Poultry production is gaining significant scope worldwide as it is considered the best and cheapest source of animal protein to address protein deficiency. Poultry is one of the fast-growing sectors of Indian agriculture, with poultry meat production increasing by 6.86% and egg production rising by 6.19% as per basic animal husbandry statistics of India1. The production of poultry meat makes up more than half of the total meat production in developing countries. The constant rise in the global demand for meat is expected to continue in the future, necessitating the implementation of processing techniques that prioritize both consumer expectations and animal welfare in order to ensure the provision of safe and high-quality products.

For consumption purposes, birds are transported alive from farms to slaughterhouses or butcher shops when they reach market age, which is more feasible than transporting processed carcasses or meat2. During this transport, birds experience multidimensional stressors from the farmer’s field to the abattoir, including handling, loading/unloading, transportation, lairage time, restraining, and sticking methods, which may adversely affect their welfare and impact meat quality traits. In a developing country like India, inadequate transportation and infrastructure often lead to rough handling of live birds, with overcrowded crates, prolonged deprivation of food as well as water, and harsh environmental conditions during transit, exacerbating their stress3. Transportation also leads to mental stressors like social mixing, fear, hunger, and pain, all of which contribute to the exhaustion of the birds4. Postharvest losses represent a significant challenge within the poultry meat supply chain, arising from both direct physical losses and quality deterioration that diminishes the economic value of the products. Various studies reported that live shrinkage loss is more in broilers during transportation, which varied from 0.18 to 0.60% in body weight for each hour of the first 5–6 h after feed withdrawal. If transit extends beyond this period, an additional body weight loss of approximately 0.30% per hour is anticipated5. Moreover, transport stress also results in higher chicken mortality and live weight loss6.

Ante-mortem stress disrupts normal homeostasis in animals, causing an increased production and consumption of epinephrine and glucocorticoids7, contributing to significant biochemical and physiological changes in the birds’ cells and consequently reducing both the quality and quantity of the meat produced. These physiological changes include heterophil/lymphocyte (H/L) ratio8, increased concentrations of corticosterone7, changes in energy and protein metabolism and an immunological challenge9. Transportation degrades post-slaughter poultry meat quality by accelerating glycolysis and lactic acid buildup, resulting in a lower pH10,11,12.

The conditions such as pale, soft, exudative (PSE) meat and dark, firm, dry (DFD) meat are indicators of compromised meat quality13. In addition to compromising meat quality, these conditions alter its color, rendering it less appealing to consumers on supermarket shelves14. A combination of high muscle temperature and low pH could lead to denaturation of sarcoplasmic protein, reducing the water-holding capacity (WHC) of muscles15. Significant bruising might reduce carcass quality and result in market rejection16,17. Transportation also impacted the expression of hepatic genes related to food metabolism and cellular regulation and immune function of broiler chickens18. Stress parameters and meat quality can be set as benchmarks for meat grading in order to attract consumer confidence; that is why the mitigation of postharvest losses is recognized as a crucial element in ensuring food security.

Animal welfare and meat quality have become crucial concerns in the meat industry. Therefore, consumers are insisting on ethical production systems and displaying an inclination towards buying products that address their concerns about animal welfare. Furthermore, consumers are becoming more selective, with mounting expectations concerning animal produce. Hence, current study was aimed to determine how different transportation times influence the body weight, meat quality, and blood properties of broiler chickens in Northern India.

Materials and methods

Ethics declarations

The study was conducted in accordance with the regulatory framework outlined by the “Committee for the Purpose of Control and Supervision of Experiments on Animals (CPCSEA) 2012,” as laid down under the “Prevention of Cruelty to Animals Act 1960” of the Indian Penal Code. The experimental protocols employed in this investigation received explicit approval from the Institutional Animal Ethics Committee (IAEC) with the project code: CARI/CPCSEA/11.03.21/Sr. no. 1. Reporting of in Vivo Experiments (ARRIVE) guidelines, ensuring the ethical conduct and reporting standards in the realm of animal experimentation. All birds were sourced from the Experimental Broiler Farm of ICAR-Central Avian Research Institute, Bareilly.

Experimental design and treatment groups

The focus of the study was to check the impact of transportation duration on body weight, blood physiology and meat quality attributes under Indian conditions. For this purpose, experimental study was executed with 120 straight run, CARIBRO-Vishal broilers (White broilers) of 42 days of age with a body weight of approximately 2.1 ± 0.03kg/bird was used for transportation. Each bird was uniquely marked with four distinct colors using paints on feathers and shank for precise identification. These distinctively marked birds were subsequently assigned to various treatment groups having 30 birds in each treatment group. Respective treatment groups were: no transport (0 h – T1), short duration (2 h – T2), medium (4 h – T3) and longer duration (8 h – T4). The time duration of transport for the present study was selected based on the common practice done by the poultry farmers/integrators in Bareilly, India, who used to transport the birds either to slaughter houses or to retailers within approximately 4 h to 8 h duration. The sustained speed of the vehicle was around 36.4 km/h speed throughout the entire journey. Before slaughter, the birds underwent a 6–8 h feed deprivation period at farm. Birds were loaded (density of 39 kg per m2) into a medium-sized transport truck equipped with crates measuring 76.2 cm x 50.8 cm x 25.4 cm (L x W x H) for transportation, which took place from 5:30 AM to 1:30 PM, IST. Transportation study was conducted in Northern part of India, i.e., to and fro journey between Bareilly to Pilibhit (51 km); where the average ambient temperature recorded was 12 to 20°C and average humidity recorded was 60–65%. The health status prior to transportation, breed and gender of the birds can affect the results therefore birds from same breed, same batch and of same average body weight were selected after health check up to avoid error. The birds were individually weighed as per the treatment groups & then all the birds were transported at the same time in same vehicle. The remaining space in the truck was filled with additional birds. This was done to replicate a realistic, stressful field condition and to ensure the results were accurate. Transportation was conducted using a Mahindra Bolero Pik-up truck equipped with standard cages. The vehicle was of an open type, lacking any covering or artificial ventilation system. Immediately, after the completion of the hauling time duration (Fig. 1) for each treatment, the birds were unloaded and weighed immediately to ensure the body weight changes which occurred due to transport stress for the birds. Subsequently, ten birds per treatment group were randomly selected and subjected to blood sample collection19 for serum biochemical estimation. The same birds were further subjected to mechanical stunning by Manual neck or cervical dislocation20,21 and proceeded to slaughter22.

Fig. 1
figure 1

Schematic diagram of the experimental trial.

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The figure illustrates the the design and workflow of the experimental trial, highlighting key phases such as animal grouping, data collection, and analysis. It provides a visual representation of the methodology for better clarity and understanding.

Parameters assessed

Any breach in the welfare of broilers during transportation was assessed by observing mortality, changes in their body weight, stress indicators and meat quality.

Estimation of mortality percentage during transport

Mortality of birds during transport was estimated to assess welfare and economic losses associated with pre-slaughter handling. The mortality percentage was calculated by using the following formula:

$$\:Mortality\:Percentage\:\left(\%\right)\:=\frac{\text{N}\text{u}\text{m}\text{b}\text{e}\text{r}\:\text{o}\text{f}\:\text{b}\text{i}\text{r}\text{d}\text{s}\:\text{d}\text{e}\text{a}\text{d}\:\text{o}\text{n}\:\text{a}\text{r}\text{r}\text{i}\text{v}\text{a}\text{l}}{\text{T}\text{o}\text{t}\text{a}\text{l}\:\text{n}\text{u}\text{m}\text{b}\text{e}\text{r}\:\text{o}\text{f}\:\text{b}\text{i}\text{r}\text{d}\text{s}\:\text{t}\text{r}\text{a}\text{n}\text{s}\text{p}\text{o}\text{r}\text{t}\text{e}\text{d}}\times\:100$$
(1)

Birds were visually inspected upon unloading, and any birds that were dead or moribund (severely weakened and unmarketable) were recorded separately. For the purpose of this study, only the birds that were confirmed dead at the point of arrival were included in the mortality count. Transport conditions, including distance, duration, vehicle type, and ambient temperature and humidity, were concurrently recorded to analyze possible correlations with mortality rates.

Percent change in body weight

The body weight change (%) was calculated by body weights recorded before and after the transportation (Eq. 1).

$$\begin{aligned}\:Body\:weight\:change\:\left(\%\right)\hspace{0.17em}=&\hspace{0.17em}Absolute\:body\:weight\:change\:\left(kg\right)\:/\:\\&Total\:body\:weight\:\left(kg\right)\:per\:replicate\:X\:100\end{aligned}$$
(2)

Computation of monetary loss

Based on assumptions of the local live market rate for broiler birds, which was Rupee 110 per kilogram according to the most recent daily market data we calculated the monetary loss by using following formula (Eq. 2):

$$\begin{aligned}Monetarily\: Loss\: in\: Rupee \:&= \:[(Initial\: weight\: of\: broiler\: birds\: in\: kg\: before\: transport\: \\&\times\: live\: bird\: market \:rate\: for\: 1\: kg)\: \\&-\: (Weight\: after\: transportation\: of\: broiler\: birds \:in \:kg \:\\&\times \:live \:bird \:market \:rate \:for \:1 \:kg)]\end{aligned}$$

Meat quality and sensory traits

Post-slaughter, breast samples (Pectoralis major) were collected and divided into two halves and assigned to the physical and sensory analyses. The ultimate pH (pHu) of 120 half breasts (30 breasts/treatment) was assessed by inserting a portable pH meter (FG2-Five GoTM Mettler Toledo, Greifensee, Switzerland) probe calibrated at pH 4.0 and 7.0 into breast muscle (Pectoralis major). For drip loss determination, meat samples of 50 g were excised from the breast and placed into an inflated food-grade plastic bag avoiding contact with meat bag. Samples were then suspended and stored at 4 ± 0.7 °C for 24 h storage. Afterwards, samples were gently blotted dry and again weighed to compute drip loss.

A total of 120 other half breasts (30 breasts/treatment - Pectoralis major) were vacuum sealed and cooked in a water bath at 80 °C until the core temperature reached 74 °C to determine the shear force and sensory traits. Cooked breast samples were cooled in an ice bath, and gently dried with a paper towel. Shear force was assessed with a TA-HDi Texture Analyzer (Stable Macro System, London, UK). The cooked meat samples were then cut into cylindrical cores of uniform diameter (1.25 cm). The V-shaped Warner-Bratzler shear blade was used to cut perpendicularly the longitudinal muscle fibres of the meat to determine Warner-Bratzler shear force (WBSF).

Furthermore, the same samples were subjected to a descriptive sensory analysis, to detect differences among the treatments. The samples were kept at room temperature for 20 min then samples were cut into small pieces and randomly served to 60 panelists. The panel received the list of descriptors (colour and appearance, flavour, texture, juiciness, and overall acceptability) to score on a numerical scale from 0 (the lowest score for each attribute) to 8 (the highest score for each attribute) as per the method acknowledged by Keeton23. All the evaluations were performed in a room where the temperature was set at 22 °C. During the sensory session, unsalted crackers and still water at room temperature were available to panelists.

Stress indicators

Biochemical profiling

The blood samples were collected from the jugular vein of the birds manually. The samples of 3 ml each were collected in the red top vacutainer followed by centrifugation (Thermo Fisher Scientific India Pvt. Ltd. Mumbai) of the samples at 1110 g for 15 min resulting in the separation of serum. From this around 1–1.2.2 ml serum were collected and stored at 4 °C at multiple aliquots for future use.

The impact of transportation on biochemical parameters including cholesterol, uric acid, creatinine, Aspartate aminotransferase (AST) and Alanine aminotransferase (ALT) was investigated. The analysis was performed using commercial kits (Coral Clinical Systems, Tulip Diagnostics (P) Ltd, India) and a spectrophotometer (Bio-Rad Laboratories, USA). The methods used were the enzymatic method (CHOD-PAP) method for cholesterol24 the Uricase method for uric acid25, the Modified Jaffe’s Kinetic method for creatinine26 and the Reitman and Frankel method27 for Alanine Transaminase (ALT) and Aspartate Transaminase (AST). To estimate oxidative stress levels among the transported birds we planned to measure the levels of lipid peroxidation (LPO), glutathione peroxidase (GSH-Px) superoxide dismutase (SOD), and Packed Cell Volume (PCV) levels using blood plasma. For this analysis, heparinized blood samples were centrifuged at 1110 g for 15 min at a refrigerated centrifuge (4 °C) to harvest the erythrocytes by maintaining a cold chain. Erythrocytes were then washed thrice with phosphate buffer saline (PBS) solution and finally, hemolysate (10%) was prepared by adding distilled water (1:9). Hemolysate will be kept at −20 °C and used within 6 h for assay. Haemoglobin concentration in 10% hemolysate was estimated by cyanmethemoglobin method. The following parameters were studied to estimate the oxidative stresses of the transported birds. LPO: Concentration of malondialdehyde (MDA), a reliable indicator of lipid peroxidation, was estimated in 10% hemolysate28 GSH-Px activity was measured in erythrocyte through a standard procedure29 Activity of SOD in hemolysate was estimated30. PCV was determined by a microhematocrit procedure31.

H/L ratio

Other stress indicators like the H/L ratio and serum corticosterone level were also examined to assess breaches in animal welfare due to transportation. The H/L ratio was calculated as per the method used by Gross and Siegel32. Briefly, thin blood smears from brachial vein blood were examined to calculate the H/L ratio. After 2 h of methyl alcohol fixation, the smear was stained with Giemsa stain procured from Hi-Media (code - S011) Company, Mumbai, Maharashtra, India. A minimum of 100 cells per field were examined under the microscope (Zeiss microscopy, Germany) to determine the ratio of H/L count.

Corticosterone Estimation

Serum corticosterone values were evaluated by competitive binding theory by using ELISA Kit (CORTICOSTERONE ELISA - MS E-5400) procured from the LDN immunoassay and services, Germany. The underlying principle of this estimation is that microtiter wells are coated with a polyclonal antibody directed towards an antigenic site on the corticosterone molecule. Endogenous corticosterone of a sample competes with a corticosterone-horseradish peroxidase conjugate for binding to the coated antibody. After incubation, the unbound conjugate is washed off. The amount of bound peroxidase conjugate is inversely proportional to the concentration of corticosterone in the sample. After addition of the substrate solution, the intensity of developed colour is inversely proportional to the concentration of corticosterone in the bird’s sample.

Statistical analysis

The experimental trial was conducted thrice and obtained data were subjected to one-way ANOVA with treatment (T1 vs. T2 vs. T3 vs. T4) as a fixed effect and single birds as an experimental unit in SPSS version 26.0. To determine significance, the means were compared through Tukey’s multiple range test with a significance level of P < 0.05.

Results

The findings on how transport duration affects marketable broilers on various parameters under field conditions are detailed below.

Mortality percentage

No mortality was recorded among the birds transported across different distances during the study period, indicating that the transport conditions were non-lethal under the prevailing ambient temperature and humidity. However, birds subjected to longer transport durations, particularly those transported for approximately 8 h, exhibited noticeable transport-related stress and physical impairments such as higher incidence of leg weakness, impaired mobility, and signs of lameness in T4 group. Additionally, a proportion of birds showed evidence of breast blisters and hock burns, likely resulting from prolonged pressure against crate surfaces during transit.

Body weight change before and after transport

Results revealed a significant (P < 0.05) change in body weight of the transported birds, presented in Fig. 2. Among the treatment groups, T4 displayed the most substantial percentage reduction in body weight of about − 8.17% in comparison to the T1 (0.00%) group, whereas T3 and T2 exhibited − 5.87% and − 4.48%, respectively. The study also calculated the monetary loss, revealing that the economic loss was significantly (P < 0.05) higher in the T4 groups, amounting to approximately Rupee 165.37, compared to the other transported groups (Fig. 2).

Fig. 2
figure 2

Impact of transport duration on body weight loss and monetary loss in poultry.

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The figure illustrates that with increasing transport duration, the percentage change in body weight and monetary loss (in Rupees) also increased.

Meat profile of transported birds

The results of the present study also showed the effect of transportation duration on breast muscle (Pectoralis major) characteristics such as pHu, drip loss, and WBSF in broiler chickens (Table 1). The ultimate pH was affected significantly (P < 0.05) due to transit duration. The highest and lowest pHu were recorded for T4 (6.22) and T1 (5.88) groups, respectively, whereas T3 (6.11) and T2 (5.92) groups remained in between. Drip loss did not show a significant (P > 0.05) effect on transportation duration, with values ranging from 0.30% to 0.51%. Slightly higher WBSF values were recorded in the longer transportation duration groups (T4: 1.73 kg/cm2 and T3: 1.62 kg/cm2), but no significant (P > 0.05) difference was observed compared to short duration (T2: 1.42 kg/cm2) or no transportation (T1: 1.41 kg/cm2) groups. However, the transportation duration significantly (P < 0.05) affected the sensory attributes (Table 1). A significant decrease in sensory attributes with increasing duration of transportation was observed. The appearance, colour, texture, and overall acceptability of the breast meat were significantly (P < 0.05) affected by the transport duration, with the highest decline after 4 h of transportation. On the other hand, flavour did not exhibit any difference among the groups. Overall, the results of this study suggest that transportation duration has a significant effect on the sensory characteristics of broiler chickens’ meat.

Table 1 Impact of transport duration on meat quality and its sensory qualities in broiler chicken.
Full size table

Stress biomarkers

Blood biochemical and haematological profile

Results on the effect of transportation duration on serum biochemical parameters such as serum cholesterol, uric acid, creatinine, alanine, and aspartate transferase levels in broiler chickens are depicted in Table 2. Results indicated that transportation duration had no significant (P > 0.05) effect on serum cholesterol and uric acid levels. However, significant (P < 0.001) variations were observed in serum creatinine, ALT, AST levels, and oxidative stress profile. The creatinine level (21.4 vs. 7.65 vs. 4.17 vs. 1.36 mg/dl for T4, T3, T2, and T1, respectively) and liver profiles (ALT: 65.1 vs. 57.1 vs. 48.7 vs. 35.8 IU/l; AST: 115 vs. 104 vs. 99.8 vs. 85.2 IU/l for T4, T3, T2, and T1, respectively) were exponentially increased with increasing transportation time, indicating the adverse impact of prolonged transportation on liver health.

In the case of oxidative stress profile, transportation durations significantly (P < 0.05) elevated levels of LPO were observed in 0 h and 2 h, but at 4 h transport, LPO level got reduced and again started increasing as the transport time (8 h) increased (5.10 vs. 5.78 vs. 3.67 vs. 2.61 nmol MDA/mg Hb for T1, T2, T4, and T3, respectively). While GSH-Px showed a decreasing trend (P < 0.001) as the transport duration increased (1.44 vs. 1.21 vs. 0.06 vs. 0.04 µmol/mg Hb for T1, T2, T3, and T4, respectively). Additionally, the values of antioxidant enzymes SOD were significantly (P < 0.001) increased with an increase in transportation duration (3.90 and 3.87 vs. 1.81 and 1.65 unit/mg Hb for T3, T4, T2, and T1, respectively). Furthermore, the PCV values were significantly (P < 0.05) decreased as the transportation duration of birds increased.

Table 2 Impact of transport duration on serum biochemical and stress indicator values in broiler chickens.
Full size table

H/L ratio and serum corticosterone levels

Table 2 shows the effect of transportation duration on H/L ratio and serum corticosterone levels in broiler chickens. The H/L ratio was exponentially increased (P < 0.05) with an increase in the transportation duration: 0.40 vs. 0.67 vs. 0.88 vs. 1.13 for T1, T2, T3, and T4, respectively. Similarly, corticosterone levels were significantly (P < 0.05) higher in transportation groups than the control group: 17.10 vs. 39.21 vs. 37.66 vs. 28.73 ng/ml for T1, T2, T3, and T4, respectively.

Discussion

Mortality

The present study observed no mortality among broiler chickens transported over varying durations, including up to 8 h. Despite the absence of mortality, birds transported for extended durations exhibited notable sub-lethal injuries. Specifically, those subjected to 8-hour transport displayed increased incidences of leg weakness, breast blisters, and hock burns. These sub-lethal effects, although not immediately fatal, may negatively impact bird welfare33, marketability, and subsequent meat quality. The development of breast blisters and hock burns is often associated with prolonged pressure on the sternal and hock regions, especially when birds are confined in transport crates for extended periods without adequate padding or movement. Such findings underscore the need for improved transport crate design, adequate bedding or padding, and minimization of journey duration to mitigate physical injuries in live bird marketing systems. These sub-lethal injuries not only compromise animal welfare but also have economic implications. Birds with physical injuries are more likely to be downgraded at processing plants, leading to financial losses. Moreover, such injuries can affect meat quality, with conditions like breast blisters potentially leading to carcass condemnations.

Body weight change before and after transport

Transportation before slaughter plays an important role in inducing stress to the birds, especially during their catching and loading and the duration of transportation2. The absence of mortality even in the longest transport duration (8 h - T4) rules out the single role of transportation duration in the mortality of broilers and indicates the importance of maintaining other managemental factors during transportation16. However, transportation duration exhibited a great impact with the change in body weight. An increase in percent body weight change was observed with an increase in transport duration. The findings were consistent with those of7, who found that an increase in transport distance leads to an increase in body weight loss of broiler chickens. Similarly, Sowińska et al.34 reported that a longer transport distance led to a greater loss of weight in broiler chickens and that the broilers transported over the farthest distance exhibited a quicker rate of glycolysis in the pectoral muscle.

In the present study, the contributory factor for losing body weight might also be the withdrawal of feed prior to transport. According to the Ministry of Food Processing Industries35 report, the post-harvest loss of meat was 2.34%, while poultry meat experienced a higher loss of 5.63%. The report highlighted that these losses could be significantly reduced by transitioning from standalone slaughterhouses to integrated facilities. Additionally, the study emphasized that transport stress not only affects the quality of the final product but also severely impacts its economic value. Prolonged fasting disrupts gut pH and microbial balance, potentially increasing pathogen growth, impairing nutrient absorption, and causing gastrointestinal discomfort, all of which elevate stress in birds. This stress can raise corticosterone levels, negatively impacting bird welfare. Unfortunately, farmers and stakeholders are often unaware of these losses, and the monetary impact has not been adequately calculated under Indian conditions, limiting their understanding of this critical issue.

Meat profile of transported birds

Higher stress levels negatively impact meat quality as, under stress, birds utilize muscle glycogen at a faster rate, which affects the rate and extent of the chemical and physical changes in the muscle during its post-slaughter conversion into meat36. One of the most important changes is the pHu of meat, as quality attributes like tenderness, WHC, color, juiciness, shelf life, etc., are directly linked to it. The exhaustion or starvation prior to slaughter due to longer transport depleted the muscle glycogen, thus minimizing post-mortem glycolysis, consequently resulting in higher pHu37.

According to the review of Adzitey and Nurul13, meat samples with high pH are affected by DFD conditions, which have poor processing characteristics and are prone to a high potential for spoilage. Therefore, in this present study, it can be confirmed that transport for more than 4 h (T3) with feed withdrawal affected the pHu of the meat significantly, and birds without transport had normal pHu in their meat samples. In addition, meat texture is a crucial quality factor that greatly affects consumer satisfaction and is determined by tenderness. Handling and transportation stress before slaughter play a major role in determining the texture of the meat5. A higher Warner-Bratzler shear force in the T4 group suggested a higher stress level that could be due to underlying fatigue in response to long transportation duration. The recent study by Hussnain et al.8 has confirmed the detrimental effect of long transportation on broiler meat tenderness. However, in the present study, we did not encounter this issue as Lyon and Lyon38 benchmark values were used to evaluate tenderness, specifically values below 3.62 kg indicate “very tender”, while values between 3.63 and 6.61 kg indicate “moderately to slightly tender”.

Another important aspect affecting meat quality is drip loss, which contributes to the toughness of the meat and results in poor mouthfeel, as myofiber leakage and the loss of water, iron, and proteins occur during the conversion of muscle to meat39. Though drip loss was found higher in birds that were under the 8 h transportation period (T4), it was insignificant. The findings were in accordance with5, who did not find any significant effect of transport on broiler meat. However, Yue et al. and Zhang et al.40,41 found a significant increase in drip loss due to an increase in transportation duration.

Sensory attributes were also found to be affected linearly with transport duration. Birds that were transported for longer durations exhibited poor sensory meat quality traits, which possibly affected consumer preference. An increase in the duration of transportation significantly affected (p < 0.05) the appearance, color, and texture of the meat and also significantly (p < 0.05) affected juiciness and overall acceptability. The significant difference (p < 0.05) between samples from the 8 h treatment (T4) and other treatments (T1, T2, and T3) indicated that meat samples from the 8 h transport group (T4) were poor in their overall acceptance due to longer transport time. The literature citing transportation’s effect on sensory attributes is scanty. Villarroel et al.42, conducted a study on the effect of transport time on the sensorial aspect of beef meet quality similar to the present study and found reduced overall acceptability of meat after 3 h of transportation. However, Lacerda et al.43, found no effect of transport on sensory attributes of Nellore bull meat up to 6 h of the pre-slaughter journey.

Stress biomarkers

Blood biochemical and haematological profile

The blood biochemical profile of the birds was evaluated to examine the impact of transport-related stress on the liver, a crucial organ that plays a role in various biochemical and metabolic processes, such as the synthesis of fat-soluble vitamins, lipids, cholesterol, and bile, blood detoxification, and gluconeogenesis in periods of starvation44. Though serum cholesterol and uric acid levels were comparable, serum creatinine, ALT, and AST levels were elevated. Elevated creatinine levels pointed to stress-related skeletal muscle breakdown caused by transportation and feed deprivation45. Increased levels of liver enzymes (AST and ALT) might signal transport-induced oxidative damage to the liver, resulting in cell and tissue damage and the release of these enzymes into the bloodstream46. These enzymes play a crucial role in gluconeogenesis and urea formation as they catalyze reactions involved in the transfer of α-amino groups to the α-keto group47.

AST is widely distributed in the liver’s mitochondria but can also be found in the cardiac, skeletal, kidney and brain tissues whereas, ALT is predominantly localized in the liver’s cytosol48. Serum AST and ALT are the most widely recognized as the most sensitive markers for detecting liver injury. An increase in serum AST and ALT levels above the normal range has been implicated to result in hypertension and high metabolic pressure further causing an increase in the level of serum AST due to the cellular damage in tissues49. Significant increase in creatinine, ALT and AST values of transported birds (highest in the T4 group) clearly indicated that transport creates stress which ultimately compromises production, meat qaulity as well as welfare. In poultry birds, the detoxification mechanism against surmountable reactive oxygen species (ROS)/reactive nitrogen species (RNS) involves activation and increase of oxidants (LPO) and antioxidant enzyme system that include glutathione (reduced, oxidised, peroxide forms) and SOD. Cells can tolerate mild oxidative stress by additional synthesis of various antioxidants (GSH, thioredoxin (Trx), SOD, CoQ, etc.). As stress levels continue to rise, they can inflict harm upon numerous biological molecules. The responsibility for mitigating this damage falls upon the intricate network of antioxidants within living organisms. However, it’s important to note that these mechanisms have inherent limitations in their capacity to enhance and fortify their protective functions50. Similar findings were also observed in the present study wherein, significantly elevated levels of LPO were observed in the initial 2 h transport but at 4 h transport, LPO level got reduced and again showed a rising trend as the transport time increased. These findings suggest the ongoing homeostasis to restore the oxidant-antioxidants imbalance imposed during moderate stress of 4 h whereas the imbalance worsened with increasing the transport period to 8 h leading to a rise in LPO. The significant decrease in value of reduced glutathione (GSH) with increasing transport time suggested higher consumption of GSH in neutralizing ROS thereby reducing their concentration in blood50. The increased SOD concentration due to additional synthesis with increased transport stress is a protective response as SOD curtails the rate of ROS generation. Additionally, it is worth noting that the significant decline in packed cell values (Table 2) may be attributed to haemodilution, wherein erythrocytes become diluted during the transportation process. This phenomenon could serve as an indicator of heightened stress levels in poultry species, emphasizing the importance of considering haematological parameters in assessing bird stress responses.

The transportation stress negatively impacts meat quality by accelerating lipid brakedown/oxidation into aldehydes, ketones, and hydrocarbons, which leads to undesirable changes in flavor (rancid, metallic tastes/aromas) and aroma. Also, lipid oxidation leads to myoglobin and other pigments damage, altering its color and appearance. The texture, overall juiciness and shelf life also negatively affected because of oxidation of protein and lipids. This stress occurs due to an imbalance of reactive oxygen species (ROS) and the bird’s ability to detoxify them, triggered by transportation stress.

H/L ratio and serum corticosterone levels

The serum stress level was further assessed by calculating the H/L ratio and serum corticosterone levels. In avian blood, heterophils and lymphocytes are the most common types of leukocytes51, and their ratio is comprehensively recognized as a precise and reliable physiological index of the stress response52. The H/L ratio is a non-destructive, easy-to-obtain, and reliable stress indicator for poultry in field studies32. The normal H/L ratio in caged chickens was 0.38, as observed by Gross and Siegel51. The highest H/L ratio value (>1) in the longest transport could be due to severe dehydration caused during transportation. Similar findings were observed by Ulupi et al.53, where the H/L ratio increased above the normal range after a 3 h period of transport. The H/L ratio exhibited a positive correlation with cortisol, a biomarker commonly used for stress evaluation and findings were supported by the observations made by other researchers54,55. In the current study, the levels increased from the control group (T1) to 2 h transport (T2) and then started decreasing with more than 4 h of transport time (T3). Kannan and Mench56, found that there is a treatment-time interaction in the level of corticosterone. Thus, it could be concluded in the present study that initial transport stress causes an increase in the level of corticosterone and a prolonged stress period causes the peak level to decline, may be due to adaptation57.

Conclusions

Tropical countries faces significant transportation challenges for broiler chickens due to poor road infrastructure, inadequate vehicle conditions, stressful handling practices, and the use of nonspecific transport crates. These factors contribute to heightened stress levels, leading to notable alterations in blood profiles, stress biomarkers, and meat quality. The present study confirms that transporting broiler chickens for durations exceeding four hours under Indian conditions induces considerable stress, thereby compromising their overall welfare, production performance, and meat quality.

Limitation of work

This study did not investigate the molecular or gene-level mechanisms underlying stress in transported birds, and therefore the physiological pathways involved in stress modulation remain unclear. Given the multitude of confounding factors such as environment, breed, road conditions, and initial bird health future replication of this study across diverse regions of India is essential to validate these findings and establish robust, generalizable conclusions.