Impact of relative humidity on the laying performance, egg quality, and physiological stress responses of laying hens exposed to high ambient temperature

Growth resilience to weather variation in commercial free-ranging chickens in Ethiopia

BACKGROUND

The poultry industry in sub-Saharan Africa is a rapidly developing sector mostly based on smallholder farming. Increased demand for poultry-derived products, driven by the growing economy and population, has intensified importations of highly productive exotic breeds and crossbreeding with local ecotypes. However, commercial chickens with exotic genes often struggle to adapt to the local climate under smallholder farmers management. Understanding the chicken response to weather changes is crucial for developing selection schemes that ensure proper adaptation. In the present study, we derived individual phenotypes for growth resilience of commercial free-ranging chickens to changing weather conditions in Ethiopia. In addition, we performed genomic association analyses to assess the genetic background of these phenotypes and identify potential candidate genes of interest.

RESULTS

Novel resilience phenotypes describing changes in chicken growth profiles in response to weather fluctuation were developed. Variations in daily air temperature, relative humidity and amount of precipitation had the strongest impact on growth. Significant genomic variance was detected for growth resilience to changes in air temperature measurements and a temperature-humidity index. Genomic markers correlated with these resilience traits were mostly located within or near candidate genes associated with lipid metabolism and adipocyte homeostasis. Some of these genes have been previously linked to animal responses to environmental stressors in other species.

CONCLUSIONS

The phenotypes of growth resilience of chickens to changing weather conditions exhibited significant genomic variation. The outcomes of this study may facilitate the genomic selection of commercial chickens that are not only highly productive, but also capable of maintaining their production levels under varying weather conditions.

The mechanism of egg production improvement in laying hens before and after molting revealed by transcriptome and metabolome integration

The objective of this research was to examine the effects and underlying mechanisms of forced molting on the laying rate of hens. A total of ninety 500-day-old laying hens were randomly assigned to three groups: a control group (CK), a starvation group (SG), and a recovery group (RG). The study evaluated follicular development in hens and measured the expression levels of antioxidant, lipid, and inflammatory factors in their serum. Additionally, transcriptomic and metabolomic analyses were performed to assess the effects of forced molting on gene expression and metabolic profiles in hens. The findings indicated that forced molting led to an increase of laying rates, a reduction in follicular closure, and a significant rise in the levels of antioxidant enzymes such as GSH, CAT, and SOD, alongside a decrease in MDA levels. Furthermore, there were significant reductions in the blood lipid levels of LDL, HDL, TC, and TG. Additionally, there were notable differences in the inflammatory markers TNF-α, IL-1, and IL-6. The transcriptomic and metabolomic data revealed that forced molting influenced the activation of the PI3K-AKT and mTOR signaling pathways, affecting fatty acid metabolism in laying hens and modulating the expression of associated genes. In conclusion, this study demonstrates that forced molting is an effective strategy for enhancing the laying rate of hens. Furthermore, it provides a valuable theoretical framework for advancing breeding practices aimed at improving egg production.

Porcine Bile Acids Improve Antioxidant Status and Immune Function by Increasing Hungatella Abundance with Different Protein Level Diets in Late-Laying Hens

The modern livestock industry faces significant challenges due to the extension of production cycles and a growing shortage of feed resources. Low-protein (LP) diets offer potential environmental advantages whereas damage intestinal integrity and increase pro-inflammatory cytokines. Bile acids (BAs), metabolic products of cholesterol in the liver, possess strong antioxidative and immune properties. This study evaluated the effects of dietary porcine BA supplementation at different protein levels on the antioxidant status, immune function, and gut microbiota of late-laying hens. A 2 × 2 factorial design was employed with 198 Hy-Line Brown laying hens (62 weeks old), randomly divided into one of four treatment groups with 8 replicates for each treatment. Diets included normal (16.42%) or low-protein (15.35%) levels, with porcine BAs supplemented at 0 or 120 mg/kg (62-69 weeks) and 0 or 200 mg/kg (70-75 weeks) over 14 weeks. Dietary protein levels and bile acids had no effect on organ development in laying hens. Low-protein diets increased serum anti-inflammatory cytokines IL-4 and IL-10 but elevated pro-inflammatory cytokines IL-1β (p < 0.05), corroborated by higher IL-10 gene expression in the ileum mucosa (p < 0.05). The supplementation of bile acids improved immune function by increasing serum IL-4 and TGF-β while decreasing IL-6 levels (p < 0.05). Moreover, bile acids treatments upregulated IL-10, TGF-β and ZO-1 gene expression in the ileum mucosa (p < 0.05) and alleviated oxidative stress by enhancing serum GSH-Px activity (p < 0.05). Additionally, both low-protein diets and bile acids enriched beneficial cecal bacteria, including Hungatella and Blautia, primarily linked to immune function. These findings demonstrate that porcine bile acids administration improve antioxidant capacity, immune function and gut microbiota dysbiosis. These beneficial effects were associated with Hungatella and Blautia levels, which may be responsible for the porcine bile acids efficacy in poultry nutrition.

Effects of heat stress on growth performance, physiological responses, and carcass traits in broilers

High environmental temperatures lead to metabolic changes, body weight reduction, and high mortality in chickens, affecting poultry production worldwide. This study aimed to evaluate the effects of heat stress, assessed by the temperature-humidity index (THI), on the growth performance, physiological response, carcasses, and hematological traits of broilers. A total of 200 broilers (between 17 and 31 days old) were kept in thermoneutral conditions (21 °C; 60% relative humidity, RH) for 3 days during the adaptation period, followed by 14 days of exposure to the experimental treatments. The broilers were randomly assigned to 4 groups of equal size and raised in a temperature-humidity controlled chamber with THI ranging from 67 (21 °C; RH 60%) to 84 (33 °C; RH 60%). In boilers subjected to severe heat stress (THI 84), feed intake (-30%) and body weight gain (-51%) were decreased (P < 0.05) in comparison with the performance parameters of broilers under thermoneutral conditions (THI 67). Moreover, under heat stress, the respiration rate and rectal temperature significantly increased (P < 0.05), whereas blood parameters showed reduced levels of red blood cells, hemoglobin, white blood cells, lymphocytes, and electrolytes (K+, Na+). Regarding carcass traits, differences were observed in broilers exposed to severe heat stress, particularly in the reduction of the bursa of Fabricius as an immune organ growth index (P < 0.05). This study shows that severe heat stress, as revealed by the high THI levels, alters the physiological reactions and metabolic processes of broiler chickens, leading to negative effects on their growth.

The influence of relative humidity during the first 21 days post-hatch on the production performance, biochemical indices, and meat quality of Pekin ducks

This study aims to investigate the effects of different relative humidity (RH) during 4-21d of Beijing ducks on their condition at 42 d. A total of 48 Pekin duck were randomly allotted into 4 treatments (A:RH60 %, B:RH67 %,C:RH74 %,D:RH81 %), each having 3 replicates of 4 ducks. Different humidity treatments were applied from 4 to 21 days. At 42 d, there were no significant differences (P > 0.05) in body weight (BW), average daily gain (ADG), average daily feed intake (ADFI), and feed conversion ratio (FCR) among the 4 groups. Oblique body length in D was significantly higher than that in A (P < 0.05). Compared with A, the chest depth of the other groups was significantly increased, and the abdominal fat weight of B and C was significantly increased (p < 0.05). Liver weight and liver index in C and D significantly higher than that in B (p < 0.05). Abdominal fat ratio in B was significantly higher than that in A (P < 0.05). Cholesterol (CHOL) in D was significantly higher than that in A and C (P < 0.05), triglyceride (TG) in C was significantly higher than that in A and B (P < 0.05), and low-density lipoprotein cholesterol (LDL-C) in B was significantly higher than that in A, C, and D (P < 0.05). pH in B was significantly higher than that in A (P < 0.05), brightness (L*) in A was significantly higher than that in B and C (P < 0.05), redness (a*) in B and C was significantly higher than that in A and D (P < 0.05), and yellowness (b*) in C was significantly lower than that in A and D (P < 0.05).The results indicate that the RH of environment during the brooding period has no impact on duck production performance but induces some oxidative stress damage and changes in meat quality. Additionally, ducks subjected to different RH treatments during the brooding period exhibit varying adaptability to the same environment as they mature.

Predisposition factors and control strategies of avian pathogenic Escherichia coli in laying hens

Shift in laying hens housing from conventional cage-based systems to alternatives has impacted their health and performance. Microorganisms colonize young chick in the early stages of their physiological and immune development. These colonizing microbes originate from parent and the environment. Escherichia coli is among the normal gut colonizing bacteria however, some E. coli strains known as avian pathogenic E. coli (APEC), cause local or systemic infections (colibacillosis) responsible of significant economic losses to the poultry industry. Potential APEC strains and other poultry gut microbiota are influenced by several factors such as housing system, and the use of feed additives (prebiotics, probiotics, symbiotic, among others). This review will discuss the status of pullets and layers immunity, gut health, and predisposing factors of colibacillosis. Dietary interventions and some colibacillosis mitigation strategies in pullets and laying hens are reviewed and discussed. With the development of sequencing technologies and the use of feed additives as alternatives to antibiotics, future studies need to understand some of the complex associations between the feed additives, the rearing environment, and their selective pressure on gut microbiota, including E. coli, and their impacts on immune development in pullets and hens.

The Beneficial Application of Turmeric (Curcuma longa L.) on Health and Egg Production, in Layers: A Review

BACKGROUND

Turmeric (Curcuma longa L.) is a widely recognized spice and medicinal plant that has gained significant attention for its potential health benefits. This review aims to provide a comprehensive overview of the beneficial applications of turmeric in improving health and egg production in layers.

OBJECTIVE

The objective of this review is to assess the current scientific literature on the effects of turmeric supplementation in layer diets and evaluate its impact on layer health and egg production.

METHODS

A systematic search was conducted in Google Scholar database to identify relevant studies published in peer-reviewed journals. Studies investigating the effects of turmeric or its bioactive compound curcumin on layer health and egg production were included. Data on various parameters, including immune function, reproductive performance, egg quality and production parameters, were extracted and analysed.

RESULTS

Turmeric contains a bioactive compound called curcumin, which possesses antioxidant, anti-inflammatory, antimicrobial and immunomodulatory effects. These properties have been extensively studied and have shown promising results in enhancing layer health and performance. Turmeric supplementation has been reported to improve the overall immune response in layers, reducing the incidence and severity of infectious diseases. It has also been shown to have positive effects on gut health by modulating the gut microbiota composition, improving nutrient absorption and reducing digestive disorders. Furthermore, studies have demonstrated that turmeric supplementation in layer diets can improve egg weight, shell quality, yolk colour and egg production rates. The mechanisms underlying these effects involve the antioxidant properties of turmeric, which protect the reproductive organs, enhance ovarian function and improve reproductive performance.

CONCLUSION

The findings underscore the potential of turmeric as a natural, cost-effective and sustainable intervention for improving layer well-being, egg quality and productivity. However, further research is needed to fully understand the mechanisms of action, optimize dosage regimens and evaluate the long-term effects of turmeric supplementation in layer diets.

Study on the changing patterns of production performance of laying hens and their relationships with environmental factors in a large-scale henhouse

The production performance of laying hens is influenced by various environmental factors within the henhouse. The intricate interactions among these factors make the impact process highly complicated. The exact relationships between production performance and environmental variables are still not well understood. In this study, we measured the production performance of laying hens and various environmental variables across different parts of the henhouse, evaluated the weight of each environmental variable, and constructed a laying rate prediction model. Results displayed that body weight, laying rate, egg weight and eggshell thickness of hens decrease gradually from WCA to FA (P < 0.05). Serum levels of FSH and LH, as well as antibody level of H5 Re-13, gradually decrease from WCA to FA (P < 0.05). Moreover, the values for temperature (T), temperature-humidity index (THI), air velocity (AV), carbon dioxide (CO2), and particulate matter (PM2.5) gradually increase from WCA to FA (P < 0.05). Conversely, the relative humidity (RH) value gradually decreases from FA to WCA (P < 0.05). Additionally, the weights of the environmental variables, determined using a combination of the grey relational analysis (GRA) and analytic hierarchy process (AHP), were as follows in descending order: RH, THI, T, light intensity (LI), AV, PM2.5, NH3, and CO2. When the number of decision trees in the laying rate prediction model was set to 2,500, the results displayed a high level of agreement between the model's predictions and the observed outcomes. The model's performance evaluation yielded an R2 value of 0.89995 for the test set, suggesting strong predictive effects. In conclusion, the current study revealed significant differences in both the production performance of laying hens and the environmental variables across different parts of the henhouse. Furthermore, the study demonstrated that different environmental factors have distinct impacts on laying rate, with humidity and temperature identified as the primary factors. Finally, a multi-variable prediction model was constructed, exhibiting high accuracy in predicting laying rate.

Effects of relative humidity on physiology and behavior of laying hens exposed to high ambient temperatures

This study investigated how different relative humidity (RH) would impact behavior and physiology of laying hens. One hundred-eighty laying hens (Hy-Line Brown), aged 68-week-old (1,908 ± 78 g), were exposed to daily ambient temperatures of 30 °C with RH set at 25% (RH25), 50% (RH50), or 75% (RH75) for 12 h a day (9:00 am to 9:00 pm) from 70 to 74 weeks of age. All hens had been raised at 24 °C and 50% RH during 2-week adaptation period. Each RH treatment consisted of 10 replicates with 6 hens each in a completely randomized design. Results indicated that rectal temperature, respiratory rate, and heart rate were increased (P ≤ 0.05) in the RH75 group compared with the RH25 and RH50 groups. Plasma malondialdehyde concentrations were elevated in the RH75 group compared RH50 at 3, 7, and 21 days (P ≤ 0.05) following the RH exposure. Plasma glutathione peroxidase activity was lowered (P ≤ 0.05) in the RH75 group compared with the RH25 and RH50 groups at 21 days. Increasing RH led to decreased feeding behavior but showed a tendency to increase drinking behavior. Wings elevated and panting behaviors were higher in the RH75 group compared with the RH25 and RH50 groups (P ≤ 0.05). In conclusion, these findings suggest that elevated RH at constant ambient temperature could negatively influence the behavior and physiology of laying hens.

Research Note: Effects of high barn temperature on group-level dispersion and individual activity in broiler chickens

Heat stress in broilers is a pressing issue in the changing climate. Data on broiler behavior might be useful for early detection of heat stress and subsequent intervention, and may provide potential indicators for heat tolerance that can be used in broiler breeding programs. Here, we used bird location data collected in a previous study during which broilers were inadvertently exposed to high ambient temperatures due to a local heat wave. We examined whether broiler behavior changed with increasing ambient temperatures, focusing on group-level dispersion behavior and individual-level locomotor activity. We observed that birds moved closer together with increasing temperatures up to 9 °C above the desired level, and remained in similar proximity or moved further apart at temperatures above that threshold. The activity level decreased or remained stable with increasing temperature during most parts of the day, but increased at the end of the day. Possibly, the birds exhibited compensatory behavior (such as drinking and eating) during the periods when the barn cooled down after a hot day, but that could not be confirmed as no behavioral observations were available. The difference in activity levels between individuals accounted for 8.4% of the total variation, suggesting that activity might be an interesting indicator trait for heat tolerance in broiler chickens. Overall, the results of this study can inform the development of behavior-based 1) early-warning systems for heat stress and 2) heat tolerance indicators, although data on behaviors that are more specific to heat stress are probably required.

Using Thermal Signature to Evaluate Heat Stress Levels in Laying Hens with a Machine-Learning-Based Classifier

Infrared thermography has been investigated in recent studies to monitor body surface temperature and correlate it with animal welfare and performance factors. In this context, this study proposes the use of the thermal signature method as a feature extractor from the temperature matrix obtained from regions of the body surface of laying hens (face, eye, wattle, comb, leg, and foot) to enable the construction of a computational model for heat stress level classification. In an experiment conducted in climate-controlled chambers, 192 laying hens, 34 weeks old, from two different strains (Dekalb White and Dekalb Brown) were divided into groups and housed under conditions of heat stress (35 °C and 60% humidity) and thermal comfort (26 °C and 60% humidity). Weekly, individual thermal images of the hens were collected using a thermographic camera, along with their respective rectal temperatures. Surface temperatures of the six featherless image areas of the hens' bodies were cut out. Rectal temperature was used to label each infrared thermography data as "Danger" or "Normal", and five different classifier models (Random Forest, Random Tree, Multilayer Perceptron, K-Nearest Neighbors, and Logistic Regression) for rectal temperature class were generated using the respective thermal signatures. No differences between the strains were observed in the thermal signature of surface temperature and rectal temperature. It was evidenced that the rectal temperature and the thermal signature express heat stress and comfort conditions. The Random Forest model for the face area of the laying hen achieved the highest performance (89.0%). For the wattle area, a Random Forest model also demonstrated high performance (88.3%), indicating the significance of this area in strains where it is more developed. These findings validate the method of extracting characteristics from infrared thermography. When combined with machine learning, this method has proven promising for generating classifier models of thermal stress levels in laying hen production environments.

Spatial Distribution of Dermanyssus gallinae Infestations in Greece and Their Association with Ambient Temperature, Humidity, and Altitude

Dermanyssus gallinae, the poultry red mite (PRM), is the most prevalent and harmful ectoparasite of laying hens globally. Although prevalence and risk factor studies can help veterinarians make decisions regarding farm treatments, relevant data are scarce. The present study investigated the prevalence and infestation severity of PRM in poultry farms across Greece and examined potential risk factors. AviVet traps were used to sample 84 farms (51 backyard, 33 industrial) over three years. Farm altitude, temperature, humidity, region, and production systems were assessed as potential risk factors with chi-square tests, initially for all the studied farms and then exclusively for backyard farms. The overall prevalence was 75.0% and was higher in backyard farms (80.4%) compared with industrial ones (66.7%), varying regionally from 66.7 to 90.9%. Altitude and temperature were not significant risk factors, but farms with humidity <60% had a lower infestation risk. Infestation severity did not significantly differ by risk factors. The poultry red mite is highly prevalent across Greek poultry production systems and regions. In the future, global warming, reduced acaricide options, and a ban on cage systems will all threaten a wider spatio-temporal distribution of the PRM, justifying the urgent need for effective monitoring and control methods to protect hen production and welfare and workers' health.

Effects of Heat Stress on the Laying Performance, Egg Quality, and Physiological Response of Laying Hens

As high temperature and relative humidity (RH) are the main environmental factors causing heat stress, the temperature-humidity index (THI) serves as an indicator of heat stress in livestock animals. This study aimed to determine the effects of heat stress on the laying performance, physiological responses, egg quality, and blood profile of laying hens by subjecting them to environmental conditions with varying THI levels (68-85) for 28 days. The indicators of laying performance, such as feed intake (-30%) and egg production rate (-11%), significantly decreased in the hens exposed to severe heat stress (33 °C, 66% RH) compared to those exposed to thermoneutral conditions (21 °C, 68% RH). Moreover, severe heat stress reduced the egg yolk color, eggshell thickness and strength, and Haugh units of the eggs produced by the laying hens. Furthermore, a significant increase in serum K+ and a decrease in Na+ levels were observed in the hens subjected to severe heat stress compared with those under thermoneutral conditions. Our results indicate that heat stress alters the physiological responses and metabolism of laying hens, resulting in a lower egg quality and production rate.

Heat stress and poultry production: a comprehensive review

The impact of global warming on poultry production has gained significant attention over the years. However, our current knowledge and understanding of the mechanisms through which heat stress (HS) resulting from global warming affects the welfare, behavior, immune response, production performance, and even transgenerational effects in poultry are still incomplete. Further research is needed to delve deeper into these mechanisms to gain a comprehensive understanding. Numerous studies have investigated various biomarkers of stress in poultry, aiming to identify reliable markers that can accurately assess the physiological status and well-being of birds. However, there is a significant amount of variation and inconsistency in the results reported across different studies. This inconsistency highlights the need for more standardized methods and assays and a clearer understanding of the factors that influence these biomarkers in poultry. This review article specifically focuses on 3 main aspects: 1) the neuroendocrine and behavioral responses of poultry to HS, 2) the biomarkers of HS and 3) the impact of HS on poultry production that have been studied in poultry. By examining the neuroendocrine and behavioral changes exhibited by poultry under HS, we aim to gain insights into the physiological impact of elevated temperatures in poultry.

The Impact of Different Relative Humidity Levels on the Production Performance, Slaughter Performance, and Meat Quality of White Pekin Ducks Aged 4 to 42 Days

This study aimed to investigate the effects of different humidity levels on the growth performance, slaughter performance, and meat quality of Pekin ducks through the artificial control of humidity, and to identify the suitable environmental humidity for Pekin duck growth. A completely randomized single-factor design was employed, selecting 144 newly hatched male Pekin ducks with healthy and similar BW (body weight) (60.92 g ± 4.38). These ducks were randomly assigned to four groups (A (RH (relative humidity) = 60%), B (RH = 67%), C (RH = 74%), D (RH = 81%)), with 12 ducks and 3 replicates in each group. The ducks were raised in a climate-controlled room for 42 days with ad libitum access to feed and water. BW and feed intake were measured every 3 days, and slaughter performance and meat quality were assessed at 42 days. There was no significant difference in the ADG (average daily gain) from 1 to 21 days (p > 0.05). The ADFI (average daily feed intake) of Group D was significantly lower than that of Groups A, B, and C (p < 0.05), with no significant differences between Groups A, B, and C (p > 0.05). At 42 days, the BW, ADG, and ADFI of Groups A and C were significantly higher than those of Group D (p < 0.05), with no significant differences among Groups A, B, and C (p > 0.05). Group C had a significantly higher breast muscle weight, breast muscle ratio, liver weight, and liver index than Groups B and D (p < 0.05), with no significant differences between Groups A, B, and D (p > 0.05). The meat shear force in Group C was significantly lower than that in Groups A, B, and D (p < 0.05). The L* (brightness) of Group C was significantly lower than that of Group A (p < 0.05), and the a* (redness) value of Group C was significantly higher than that of Groups A and B (p < 0.05), with no significant difference compared to Group D (p > 0.05). Group B had a significantly higher cooking loss than Groups A, C, and D (p < 0.05), with no significant differences among Groups A, C, and D (p > 0.05). Under 26 °C conditions, Pekin ducks perform best in terms of the production performance and feed efficiency, with high-quality meat, especially when reared at 74% humidity.

Effects of dietary protein levels on performance, nitrogen excretion, and odor emission of growing pullets and laying hens

The objective of this study was to determine the effects of dietary crude protein (CP) levels on production performance, nitrogen balance, and odor emission of excreta in growing pullets and laying hens from 13 to 32 wk of age. Two hundred and forty pullets (Hy-Line Brown) were randomly assigned to 1 of 4 dietary groups with 10 replicates per group, and 6 birds per replicate. Experimental diets were formulated to contain 4 graded CP levels in the diets of pullets ranging from 180, 160, 140, and 120 g/kg of diet during 13 to 18 wk (phase 1) and in the diets of laying hens from 190, 170, 150, and 130 g/kg of diet during 19 to 32 wk (phase 2). The limiting amino acids including lysine, methionine, and threonine were supplemented to maintain constant equal amino acid concentrations in all experiment diets. In phase 1, decreasing dietary CP levels did not affect growth performance but increased (linear and quadratic effect, P < 0.05) the relative abdominal fat contents and triglyceride concentration in serum samples. High-density lipoprotein cholesterol in serum samples decreased as the CP levels decreased in the diets of pullets. Dietary CP levels quadratically increased (P < 0.05) the villus height and the villus height to crypt depth ratio but did not affect tibia traits and relative organ weights in pullets at 18 wk. Apparent digestibility of dry matter and ether extract increased with decreasing dietary CP levels in pullets. Graded CP levels linearly increased the digestibility of dry matter, CP, and ether extracts but lowered that of crude ash in laying hens. Nitrogen excretion was linearly decreased (P < 0.05) as the dietary CP levels decreased in both pullets and laying hens. Dietary CP levels only affected carbon dioxide emission in pullets. In phase 2, dietary CP levels did not affect growth performance and the ages at first egg laying and to reach 50% egg production in laying hens. However, egg weights were decreased (linear and quadratic effect, P < 0.05) as the dietary CP level decreased in laying hens. Increasing dietary CP levels increased Haugh unit at 26 wk but lowered corticosterone concentrations in yolk samples at 22 wk. Collectively, this study shows that dietary CP levels could be decreased to reduce nitrogen excretion without adverse effects on performance and egg quality of growing pullets and laying hens.

The genetic impact of heat stress on the egg production of Thai native chickens (Pradu Hang dum)

Sustainable poultry production in adverse weather conditions is a widely debated issue, which has led to research into the development of breeds of poultry that are genetically resistant to heat. This study aimed to investigate the effects of heat stress on the genetics of monthly egg production and examine the threshold point of heat stress for preventing thermal stress and its effects on chicken productivity. The data of 5,965 monthly egg production records of 629 Thai native Pradu Hang dum chickens were used for analysis in combination with the temperature-humidity index (THI) calculated by meteorological data near the testing station. The average THI throughout the year was 76.6, and the highest was 82. The THI data were subsequently used to find the threshold point of heat stress. The THI equation used in this study was chosen by its highest correlation (-0.306) between THI values and monthly egg production. At a THI of 74, the lowest -2 logL was found and was considered the threshold point of heat stress. This means that monthly egg production would start decreasing when the THI was 74. Heritability was 0.15±0.03, and genetic and permanent environmental correlations were -0.29 and -0.48, respectively. The threshold point was used to estimate the estimated breeding values (EBVs) of the monthly egg production and heat stress individually, and EBVs were calculated into the selection index. The selection index values when the animal was selected for the replacement herd for all chickens (top 50%, 30%, 20%, and 10%) were 0.14, 0.90, 1.27, 1.53, and 1.91, respectively, and the genetic progress was 0.55, 0.60, 0.68, 0.75, and 0.77, respectively. This shows that the selection index values are lower if there are many selected animals. The recommendation for animal genetic selection is that the top 10% is appropriately because it seems to be most preferred. Therefore, using a selection index for high egg production and heat tolerance in Thai native chickens is possible to achieve genetic assessment in a large population.

Tracking the dynamics of female germ cell development during peri-hatch periods using a gene-edited chicken model

In hens, egg production depends on the development of germ cells in the ovary. Germ cells are established before birth, and their number gradually decreases during their lifespan. Therefore, it is essential to determine the time points of massive germ cell loss and the underlying mechanism. In this study, a gene-edited chicken with mCherry fluorescence specifically expressed in the germline was generated by the integration of the mCherry gene into the 3'-end of the DAZL locus, which facilitated the isolation of germ cells from the gonads of DAZL-mCherry embryos or chicks and quantification using flow cytometry based on the observation of red fluorescence. The results demonstrated the dynamics of germ cell development from embryos at 17 d of hatching (dh) to chickens at 7 d post-hatch (dph) and revealed a substantial loss of germ cells in the late embryonic stage (18 -19 dh) and post-hatch period (2 -3 dph). Additionally, the number of germ cells in DAZL × Guangxi Ma chicken was significantly higher than that in DAZL × Lohmann Pink chicken at 19 dh and 3 dph (P < 0.05). Furthermore, the numbers of germ cells positively correlated with the body weight in DAZL × Lohmann Pink chicken. In conclusion, our results showed the dynamics of germ cell development in chicken ovaries during peri-hatch periods and indicated the time point of substantial germ cell loss. The results provide evidence for further exploration of the underlying mechanism and serve as a reference for chicken breeding and management.