Egg injection studies were performed to confirm a proposed model of relative sensitivity of birds to 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD). In this model, species are classified as belonging to one of three categories of sensitivity based on amino acid substitutions in the ligand-binding domain of the aryl hydrocarbon receptor. Embryo lethality and relative potencies of 2,3,7,8-tetrachlorodibenzofuran (TCDF) and 2,3,4,7,8-pentachlorodibenzofuran (PeCDF) were compared with TCDD for Japanese quail (Coturnix japonica; least sensitive), Common pheasant (Phasianus colchicus; moderately sensitive), and White Leghorn chicken (Gallus gallus domesticus; most sensitive). Doses ranging from 0.044 to 37 pmol/g egg (0.015-12 ng/g egg) were injected into the air cell of eggs prior to incubation. LD(50) (95% confidence intervals) values, based on rate of hatching for TCDD, PeCDF, and TCDF, were 30 (25-36), 4.9 (2.3-9.2), and 15 (11-24) pmol/g egg for the quail, 3.5 (2.3-6.3), 0.61 (0.28-1.2), and 1.2 (0.62-2.2) pmol/g egg for pheasant, and 0.66 (0.47-0.90), 0.75 (0.64-0.87), and 0.33 (0.23-0.45) pmol/g egg for chicken, respectively. LD(50)-based relative potencies of PeCDF and TCDF were 6.1 and 2.0 for quail, 5.7 and 2.9 for pheasant, and 0.88 and 2.0 for chicken, respectively. TCDD was not the most potent compound among the species tested, with PeCDF and TCDF being more potent than TCDD in the quail and pheasant. TCDF was the most potent in chicken. Species sensitivity was as expected for TCDD and TCDF, whereas for PeCDF, the chicken and pheasant were similar in sensitivity and both were more sensitive than the quail. Results from companion in vitro studies are generally similar to those reported here with a few exceptions.

In Australia, free-range layer pullets are typically reared indoors, but adult layers go outdoors, and this mismatch might reduce adaptation in laying environments. Enrichments during rearing may optimise pullet development and subsequent welfare as adult free-range hens. In the outdoor environment, hens may have greater opportunities for exercise and natural behaviours which might contribute to improved health and welfare. However, the outdoor environment may also result in potential exposure to parasites and pathogens. Individual variation in range use may thus dictate individual health and welfare. This study was conducted to evaluate whether adult hens varied in their external and internal health due to rearing enrichments and following variation in range use. A total of 1386 Hy-Line Brown® chicks were reared indoors across 16 weeks with three enrichment treatments including a control group with standard housing conditions, a novelty group providing novel objects that changed weekly, and a structural group with custom-designed structures to increase spatial navigation and perching. At 16 weeks of age the pullets were moved to a free-range system and housed in nine identical pens within their rearing treatments. All hens were leg-banded with microchips and daily ranging was assessed from 25 to 64 weeks via radio-frequency identification technology. At 64–65 weeks of age, 307 hens were selected based on their range use patterns across 54 days up to 64 weeks: indoor (no ranging), low outdoor (1.4 h or less daily), and high outdoor (5.2–9 h daily). The external and internal health and welfare parameters were evaluated via external assessment of body weight, plumage, toenails, pecking wounds, illness, and post-mortem assessment of internal organs and keel bones including whole-body CT scanning for body composition. The control hens had the lowest feather coverage (p < 0.0001) and a higher number of comb wounds (P = 0.03) than the novelty hens. The high outdoor rangers had fewer comb wounds than the indoor hens (P = 0.04), the shortest toenails (p < 0.0001) and the most feather coverage (p < 0.0001), but lower body weight (p < 0.0001) than the indoor hens. High outdoor ranging decreased both body fat and muscle (both p < 0.0001). The novelty group had lower spleen weights than the control hens (P = 0.01) but neither group differed from the structural hens. The high outdoor hens showed the highest spleen (P = 0.01) and empty gizzard weights (P = 0.04). Both the rearing enrichments and ranging had no effect on keel bone damage (all P ≥ 0.19). There were no significant interactions between rearing treatments and ranging patterns for any of the health and welfare parameters measured in this study (P ≥ 0.07). Overall, rearing enrichments had some effects on hen health and welfare at the later stages of the production cycle but subsequent range use patterns had the greatest impact.

No abstract

In birds, activation of the aryl hydrocarbon receptor (AhR) by some polychlorinated dibenzo-p-dioxins (PCDDs) and polychlorinated dibenzofurans (PCDFs) results in induction of cytochrome P4501A (CYP1A) expression. This response has been useful for predicting relative sensitivity of birds to dioxin-like compounds. To further investigate species-sensitivity to dioxins and dioxin-like compounds induction of cytochrome P450 1A4 and 1A5 (CYP1A4 and CYP1A5) mRNA and ethoxyresorufin O-deethylase (EROD) activity were quantified in liver of posthatch white leghorn chicken, common pheasant, and Japanese quail exposed to 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD), 2,3,4,7,8-pentachlorodibenzofuran (PeCDF), or 2,3,7,8-tetrachlorodibenzofuran (TCDF) via air cell injection. The rank-order of sensitivity of TCDD- and TCDF-exposed birds, based on CYP1A, was chicken>pheasant>quail. Based on CYP1A5 mRNA expression and EROD induction, the order of sensitivity of PeCDF-exposed birds was identical to that for TCDD and TCDF. However, based on CYP1A4 mRNA expression the rank-order was pheasant>chicken>quail. When comparing the potency of the three compounds in each species, based on CYP1A4 mRNA expression, TCDD was the most potent compound in chicken. However, PeCDF was equally potent to TCDD in quail and was more potent than TCDD in pheasant. These results suggest that quantitative real-time polymerase chain reaction (Q-PCR) analysis of CYP1A expression, particularly CYP1A4 mRNA expression, may be a more sensitive biomarker of exposure than analysis of EROD induction, especially in less responsive avian species. Based on these findings future risk assessments should consider the sensitivity of the species inhabiting a site and the congeners of concern that are present.

Within Australia, free-range systems are prevalent, but pullets destined for range access are reared indoors. This mismatch between rearing and layer housing may hinder adaptation to the free-range environment. Rearing enrichments could enhance pullet development. A total of 1,386 Hy-Line Brown® chicks were reared inside an experimental facility across 16 weeks with 3 enrichment treatments including (1) a control group with standard floor-housing, (2) a novelty group providing novel objects that changed weekly ("novelty" hens), and (3) a structural group with custom-designed H-shaped structures including opaque sides ("structural" hens). At 16 weeks of age, all pullets were leg-banded with microchips and moved to an experimental free-range system with 9 identical pens (n = 3/rearing treatment). From 25 to 64 weeks, individual hen daily ranging behavior was tracked via radio-frequency identification technology and grouped into 6 age periods per rearing treatment. Video footage was used to count the number of hens at different distances on the range for the first 14 days of access, and eggs were assessed for albumen corticosterone concentrations 4 days prior to (n = 450) and 1 week after first range access (n = 450). Across most age periods, the structural hens spent the most time ranging (P ≤ 0.01), the novelty hens showed the fewest number of visits to the range (P < 0.0001), and both enriched hen groups had the longest maximum visit durations (P ≤ 0.02). Range use increased with age across all treatments with only 3% of hens never going outside. All hens were initially slow to use the range area with fewer novelty hens venturing farther onto the range (P ≤ 0.03). The structural hens had higher albumen corticosterone concentrations and variance (both P ≤ 0.004) prior to range access. All hens showed an increase in albumen corticosterone following the first week of range access resulting in no differences between rearing treatments in means (P = 0.92) and variance (P = 0.63). Different enrichments have differing impacts on ranging behavior, but further research is needed to understand the mechanisms of effects, with differences in brain lateralization a potential hypothesis to be tested.

In Australia, free-range egg production pullets are typically reared indoors, but adult layers get outdoor access. This new environment may be challenging to adapt to, which could impair egg production and/or egg quality. Adaptation might be enhanced through rearing enrichments. We reared 1386 Hy-Line Brown® chicks indoors with three treatments across 16 weeks: (1) a control group with standard litter housing conditions, (2) a novelty group providing novel objects that changed weekly, and (3) a structural enrichment group with custom-designed structures to partially impair visibility across the pen and allow for vertical movement. Pullets were transferred to a free-range system at 16 weeks of age with daily outdoor access provided from 25 until 64 weeks. Daily egg production at different laying locations (large nests, small nests and floor), weekly egg weights and egg abnormalities were recorded from 18 to 64 weeks old. External and internal egg quality parameters of egg weight, shell reflectivity, albumen height, haugh unit, yolk colour score, shell weight and shell thickness were measured at 44, 52, 60 and 64 weeks. There was a significant interaction between rearing treatment and nest box use on hen-day production from weeks 18 to 25 (P < 0.0001) with the novelty hens laying the most eggs and the control hens the fewest eggs in the nest box. Similarly, from 26 to 64 weeks, the novelty hens laid more eggs in the large nest boxes and fewer eggs on the floor than both the structural and control hens (P < 0.0001). Egg weight and abnormalities increased with age (P < 0.0001), but rearing treatment had no effect on either measure (both P ≥ 0.19). Rearing treatment affected shell reflectivity and yolk colour with the control hens showing paler colours across time relative to the changes observed in the eggs from enriched hens. The novelty hens may have established nest box laying patterns as they were more accustomed to exploring new environments. The differences in egg quality could be related to stress adaptability or ranging behaviour. This study shows that enriching environments during rearing can have some impacts on production parameters in free-range hens.

An egg injection study was conducted to confirm a proposed model of relative sensitivity of three avian species to 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD)-like chemicals. It was previously reported that the order of species sensitivity to in ovo exposure to TCDD, 2,3,4,7,8-pentachlorodibenzofuran (PeCDF), or 2,3,7,8-tetrachlorodibenzofuran (TCDF) at doses ranging from 0.044 to 37 picomoles (pmol)/g egg was the chicken (Gallus gallus domesticus), common pheasant (Phasianus colchicus), and Japanese quail (Coturnix japonica) based on embryo mortality and hepatic enzyme induction. In the present study, the incidence of developmental deformities, changes in body and relative organ masses, and organ pathology of hatchlings as additional indicators of species sensitivity were assessed; in addition, embryo mortality in the three species was categorized by stage of development. Embryo mortality varied temporally with significant increases generally occurring after organogenesis and just prior to hatching. A significant increase in the percentage of developmental deformities was observed only in Japanese quail exposed to TCDF. Body and relative organ masses of quail, pheasants, and chickens dosed in ovo with TCDD, PeCDF, or TCDF were not consistently affected. Chemical-related pathology occurred only in livers of quail at the greatest doses of each compound. These results indicated that the incidence of developmental deformities, changes in body and relative organ masses and organ pathology could not be used as indicators of species sensitivity or chemical potency.

Sunlight intensity and UV radiation may affect free-range hens' use of the outside range, particularly when sunlight is intense with a high UV index. However, it is uncertain what aspect of sunlight (brightness or UV) may be most aversive to hens to discourage them from leaving standard indoor lighting conditions to venture outdoors. A controlled indoor-based choice study was conducted to determine whether hens showed preferences for different light wavelengths and intensities that may affect outdoor range usage. Cage-reared ISA Brown laying hens (n = 84) at 44 wk of age in 3 groups (28 hens/group) were tested for preferences of indoor standard light emitting diode ( LED ) white light (control) vs. one of three different treatment lights: 1) visible spectrum plus infrared wavelengths (VIS); 2) visible spectrum plus UVA wavelengths (UVA); and (iii) visible spectrum plus UVA and UVB wavelengths (UVA/B) presented successively at low, medium, or high levels of intensity. Hens within each group were individually tested for 2 h in an apparatus with 2 compartments (control vs. treatment) connected by a tunnel on both sides. Videos of hens' time spent in each compartment and behaviors were decoded and analyzed using GLMM. Hens spent more time under the low intensity of the UVA/B light treatment (62%), the low intensity of VIS light (61%), medium intensities of both UVA/B light (60%), and UVA light (59%), and the high intensity of the VIS light (58%) when compared with control light (all P ≤ 0.05). Hens spent less time feeding under all intensities of UVA light (all P ≤ 0.03) and showed more foraging, ground pecking, and preening at lower levels of UVA/B light ( P < 0.05). The study suggests that UVA/B light (sunlight) may have positive effects for hen range use, but during peak sun intensities, hens may need additional measures (e.g., shelter) to protect themselves. Confirmation of these findings in a free-range setting is needed.