The impact of relaxation music (Weightless by Marconi Union) on production performance, welfare, and hematological and biochemical blood parameters in broiler chickens

Abstract

The study evaluated the impact of relaxation music on the production performance, welfare, and blood parameters of broiler chickens. Literature indicates that specific music genres, as environmental enrichment, can improve animal welfare and production outcomes.

The research involved 1,200 Ross 308 chickens divided into control (C) and experimental (M) groups. The rearing period lasted 42 days, and was conducted according to the flock management guide (Aviagen, 2019). The M group was exposed to relaxation music (Weightless by Marconi Union), played for two hours daily (08:00–10:00) and for 30 minutes before slaughter, at 70 dB. Body weight, feed consumption (FCR), mortality, and rearing conditions (litter pH, harmful gases) were monitored. On day 35, excreta samples were collected to analyze cortisol concentrations and assess welfare. Blood was also collected at slaughter for analysis. Statistical analysis was performed using SPSS software (PS IMGO PRO 8.0).

Significantly higher final body weights and lower FCRs were observed in the M group chickens (p ≤ 0.05). Enriching the chickens' environment with relaxation music also resulted in lower cortisol concentrations in excreta samples and improved welfare levels (p ≤ 0.01). Blood analysis of the M group showed a significant increase in the average number of red blood cells and the calcium content, while glutamate dehydrogenase (GDH) concentrations were lower (p ≤ 0.01). The hematocrit percentage, total protein, and uric acid concentrations were significantly lower in the M group compared to the C group (p ≤ 0.05). Litter pH monitoring showed significantly lower pH values for the M group on days 22 and 35 (p ≤ 0.01 and p ≤ 0.05, respectively). However, on day 10, litter pH was lower for the C group chickens (p ≤ 0.05). No significant differences were found for the other results.

Relaxation music can serve as environmental enrichment for broiler chickens, potentially improving their production performance and welfare quality. However, further research is necessary to verify the mechanism behind these effects.

Introduction

Music has accompanied humans since ancient times—believed to possess mystical properties that restore balance to the soul and the body (Lippi et al., 2010). It has been proven that appropriately selected music genres can positively impact the human body, reducing anxiety and pain, and lowering stress hormone levels in the blood (Trappe, 2012; Vaajoki et al., 2012; Nam et al., 2017). Enriching the environment of livestock, which regularly encounter numerous stressors, with music has also been shown to be beneficial. Reducing stress is crucial, as it leads to improved welfare and increased productivity in animals (Ciborowska et al., 2021; Narayan et al., 2021). Trappe (2010) emphasized the importance of selecting the appropriate music genre for human therapy. Meditation/relaxation music, which can even serve as an alternative to pharmacological anxiolytics, and classical music, which has been shown to significantly reduce cerebral blood flow and promote relaxation in patients, offer the most health benefits. In contrast, loud and intense music genres like heavy metal and techno are considered hazardous to health, causing heart rhythm disturbances and increased stress (Trappe, 2010). Particular attention has been drawn to the composition Weightless by Marconi Union for its ability to induce deep relaxation. This piece reduces patients' heart rates and skin conductivity (SC; aids in interpreting emotional presence) by up to 36.09%. Consequently, it has been suggested that this piece could be used as a relaxant in systematic-desensitization techniques or as a general relaxant to reduce acute stress (Agrawal et al., 2013; Shepherd et al., 2023).

In light of modern animal husbandry, attention has been drawn to various methods for improving animal health and welfare, the decline of which is associated with the intensification of production. Moreover, enhancing these aspects can simultaneously improve production outcomes in animals (Čobanović and Magrin, 2023). The most common aspect highlighted in this regard is the improvement of environmental conditions. Adequate ventilation in breeding facilities, control of bedding quality, or the introduction of enrichments for animals such as toys or mechanical brushes, are among methods currently being used to reduce stress while improving animal welfare at the same time (Dawkins et al., 2004; Ciborowska et al., 2021).

According to USDA Foreign Agricultural Service (2024) forecasts, the scale of poultry production is steadily increasing, and is projected to be nearly 1% higher in 2024 compared to the previous year. Environmental enrichment through the use of music, though not yet widely practiced, is gaining in importance. Some scientists have advocated for its implementation based on studies on the effects of music on humans and other animal species (Agrawal et al., 2013; Alworth and Buerkle, 2013). Additionally, this method has the potential to increase production efficiency for a relatively low financial investment.

When utilizing music in animal production, it is essential to ensure that such environmental enrichment does not become a stressor for the animals. Music played at excessive volumes can reduce welfare; therefore, it is important for producers to familiarize themselves with the regulations regarding sound pressure levels in livestock buildings (measured in decibels; dB). Music should be played at a volume that, when combined with ambient sounds, does not exceed the specified limits. Additionally, it has been found that animals also have their own musical preferences. Dairy cows show calmer behavior when played music with a gentle sound, such as lullabies or classical music pieces. Music with a strong and heavy sound, such as heavy metal or rock, negatively affects cows' physiology, as evidenced by increased heart rate and respiratory frequency (Kemp, 2020). Conversely, cows exposed to Indian classical music showed over a 12% increase in milk yield compared to those without such environmental enrichment (Moregaonkar et al., 2006). Mozart's compositions also have positive effects—Sonata for Two Pianos in D (Mozart, K.448) reduced cortisol levels in piglets while increasing IgG, IL-2 and IFN-γ levels, and decreasing IL-4 (Li et al., 2020).

In the 1970s, it was found that music at a volume of 70 dB led to better production outcomes in chickens compared to music at 85 dB. It is also noteworthy that, in a similar way to dairy cows, broiler chickens react negatively to hard and fast-paced music (such as rock and roll) at both 70 dB and 85 dB. Birds exposed to this type of music showed increased feed consumption without corresponding body weight gains (Christensen and Knight, 1975). Gao et al. (2022) highlighted the importance of selecting the appropriate music genre in poultry production, suggesting that classical music is more suitable for broiler chicken rearing than pop or folk music. The positive effects of Mozart's classical music were observed in chickens reared up to 10 weeks of age. The sounds provided the birds with greater comfort, reducing aggressive pecking and feather pecking (Zhao et al., 2023). Vivaldi's compositions reduced stress hormone levels in chickens and were considered a type of growth promoter (Gvaryahu et al., 1989; Hafizah et al., 2015). Similarly, classical music selected from Indian Raga has been shown to decrease CORT (corticosterone), ACTH (adrenocorticotropic hormone), and GLU (glucose) levels in broiler chicken serum (Gao et al., 2023). These findings indicate that classical music is predominantly used in animal studies. However, it is worth exploring other music genres that have had positive effects in human music therapy, in animal production—such as relaxation music. Therefore, this study aimed to analyze the impact of relaxation music (Weightless - Marconi Union) on broiler chicken growth performance and welfare.

Materials and methods

The experiment was conducted in a poultry house belonging to the Warsaw University of Life Sciences, RZD Wilanów, Obory during the spring-summer period.

Facilities designated for broiler chicken rearing

The necessary equipment for the experiment was installed in a hall designated for the experimental group of chickens (M) that would receive environmental support in the form of music. A similar hall within the same space was designated for the control group (C) chickens, which would be reared under standard conditions. Soundproofing material, in the form of self-adhesive polyurethane foam (PU) with a thickness of 3 cm, was mounted on the experimental group's side of the wall that separated the two halls to prevent sound waves from penetrating into the control group's hall. The acoustic insulation was protected to a height of 0.85 m with material to prevent the birds from pecking at the foam (Fig. 1). One speaker was mounted in each box (5 in total). They were then connected by cables to a zone controller and an amplifier connected to a player. The track Weightless by Marconi Union was played from a CD. The electronic equipment was placed outside the hall, near the entrance, to avoid any negative impact on the electronics from the microclimate within the hall during chicken rearing (Fig. 2, Fig. 3). After the equipment was installed, the hall was properly disinfected.

Fig. 1.

Projection of the wall separating the experimental group's hall from the control group's hall.

Fig. 2.

Projection of the experimental hall from above; arrangement of audio equipment.

Fig. 3.

Projection of the experimental hall from the front; layout of the speaker system.

Animals

In accordance with the Act of January 15, 2015, the Second Local Ethical Committee for Animal Experiments at SGGW issued a written statement indicating that the planned research project did not require the Ethical Committee's approval to conduct the experiment (Justification dated November 24, 2021). The research material consisted of 1,200 male Ross 308 chicks divided into two equal groups, each in five replicates, containing 120 chicks per box:

• ·Control group (C) - without music (600 chicks),
• ·Experimental group (M) - with relaxation music played (600 chicks).

The rearing of the chickens lasted 42 days. During this period, both groups of chickens were kept under standardized conditions, provided with free access to water, and fed ad libitum with a commercial feed mix appropriate for each rearing stage (starter: days 0–9; grower 1: days 10–21; grower 2: days 22–35; finisher: days 36–42) (Table 1). The light cycle was maintained according to the flock management guide (Aviagen Ross 308, 2022).

Table 1.

Nutritional value of the complete feed mixtures provided to broiler chickens during the experiment.

Analytical components [%]	Nutritional phases
	Starter	Grower 1	Grower 2	Finisher
Crude protein	21.74	20.57	18.54	18.03
Crude fat	4.62	4.70	5.20	6.05
Crude fiber	3.18	3.13	2.96	2.83
Crude ash	5.44	4.65	4.10	3.85
Lysine	1.39	1.30	1.14	1.11
Methionine	0.63	0.58	0.50	0.52
Calcium	0.77	0.56	0.49	0.45
Phosphorus	0.58	0.47	0.40	0.35
Sodium	0.14	0.14	0.13	0.13

At the end of the rearing period, at 42 days of age, the chickens were properly prepared for slaughter, which was carried out by stunning followed by decapitation. The control group was slaughtered first, followed by the experimental group.

Environmental enrichment with music

The environment of the experimental group (M) was enriched with ambient relaxation music (Weightless - Marconi Union). The track was played for two hours daily from 8:00 to 10:00 during the birds' waking period to reduce stress hormone release, which, according to de Jong et al. (2001), occurs immediately after the lights are turned on. This routine was repeated daily throughout the rearing period.

During music playback, a sound-level meter was used to measure the sound levels in the box, which included both the music and ambient noise. Measurements were taken at three points within the box (Fig. 4). The volume in the hall was approximately 70 dB, which did not exceeding the level that indicated excessive noise in the room (according to the Council of the European Union, 2007: "noise levels in broiler chicken houses should be minimized").

Fig. 4.

Projection of the experimental hall from above; the locations from which the sound level measurements were taken with a sound-level meter.

Just before slaughter, the birds in the experimental group were placed in transport crates and moved to a room adjacent to the slaughterhouse, where the track Weightless by Marconi Union was played again at a volume of approximately 70 dB. This lasted for about 30 minutes, until the slaughter of the individuals designated for analysis was completed.

Analysis of parameters

On day 42 of rearing, which was also the slaughter day, individuals from each group were weighed. Ten chickens from each group (selected based on body weight closest to the average body weight of the control and experimental groups), were designated for analysis.

Production performance. On the day of chick placement, during each feed change (on days 10, 22, and 35), and on the day of slaughter (day 42), the body weights from both groups were monitored, and feed intake and mortality were recorded. At the end of the rearing period, the feed conversion ratio (FCR) was calculated.

Animal welfare. A welfare assessment of the birds was conducted on day 35 of rearing. Excreta samples (approximately 5 g, three samples from randomly selected locations within three boxes for both groups) were collected to analyze cortisol content. The samples were transported to the laboratory and prepared for analysis by creating a solution of 1 g of excreta matter in 2 ml of ultrapure water. The solution was then homogenized and centrifuged, and the resulting supernatant was collected. The prepared samples were analyzed using a DetectX® Cortisol Enzyme Immunoassay Kit (catalog number: K003-H1W) following the kit's instructions for measuring glucocorticoids in excreta. On this day, gait score (GS), in accordance with Kestin et al. (1992), and footpad dermatitis (FPD); hock burns (HB); and plumage cleanliness (PC), according to the Welfare Quality® Consortium (2009), were also evaluated.

Determination of Blood Parameters. Blood samples (2 × 1 mL) were collected from the jugular veins of 10 randomly chosen chickens from each group at 42 days of life. The blood was collected from each bird in one tube coated with EDTAK3 (ethylenediaminetetraacetic acid tripotassium salt dehydrate) for hematological analysis, and in a separate tube without additives for biochemical tests. These were sent to a commercial laboratory for analysis (Vetlab sp. z o. o., Poland).

The number of red blood cells (RBCs, 10⁶/µL), concentration of hemoglobin (g/dl), and hematocrit (%) were determined in a Sysmex-XN-VET impedance analyzer. The white blood cell (WBC, 10³/µL) counts were determined manually in a Burker's hematological chamber, while the percentage of heterophiles, lymphocytes, monocytes, eosinophils, and basophils were established by manual counting in slide blood smears.

A chemistry analyzer (Beckman Coulter AU680/AU5800) was used for determining the following biochemical serum parameters: alanine transaminase (ALT, U/l), α-Amylase (U/l), alkaline phosphatase (AP, U/l), aspartate transaminase (AST, U/l), total protein (TP, g/l), cholesterol (mmol/l), triglycerides (TG, mmol/l), creatine kinase (CK, U/l), glutamate dehydrogenase (GDH, U/l), γ-glutamyltranspeptidase (γ-GT, U/l), uric acid (mmol/l), lactate dehydrogenase (LDH, U/l), bile acids (µmol/l), and ions: total calcium (Ca, mmol/l), phosphorus (P, mmol/l), potassium (K, mmol/l), sodium (Na, mmol/l), iron (Fe, µmol/l).

Rearing conditions. During the rearing period, rearing conditions were also monitored. The pH of the litter was analyzed using a soil and liquid pH tester (Elmetron pH meter, Poland). Litter samples of 5 g were collected from three boxes in each group (from three random locations in each box). These samples were then thoroughly mixed with 20 ml of distilled water. After leaving the mixtures for 15 minutes, the pH was measured using an ELMETRON CP-401 pH meter with a glass electrode and temperature sensor (Elmetron, Poland). Each sample's pH was measured three times.

Statistical analysis. Statistical analysis was performed using SPSS software (PS IMGO PRO 8.0) (2022). Arithmetic means and standard deviations were also considered during the analysis. The significance of the differences between mean values of the included parameters was verified using the Student's t-test, assuming significance levels of p ≤ 0.05 and p ≤ 0.01. The Mann-Whitney U test was used to verify welfare quality results, assuming significance levels of p ≤ 0.05 and p ≤ 0.01.

Results

Production performance of the broiler chickens

The production performance of chickens is one of the most important pieces of information for poultry producers. Table 2 presents the production results for the broiler chickens in the study, including initial and final body weights, feed conversion ratio (FCR), and flock mortality (Table 2). The results indicated a significantly higher final body weight in the M group chickens compared to the C group chickens (p ≤ 0.05). The FCR, which indicates the amount of feed consumed per kilogram of body weight gain, was significantly lower in the M group than in the C group (p ≤ 0.05) (Table 2). There were no significant differences in mortality (p ≥ 0.05).

Table 2.

Mean initial and final body weights of broiler chickens, along with the average feed conversion ratio (FCR) and mortality rates for chickens in the experimental (M) and the control (C) groups (n=600).

Parameter	Group	Average	SD1	p-value
Initial body weight [g]	C2	40.33	2.95	0.269
	M3	40.24	3.01
Final body weight [g]	C	3107.92b	341.09	0.043
	M	3165.73a	391.17
FCR [kg:kg]	C	1.66a	0.03	0.028
	M	1.58b	0.02
Mortality	C	6.67	2.20	0.667
	M	5.83	2.20

¹SD - standard deviation.

^2,3C - non-treated control group; M - group treated with music

a, b - mean values marked with different letters differ significantly, p ≤ 0.05

Welfare assessment of the broiler chickens

Welfare quality was assessed on day 35 of the broiler chicken rearing period, as presented in Table 3, Table 4.

Table 3.

Cortisol concentration results in broiler chicken excreta on day 35 of rearing (n=10).

Cortisol	Group	Average	SD1	p-value
	C2	9.76A	0.211	<0.01
	M3	6.40B	0.587

¹SD - standard deviation.

^2,3C - non-treated control group; M - group treated with music

A, B - mean values marked with different letters differ significantly, p ≤ 0.01

Table 4.

Results of broiler chicken welfare quality assessment, in accordance with Kestin et al. (1992) and the Welfare Quality® Consortium (2009) on the 35th day of rearing (n=600).

Parameter	Group	Average	SD1	p-value
GS4	C2	1.60A	0.71	<0.001
	M3	0.18B	0.46
FPD5	C	0.92A	0.39	<0.001
	M	0.48B	0.51
HB6	C	0.78A	0.43	<0.001
	M	0.16B	0.37
PC7	C	1.19A	0.42	<0.001
	M	0.49B	0.54

¹SD - standard deviation.

^2,3C - non-treated control group; M - group treated with music

^4,5,6,7GS - gate score; FPD - footpad dermatitis; HB - hock burns; PC - plumage cleanliness

A, B - mean values marked with different letters differ significantly, p ≤ 0.01

Cortisol levels in the chickens’ excreta were measured using a DetectX® Cortisol Enzyme Immunoassay Kit (catalog number: K003-H1W). The results in Table 3 indicate a significantly lower concentration of this glucocorticoid in the music-enriched group (M) compared to the control group (C) (p ≤ 0.01).

The welfare quality assessment of the chickens conducted on the same day, in accordance with Kestin et al. (1992) and the Welfare Quality® Consortium (2009), also showed highly significant differences for each evaluated parameter (p ≤ 0.01): gait score (GS), footpad dermatitis (FPD), hock burns (HB), and plumage cleanliness (PC). These indicators were significantly better in the M group than in the C group (Table 4).

Determination of blood parameters

None of the birds presented any gross lesions at necropsy or the clinical symptoms of any diseases.

The results of the analysis of the blood parameters is presented in Table 5, Table 6.

Table 5.

Average red blood cell (RBC) and white blood cell (WBC) counts, concentration of hemoglobin, and the percentage of hematocrit, heterophiles, lymphocytes, monocytes, eosinophils, and basophils in the blood of the experimental chickens from group M and non-treated control group C (n=10).

Parameter	Group	Mean	SD1	p-value
RBC (106/µL)	C2	2.516B	0.298	0.01
	M3	2.947A	0.316
WBC (103/µL)	C	22.287	8.810	0.294
	M	27.730	11.751
Hemoglobin (g/dl)	C	7.137	0.824	0.057
	M	7.878	0.657
Hematocrit (%)	C	30.825b	3.545	0.013
	M	36.489a	4.567
Heterophiles (%)	C	36.125	7.140	0.356
	M	40.500	11.316
Lymphocytes (%)	C	43.125	8.935	0.396
	M	39.100	10.311
Monocytes (%)	C	4.875	3.356	0.727
	M	5.400	2.913
Eosinophils (%)	C	4.875	3.356	0.727
	M	5.400	2.913
Basophils (%)	C	9.000	3.891	0.342
	M	7.500	2.592

¹SD - standard deviation.

^2,3C - non-treated control group; M - group treated with music

a, b - mean values marked with different letters differ significantly, p ≤ 0.05; A, B - mean values marked with different letters differ significantly, p ≤ 0.01

Table 6.

Results of biochemical parameters in the serum of the experimental chickens (n=10).

Parameter	Group	Mean	SD1	p-value
ALT (U/l)	C2	1.870	0.865	0.978
	M3	1.880	0.713
α-Amylase (U/l)	C	532.200	108.338	0.936
	M	537.430	169.945
AP (U/l)	C	3120.630	1793.193	0.586
	M	2760.220	1005.526
AST (U/l)	C	531.730	291.685	0.632
	M	474.190	233.515
TP (g/l)	C	31.370b	3.586	0.023
	M	35.290a	3.464
Cholesterol (mmol/l)	C	3.585	0.334	0.466
	M	3.687	0.275
TG (mmol/l)	C	0.803	0.229	0.393
	M	0.719	0.199
CK (U/l)	C	31885.0	25389.32	0.930
	M	33007.0	31388.91
GDH (U/l)	C	4.030A	1.419	0.007
	M	2.440B	0.874
γ-GT (U/l)	C	20.810	3.612	0.798
	M	21.180	2.688
Uric acid (mmol/l)	C	0.295a	0.095	0.04
	M	0.221b	0.044
LDH (U/l)	C	2482.090	1439.829	0.979
	M	2465.310	1335.161
Bile acids (umol/l)	C	15.730	2.645	0.931
	M	15.573	4.962
Ca (mmol/l)	C	2.602B	0.113	0.004
	M	2.752A	0.091
P (mmol/l)	C	2.105	0.157	0.718
	M	2.130	0.146
K (mmol/l)	C	5.305	0.430	0.242
	M	5.015	0.624
Na (mmol/l)	C	151.130	2.793	0.672
	M	151.630	2.383
Fe (umol/l)	C	17.80	2.622	0.924
	M	17.71	1.373

¹SD - standard deviation.

^2,3C - non-treated control group; M - group treated with music

a, b - mean values marked with different letters differ significantly, p ≤ 0.05; A, B - mean values marked with different letters differ significantly, p ≤ 0.01

A significantly higher erythrocytes count (p ≤ 0.01) was observed in the blood of birds from group M compared to those from group C, while the hematocrit percentage in group M was also significantly higher (p ≤ 0.05). There was no statistically significant differences in the number of WBCs, hemoglobin concentrations, or the percentage of heterophiles, lymphocytes, monocytes, eosinophils, or basophils between groups M and C (Table 5).

A statistically significant, higher concentration of total protein and calcium in the serum was observed in group M in comparison to group C (p ≤ 0.05 and p ≤ 0.01, respectively). However, in the case of GDH and uric acid, the concentrations were significantly higher in the blood of chickens from group C than that from chickens from group M (p ≤ 0.01 and p ≤ 0.05, respectively) (Table 6).

Rearing conditions of the broiler chickens

The pH measurement results from litter samples collected from the boxes where the chickens were reared—presented in Table 7—indicated statistically significant differences between groups C and M on the 10th (p = 0.02) and 35th (p = 0.037) days of rearing, and highly significant differences on the 22nd day (p = 0.05). The sample from group M taken on the 10th day was slightly more acidic (lower pH level) than the samples from group C. For the samples collected on the 22nd and 35th days, the results were reversed, with higher pH values recorded for group C: on the 22nd day, the measurement for group C indicated a more alkaline pH (above 8.0), whereas on the 35th day, it did not exceed this value, and was similar to the measurement for group M on the 10th day (Table 7).

Table 7.

Average litter pH for samples collected on days 1, 10, 22, 35, and 42 of broiler chicken rearing (n=9).

Day of sample collection	Group	Average	SD1	p-value
Day 1	C2	6.38	0.02	0.189
	M3	6.40	0.01
Day 10	C	7.01b	0.23	0.02
	M	7.53a	0.09
Day 22	C	8.18A	0.06	0.005
	M	7.54B	0.18
Day 35	C	7.92a	0.03	0.037
	M	7.56b	0.20
Day 42	C	8.82	0.14	0.599
	M	8.76	0.10

¹SD - standard deviation.

^2,3C - non-treated control group; M - group treated with music

a, b - mean values marked with different letters differ significantly, p ≤ 0.05; A, B - mean values marked with different letters differ significantly, p ≤ 0.01

Measurements of harmful gas concentrations in the broilers’ housing were conducted on days 1, 10, 22, 35, and 42. No statistically significant differences were found in the measurements. Additionally, the values presented in Fig. 5, Fig. 6, Fig. 7 do not exceed the permissible concentrations specified in Council Directive 2007/43/EC (Council of the European Union, 2007), which establish minimum rules for the protection of chickens kept for meat production, or the Regulation of the Minister of Agriculture and Rural Development of 15 February 2010, on detailed conditions for keeping broiler chickens (Minister of Agriculture and Rural Development, 2010).

Fig. 5.

The average ammonia (NH3) concentration measured on the 1st, 10th, 22nd, 35th, and 42nd day of broiler chicken rearing at heights of 10 cm, 40 cm, and 180 cm.

Fig. 6.

Average carbon dioxide (CO2) concentration measured on the 1st, 10th, 22nd, 35th, and 42nd day of broiler chicken rearing at heights of 10 cm, 40 cm, and 180 cm.

Fig. 7.

The average concentration of hydrogen sulfide (H2S) measured on the 1st, 10th, 22nd, 35th, and 42nd day of broiler chicken rearing at heights of 10, 40, and 180 cm.

Discussion

Production performance of broiler chickens

The current experiment revealed highly significant differences in the final body weights of the chickens on day 42 of rearing. The greater body weights of the broilers in the group exposed to relaxation music (M) compared to the standard conditions group (C) likely results from the presence of music during rearing. Additionally, significant differences were observed in the FCR index, with chickens in group M requiring less feed to gain 1 kg of body weight compared to those in group C. Similar observations were noted by Gvaryahu et al. (1989) with classical music (Vivaldi's Four Seasons) using the IEM configuration (combined effects of imprinting, environmental enrichment, and music). The authors conducted two experiments. They indicated that the mentioned environmental enrichment using the IEM system for broiler chickens at eight weeks of age, resulted in higher body weights (p < 0.05) compared to the control group. Over the seven-day application of the IEM procedure, significantly lower feed intake by the birds was observed (p < 0.05) (Gvaryahu et al., 1989). Hafizah et al. (2015) noted the potential for stimulating higher feeding activity in chickens using the same piece (Vivaldi's Four Seasons) during the first week of their lives. The studied group of chickens consumed more feed than those in the control group or those in a group enriched by a recital of the holy Qur'an (Yaseen chapter), thus simultaneously achieving greater body weight gains. However, no significant differences were observed at the end of the broiler chicken rearing period (day 35) (Hafizah et al., 2015). Gao et al. (2023) also confirmed that classical music, although from Indian raga, contributed to improved body weight gains in chickens exposed to high stocking densities. Other publications have indicated the positive impact of classical music on chicken body weight and FCR (Tolun and Rathert, 2019). Relaxation music has not yet been widely analyzed concerning livestock. However, in those studies that have been done, authors have often mentioned the significant importance of the sound and structure of the music used in their studies, i.e., gentle sounds, calm tempo, and repetitive patterns. This likely links classical music with relaxation music. Most publications reference the significant effect of this type of music, which may contribute to improved production outcomes through processes occurring in the organism that result in stress reduction (Ciborowska et al., 2021). This aspect is analyzed later in this discussion section.

Welfare assessment of broiler chickens

The welfare of broiler chickens is a multifaceted issue requiring a holistic approach to production management. This experiment analyzed cortisol concentrations in samples taken during rearing (day 35) and assessed broiler chicken welfare based on Kestin et al. (1992) and the Welfare Quality® Consortium (2009). Although cortisol is less commonly used than corticosterone as a stress indicator in chickens, research has highlighted its significance in welfare contexts (Li et al., 2022; Yang et al., 2023). Additionally, the method for detecting glucocorticosteroid metabolites in animal feces is considered non-invasive, minimizing additional stress compared to methods like blood sampling (Dehnhard et al., 2003; Grundei et al., 2024). In the discussed experiment, the significantly lower cortisol concentration in samples from the M group compared to the C group indicates reduced stress in chickens related to standard rearing stimuli such as rapid growth, crowding, and feed changes. Similar results concerning classical music were observed by Dávila et al. (2011) and Gao et al. (2023). Conversely, Hafizah et al. (2015) noted that the stress-reducing effect of classical music in their study was present only during the first week of rearing. By the production age of 35 days, corticosterone levels were similar to those in the control group (Hafizah et al., 2015). However, research on other animal species suggests that music generally has a calming effect on stress (Alworth and Buerkle, 2013). This implies that relaxation music, like classical music, would have a stress-reducing effect on broiler chickens. This is likely possible through changes in brain physiology, chemistry, and morphology, influenced by music (Alworth and Buerkle, 2013). Gao et al. (2023) suggested that music likely reduces the stress response on the HPA axis (hypothalamic pituitary adrenocortical system) by inducing activity in brain structures such as the hippocampus. Additionally, studies on animal models have provided evidence for the significance of stress in altering gut microbiota composition, which in turn affects individual behavior (Wu et al., 2021; Johnson et al., 2024). Zhang et al. (2023) noted that relaxation music indirectly affects gut microbiota by modulating stress levels. Confirming these findings in broiler chickens requires further research on the impact of relaxation music on their physiology.

The results of the assessment of the welfare quality of the chickens clearly show a definite improvement in the welfare quality of group M chickens compared to group C. The Welfare Quality® Consortium (2009) emphasizes the importance of monitoring the health of chickens by observing, among other things, the welfare indicators mentioned in Table 4. This is a key element in correcting possible adverse factors in chicken production (Nielsen et al., 2023). Due to intensive genetic selection for body weight and growth rate, compensatory gait adaptation to minimize energy expenditure has started to emerge in broiler chickens. A correlation between body weight, growth rate, and the occurrence of lameness has been proven (Caplen et al., 2012). Kestin et al. (1992) developed a method for observing the gait of chickens, in which the relevance of the pace and frequency of the movement of birds is indicated: the evaluation is applied on a scale of 0–5, where the best score, 0, indicates a bird moving fast with little walking deficit, while the worst score, 5, indicates when the bird barely moves and often uses its wings to assist in movement. Lameness is also associated with the occurrence of FPD (foot pad dermatitis), hock burns (HB), and plumage cleanliness (PC). The first two conditions are linked to pain, which increases the potential for stress to affect production outcomes through reduced activity (Granquist et al., 2019). This, in turn, raises the risk of plumage soiling due to increased contact between the feet, hocks and breast, and the litter. Environmental conditions, such as litter humidity and ammonia concentration, are also cited as causes of issues with these parameters (Freeman et al., 2020). The authors of the current study suggest that the aforementioned impact of music on gut microbiota, and thus on excreta, may be related to litter quality.

Determination of blood parameters

All measured hematological and biochemical parameters were within the normal ranges for poultry, but some differences were noted between the groups. A higher red blood cell count, a higher hematocrit level, and no changes in the white blood cell count may be related to a more efficient use of the feed's nutrients by the birds, related to reduced stress resulting from the beneficial effect of music. The stress-induced release of cortisol leads to an increase in the number of leukocytes released from the marginal pool, while long-term stress could negatively affect their number. The negative effect of stress on the number of leukocytes was demonstrated by Derkho et al. (2021); although, the same authors did not find any differences in the number of RBCs between their groups; however, they did observe differences in heterogeneity between the groups. It has been postulated that strong interactions between leukocytes and red blood cells exist during stress. This could also have occurred in the current experiment, which manifested in changes to the RBC quantity. However, in-depth research is necessary to explore this interaction. In the experiment, a statistically higher level of TP was found in the serum of chickens from group M. This may be related to better feed utilization due to reduced stress from the relaxation music during potential daily stressors. This is reflected in the results presented in Table 2, which show significantly higher body weight in the M group chickens (p = 0.043) and improved FCR (p = 0.028). Additionally, better protein metabolism, with a predominance of anabolism over catabolism, is suggested by lower levels of GDH and uric acid. GDH, a mitochondrial enzyme present in high amounts in hepatocytes, is a sensitive indicator of liver function (Thrall et al., 2012; Lumeij, 2008). The statistically lower GDH levels in the serum of M group birds may indicate reduced hepatocyte breakdown. One of the functions of this enzyme is to catalyze the ammonia reaction, in which glutamate dehydrogenase deaminates amino acids in the liver and introduces ammonia into the uric acid cycle (Elowe and Gerson, 2022). Uric acid is the main product of protein nitrogen and purine metabolism in poultry, and approximately 90% of uric acid is secreted by the proximal convoluted tubules in healthy broilers (Harr, 2002). Lower levels of both GDH and uric acid may also be the result of decreased protein catabolism, which matches with the higher body weight, lower FCR, and higher TP in the serum. Calcium provides structural strength and support (bones and eggshell), and plays vital roles in many of the biochemical reactions in the body. Its absorption is via active transport and about 45% is transported in the serum with albumin (de Matos, 2008). The statistically higher level of Ca in the serum of birds from group M can also be explained by calcium being absorbed better from the feed. Also, the previously observed higher concentrations of TP in the serum may partially explain this level of Ca, as this chemical element is transported by proteins in high quantities. Studies have demonstrated that music affects blood parameters in humans and various animal species (Sharma and Mathur, 2011; Erken et al., 2008; Li et al., 2022). It is therefore possible that in our experiment, sound waves, in the form of relaxation music, influenced the physiological levels of the blood parameters in the broiler chickens.

Rearing conditions of broiler chickens

During the experiment, pH measurements of the litter and concentrations of harmful gases were taken on days 1, 10, 22, 35, and 42 of the chicken rearing period. Litter quality determines later production outcomes in chickens (de Toledo et al., 2020). The substrate on which chickens are reared affects the welfare indicators discussed above. It is crucial to monitor ammonia emissions, which are introduced into the environment through the decomposition of uric acid and undigested proteins in bird droppings (Nahm, 2003; Jacquier et al., 2022). Notably, there is a positive correlation between ammonia and litter pH—ammonia concentration increases with higher pH. Ammonia release is lower when litter pH is <7.0 and higher when pH >8.0 (de Toledo et al., 2020). In our experiment, litter pH was significantly higher for the M group compared to the C group on day 10 of rearing. Conversely, significantly lower pH was observed for the M group on days 22 and 35. In both these cases, pH values were above 7 but below 8. However, the pH value for the C group on day 22 exceeded 8. Given the lack of significance in the concentrations of harmful gases (NH3, CO2, H2S) presented in Fig. 5, Fig. 6, Fig. 7, the impact of environmental enrichment through music on the outcomes cannot be definitively established. The litter pH values (Table 7) may also have been influenced by the transition from one nutritional phase to another on the sample collection day. Further studies are needed to verify these findings.

Conclusions

The results of the conducted experiment demonstrate that environmental enrichment using relaxation music during broiler chicken rearing positively affects production outcomes and reduces bird stress. It was found that this intervention significantly improves chicken welfare; however, the mechanism by which such sounds exert their effects is not yet fully established. Further research is needed to verify the impact of relaxation music on broiler chicken physiology. The significance of this research is underscored by the global scale of poultry production and the low cost of implementing environmental enrichment through music.

Declaration of competing interest

As a courtesy, we would like to inform you that the authors declare that there is no conflict of interest in relation to the article "The Impact of Relaxation Music (Weightless by Marconi Union) on Production Performance, Welfare, and Hematological and Biochemical Blood Parameters in Broiler Chickens” to the journal Poultry Science, whose authors are Patrycja Ciborowska, Damian Bień, Artur Żbikowski, Karol Pawłowski, Jakub Urban, Anna Zalewska, Arkadiusz Matuszewski, Karwan Yaseen Kareem, Klara Piotrowska, Monika Michalczuk.