| Livestock Research for Rural Development 30 (4) 2018 | Guide for preparation of papers | LRRD Newsletter | Citation of this paper |
Stress generally deteriorates meat quality. The current study aims to evaluate the influence of the pre-slaughter transportation duration stress on carcass and meat quality in local chicken of Benin. Sixty-four chickens of 6 to 7 months old divided into 4 flocks of 8 males and 8 females each reared under traditional system were used. Chickens of the first group were not transported before slaughter. Whereas, chickens of the second group were slaughtered after 30 minutes of transportation, those of the third group, after one hour of transportation and the one of the fourth group, after two hours of transportation by motorcycles. Carcass and meat quality was evaluated.
Carcass quality traits didn’t vary according to the pre-slaughter transportation duration stress. The long transportation stress chickens had the higher pH values. Drip loss at 24 hours after slaughter didn't vary by transport duration. Meat lightness in the breast and in the thigh was higher for the 30 minutes of transportation chickens and for the unstressed one. The higher redness (a*) of breast meat was observed with chickens transported during two hours. The yellowness (b*) of the thigh was the same for the transport durations on the slaughter day but lower with the chickens transported during two hours the following day. The meat flavor, juiciness, tenderness and global acceptance didn't vary according to the transport durations. In general meat color and its technological quality decreased linearly with transport duration prior to slaughter.
Key words: animal welfare, chicken, products quality, transport stress
Stress can be considered as the reaction of the organism or the biological response to stimuli that disturb its normal physiological equilibrium or homeostasis (Lara et al 2013). This response results in the increasing of poultry plasma corticosterone concentration. According to Selye (1976), stress is a nonspecific response of the body to any demand whereas the stressor is an agent that produces stress at any time.
For animals destined to slaughter, the environmental conditions, the capture, the manipulations, the transportation, the feed withdrawal are some stress factors that can have consequences on the production (Lara et al 2013), animal welfare (Voslarova et al 2007) and on carcass and meat quality (Radu et al 2012). But genetics and biotope can affect the extent of these consequences. Genetics can explain 40% to 50% of the variability of breast ultimate pH observed within a population (Le Bihan-Duval et al 2001 and 2008; Chabault et al 2012).
Researchers are already working on how to control carcass and meat quality changings due to pre-slaughter stress factors across America, Europe, Asia and North Africa (González et al 2007; Perai et al 2014; Zhang et al 2014) where, the consequences of these factors on their genetic resources are already known. Meanwhile, the influence of local pre-slaughter stress conditions on indigenous chicken carcass and meat quality isn’t fully investigated in West Africa in general and in Benin in particular. It has been recorded that most of the indigenous chickens are often slaughtered after an important transportation of which stress has detrimental effects on the meat quality (Bonou et al 2014). One hour of pre-slaughter transportation by motorcycle had negatively affected meat pH, lightness and its red index mostly those of the thigh. Meat was darker, redder with a lower acidity degree and then, could be favorable to microorganism proliferation (Bonou et al 2017). Or, a prior survey revealed that in the Atlantic region of Benin, local chickens are transported by cars, motorcycles, bicycles or by people walking on 7 to 60 km during 33 to 169 minutes (Bonou 2014). But the reaction of the meat quality of this animal resource to stress factors duration is less reported. Thus, from which minor transportation duration meat and carcass quality attributes of these chickens are affected and what are the consequences when the duration flows? This work is to answer these questions by the assessment of the influence of pre-slaughter transportation duration stress on carcass and meat quality of indigenous chicken reared under traditional system in Benin.
The study was carried out in the Laboratory of Animal Biotechnology and Meat Technology of the Department of Animal Production and Health of the Polytechnic School of Abomey-Calavi. The chickens used were produced under traditional breeding system in Abomey-Calavi. This area benefits from climatic conditions of subequatorial type characterized by two rainy seasons with an uneven spatial and temporal repartition of rainfall (the major, from April to July and the minor, from September to November). These seasons are separated by two dry seasons. Average rainfall is close to 1200 mm per year. The monthly average temperatures vary between 27°C and 31°C. The relative air humidity fluctuates between 65% from January to March and 97% from June to July.
Sixty-four (64) local chickens of six to seven months old produced from two (2) roosters and ten (10) hens all of South ecotype of Benin were used. These birds were reared under traditional breeding system where, they have a habitat for night housing or protection against bad weather and a course of 400 m2. They fed themselves around and also received grains, agricultural by-products and kitchen rests. Birds were vaccinated against fowl pox and Newcastle disease. On the eve of the slaughter day, chickens were divided into four homogeneous flocks of 8 males and 8 females each and registered.
Birds of the flock 1 were the control chickens and didn't undergo any stress before slaughter. The others were attached on legs and kept until the following day morning where, they were transported with motorcycles and slaughtered immediately after. Chickens of the flock 2 were transported during 30 minutes on 15 km, those of the flock 3 during 1 hour on 25 km and the one of the flock 4 during 2 hours on 70 km. While transporting, they were all hung behind to motorcycles upside down. At the arrival, birds were weighted and immediately slaughtered by section of the jugular vein. After slaughter, chickens were scalded in a hot water (75°C) and plucked manually. Legs have been sectioned at the tibio-tarsusmetastasal joint level. The head were separated from the neck at the skull-atlas junction. The abdominal and thoracic cavities organs were taken off. Hot carcasses have been weighed and immediately cut.
Live weight before slaughter, hot carcass weight and carcass cuts weight (breast, wings, thigh-drumstick) were registered. Carcass yield was determined from the live weight and the percentage of each carcass cut from the hot carcass weight.
The pH was measured in the right slice of the breast muscle (Pectoralis major) and in the right thigh muscle ( Iliotibialis superficialis) at 2 cm depth with a portable pH-meter (HANNA Instrument R, Italy) provided with a specialized probe and a temperature control system. Measures were taken at 1h, 12h, 24h and 48h after slaughter. For every measure, 5 repetitions were performed. On each measure day, the pH-meter has been calibrated previously with two buffers pH-meter: pH 4 and pH 7 following a procedure described by the manufacturer.
The drip loss was determined with the left slice of the breast muscle according to the procedure described by Honikel (1987). Each sample was suspended to a hook, put into a refrigeration bag without touching its bottom. After 24 hours at 4°C in hung position, the samples were taken out of the bag without touching the bottom that contains the draining juice. They were mopped, weighted and drip loss was calculated as the percentage of weight loss during the storage.
The meat color was determined using a Minolta Chromameter CR-400 (Japan) in the trichromatic system (CIE L*a*b *) after storage of the samples at 4°C during 1 h 30 min. This is based on three dimensional space with one dimension for luminance (L* is the lightness) and two for color a* (a* is the redness) and b * (b* is the yellowness) (Zhang and Barbut 2005). The chroma (C) and the hue angle (h) were determined as followed: C= (a*2+ b*2)1/2 and h = tan-1b*/a*. For each measure, 5 repetitions were performed. The measures were taken on the ventral face, at the third superior on the thickest part of the breast muscle left slice and on the middle of the ventral face of the left thigh muscle. The Minolta was calibrated using standard color tiles. The color was measured on the slaughter day and at 24 hours post mortem.
The right slice of the Pectoralis major of each chicken was used for the sensory analysis. The samples were put in cooking bags separately without seasoning and boiled in a bain-marie until the meat core temperature reached 75°C. A trained jury of 10 members was used for the test. After cooling to room temperature, each sample of meat cooked was cut into ten identical pieces at least. Every judge received in a plate divided by the manufacturer in four parts of different colors a piece of each category and each flock of chicken and filled in a recapitulative results form. In total, eight samples of which two by flock (one from a male and one from a female) were put by turn in the plate under numbers 1 to 8. The judges have appreciated the tenderness, the juiciness, the flavor and the global acceptance of the meat under marks going from 1 to 5.
The data collected on carcass and meat quality were analyzed using the software SAS (Statistical Analysis System, 2006). The General Linear Model procedure was used for the variance analysis. The Fisher test was used to test the significance of the transportation duration stress, the sex effects on carcass and meat quality traits and the interaction between sex and transportation duration stress, being then in total, 8 treatments. For each flock, means were calculated and compared by transport duration. Means were compared pairwise by the Student test.
There was no effect of transportation time on live weight, or weight of hot carcass, breast, thigh-drumstick and the wings (Table 1).
The carcass traits of males and of females by sex are presented in the table 2. The thigh-drumstick weight, the wings weight, the thigh-drumstick yield and wings yield of males were higher than those of the females in the 30 minutes and in the 2 hours transported chickens (p<0.05). No significant variation was observed for the others parameters by sex.
The variation of the pH by transportation duration is given in the table 3. The pH of the breast muscle at the measures times was higher in the one and two hours transported birds than in the 30 minutes stressed one (p<0.001). These last chickens had pH values superior to those of the control group except at one hour post-mortem where they were similar. The same tendency was observed in the thigh muscles. The most important pH fall was observed in the two muscles during the first twelve hours post mortem (figure 1 and figure 2). The pH values varied with transport durations following a linear regression most evident at 1 hour after slaughter (figure 3 and figure 4).
The variation of the pH by sex is presented in the table 4. The breast meat pH of the males was higher than the one of females at one hour in the two hours transportation birds (p<0.05) and at the others measure times in the chickens transported for one hour ( p<0.01). Beyond the first measure time, the same tendency was observed in the thigh among one hour transported chickens and at 48 hours post-mortem with the control group.
There was no effect of transport duration and of sex on the drip loss (Table 1 and table 2).
|
Table 1. Carcass traits, drip loss and sensory quality of the Pectoralis major of indigenous chicken according to the pre-slaughter transportation duration |
||||||||||||
|
Variable |
Transportation time |
SEM |
p |
|||||||||
|
0.0h |
0.5h |
1.0h |
2.0h |
|||||||||
|
Live weight, g |
828 |
848 |
828 |
825 |
27.7 |
0.81 |
||||||
|
Hot carcass weight, g |
508 |
523 |
508 |
502 |
19.4 |
0.74 |
||||||
|
Breast weight, g |
116 |
117 |
116 |
112 |
4.41 |
0.63 |
||||||
|
Thigh-drumustick weight, g |
153 |
164 |
155 |
157 |
7.49 |
0.72 |
||||||
|
Wings weight, g |
63.0 |
63.5 |
63.0 |
62.4 |
2.50 |
0.95 |
||||||
|
Hot carcass yield, % |
61.2 |
61.6 |
61.2 |
60.9 |
0.73 |
0.80 |
||||||
|
Breast yield, % |
22.9 |
22.5 |
22.9 |
22.3 |
0.51 |
0.70 |
||||||
|
Thigh-drumustick yield, % |
30.0 |
31.2 |
30.7 |
31.2 |
0.72 |
0.87 |
||||||
|
Wings yield, % |
12.5 |
12.2 |
12.5 |
12.4 |
0.36 |
0.80 |
||||||
|
Drip loss, % |
0.58 |
0.52 |
0.45 |
0.40 |
0.08 |
0.54 |
||||||
|
Flavor |
3.10a |
3.08a |
2.90ab |
2.86b |
0.06 |
0.04 |
||||||
|
Juiciness |
2.98 |
2.95 |
2.85 |
2.82 |
0.06 |
0.30 |
||||||
|
Tenderness |
3.02 |
2.96 |
3.04 |
3.10 |
0.08 |
0.51 |
||||||
|
Global Acceptance |
3.25 |
3.22 |
3.11 |
3.06 |
0.06 |
0.18 |
||||||
|
CTL/ 0.0h : Not transported ; 0.5h : transported for 30 minutes ; 1.0h : transported for one hour ; 2.0h : transported for 2 hours ; Means of the same line followed by different letters differ significantly at the threshold of 5%. |
||||||||||||
|
Table 2. Effect of sex on carcass traits, drip loss and sensory quality of the Pectoralis major of the indigenous chicken according to the pre-slaughter transportation duration stress |
||||||||||||
|
Variable |
Transportation time |
SME |
p |
|||||||||
|
0.0h |
0.5h |
1.0h |
2.0h |
|||||||||
|
Female |
Male |
Female |
Male |
Female |
Male |
Female |
Male |
|||||
|
Live weight, g |
815 |
841 |
816 |
881 |
815 |
841 |
784 |
866 |
38.8 |
0.75 |
||
|
Hot carcass weight, g |
494 |
522 |
495 |
551 |
494 |
522 |
480 |
525 |
27.1 |
0.87 |
||
|
Breast weight, g |
119 |
114 |
114 |
120 |
119 |
113 |
108 |
115 |
6.35 |
0.56 |
||
|
Thigh-drumustick weight, g |
144a |
162a |
147a |
180b |
149a |
162a |
142a |
173b |
9.69 |
0.04 |
||
|
Wings weight, g |
60.0a |
66.5a |
56.4a |
70.6b |
59.6a |
66.5a |
56.4a |
68.4b |
2.95 |
0.04 |
||
|
Hot carcass yield, % |
60.6 |
61.8 |
60.7 |
62.4 |
60.6 |
61.8 |
61.2 |
60.6 |
1.05 |
0.51 |
||
|
Breast yield, % |
23.9 |
21.8 |
23.1 |
21.9 |
23.9 |
21.8 |
22.2 |
22.0 |
0.69 |
0.54 |
||
|
Thigh-drumustick yield, % |
28.7a |
31.4a |
29.8a |
32.6b |
30.1a |
31.4a |
29.7a |
32.7b |
0.94 |
0.03 |
||
|
Wings yield, % |
12.2a |
12.9a |
11.4a |
12.9b |
12.1a |
12.9a |
11.8a |
13.1b |
0.47 |
0.04 |
||
|
Drip loss, % |
0.60a |
0.56a |
0.61a |
0.43a |
0.51a |
0.40a |
0.41a |
0.38a |
0.11 |
0.55 |
||
|
Flavor |
3.08a |
3.12a |
3.07a |
3.10a |
3.06b |
2.75a |
2.86a |
2.86a |
0.09 |
0.04 |
||
|
Juiciness |
2.97 |
2.98 |
2.93 |
2.97 |
2.85 |
2.86 |
2.78 |
2.86 |
0.08 |
0.94 |
||
|
Tenderness |
3.00 |
3.04 |
2.86 |
3.07 |
2.95 |
3.13 |
3.01 |
3.18 |
0.11 |
0.98 |
||
|
Global Acceptance |
3.27a |
3.23a |
3.08a |
3.36b |
3.18a |
3.03a |
3.01a |
3.12a |
0.08 |
0.04 |
||
|
CTL/ 0.0h : Not transported ; 0.5h : transported for 30 minutes ; 1.0h : transported for one hour ; 2.0h : transported for 2 hours ; Means between the classes of the same line followed by different letters differ significantly at the threshold of 5%. |
||||||||||||
|
Table 3. Breast and thigh muscles pH of indigenous chicken according to the pre-slaughter transportation duration stress |
||||||||
|
Moment (hour) |
Muscle |
Transportation time |
SME |
p |
||||
|
0.0h |
0.5h |
1.0h |
2.0h |
|||||
|
1 |
Breast |
6.05b |
6.02b |
6.21a |
6.33a |
0.05 |
0.0005 |
|
|
Thigh |
6.20b |
6.23b |
6.26ab |
6.33a |
0.02 |
0.04 |
||
|
12 |
Breast |
5.74c |
5.92b |
6.12a |
6.12a |
0.03 |
0.0001 |
|
|
Thigh |
5.93c |
6.18b |
6.21b |
6.29a |
0.02 |
0.001 |
||
|
24 |
Breast |
5.69c |
5.91b |
6.10a |
6.11a |
0.03 |
0.0001 |
|
|
Thigh |
5.87c |
6.16b |
6.21b |
6.30a |
0.02 |
0.0008 |
||
|
48 |
Breast |
5.72c |
5.91b |
6.09a |
6.10a |
0.03 |
0.0001 |
|
|
Thigh |
5.88c |
6.16b |
6.23ab |
6.29a |
0.02 |
0.007 |
||
|
CTL/ 0.0h : Not transported ; 0.5h : transported for 30 minutes ; 1.0h : transported for one hour ; 2.0h : transported for 2 hours ; Means of the same line followed by different letters differ significantly at the threshold of 5%. |
||||||||
|
Table 4. Effect of sex on breast and thigh muscles pH of the indigenous chicken according to the pre-slaughter transportation duration stress |
||||||||||||
|
Moment
|
Muscle |
Transportation time |
SME |
p |
||||||||
|
0.0h |
0.5h |
1.0h |
2.0h |
|||||||||
|
Female |
Male |
Female |
Male |
Female |
Male |
Female |
Male |
|||||
|
1 |
Breast |
6.00a |
6.10a |
5.95a |
6.10a |
6.12a |
6.29a |
6.20a |
6.46b |
0.07 |
0.04 |
|
|
Thigh |
6.15 |
6.25 |
6.25 |
6.22 |
6.22 |
6.30 |
6.30 |
6.36 |
0.04 |
0.72 |
||
|
12 |
Breast |
5.75a |
5.72a |
5.92a |
5.93a |
6.01a |
6.23b |
6.11a |
6.13a |
0.05 |
0.008 |
|
|
Thigh |
5.93a |
5.93a |
6.17a |
6.19a |
6.14 a |
6.28b |
6.27a |
6.31a |
0.04 |
0.04 |
||
|
24 |
Breast |
5.68a |
5.71a |
5.91a |
5.91a |
5.99a |
6.21b |
6.10 a |
6.12a |
0.05 |
0.005 |
|
|
Thigh |
5.81a |
5.93a |
6.13a |
6.18a |
6.14a |
6.28b |
6.27a |
6.34a |
0.03 |
0.004 |
||
|
48 |
Breast |
5.70a |
5.73a |
5.91a |
5.91a |
5.99a |
6.20b |
6.09 a |
6.11a |
0.04 |
0.004 |
|
|
Thigh |
5.83b |
5.94a |
6.13a |
6.18a |
6.16a |
6.29b |
6.26a |
6.32a |
0.04 |
0.004 |
||
|
CTL/ 0.0h : Not transported ; 0.5h : transported for 30 minutes ; 1.0h : transported for one hour ; 2.0h : transported for 2 hours ; Means between the classes of the same line followed by different letters differ significantly at the threshold of 5%. |
||||||||||||
|
| Figure 1. Breast meat pH fall according to the transportation duration stress during the 48 hours post-mortem |
 |
| Figure 2. Thigh meat pH fall according to the transportation duration stress during the 48 hours post-mortem |
 |
| Figure 3. Breast meat pH at one hour post-mortem according to the transportation duration |
 |
| Figure 4. Thigh meat pH at one hour post-mortem according to the transportation duration |
Color traits on the slaughter day and at 24 hours post mortem are presented in tables 5. For both breast and thigh meat the lightness was higher with the control and the short transportation animals at the two moments but with very higher difference in the breast the first day. The most transported chickens showed the smaller values. The red index a* was higher in the breast of the two hours transported birds at the measures times but similar for those of the others durations. The yellow index b * was the same on the slaughter day but higher in the control and 30 minutes transportation birds at 24 hours post-mortem. The hue angle was lower in the thigh of the control and of the short transported chickens 24 hours after slaughter (p<0.01). The chroma of the breast muscle showed that same tendency in the control and in the one hour transported chickens at the measure times.
The variation of color by sex for the four groups is presented in tables 6. In the thigh muscle the yellow index in females transported for 30 minutes and for one hour was higher than the one of their correspondent males on the slaughter day (p <0.05). At 24 hours post mortem, the lightness of females transported during 30 minutes was also higher (p<0.05) than that of their homologue males. The chroma is higher in females than in males with one hour transportation chickens but it was the opposite in the birds transported for two hours.
In the breast meat, on the first day, the lightness was higher in females of 30 minutes transported chickens whereas similar for both sexes in the others flocks. The yellow index was also superior in females with 30 minutes and one hour transported birds (p <0.01) than in their homologue males. The red index a* was higher in the males than in the females of two hours of transportation chickens. The chroma was also higher in these males and in the females transported during 30 minutes. On the following day, the higher lightness was found in females transported for one hour. The red index of males was superior to the one of females in poultry transported for 30 minutes and for one hour (p<0.05) whereas their yellow index were lower. The hue angle in the males was higher than the one in their homologue females with one hour transported fowls.
|
Table 5. Color of the Pectoralis major and of the Iliotibialis superficalis muscles of indigenous chicken according to the pre-slaughter transportation duration stress on the slaughter day and 24 hours after |
||||||||
|
Moment |
Muscle |
Variable |
Transportation time |
SME |
p |
|||
|
0.0h |
0.5h |
1.0h |
2.0h |
|||||
|
Slaughter day |
Thigh |
L* |
49.1a |
49.6a |
46.9b |
47.1b |
0.80 |
0.04 |
|
a* |
17.2 |
17.3 |
18.3 |
17.1 |
0.56 |
0.27 |
||
|
b* |
9.59 |
10.9 |
9.59 |
9.61 |
0.48 |
0.10 |
||
|
Hue angle |
1.75 |
1.43 |
2.03 |
1.72 |
0.25 |
0.25 |
||
|
Chroma |
21.2 |
21.0 |
21.0 |
20.3 |
0.55 |
0.57 |
||
|
|
|
|
|
|
|
|
|
|
|
a* |
6.01a |
6.00a |
6.99a |
7.19b |
0.31 |
0.01 |
||
|
b* |
7.64 |
8.67 |
7.72 |
9.00 |
0.51 |
0.18 |
||
|
Hue angle |
0.65 |
0.23 |
0.93 |
0.43 |
0.43 |
0.50 |
||
|
Chroma |
10.5a |
10.9ab |
10.4a |
11.8b |
0.49 |
0.04 |
||
|
24 hours after slaughter |
Thigh |
L* |
48.6a |
48.5a |
47.6a |
46.6b |
0.64 |
0.04 |
|
a* |
16.6 |
16.8 |
17.1 |
17.4 |
0.45 |
0.59 |
||
|
b* |
10.5a |
10.5a |
10.4ab |
9.18b |
0.47 |
0.04 |
||
|
Hue angle |
1.50a |
1.53a |
1.91ab |
2.53b |
0.24 |
0.01 |
||
|
Chroma |
20.1 |
20.1 |
20.4 |
20.2 |
0.48 |
0.86 |
||
|
|
|
|
|
|
|
|
|
|
|
a* |
5.30a |
6.08ab |
5.33a |
6.17b |
0.29 |
0.04 |
||
|
b* |
8.92a |
8.90a |
7.18b |
8.58a |
0.40 |
0.01 |
||
|
Hue angle |
0.48 |
0.43 |
0.42 |
0.51 |
0.24 |
0.96 |
||
|
Chroma |
9.48b |
11.21a |
9.46b |
10.95a |
0.36 |
0.001 |
||
|
L* : lightness ; a* : red index ; b* : yellow index ; CTL/0.0h : Not transported ; 0.5h : transported for 30 minutes ; 1.0h : transported for one hour ; 2.0h : transported for 2 hours ; Means of the same line followed by different letters differ significantly at the threshold of 5%. |
||||||||
|
Table 6. Effect of sex on color of thePectoralis major and of the Iliotibialis superficalis muscles of indigenous chicken according to the pre-slaughter transportation duration stress |
||||||||||||
|
Moment |
Muscle |
Variable |
Transportation time |
SME |
p |
|||||||
|
0.0h |
0.5h |
1.0h |
2.0h |
|||||||||
|
Female |
M ale |
Female |
M ale |
Female |
M ale |
Female |
Male |
|||||
|
Slaughter day |
Thigh |
L* |
49. 2 |
49.0 |
49.7 |
48.6 |
46.9 |
46.8 |
45.5 |
48.6 |
1.12 |
0.15 |
|
a* |
16.4 |
17.9 |
16.6 |
18.1 |
18.6 |
18.0 |
16.6 |
17.7 |
0.80 |
0.38 |
||
|
b* |
9.69a |
9.49a |
12.0b |
9.76a |
10.7b |
8.43a |
10.3a |
8.95a |
0.67 |
0.04 |
||
|
Hue angle |
1.61 |
1.89 |
1.34 |
1.52 |
1.67 |
2.39 |
1.68 |
1.76 |
0.36 |
0.63 |
||
|
Chroma |
21.3 |
21.2 |
21.2 |
20.8 |
21.8 |
20.2 |
20.1 |
20.4 |
0.77 |
0.46 |
||
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
a* |
5.93a |
6.09a |
5.82a |
6.18a |
5.53a |
6.45a |
6.26a |
8.12b |
0.44 |
0.04 |
||
|
b* |
7.85a |
7.43a |
10.56a |
6.78b |
8.73a |
6.71b |
8.62a |
9.37a |
0.69 |
0.01 |
||
|
Hue angle |
0.50 |
0.80 |
-0.12 |
0.58 |
1.04 |
0.81 |
0.36 |
0.50 |
0.61 |
0.74 |
||
|
Chroma |
10.5a |
10.4a |
12.5a |
9.35b |
10.9a |
9.98a |
10.9b |
12.8a |
0.67 |
0.001 |
||
|
24 hours after slaughter |
Thigh |
L* |
48.8a |
48.3a |
49.8b |
47.2a |
47.9a |
47.4a |
46.3a |
46.9a |
0.90 |
0.04 |
|
a* |
16.4 |
16.7 |
16.0 |
17.5 |
17.7 |
16.6 |
17.5 |
17.4 |
0.63 |
0.12 |
||
|
b* |
10.6a |
10.4a |
11.8b |
9.18a |
11.5b |
9.25a |
10.1b |
8.24a |
0.65 |
0.04 |
||
|
Hue angle |
1.45a |
1.55a |
1.19a |
1.87a |
1.75a |
2.07a |
1.95a |
3.10b |
0.34 |
0.04 |
||
|
Chroma |
20.1a |
20.0a |
20.3a |
19.9a |
21.5b |
19.4a |
20.9a |
19.4a |
0.67 |
0.04 |
||
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
a* |
5.20a |
5.40a |
5.24a |
6.92b |
4.75a |
5.92b |
5.92a |
6.43a |
0.40 |
0.04 |
||
|
b* |
8.95a |
8.89a |
9.39b |
8.42a |
7.73b |
6.63a |
8.44a |
8.72a |
0.57 |
0.04 |
||
|
Hue angle |
0.46a |
0.50a |
0.35a |
0.51a |
-0.06a |
0.92b |
0.40a |
0.61a |
0.34 |
0.04 |
||
|
Chroma |
9.49 |
9.47 |
11.2 |
11.2 |
9.31 |
9.61 |
10.6 |
11.3 |
0.51 |
0.77 |
||
|
L* : lightness ; a* : red index ; b* : yellow index ; NT : CTL/0.0h : Not transported ; 0.5h : transported for 30 minutes ; 1.0h : transported for one hour ; 2.0h : transported for 2 hours ; Means between the classes of the same line followed by different letters differ significantly at the threshold of 5%. |
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The juiciness, the tenderness and the global acceptance of the breast meat didn't vary between the four groups of chickens (Table 1). On the contrary, the flavor was more intense in the control and in the 30 minutes transportation chickens followed respectively by the one and the two hours stressed birds. From one sex to the other, only flavor and global acceptance of meat varied (Table 2). The flavor was higher in females than in males with two hours of transportation (p <0.05). Meat of males transported during 30 minutes was more appreciated than the one of their correspondent females (p <0.05).
There was no effect of transportation duration on carcass parameters. The similarity observed first shows that the experimental flocks are homogenous. The weight and the yield results of the current study are close to those recorded by Youssao et al (2009) and Bonou et al (2017). Then, the non-existence of significant difference between weight and yield parameters according to the stress in the present study was also reported by Bonou et al (2017) with stress of one hour of transportation and of 10 minutes of capture chase. This situation could be explained by the short stress durations and the immediate slaughter of birds after the process. Otherwise, the immune reaction could result in reduction of feed intake, growth disturbance and weight loss. As example, Sohail et al (2012) recorded in broiler exposed to chronic heat stress a reduction of 16.4% of feed intake, of 32.6% of body weight and an increasing of feed conversion ratio of 25.6%.
The pH of the breast and of the thigh muscles of chickens stressed during one or two hours of transportation was superior to the one of the 30 minutes of transportation of which pH was also most of the time higher than those of the control chickens. The pH recorded with the most transported chickens was the highest especially in the thigh. The muscle acidification was then lower with chickens stressed by the long transportation duration. Their glycogen stock level could be lower. They could have certainly use part of their reserve to produce energy during the physical activities they endured in the transportation process. According to Berri (2015), the ultimate pH depends on the glycogen concentration of the muscles at the slaughter time. Transportation for 3 hours decreases the plasma glycogen concentration in broilers (Zhang et al 2014). Animal’s disturbance lead to the depletion of muscle glycogen content and then to a higher meat pH (Cartier and Moëvi 2007). The wings flapping duration on the slaughter line is negatively correlated to the muscle glycogen potential (Berri et al 2005).
The results of the current study are similar to those of other authors. Gigaud et al (2007) observed with the free-range chicken that as for the transportation duration, a long waiting time (superior to 4 hours) result in highest pHu. Longer is the transportation duration, higher is the pHu (Gigaud et al 2007). Berri et al (2005) studying the effect of the activity on the slaughter line recorded that the increasing of the wings flapping duration provokes a higher pHu in broilers. Debut et al (2003) noticed that the thigh pHu is one of the main parameters influenced by pre-slaughter stress conditions. They observed that a two hours of transportation leads to a higher ultimate pH (6.21). But, they remarked no difference in the breast meat pH of transported and control chickens. Besides, Barbut et al (2005), Oba et al (2009), Langer et al (2010) and Xing et al (2015) have recorded Pale Soft and Exudative (PSE) chicken’s meat with short lengths of transportation at high temperature.
The pHu usually observed in chicken meat is around 5.8 (Gigaud et al 2007). The pH48 of the breast of the chickens transported for one hour (6.08) and for two hours (6.10) are too superior to the normal. Only the one of 30 minutes transportation (5.91) birds seem little close. These values of pHu are not comparable to normal values reported in the literature (Berri and Jehl 2001; Debut et al 2003; Quentin et al 2003; Fanatico et al 2005; Bonou et al 2017). Even, in the thigh of the 30 minutes (6.16), of the one hour (6.23) and of the two hours (6.29) transported chickens, pH48 is relatively higher. Bonou et al (2017) also registered similar result with local chickens transported during 10 minutes. So, the meat of the local transported chickens could be favorable for microbial proliferation and then, presents important sanitary risks for the consumers.
In the two muscles, the most important pH fall occurred in the first twelve hours post mortem. Bonou et al (2017) found a similar result. During this period, the muscle glycogen was more available for anaerobic glycolysis reactions that take place in meat maturation process.
Besides, from one sex to the other, males showed higher pH values than their homologues females at several measures times. Bonou et al (2017) also recorded similar situation. The glycogen potential was therefore least in males. They seem more sensitive to the stress than females. Schneider et al (2012) reported an ultimate breast pH in the males higher than the one in the females (5.96 vs 5.87).
The drip loss didn’t vary according to the transportation duration. On the other hand, Berri et al (2005), studying the effect of the stress of the activity on the slaughter line preceded or not by heat exposure, found that drip loss was more important in the stressed chickens of which pHu was relatively lower. Schneider et al (2012) and Zhang et al (2014) also reported lower drip loss when the pH was higher. This relation is not clearly statistically perceptible in the current study.
Drip loss didn’t statistically vary by sex but females showed the important arithmetic proportions. This tends to confirm the negative correlation that exists between meat pH and meat drip loss. In the study of Schneider et al (2012), the difference was clear. The drip loss of females (2.34) was significantly superior to the one of the males (1.99%).
In the breast and thigh meats, the lightness was higher in the control and in the 30 minutes of transportation chickens at the two measure moments but smaller with the most transported birds. The lower values observed in theses chickens indicate that their muscles are darker. Thus, the pre-slaughter stress of two hours of transportation influences more negatively the lightness of the local chicken’s meat. A negative effect of stress on the meat lightness was also recorded by other authors in chickens. Gigaud et al (2007) observed that as for the transportation duration, a long waiting time, (superior to 4 hours) result in a lower lightness. Debut et al (2003) observed a similar effect also after two hours of transportation but only in the thigh meat. Bonou et al (2017) registered lower lightness with local chickens stressed by the transportation or by the capture chase. On the contrary, higher lightness was reported with other pre-slaughter stress factors. For example, the activity on the slaughter line was associated with higher value of meat lightness (Berri et al 2005).
The red index a* was lower in the breast of the control, the 30 minutes and of the one hour of transportation chickens at the two times. The high tendency in the two hours transported chickens indicates that the red color of the breast is influenced by the transportation duration stress. Bonou et al (2017) also got redder breast meat in local chickens stressed by the transportation or by the capture chase. Bianchi et al (2006) reported a significant effect of the transportation on poultry meat color. Birds transported on a short distance (<40 km) presented in the breast higher red index than (a * = 3.59) those transported on 40 to 210 km or more (a * = 3.28 and 3.04 respectively). The transportation length has affected the red index. However, the non-presentation of this result by the transportation duration didn’t allow a deep comparison. The redder could be explained by an increasing of the hemoglobin rate due to an important blood influx in the muscle in activity. However, Debut et al (2003) didn't observe a significant difference between the transported chickens and the control one.
The yellow index b * registered in the thigh was identical for all the four flocks on the slaughter day but lower with the two hour transported birds at 24 hours post mortem. Then, it’s thinkable that the yellow index in the local chicken thigh is as well as the lightness negatively influenced by the transportation duration stress at 24 hour post mortem. Bonou et al (2017) obtained similar results. On the contrary, Debut et al (2003) didn't observe a significant difference between the transported chickens and the control one for this parameter in the thigh and breast muscles.
The local chicken meat pH and color of the current study results analysis reveals that higher pH is associated to lower lightness and to higher red index. A similar relation was described in several studies. Thus, Berri et al (2005), Gigaud et al (2006), Gigaud and Berri, (2007), Gigaud et al (2007 and 2008), Sheard et al (2012), Harford et al (2014) and Xing et al (2015) reported that the color of meat in poultry especially the lightness and the ultimate pH are in significant negative correlation. In addition, this study showed that the higher lightness tend to be associated with higher yellow index. Bonou et al (2017) also remarked such relation. Harford et al (2014) observed that when the lightness and the yellow index increase, the red index decreases. Indeed, the selection for the increasing of the lightness resulted in an increasing of the yellow index.
In general, the higher lightness and yellow index were found in females whereas the higher values of the red index were observed in males. These reports are the consequence of pH that tends to be higher in males. The results correspond to the relations described above between these parameters of color and the pH (Sheard et al 2012; Harford et al 2014; Xing et al 2015; Bonou et al 2017). Besides, El Rammouz (2005) indicated that in poultry, the concentration of the myoglobin, pigment responsible for the red color, is more abundant in the breast and thigh muscles of the males than in those of the females.
The juiciness, the tenderness and the global acceptance of the breast meat didn't vary between transport durations. This non-existence of difference between sensory quality attributes according to the stress could be explained by the non-conservation of the meat used for the test during a long time. The analysis was done at 48 hours after slaughter. Otherwise, although the difference of the pH is not too higher, at that time, it could affect meat juiciness and tenderness which are directly in relationship with meat pH (Hocquette et al 2000; Geay et al 2002).
The marks given by the jury to the sensory meat attributes are around 3/5. Similar results were gotten by Youssao et al (2009), and Bonou et al (2017) for the sensory quality of the local chicken. The flavor, the juiciness, the tenderness and the global acceptance of the breast meat were also similar from males to females of the flocks. One the contrary, the flavor was more intense for birds transported during 30 minutes and for the control one. Since chickens have the same age, the denaturation of lipid that imprison meat aroma could explain the lower value of flavor registered with the most transported birds. Micol et al (2010) reported that meat tenderness and flavor increase progressively with the animal age in relation with the augmentation of the Intra-Muscular Lipid rate. Salifou et al (2013) recorded that the meat of males castrated has higher flavor in relationship with their fattening more elevated. Moreover, the flavor was higher in females than in males of one hour of transportation. This could be explained by the difference in the fattening state of the two sexes. More important is muscle fat content, more intense is the meat flavor up to threshold of 10% (Lebret et al 2015).
The study of the influence of the pre-slaughter transportation duration stress on carcass and meat quality of indigenous chicken reared under traditional system in Benin reveals that these stress conditions doesn't influence the carcass quality but, from 30 minutes of transportation, the meat quality is negatively affected. They lead to a low meat acidification degree. The phenomenon is pronounced in the thigh meat. The long transportation durations also result in redder, darker, less yellow and less tasty meat.
The authors thank “ la Commission de l’Union Economique et Monétaire Ouest Africaine” for its financial support.
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Received 20 September 2017; Accepted 30 January 2018; Published 1 April 2018