Density of Contour Feathers and Heat Tolerance in Chickens

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.

Emerging Genetic Tools to Investigate Molecular Pathways Related to Heat Stress in Chickens: A Review

Simple Summary

New genomic tools have been used as an instrument in order to assess the molecular pathway involved in heat stress resistance. Local chicken breeds have a better attitude to face heat stress. This review aims to summarize studies linked to chickens, heat stress, and heat shock protein.

Abstract

Chicken products are the most consumed animal-sourced foods at a global level across greatly diverse cultures, traditions, and religions. The consumption of chicken meat has increased rapidly in the past few decades and chicken meat is the main animal protein source in developing countries. Heat stress is one of the environmental factors which decreases the productive performance of poultry and meat quality. Heat stress produces the over-expression of heat shock factors and heat shock proteins in chicken tissues. Heat shock proteins regulate several molecular pathways in cells in response to stress conditions, changing the homeostasis of cells and tissues. These changes can affect the physiology of the tissue and hence the production ability of chickens. Indeed, commercial chicken strains can reach a high production level, but their body metabolism, being comparatively accelerated, has poor thermoregulation. In contrast, native backyard chickens are more adapted to the environments in which they live, with a robustness that allows them to survive and reproduce constantly. In the past few years, new molecular tools have been developed, such as RNA-Seq, Single Nucleotide Polymorphisms (SNPs), and bioinformatics approaches such as Genome-Wide Association Study (GWAS). Based on these genetic tools, many studies have detected the main pathways involved in cellular response mechanisms. In this context, it is necessary to clarify all the genetic and molecular mechanisms involved in heat stress response. Hence, this paper aims to review the ability of the new generation of genetic tools to clarify the molecular pathways associated with heat stress in chickens, offering new perspectives for the use of these findings in the animal breeding field.

Genetic architecture related to contour feathers density in an F2 resource population via a genome-wide association study

The density of contour feathers is an important trait as it is closely related to heat dissipation in birds. Thus, identification of the major genes that control this trait will be useful to improve heat tolerance in chicken. So far, no GWAS study for the density of contour feathers in birds has been previously published; therefore, this study was aimed to identify genomic regions controlling the density of contour feathers. A total of 1252 hens were genotyped, using the 600 K Affymetrix Axiom Chicken Genotyping Array. The association analyses were performed using the GenABEL package in the R program. In brief, 146 significant SNP markers were mainly located on chromosome 1 and were identified to associate with the density of contour feathers in the current GWAS analysis. Moreover, we identified several within/nearby candidate genes (SUCLA2, DNAJC15, DHRS12, MLNR, and RB1) that are either directly or indirectly involved in the genetic control of the density of contour feathers in chicken. This study laid the foundation for studying the mechanism that underlies the density of chicken feathers. Furthermore, it is feasible to shear the back feathers of live chickens and measure the density of the feathers to improve heat tolerance in breeding practice.

Rectal temperature as an indicator for heat tolerance in chickens

High environmental temperature is perhaps the most important inhibiting factor to poultry production in hot regions. The objective of this study was to test adaptive responses of chickens to high ambient temperatures and identify suitable indicators for selection of heat-tolerant individuals. Full-sib or half-sib Anak-40 pullets (n = 55) with similar body weights were raised in a room with a temperature ranging from 24°C to 28°C, and relative humidity of 50% from 61 to 65 days of age. On day 66, the ambient temperature was increased within 60 min to 35 ± 1°C which was defined as the initial of heat stress (0 h). Rectal temperature (RT) was measured on each pullet at 0, 6, 18, 30, 42, 54 and 66 h. After 66 h the ambient temperature was increased within 30 min to 41 ± 1°C and survival time (HSST) as well as lethal rectal temperatures (LRT) were recorded for each individual. The gap between the RT and initial RT was calculated as ΔTn (ΔT6, ΔT18, ΔT30, ΔT42, ΔT54 and ΔT66), and the interval between LRT and initial RT as ΔTT, respectively. A negative correlation was found between HSST and ΔTn as well as ΔTT (rΔ T 18  = -0.28 and rΔ TT  = -0.31, respectively, P < 0.05; rΔT30  = -0.36, rΔ T 42  = -0.38, rΔT54  = -0.56, P < 0.01). Importantly, pullets with low ΔT18 showed a longer HSST (256.0 ± 208.4 min) than those with high ΔT18 (HSST = 123.7 ± 78.3 min). This observation suggested that the ΔT18 or early increment of RT under heat stress might be considered as a reliable indicator for evaluation of heat resistance in chickens.