4.1. Carcass Characteristics, Livability, and Bleeding Out
Because birds with a similar body weight range were selected and slaughtered after the treatments, there were no differences in the general carcass characteristics. On the other hand, there were some differences in the internal organ weight among the slaughter treatments. The actual reasons for the differences in the internal organ weight are unclear. The electrical stunning frequency with time combination and halal neck cutting might affect the internal organ weight. The differences in the liver, gall bladder, large intestine, and kidney weight among the slaughter groups might be due to the pre-slaughter electrical stunning stress due to the flow of current and time combinations along the bird’s body, and convulsions. Gregory and Wilkins [
31] reported a higher frequency of damage to the carcasses when electrical stunning was used. Sances and Larson [
32] reported that electrical stunning with an extremely high current might cause problems during the induction of unconsciousness. On the other hand, ventricular fibrillation, cardiac arrest, and physiological activity caused by the frequency of current during electrical stunning might explain the variations in the internal organ weight observed in the current study [
33,
34]. Inconsistent with the present result, there was no significant impact on the liver in a goose study [
35,
36].
The total blood loss of the birds was affected by halal neck cutting after electrical stunning and subsequent bleeding (NSHS vs. LSHS, MSHS, and HSHS). The highest and lowest blood loss was observed in the NSHS and HSHS group, respectively. The blood loss from the birds in the NSHS group was different from that in the MSHS and HSHS groups. The LSHS and MSHS groups differed from that of the HSHS group. On the other hand, NSHS and LSHS did not differ significantly. The reason for the difference in blood loss after slaughter with or without electrical stunning might be the livability (higher percentage of birds were alive before slaughter) of the birds and cardiac and circulatory function, which alter the loss of blood from the carcass of broiler chickens. Stunning can result in a loss of blood pressure, heart attack, and loss of oxygen to the brain [
37], which would lead to insensibility and aggravation of the birds. These conditions lead to arrest of the cardiac system and less bleeding out after slaughter [
38,
39]. The association between stunning and bleeding out in broilers, turkeys, and rabbits has been reported earlier [
18,
39,
40], and it was suggested that higher levels of electric stunning affect the avian circulatory system.
The stress and factors that influence the mortality of birds are temperature and RH, daily periods, season, density of broilers per crate, stocking density per lorry, distance between farms and slaughterhouse, pre- and post-slaughter factors, transportation, transport time, lairage, lairage time, and lung congestion [
41,
42]. Current research has shown that level of electrical stunning with frequency and time, and neck cutting, could affect the welfare, livability, and carcass appearance of birds. Gregory and Wilkins [
43] suggested that stunning led to a higher incidence of carcass damage, with approximately 90% of animals undergoing heart fibrillation, which resulted in inefficient bleeding, severe muscle contraction, hemorrhage, and death of the birds, and ultimately lower meat quality. No or lower electrical stunning along with halal neck cutting methods (NSHS and LSHS) might initiate rapid blood flow into the blood vessels before clotting compared to higher stunning and slaughter (HSHS) [
44]. The LSHS, MSHS, and HSHS groups showed more than the NSHS group. Raj et al. [
17] also reported appearance defects due to different types of stunning.
In addition to the level of electric stunning, multiple factors might be associated with the livability and carcass conditions with hemorrhage. A previous study suggested that electrical stunning can cause the breaking of bones and hemorrhaging of muscles [
38], with higher incidences of damage being observed in response to higher levels of electricity [
43]. Current research findings also support previous studies, which revealed higher hemorrhage of muscles and carcass damage of the birds subjected to the MSHS and HSHS slaughter group than the NSHS and LSHS groups. Consistently, electrical stunning passes a current through the whole body, which can stimulate the muscles directly, cause convulsions in chickens [
45,
46], unconsciousness in cattle [
47,
48] and cause more damage to the carcass [
49].
4.2. Pectoralis Major and Flexor Cruris Medialis Proximate Composition, Cholesterol Content, and Fatty Acid Profile
Several studies have investigated electrical stunning [
11,
50], effectiveness of stunning with various concentrations of gases [
9,
46], the effects of stunning with different types of gases [
46,
51], and a comparison of gaseous and electrical stunning on post-mortem muscle and meat quality [
9,
10,
17]. On the other hand, halal slaughter following different levels of electrical stunning is another study interest in terms of meat quality for the broiler meat industry based on global halal meat market capture and creation of opportunities. Therefore, this study compared halal neck cutting with or without electrical stunning (NSHS vs. LSHS, MSHS, and HSHS). No variations in the proximate composition of
Pectoralis major and
Flexor cruris medialis were observed.
Addeen et al. [
44] reported no variations in the protein content in a study of Islamic or halal slaughtering, decapitation, conventional neck cutting, and un-bled slaughter of chickens. Bostami et al. [
29] reported no negative impact on meat composition except the ash content in Hanwoo cattle subjected to halal slaughter following stunning with or without pithing. The cholesterol content in the
Pectoralis major and
Flexor cruris medialis was unaffected by halal neck cutting after electrical stunning (NSHS vs. LSHS, MSHS, and HSHS). Generally, the genotype or breed, age at slaughter, feeding regime, castration, or other factors can alter the meat or
longissimus thoracic,
infraspinatus, and
biceps femoris muscle cholesterol [
52,
53].
The current study indicates similar
Pectoralis major and
Flexor cruris medialis cholesterol contents regardless of electrical stunning, halal neck cutting, and subsequent bleeding. In cattle, sheep, goats, or poultry, the fatty acid profile of the animal is generally influenced by the body weight, gender and breed of animals, weight of the animal, age at slaughter, geographical factors, genotype, season, and nutritional regime [
54,
55,
56,
57]. This study showed that halal neck cutting after electrical stunning (NSHS vs. LSHS, MSHS, and HSHS) did not affect the fatty acid profile of broiler chicken.
4.3. Pectoralis Major and Flexor Cruris Medialis pH, Microbial Loads, and Oxidative Stability
The meat pH is related to the biochemical state of the muscle at the time of slaughter and after the development of rigor mortis. This affects both the light reflectance properties of the meat and the chemical reactions of myoglobin [
58]. The muscle pH and meat color are highly correlated. A higher muscle pH is associated with darker meat, whereas lower muscle pH values are associated with lighter meat [
58,
59]. In extremes cases, meat with higher pH values was dark, firm, and dry (DFD), and the lighter meat was pale, soft, and exudative (PSE).
Generally, stunning can suppress the rate of pH decline in the early post-mortem stages, but it does not always affect the ultimate pH [
11]. Stunning of broilers can influence adenosine triphosphate (ATP), creatine phosphate (CP), pH, and lactate [
60]. Although convulsions affect the post-mortem muscle pH, they might not change the overall pH [
17,
45]. Hillebrand et al. [
45] and Önenç and Kaya [
61] reported no variations in the post-mortem pH following different stunning of broilers and cattle. Consistent with previous studies, the present study shows no differences in
Pectoralis major and
Flexor cruris medialis pH during one to 15 days post-mortem among the slaughter treatments. Better quality meat pH ranges from 5.3 to 5.8 [
62], while the pH of breast and thigh meat of chicken usually ranges from 5.4 to 5.8 for breast meat and from 5.7 to 6.2 for thigh meat [
63,
64]. The pH values of the present study are within the ranges of standard values reported in earlier research, indicating no negative impact among the levels of electrical stunning and slaughter treatments. Regarding the increasing trend of pH in all groups, there are a number of factors associated with meat pH change during storage such as genetics, pre- and post-slaughter factors, and handling process. However, there were no statistical differences found among the groups and the trend was similar for all groups.
In the current study, higher amounts of blood were retained (due to less blood loss) in the muscles of the birds following different levels of electrical stunning (LSHS, MSHS, and HSHS) compared to the no electrical stunning group (NSHS). The association of the amount of blood remaining in the carcass with the microbial count was reported by Ali et al. [
39] in a broiler chicken study and Nakyinsige et al. [
18] in a rabbit study. During the investigation of different slaughtering methods (Islamic or halal slaughtering, decapitation, conventional neck cutting, and an un-bled method), a lower total viable microbial count was reported in the halal method [
44]. On the other hand, the current study reveals no significant differences in the total microbial loads during post-mortem storage. The results presented in the current study show that samples of broiler chicken meat exceeded the permissible limit (log
107 cfu/g) of the total bacterial count recommended by the ICMSF [
65]. Regarding crossing, the critical levels of microbial loads might be due to cross-contamination during handling, processing, and storage, warranting further detailed study.
Consumers rate the ultimate food quality and safety as the most significant concerns [
66]. The spoilage of meat is associated with the characteristics of the meat, lipid oxidation or shelf life, type of microflora, composition of the meat, and environmental conditions under which meat is stored [
67,
68]. Lipid oxidation and microbial growth are critical limiting factors that determine the safety and oxidative stability of meat. Insausti et al. [
69] established a detectable concentration of 5 mg malondialdehyde/kg of meat for humans. Nevertheless, this value is much higher than that indicated to detect oxidized flavors by other authors. Camo et al. [
70] reported that in lamb, a TBARS value above 2 was detectable; Greene and Cumuze [
71] stated the TBA range of 0.6–2.0 was detectable.
The feeding regime, management factors, pre- and post-slaughter associates, and meat processing can affect the oxidative stability or shelf life of meat. An investigation that compared Islamic slaughtering, decapitation, conventional neck cutting, and an un-bled method showed that TBARS value, as an indicator of oxidative stability or shelf life, was lower in response to Islamic/halal slaughter than the un-bled method [
44]. The present study indicates that the level of electrical stunning could affect the oxidative stability of muscle.
The microbial activity is the most important factor responsible for the spoilage of meat, but some other factors are also associated with meat storage. The availability of energy substrates in meat (low molecular weight compounds, such as lactate or glucose) [
72,
73], as well as the microbial enzyme activity, metabolic byproducts, and proteolytic meat enzymes, can characterize meat spoilage [
74]. Moreover, the decreased extract-release volume (ERV) and lactate, as well as elevated pH during storage, can also contribute to the spoilage of meat [
75]. Therefore, a combination of several factors might have resulted in variation in the oxidation of meat among slaughter treatments (NSHS vs. LSHS, MSHS, and HSHS) in the present study. Therefore, a more detailed study is warranted to confirm the impact of electrical stunning (with frequency of current and time combination) and neck cutting on the meat oxidative stability or shelf life and the detailed mechanisms by which these changes occur.