Responses to heat stress in commercial and local broiler stocks. 2. Developmental stability of bilateral traits

Effect of different pasture species on welfare and behavior of slow-growing broiler chickens in free-range production system

This study investigated the effect of various pasture species on the welfare and behavior of slow-growing broiler chickens in the free-range production system. After 21 days completely indoors, the birds were permitted access to outdoor pens cultivated with one of the following pasture treatments: Medicago sativa (A), Trifolium repens (WC), Lolium perenne (PR), and a mixture (Mix, A + WC + PR). The range availability was restricted between 08:30 and 16:30 daily. It was found that pasture type had a significant effect on the fluctuating asymmetry of the face and radius length (P < 0.01). Duration of tonic immobility and blood parameters did not differ among the pasture species and between sexes at 11 weeks of broiler age (P > 0.05). Pasture treatment had no significant effect on broiler behaviors (P > 0.05). However, the age of broilers had a significant effect on pecking, dustbathing, and scratching (P < 0.01). Pecking behavior was affected by the time of the day; morning and afternoon (P < 0.01). Location had a significant effect on pecking and stretching behaviors (P < 0.01). In the study, dustbathing behavior was significantly affected by the interaction between location and age (P < 0.01), age and time of the day (P < 0.01), and location, age, and time of the day (P < 0.05). Scratching behavior was significantly affected by the interaction between location and time of the day (P < 0.05) and location, age and time of the day (P < 0.01). Stretching behavior was significantly affected by the interaction between location and age (P < 0.05) and location, age and time of the day (P < 0.05). It was concluded that access to the studied pasture species does not affect the evaluated welfare traits and observed behaviors. Therefore, it is suggested that other pasture species should be investigated to identify their effect on slow-growing strains in the free-range production system.

In ovo nano-silver and nutrient supplementation improves immunity and resistance against Newcastle disease virus challenge in broiler chickens

Silver nanoparticles (AgNPs) interact with the microbes and host immune system to protect against diseases. Fertile broiler eggs (n = 900) were allotted to six groups: un-injected control, sham (sterile water), AgNPs (50 μg), AgNPs+Amino acids (Methionine-10 mg + Arginine-25 mg), AgNPs+Vitamins (Vit B1-72μg + Vit B6-140μg), and AgNPs+Trace Elements (Zn-80 μg and Se-0.3 μg) and incubated for 18 days. On 18th embryonic day, 0.6 ml test solution was injected at the broad end of egg using 25 mm needle and transferred to hatcher. Post-hatch, half of the chicks from each group were vaccinated with Newcastle disease (ND) vaccine, and the other half were kept as unvaccinated unit and reared for 42 d with standard management practices. Hatchability, 1st and 42nd d body weight, feed intake, and feed conversion ratio were similar between treatment groups in both vaccinated and unvaccinated units. The relative weight of bursa Fabricius and thymus was similar, but spleen weight was higher (P ≤ 0.05) in AgNPs, AgNPs+Vits, and AgNPs+TEs chicks than control group. Cellular immune response (against mitogen phytohemagglutinin-P) was higher (P ≤ 0.05) in AgNPs+TEs chicks, whereas HA titer against sheep red blood cells antigen, serum IgG, IgM, and HI titer against ND vaccine was apparently higher in AgNPs+Vits group chicks than control. No clinical symptoms were observed in the vaccinated groups except for a few control birds 6 days postchallenge (PC). Three days PC, unvaccinated birds show depression, off feed, greenish diarrhea, and nasal discharge and the control group started dying. The highest cumulative infection (CI) was observed in sham (79.17%) and un-injected control (75%), but lowest in AgNPs+AAs birds (58.33%) on 3rd dpi. The CI reached 100% on 5th dpi in control groups and AgNPs, and 91.67% and 93.75% in AgNPs+TEs and AgNPs+AAs group, respectively. The AgNPs+TEs and AgNPs+AAs group birds lived for more than 90 h compared to 75 h in control groups and also had higher IL-6 and IL-2 gene expressions at 24 h PC. It was concluded that 50 μg/egg AgNPs with vitamins (B1 and B6) and trace elements (Zn and Se) improved performance, but AgNPs with trace elements and amino acids enhanced immune response and resistance against vND virus challenge in broilers.

Transcriptome responses to heat stress in hypothalamus of a meat-type chicken

Background

Heat stress has resulted in great losses in poultry production. To address this issue, we systematically analyzed chicken hypothalamus transcriptome responses to thermal stress using a 44 k chicken Agilent microarray,

Methods

Hypothalamus samples were collected from a control group reared at 25°C, a heat-stress group treated at 34°C for 24 h, and a temperature-recovery group reared at 25°C for 24 h following a heat-stress treatment. We compared the expression profiles between each pair of the three groups using microarray data.

Results

A total of 1,967 probe sets were found to be differentially expressed in the three comparisons with P < 0.05 and a fold change (FC) higher than 1.5, and the genes were mainly involved in self-regulation and compensation required to maintain homeostasis. Consistent expression results were found for 11 selected genes by quantitative real-time PCR. Thirty-eight interesting differential expression genes were found from GO term annotation and those genes were related to meat quality, growth, and crucial enzymes. Using these genes for genetic network analysis, we obtained three genetic networks. Moreover, the transcripts of heat-shock protein, including Hsp 40 and Hsp 90, were significantly altered in response to thermal stress.

Conclusions

This study provides a broader understanding of molecular mechanisms underlying stress response in chickens and discovery of novel genes that are regulated in a specific thermal-stress manner.

Electronic supplementary material

The online version of this article (doi:10.1186/s40104-015-0003-6) contains supplementary material, which is available to authorized users.

The influence of stocking density on broiler chicken bone quality and fluctuating asymmetry

Because broiler chickens are juvenile animals undergoing physical development, stocking density during rearing may influence this development. Some of these physical changes may cause welfare problems, for example, decreased bone quality, which may lead to fracture during catching and transport. Others do not influence welfare directly but can be used as indicators of the animal's ability to cope with its environment (e.g., fluctuating asymmetry). The present study evaluates the effect of stocking density on bone quality and fluctuating asymmetry. Birds were stocked at densities of 2.4, 5.8, 8.8, 12.1, 13.6, 15.5, 18.5, and 21.8 birds/m(2) from 1 until 39 d of age. Increased stocking density had a negative effect on some aspects of bone quality (tibia curvature and shear strength). Tibias were shorter at high density, possibly due to increased curvature. Several other bone quality aspects (tibia weight, torsion, and dyschondroplasia, and femur curvature and epiphysis shape) remained unaffected. Middle-toe length was the only character that showed a significant increase with increasing density when each character was analyzed separately. Nevertheless, a composite index of fluctuating asymmetry, which combined data on all 11 measured characters, tended to increase with stocking density. Such increased fluctuating asymmetry may indicate decreased welfare. However, one of the assumptions of fluctuating asymmetry is that the animal is subjected to the same environmental influences on both sides. This assumption may not be fulfilled when leg deformations occur, as these may lead to asymmetric changes in bone growth by altering the division of force over the 2 legs. In addition, leg deformations decrease the accuracy of bone length measurements made in a straight line. This raises some concerns on the applicability of fluctuating asymmetry measurements on broiler chicken legs, especially because stocking density did not effect the asymmetry of the head.

Pre- and postnatal conditioning induced thermotolerance on body weight, physiological responses and relative asymmetry of broilers originating from young and old breeder flocks

The present experiment was conducted to examine the effects of pre- and postnatal conditioning to induce thermotolerance in broilers hatching from eggs orginating from younger and older breeder flocks. From each flock, 500 eggs were randomly divided into 2 groups and incubated at standard (SIT) and high (HIT) temperatures. At hatch, chicks were allotted to 36 floor pens. At 5 d of age 3 pens per parent age per incubation temperature were heat conditioned (C) for 24 h. At 21 d of age, 3 pens per parent age per incubation temperature were kept under standard (S) rearing temperatures, whereas the remaining broilers (including C) were moved to a heated room (H). Thus, there were 3 groups from 21 to 49 d including S, H, and C+H. The results indicated that to incubate eggs from younger parents at HIT before conditioning at 5 d may reduce deleterious effects of heat stress on body weight at slaughter age. However, HIT temperature decreased slaughter weight of broilers from older parents regardless of rearing temperature. Although conditioning did not prevent increments in rectal temperatures of broilers after 1 wk of heat stress (28 d), adaptation occurred thereafter for broilers from younger parents but not for broilers from older parents. Incubation temperature had no effect on plasma glucose, creatine kinase, uric acid, or triiodotryronine (T3) levels at d 21. There were no differences at 22, 25, or 28 d for T3 concentrations between the H and C+H groups. Overall relative asymmetry was not influenced by treatments on d 49. The results suggest that although pre- and postnatal conditioning may help broilers cope with heat stress, age of parent plays a major role in the ability of broilers to thermoregulate. This is especially the case for broilers originating from younger parents.

Measures of Developmental Instability as Integrated, A Posteriori Indicators of Farm Animal Welfare: A Review

Developmental instability, of which fluctuating asymmetry is the most commonly used and recommended measure, has recently been claimed to be an objective, integrated and retrospective indicator of animal welfare. The theoretical and empirical grounds for these claims are reviewed. In theory, carefully selected composite indices of fluctuating asymmetry are valid indicators of animal welfare in the sense that they reflect the ability of the developmental processes of an animal, with a given genetic constitution, to cope with environmental stressors. Relevant scientific experiments are scant and are mainly restricted to poultry, but they are on the increase and they largely support the application of developmental instability for assessing animal welfare. A scheme for monitoring farm animal welfare based purely on measures of developmental instability would have important advantages, but cannot be recommended yet. It cannot be ruled out that certain factors are clearly relevant to the welfare status of an animal but do not notably/proportionally affect its morphogenesis. Moreover, such a monitoring scheme would not be appropriate for applications with an emphasis on problem analysis/management.

Growth and developmental instability

Developmental stability reflects the ability of an individual to develop a regular phenotype under given environmental and genetic conditions. Measures of developmental instability include the degree of fluctuating asymmetry and the frequency of phenodeviants. Endocrine, neural and circulatory mechanisms that control similar development of morphological characters on the two sides of the body are also involved in controlling overall development. Cross-validation studies have shown that measures of developmental instability are positively correlated with other measures of welfare such as tonic immobility in poultry. Asymmetric animals grow less rapidly than symmetric individuals. Eleven studies have investigated the relationship between growth rate and developmental instability, and the observed effect size (Pearson correlation coefficient adjusted for sample size) is -0.15. Studies of chickens have shown that asymmetry increases as a response to selection for increased growth rate. As conditions for rearing deteriorate by higher density, fluctuating asymmetry increases and growth rate decreases, both within and among farms. Fluctuating asymmetry can be considered a measure of animal welfare since larger values reflect worse environmental conditions as experienced by the individual animal itself. Since growth rate and fluctuating asymmetry are negatively correlated, we can infer that improvement of rearing conditions leading to reduced asymmetry will both benefit the producer (in terms of increased growth), but also the animals in terms of better conditions for rearing.