of the large eggs had greater YFB weight from d 14 to hatching. At hatch, these chicks were also heavier, longer, and had higher wet and dry YFB and residual yolk weight. Yolk absorption at d 18 and at hatch of embryos and chicks of the old flock was higher than that of the young flock, both in absolute values and percentages. Rates of absolute and percentage yolk absorption through d 18 and percentage yolk absorption at hatch were higher in the small eggs than in the large eggs. It can be concluded that egg size influences chick length at hatch and embryo development when expressed in terms of total and YFB weight. Although yolk availability and rate of absorption may have influenced dry YFB weight, they did not influence hatching chick length or total and YFB weight.

Morphometric abnormalities in brains of great blue heron hatchlings exposed in the wild to PCDDs.

Great blue heron hatchlings from colonies in the Strait of Georgia, British Columbia, Canada are being monitored for environmental contaminant exposure and effects by the Canadian Wildlife Service. The contaminants of concern are polychlorinated dibenzodioxins (PCDDs) and polychlorinated dibenzofurans (PCDFs), primarily derived from kraft pulp mill effluent. The levels of PCDDs and PCDFs in eggs from the most contaminated colonies peaked in 1988 and 1989 and dropped dramatically through 1990 to 1992. Brains of heron hatchlings (taken as eggs from the wild and hatched in the laboratory) were analyzed for gross morphological abnormalities. Brains from highly contaminated colonies (Crofton, British Columbia and University of British Columbia Endowment Lands) in 1988 exhibited a high frequency of intercerebral asymmetry. The frequency of this abnormality decreased in subsequent years as the levels of TCDD and TCDD-TEQs (toxic equivalence factors) decreased. The asymmetry was significantly correlated with the level of TCDD and TCDD-TEQs in eggs taken from the same nest. Yolk-free body weight negatively correlated and the brain somatic index positively correlated with the TCDD level in such pair-matched eggs. These results indicate that gross brain morphology, and specifically intercerebral asymmetry, may be useful as a biomarker for the developmental neurotoxic effects of PCDDs and related chemicals.

The Concentration of Different Lipid Classes During Late Embryonic Development in a Randombred Turkey Population and a Subline Selected for Increased Body Weight at Sixteen Weeks of Age

Lipid changes in the yolk sac of the embryo were studied in a randombred population of turkeys (RBC2) and a subline of the RBC2 selected for increased BW at 16 wk (F line). Comparisons of yolk sac and embryonic development were made between 22 d of incubation and hatch (28 d). Poults from the F line had heavier yolk sacs from 24 to 28 d and yolk free body weight was also heavier at hatch (61.1 vs 52.8 g). Yolk sac lipid (percentage of DM) declined faster in F line embryos (69 to 39%) compared with the RBC2 line (62 to 48%). In both lines, embryonic liver dry matter and lipids (percentage of DM) were similar. Yolk sac neutral lipids increased from 22 to 28 d (70 to 80% total lipid) in both lines and there was a concomitant decline in phospholipids (30 to 20%). The direction of the changes was similar for embryonic liver lipid. At 26 and 28 d, there were significantly increased neutral lipids (94 vs 88%) and decreased phospholipids (6 vs 12%) in RBC2 compared with F line embryonic livers. The concentration of cholesterol esters (percentage of total lipid) increased in the yolk sac and embryonic liver during the course of incubation. At 26 and 28 d, livers from RBC2 embryos had increased cholesterol ester concentration compared with livers from the F line. These results suggest that selection for body weight at 16 wk of age has not changed total lipid content of the yolk, but there was a significant decline in the proportion of triacylglycerol (percentage of total lipid) and diacylglycerol (percentage of total lipid) in the F line during embryonic development. Selection also resulted in significantly increased hepatic total lipid in F line embryos but significantly decreased the proportion of hepatic neutral lipid.

Dioxin contamination and growth and development in great blue heron embryos

A great blue heron colony located near a pulp mill in British Columbia failed to fledge young in 1987, with a concurrent sharp increase in polychlorinated dibenzo-p-dioxin (PCDD) and polychlorinated dibenzofuran (PCDF) levels in their eggs. In 1988 we tested the hypothesis that the PCDD and PCDF contamination caused reproductive failure by increasing mortality of the heron embryos in ovo. Pairs of great blue heron eggs were collected from three British Columbia colonies with low, intermediate, and high levels of dioxin contamination: Nicomekl, Vancouver, and Crofton, respectively. One egg of each pair was incubated under laboratory conditions at the University of British Columbia (UBC) while the other egg was analyzed for PCDDs and PCDFs. All incubated eggs were fertile. All eggs from the Nicomekl colony hatched, while 13 of 14 eggs from Vancouver and 12 of 13 eggs from Crofton hatched. Subcutaneous edema was observed in 4 of 12 chicks from Crofton and 2 of 13 chicks from Vancouver. No edema was seen in the chicks from Nicomekl. There was a small, but significant, negative regression of plasma calcium concentration, yolk-free body weight, tibia length, wet, dry, and ash weight, beak length, and kidney and stomach weight of the hatched chicks on the tetrachlorodibenzo-p-dioxin (TCDD) level of the paired eggs. Fewer down follicles were present on the heads of TCDD-contaminated chicks. Hence while dioxins did not cause mortality of the heron embryos in ovo, the depression of growth and the presence of edema are suggestive that dioxins at the levels found in the environment have an adverse effect on the development of great blue heron embryos.