Behavioral responses of neonatal chicks exposed to low environmental temperature

Impact of increased pre-start diet density on broiler chick behavior, corticosterone levels, and performance responses under cold stress during early life

This study assessed the effects of increased pre-start diet density on the metabolism, crop filling, and overall performance of broilers under cold stress during their initial 14 days of life. Using 576 one-day-old Cobb500 male chicks from 27-week-old breeders, the experiment employed a 2 × 2 arrangement, varying thermal conditions (thermoneutrality or cold stress at 18 °C for 8 h) and pre-start diet composition (21.5% crude protein, 2970 kcal/kg or 22.5%, 3050 kcal/kg). The cold stress group exhibited lower cloacal temperature and decreased crop filling rate during the first two days (P < 0.05). Chick behavior was significantly affected at 1 and 5 days (P < 0.05), and corticosterone levels in serum were higher for the cold stress group at 7 days (P < 0.05). Feed intake at 7 days was lower in the high-density feed group (P < 0.05). No significant interactions were observed for feed intake, body weight gain, or feed conversion ratio at 7 and 35 days (P > 0.05). Cold stress resulted in performance losses, impacting feed conversion and the Productive Efficiency Index. The dense diet influenced performance only within the first week, with subsequent diets showing no effect, suggesting dietary manipulation alone was insufficient to mitigate cold stress-induced losses.

Unpredictable chronic mild stress shows neuronal remodeling in multipolar projection neurons of hippocampal complex in postnatal chicks

The hippocampal complex of birds is a narrow-curved strip of tissue that plays a crucial role in learning, memory, spatial navigation, and emotional and sexual behavior. This study was conducted to evaluate the effect of unpredictable chronic mild stress in multipolar neurons of 3-, 5-, 7-, and 9-week-old chick's hippocampal complex. This study revealed that chronic stress results in neuronal remodeling by causing alterations in dendritic field, axonal length, secondary branching, corrected spine number, and dendritic branching at 25, 50, 75, and 100 µm. Due to stress, the overall dendritic length was significantly retracted in 3-week-old chick, whereas no significant difference was observed in 5- and 7-week-old chick, but again it was significantly retracted in 9-week-old chick along with the axonal length. So, this study indicates that during initial days of stress exposure, the dendritic field shows retraction, but when the stress continues up to a certain level, the neurons undergo structural modifications so that chicks adapt and survive in stressful conditions. The repeated exposure to chronic stress for longer duration leads to the neuronal structural disruption by retraction in the dendritic length as well as axonal length. Another characteristic which leads to structural alterations is the dendritic spines which significantly decreased in all age groups of stressed chicks and eventually leads to less synaptic connections, disturbance in physiology, and neurology, which affects the learning, memory, and coping ability of an individual.

TRPM8-dependent shaking in mammals and birds

Removing water from wet fur or feathers is important for thermoregulation in warm-blooded animals. The "wet dog shake" (WDS) behavior has been largely characterized in mammals but to a much lesser extent in birds. Although it is known that TRPM8 is the main molecular transducer of low temperature in mammals, it is not clear if wetness-induced shaking in furred and feathered animals is dependent on TRPM8. Here, we show that a novel TRPM8 agonist induces WDS in rodents and, importantly, in birds, similar to the shaking behavior evoked by water-spraying. Furthermore, the WDS onset depends on TRPM8, as we show in water-sprayed mice. Overall, our results provide multiple evidence for a TRPM8 dependence of WDS behaviors in all tested species. These suggest that a convergent evolution selected similar shaking behaviors to expel water from fur and feathers, with TRPM8 being involved in wetness sensing in both mammals and birds.

Effects of cold stress on physiologic metabolism in the initial phase and performance of broiler rearing

This study aimed to investigate the effects of 8 h of cold stress (18 °C) every day in broiler chicks during the first 7 days of rearing on crop filling analysis, yolk sac consumption, digestive and immune organs weights, and physiological metabolism at seven days and performance between 1 and 35 days. Cobb500 male broiler chickens (n = 274) were randomly assigned to two treatments. The treatments consisted of varying environmental temperatures during the first week post-housing. Chicks were reared at a thermoneutral temperature (32 °C) or under cold stress (18 °C) for 8 h/day during the first week, and both groups were subsequently reared at a thermoneutral temperature for 8-35 days. The thermoneutral group reached 90% full crop after 48 h of housing (P < 0.05), while the cold-stressed group had more empty crops at 2 h and 48 h after housing (P < 0.05). The chick cloacal temperature was not affected by the treatments (P > 0.05). Additionally, the treatment did not affect serum amylase and corticosterone levels, feed intake, body weight gain, or feed conversion ratio (P > 0.05, while the cold-stressed group had elevated heterophil/lymphocyte count at day 7 (P < 0.05). The thermoneutral group showed higher viability (%) at 7 and 35 days and a higher production factor at 35 days (P < 0.05). Broiler chickens under cyclic cold stress experienced decreased yolk sac absorption during the first week and increased feed intake and feed conversion ratio after 35 days of rearing. Viability was also lower in the cold-stressed group. An appropriate strategy to minimize these adverse effects is to rear the chicks in a thermoneutral environment during the first week.

Welfare of broilers on farm

This Scientific Opinion considers the welfare of domestic fowl (Gallus gallus) related to the production of meat (broilers) and includes the keeping of day-old chicks, broiler breeders, and broiler chickens. Currently used husbandry systems in the EU are described. Overall, 19 highly relevant welfare consequences (WCs) were identified based on severity, duration and frequency of occurrence: 'bone lesions', 'cold stress', 'gastro-enteric disorders', 'group stress', 'handling stress', 'heat stress', 'isolation stress', 'inability to perform comfort behaviour', 'inability to perform exploratory or foraging behaviour', 'inability to avoid unwanted sexual behaviour', 'locomotory disorders', 'prolonged hunger', 'prolonged thirst', 'predation stress', 'restriction of movement', 'resting problems', 'sensory under- and overstimulation', 'soft tissue and integument damage' and 'umbilical disorders'. These WCs and their animal-based measures (ABMs) that can identify them are described in detail. A variety of hazards related to the different husbandry systems were identified as well as ABMs for assessing the different WCs. Measures to prevent or correct the hazards and/or mitigate each of the WCs are listed. Recommendations are provided on quantitative or qualitative criteria to answer specific questions on the welfare of broilers and related to genetic selection, temperature, feed and water restriction, use of cages, light, air quality and mutilations in breeders such as beak trimming, de-toeing and comb dubbing. In addition, minimal requirements (e.g. stocking density, group size, nests, provision of litter, perches and platforms, drinkers and feeders, of covered veranda and outdoor range) for an enclosure for keeping broiler chickens (fast-growing, slower-growing and broiler breeders) are recommended. Finally, 'total mortality', 'wounds', 'carcass condemnation' and 'footpad dermatitis' are proposed as indicators for monitoring at slaughter the welfare of broilers on-farm.

Welfare of domestic birds and rabbits transported in containers

This opinion, produced upon a request from the European Commission, focuses on transport of domestic birds and rabbits in containers (e.g. any crate, box, receptacle or other rigid structure used for the transport of animals, but not the means of transport itself). It describes and assesses current transport practices in the EU, based on data from literature, Member States and expert opinion. The species and categories of domestic birds assessed were mainly chickens for meat (broilers), end-of-lay hens and day-old chicks. They included to a lesser extent pullets, turkeys, ducks, geese, quails and game birds, due to limited scientific evidence. The opinion focuses on road transport to slaughterhouses or to production sites. For day-old chicks, air transport is also addressed. The relevant stages of transport considered are preparation, loading, journey, arrival and uncrating. Welfare consequences associated with current transport practices were identified for each stage. For loading and uncrating, the highly relevant welfare consequences identified are handling stress, injuries, restriction of movement and sensory overstimulation. For the journey and arrival, injuries, restriction of movement, sensory overstimulation, motion stress, heat stress, cold stress, prolonged hunger and prolonged thirst are identified as highly relevant. For each welfare consequence, animal-based measures (ABMs) and hazards were identified and assessed, and both preventive and corrective or mitigative measures proposed. Recommendations on quantitative criteria to prevent or mitigate welfare consequences are provided for microclimatic conditions, space allowances and journey times for all categories of animals, where scientific evidence and expert opinion support such outcomes.

Environmental Stress in Chickens and the Potential Effectiveness of Dietary Vitamin Supplementation

Environmental stressors can promote the vulnerability of animals to infections; it is therefore, essential to understand how stressors affect the immune system, the adaptive capacity of animals to respond, and effective techniques in managing stress. This review highlights scientific evidence regarding environmental stress challenge models and the potential effectiveness of vitamin supplementation. The major environmental stressors discussed are heat and cold stress, feed restriction, stocking density, and pollutants. Much work has been done to identify the effects of environmental stress in broilers and layers, while few involved other types of poultry. Studies indicated that chickens' performance, health, and welfare are compromised when challenged with environmental stress. These stressors result in physiological alterations, behavioral changes, decreased egg and meat quality, tissue and intestinal damage, and high mortalities. The application of vitamins with other nutritional approaches can help in combating these environmental stressors in chickens. Poultry birds do not synthesize sufficient vitamins during stressful periods. It is therefore suggested that chicken diets are supplemented with vitamins when subjected to environmental stress. Combination of vitamins are considered more efficient than the use of individual vitamins in alleviating environmental stress in chickens.

Decision Trees for Predicting the Physiological Responses of Rabbits

Simple Summary

The primary aim of this paper is to develop decision trees to predict rabbits’ physiological responses, such as the respiratory rate or ear temperature, based on environmental variables (dry bulb temperature and relative humidity). The decision tree for ear temperature exhibited better statistical indices, indicating the benefits of using the ear temperature as an indicator of thermal stress. Our findings confirm that the resulting decision trees are powerful classifiers, and the results can be easily understood. Hence, the proposed decisions trees can aid in investigating the influence of environmental conditions on physiological responses and, consequently, the rabbits’ welfare. These results can be used in practical situations and can be obtained in real time to support rabbit breeders in decision-making to improve environmental conditions for rabbits.

Abstract

The thermal environment inside a rabbit house affects the physiological responses and consequently the production of the animals. Thus, models are needed to assist rabbit producers in decision-making to maintain the production environment within the zone of thermoneutrality for the animals. The aim of this paper is to develop decision trees to predict the physiological responses of rabbits based on environmental variables. The experiment was performed in a rabbit house with 26 rabbits at eight weeks of age. The experimental database is composed of 546 observed data points. Sixty decision tree models for the prediction of respiratory rate (RR, mov.min⁻¹) and ear temperature (ET, °C) of rabbits exposed to different combinations of dry bulb temperature (t_db, °C) and relative humidity (RH, %) were developed. The ET model exhibited better statistical indices than the RR model. The developed decision trees can be used in practical situations to provide a rapid evaluation of rabbit welfare conditions based on environmental variables and physiological responses. This information can be obtained in real time and may help rabbit breeders in decision-making to provide satisfactory environmental conditions for rabbits.

Impact of exposure time to harsh environments on physiology, mortality, and thermal comfort of day-old chickens in a simulated condition of transport

The aim of this study was to assess the variation of physiological responses and mortality of day-old chicks subjected to different thermal conditions and exposure times during simulated transport. For this purpose, day-old chicks (n = 900) were used and subjected to simulated conditions of transport in a climate chamber. The experimental design was a completely randomized block design, with the structure of the treatments in a 3 × 3 factorial scheme (thermal ranges and time intervals) and each level of containers considered a block. The physiological variables used in this trial were body weight, respiratory rate, cloacal temperature, average surface temperature, and gene expression of heat shock protein (HSP70). Regarding body weight, a small variation was observed between treatments (P > 0.05). The animals subjected to the heat treatment exhibited respiratory rates above 100 movements per minute (P < 0.05), average cloacal temperatures above 44.7 °C, surface temperatures above the comfort zone (greater than 39.6 °C; P < 0.05), and increased gene expression of HSP70 (P < 0.001), especially after 3 initial hours of exposure. In addition, the heat treatment lead to increased mortality of the animals (over 6%). Also in the cold treatment, despite the absence of mortality, the animals showed hypothermia from 3 h of exposure, based on the results of the average surface (28 °C) and cloacal temperatures (39.6 °C; P < 0.05). In this way, the results imply that the effects of thermal stress caused by heat as well as by cold in a simulated transport condition are increased when traveling for more than 3 h, indicating a trend of rising mortality after long-term transportation of day-old chickens.

Environmental complexity: A buffer against stress in the domestic chick

Birds kept in commercial production systems can be exposed to multiple stressors from early life and this alters the development of different morphological, immunological and behavioural indicators. We explore the hypothesis that provision of a complex environment during early life, better prepares birds to cope with stressful events as well as buffers them against future unpredictable stressful episodes. In this study, 96 one day old pullets were randomly distributed in eight pens (12 birds/pen). Half of the chicks (N = 48) were assigned to a Complex Environment (CENV: with perches, a dark brooder etc.) the others to a Simple Environment (SENV: without enrichment features). Half of the birds from each of these treatments were assigned to a No Stress (NSTR, 33°C) or to an acute Cold Stress (CSTR, 18–20°C) treatment during six hours on their second day of life. At four weeks of age, chicks with these four different backgrounds were exposed to an Intermittent Stressful Challenges Protocol (ISCP). In an immunological test indicative of pro-inflammatory status Phytohemagglutinin-P (PHA-P), the response of CSTR birds was ameliorated by rearing chicks in a CENV as they had a similar response to NSTR chicks and a significantly better pro-inflammatory response than those CSTR birds reared in a SENV (five days after the CSTR treatment was applied). A similar better response when coping with new challenges (the ISCP) was observed in birds reared in a CENV compared to those from a SENV. Birds reared in the CENV had a lower heterophil/lymphocyte ratio after the ISCP than birds reared in SENV, independently of whether or not they had been exposed to CSTR early in life. No effects of stress on general behaviour were detected, however, the provision of a CENV increased resting behaviour, which may have favoured stress recover. Additionally, we found that exposure to cold stress at an early age might have rendered birds more vulnerable to future stressful events. CSTR birds had lower humoral immune responses (sheep red blood cells induced antibodies) after the ISCP and started using elevated structures in the CENV later compared to their NSTR conspecifics. Our study reflects the importance of the early provision of a CENV in commercial conditions to reduce negative stress-related effects. Within the context of the theory of adaptive plasticity, our results suggest that the early experience of the birds had long lasting effects on the modulation of their phenotypes.

Melatonin modulates tonic immobility and vigilance behavioural responses of broiler chickens to lighting regimens during the hot-dry season

Experiments were conducted with the aim of determining the influence of melatonin administration on vigilance and tonic immobility (TI) responses of Marshall broiler chickens. The broiler chickens were reared on different lighting regimens and subjected to heat stress during the hot-dry season. Simple random sampling was used to assign 300 broiler chicks into three groups, comprising 100 broiler chicks each. Group I (12D:12L cycle) was raised under natural photoperiod of 12-h light and 12-h darkness, without melatonin supplementation. Group II (CL) was kept under 24-h continuous lighting, without melatonin administration. Group III (CL+MEL) was raised under 24-h continuous lighting; with melatonin supplementation at 0.5mg/kg per os, via drinking water using a syringe. Beginning from day-old, broiler chickens in group III were individually administered with melatonin once daily for 8weeks at 17:00h. TI was induced by manual restraint, and vigilance elicited at self-righting graded for three days, two weeks apart, in 15 labeled broiler chickens from each of the three groups; at 06:00h, 13:00h and 18:00h, starting from week 4-8. Each broiler chicken was laid on its back in a U-shaped cradle, covered with cloth. Thermal microenvironment parameters of dry bulb temperature (DBT) and relative humidity (RH) were recorded at the experimental site, concurrently during the vigilance and TI tests. Inside the broiler chickens' house, the weekly temperature-humidity index (THI) was lowest at week 4 of the study, with the value of 48.60±0.08°C. At week 4, the relationship between the THI and TI induction attempts was stronger in 12D:12L cycle (r=0.589, P<0.001) than CL (r=0.264, P>0.05) or CL+MEL (r=0.096, P>0.05) broiler chickens. This indicated that the broiler chickens on 12D:12L cycle were more active compared to their melatonin-treated counterparts, apparently due to adverse effects of high DBT and high RH on the broiler chickens during the hot-dry season. The highest numbers of TI induction trial attempts were recorded at 13:00h in 12D:12L cycle and CL groups (2.13±0.34 and 2.15±0.22, respectively), when the broiler chickens were at week 8. The overall mean values of induction trial attempts differed significantly (P<0.0001) between the groups; with the lowest mean values of 1.22±0.4 recorded in CL+MEL broiler chickens. At day 42, the lowest mean TI duration of 101.87±10.24s in the CL group, recorded at 06:00h rose (P<0.001) to 184.07±23.69s at 13:00h. The overall mean duration of TI differed significantly (P<0.0001) again between the groups; with the highest mean duration of 167.82±8.35s, recorded in CL+MEL broiler chickens administered with melatonin. The overall mean vigilance behavioural ranking values of 1.85+0.07 and 1.70+0.08, obtained in 12D:12L cycle and CL broiler chickens, respectively were higher (P<0.0001) than the value of 1.44+0.05 recorded in melatonin-treated broiler chickens. The results indicated that broiler chickens belonging to both 12D:12L cycle and CL groups were more emotional, fearful or anxious, compared to CL+MEL broiler chickens. It was concluded that melatonin administration elicits boldness and confidence by suppressing freezing behaviour in broiler chickens, and it may improve their welfare and productivity.

Broiler chicks with slow-feathering (K) or rapid-feathering (k+) genes: Effects of environmental stressors on physiological adaptive indicators up to 56 h posthatch

Two experiments were conducted to examine the effects on the physiological responses of slow-feathering (K) and rapid-feathering (k(+)) genes in neonate broiler chicks subjected to posthatch fasting (PHF). In the first experiment, 300 Ross 308 chicks were denied access to feed and water for 0, 7, 14, 21, 28, 35, 42, 49, and 56 h posthatch. In the second experiment, 625 Ross 308 chicks were subjected to PHF for 0, 12, 24, 36, and 48 h. In experiment 1, the weight loss rate increased over 56 h PHF and did not differ between fast- and slow-feathering chicks up to 28 h posthatch but was greater (P < 0.05) in fast-feathering birds from 28 to 56 h posthatch. The fast-feathering genotypes demonstrated greater serum K levels following 7, 21, and 56 h (P < 0.05) and serum uric acid (UA) levels after 7, 21, 28, 49, and 56 h PHF (P < 0.01). In experiment 2, weight loss increased linearly with no difference between fast- and slow-feathering chicks through 36 h PHF but increased in fast-feathering birds when PHF continued for 48 h. Neonatal fasting periods of 12 to 48 h decreased breast and thigh percentage (P < 0.01), with no difference between feathering genotypes. The fast-feathering genotypes showed greater serum HDL levels at 24 h (P < 0.05) and greater serum UA concentration following 12, 36, and 48 h PHF (P < 0.05). The mean frequency of jumping (P < 0.01) and active wakefulness (P > 0.01) was increased as PHF continued from 12 to 48 h across genotypes. At 48 h, the fast-feathering chicks showed greater frequency of escape attempts from the test field (P < 0.01). It was concluded that slow-feathering chicks are more capable of withstanding PHF periods lasting more than 28 h. This is important to consider when day-old chicks are transported for extended periods without access to feed.

Changes in body temperature during growth and in response to fasting in growing modern meat type chickens

1. Rectal or core body temperature was determined in a study to examine the effects of fasting in modern meat type broilers at three stages of growth, namely d 19, 33 and 47. 2. There were two treatment groups: fed with feed available ad libitum and fasted. Rectal temperatures were determined at noon (1200 h). At that time, feed was removed from the fasted group. The body temperatures were then determined again after 6, 12, 18 and 24 h. 3. Core body temperatures decreased with fasting. The decrease was evident after as little as 6 h of fasting with a further decline evident by 12 h. 4. Accompanying the decrease in body temperature with fasting there were decreases in the venous concentrations of carbon dioxide in the blood and sodium in the plasma. 5. The decrease in both body temperature and carbon dioxide presumably reflects depressed metabolic rate. 6. Unexpectedly, the core body temperature increased progressively with age in the control fed group (d 19 = 41·04 ± 0·02°C, d 33 = 41·65 ± 0·05°C, d 47 = 42·21 ± 0·12°C). 7. In the fed control group, core body temperatures were reduced at night, when feeding activity would be anticipated to be greatly reduced.