The swine slaughtering process is affected by practices that go from the establishment of fasting on the farm to the slaughtering stage in the slaughterhouse. Animals are subjected to practices that will directly reflect on the quality of their carcass, and on how meat cuts will be ranked as more or less valuable in the market. Thus, pre-slaughter phases are fundamentally relevant to the quality of the final product, once they affect the living experience of animals before slaughter, the quality of their meat, and carcass yield.
One of the phases that require the most attention in this process is that when animals are kept in the waiting area of slaughterhouses. When pigs arrive at the slaughterhouse, they are unloaded from the truck in a condition of extreme tiredness and stress due to the pre-slaughter handling to which they had been subjected. These animals need to eliminate excess lactic acid accumulated in muscle and restore their homeostatic balance, which can only be achieved with appropriate resting periods (1). Resting allows animals to recover their muscle glycogen reserves, to rehydrate after experiencing dehydration caused by transport, and it eases the elimination of gastrointestinal content, to avoid contamination in the slaughterhouse.
High injury and wound rates in this area occur due to the handling of animals by employees, and to the fact that animals from different lots are mixed together. Animal fights for hierarchal reasons constantly occur when pigs from different lots are mixed up, and that result in high rates of skin damage caused by biting.
Fasting is another practice in pre-slaughter management; it starts at 8-12 hours before transport and lasts until slaughter. In this period time, animals have no access to feed, but are able to drink water anytime. It is greatly important as it contributes to animal well-being, reduced vomiting during transport (2), reduced feeding costs, reduced mortality rates during transport, increased speed and ease in gutting process, reduced volume of waste in slaughterhouses, and standardization of carcasses yield and meat quality (1), and it also contributes to preventing carcass contamination caused by leakage of stomach or intestinal contents during evisceration.
However, some deleterious effects on the carcasses and organs resulting from fasting can be noted. Pre-slaughter fasting negatively affects carcass yield of pigs, causing up to 5% of body weight loss, at a rate of 0.20% per hour, when subjected to 24 hours of fasting, and such losses can be even greater in heavier animals (3).
The quality of meat can also be affected, since there may be depletion of muscle glycogen reserves, which are important for the final process of “rigor mortis” and final aging of meat. Immediately after slaughter, glycogen reserves are consumed by the cells of the muscle tissue, in an anaerobic process that generates lactate as a residual metabolite that contributes to the reduction of final pH, an important element for final meat aging. With the lack of glycogen, there will be less production of lactate (4), and the final pH will be higher, resulting in DFD (dark, firm and dry) meats.
The use of large amounts of carbohydrates in the diet has been investigated with the goal of reducing meat quality problems associated with high pH 24 hours after slaughter (DFD). A diet with high levels of sucrose or other carbohydrate source for rapid absorption, a few days before slaughter or in the pre-slaughter resting area, can increase the supply of muscle glycogen and thereby reduce pH 24 hours post mortem.
Sodium bicarbonate has been frequently used in animal feed, with the goal of increasing water intake, which indirectly improves animal thermal comfort when facing conditions of heat stress. When the intake of water is increased, chime becomes more liquid and food content flow accelerates, reducing the time required for gastric emptying, thus the fasting period may be reduced in the farm. Moreover, the supply of electrolyte to animals increases tissue hydration, reducing the effects of body weight loss when subjected to extended periods of fasting.
Several researches have been conducted to evaluate the beneficial effects of vitamin E on the quality of pork meat. Vitamin E is a robust antioxidant, and its supply in diets has caused decreased in lipid oxidation, drip loss and improved coloring of pork cuts (5). Diets supplemented with vitamin E have also improved average daily weight gain, feed conversion, reduced backfat thickness and increased the amount of lean meat in the carcass (6). When adding higher doses than those recommended as animal daily nutritional requirements, it is possible to note improvements on meat color and oxidation resistance, with feed ranging from 100-200 mg/kg (7).
This present study was carried out aiming to evaluate and quantifying the leading causes of damage to animal skin and carcass associated with pig slaughterhouse waiting and resting area management, along with assessing how glucose, sodium bicarbonate and vitamin E added to drinking water during pre- slaughter fasting in the farm may affect carcass yield, relative organ weights (liver, heart, stomach and kidneys) and the quality of pork meat.
MATERIALS AND METHODS
Local. The first experiment was conducted on the premises of a business company located in the city of Xanxerê/SC. The second experiment was conducted on the premises of a business farm in the city of Xanxerê/SC, with animals raised in accordance with the regular procedures of commercial farms, including loading, pre-slaughter, and slaughter standards of integrating businesses.
Animals and experimental design. In first experiment were used 1000 Topigs animals, both female and male (immunocastrated). Pigs were transported to the slaughterhouse at dawn and slaughtered in the morning, remaining for three hours at the resting area, at 0.60m2/ animal. The animals were kept in cement non-slip floor pens during the waiting period, with 30 animals per pen. The second study included 500 Topigs animals at 150 days of age and weighing approximately 110 kg, distributed on the last pre-slaughter day during the liquid diet period on the farm in completely randomized design (Table 1), comprising the treatments: water as control; 50 g/L glucose; 50 g/L glucose + 200 mg/L of vitamin E; 75 g/L glucose; 75 g/L + 200 mg vitamin E; 0.45% sodium bicarbonate; 0.45% sodium bicarbonate + 200 mg/L of vitamin E; 0.55% sodium bicarbonate; 0.55% sodium bicarbonate + 200 mg/L of vitamin E; 200 mg/L of vitamin E, with 10 treatments consisting of 10 replicates, which included five animals each.
Methodology. The parameters assessed included injuries to body surface, bruising and existing wounds, sorted by body part: neck, back, chest, right limb and left limb (front and rear) and abdomen. The evaluation criteria of body surface were made up of carcasses bite marks, bruises and wounds.
Table 1. Treatments used for pigs during pre-slaughtering.
To assess body surface damage (bite marks, bruises and wounds), animals were examined from their arrival at the slaughterhouse up to the moment they entered the stunning area. Animals that presented lesions at unloading and when moved to the stunning area were quantified. The number of animals with skin lesions (in each of the segments described above) was determined by subtracting the number of animals with lesions at entrance to the stunning area and the number of animals with lesions in the unloading area.
Lesion assessment was made inside the slaughterhouse, just after the evisceration process. The evaluation carried out to ascertain the presence of hematoma followed the classification of purple-blue hematoma (indicative of being punched less than 24 hours ago) and greenish hematoma (indicative of being punched over 24 hours ago).
Six hours before the start of fasting, additives were given through liquid diet, until the end of the fasting period in the farm, where buckets and hoses were adjusted to drinkers so that the nutrients could be provided. The animals underwent an eight-hour fasting period on the farm, totaling 14 hours of nutrient consumption via water. Animal transport time to the slaughterhouse took one hour, at dawn. Animals spent three hours in the waiting area of the slaughterhouse, in a 0.6m2/animal density, completing a 12-hour fasting period in total.
Animals were weighed before loading, insensibilizated by electric system, according to welfare norms, slaughtered and eviscerated prior to carcass, liver, heart, stomach (empty) and kidney weighting, in order to assess carcass and organ yield. Hot carcass yield and relative organ weights were calculated using the following formulas:
Laboratory analysis. In experiment 2, after slaughter, three samples of approximately 2.5 cm in width were taken from the longissimus dorsi muscle, from between the 10th and 11th ribs of each half right-side carcass, to assess pH and color. Meat pH was determined 24 hours post mortem. The samples were stored at 4°C, and underwent penetration electrode analysis. For color analysis, the samples remain at rest in a 15°C room, throughout 30 minutes, for surface oxygenation, and coloring was determined using a portable colorimeter (Hunterlab MiniScan XE), and the scales L* (lightness), a* (red pigment intensity) and b* (yellow pigment intensity) were used as parameters.
Data analysis. Skin and carcass injury assessment results, in the waiting area of the slaughterhouse, were analyzed using the chi-square test. Carcass yield, relative organ weight (liver, heart, stomach and kidneys) and quality of meat data were subjected to analysis of variance. When significant differences were found, means were compared through Student-Newman-Keuls test, at 0.05 level of significance using the R statistical software.
Body surface injury quantification results are shown in Table 2, with prevalence of skin damage caused by bites in animal fights, especially on the back and limbs.
Significant difference was noted for the frequency of bite marks on animal body parts (p< 0.05), with higher incidence of bite marks on the dorsal region, followed by the front left limb, front right limb, left rear limb, right rear limb, and neck. In addition, there were contusions (Table 2) caused by instruments used by employees and collaborators in charge of moving animals.
There was a significant difference (p< 0.05) in the frequency of contusions among different regions of the body. It occurred more frequently in the forelimbs, rear limbs, and back, with lower incidence in the chest, neck and abdomen. This occurred during the stages of moving animals (from the unloading area to the inside of pens, and from the pens to the stunning area), in an attempt by employees to perform this operation faster. The highest incidence of bruising in the limbs and on the back of the animals occurred because these are the most vulnerable areas of the body, thus more susceptible to any type of injury, besides the fact that electric poles and other sharp objects are commonly used on such regions when moving the animals around.
Table 2. Occurrence of pig skin injury (frequency found for 1000 animals) during the period of stay in the waiting area of the slaughterhouse.1
Significant results were found for the occurrence of animal skin wounds (Table 2), seen most often on the backs of pigs, followed by hind limbs and forelimbs in less occurrence. Wounds were noted in similar amounts of contusions, in almost all regions of animal body, except for the back, which showed greater occurrence of hematomas. Table 2 presents data on hematoma examination, with no differences (p> 0.05) in the frequencies of purple-blue or greenish hematomas.
Experimental results of carcass yield and relative organ weight are shown in Table 3, with same values (p> 0.05) on carcass yield, mainly due to the short supply of nutrients, not enough to promote changes to this parameter.
No significant differences (p> 0.05) on relative heart weight (Table 3) were observed. Also no significant differences were observed in relative liver weight (p> 0.05), but significant values (p< 0.05) were observed in the relative weight of the kidneys (Table 3), with a higher percentage yield in pigs supplemented with 0.45% sodium bicarbonate + vitamin E when compared to animals receiving 50 g/L glucose, 50 g/L glucose plus vitamin E, and 75 g/L glucose plus vitamin E. This is due to the higher amount of sodium provided, which is absorbed and reaches the bloodstream, causing an increase in renal retention even with water, for subsequent excretion, thereby increasing kidney relative weight. No differences (p> 0.05) were found for the remaining treatments,
There were significant effects of treatments on quality parameters of meat (Table 4), with significant values (p< 0.05) between treatments being observed regarding the evaluation of meat pH, lower in animals receiving 0.55% of bicarbonate sodium plus vitamin E when compared to values obtained from carcass from animals supplemented with 0.45% sodium bicarbonate (with or without vitamin E), those who received only 0.55% of sodium bicarbonate and water to those who received only did not differ from the other treatments.
Table 3. Values of percentage yield (%) of hot carcass and relative weight of organs of pigs treated with different levels of glucose, sodium bicarbonate and vitamin E during pre-slaughtering.
Table 4. Meat quality characteristics of Longissimus dorsi muscle of pigs treated with different levels of glucose, sodium bicarbonate and vitamin E during pre-slaughter.
No differences (p> 0.05) were found for animals of different treatments in parameter L* (lightness) of meat coloring.
There were differences (p< 0.05) for the parameter a* (red pigment intensity), while no differences (p> 0.05) were found for the parameter b* (yellow pigment intensity). Animals that received 0.45% NaHCO3 showed lower a* in relation to others, except for animals supplemented with 0.45% NaHCO3 + 200 mg/L of vitamin E and those who received 50 g/L glucose.
These data are consistent with the observations described in other studies (8,9), which describe high frequency of injuries caused by fights, especially during transport and accommodation in the waiting area of the slaughterhouse. According Dalla Costa et al (9), 17.26% on the percentage of pigs with skin lesions are caused at the resting pen of the slaughterhouse, after a resting period of three hours.
Poorly designed facilities can be harmful to the welfare and quality of the carcasses of animals, since to keep the flow of pigs to the stunning area at a proper speed, it becomes necessary to use electric and sharp pods, thus increasing the occurrence of animal injury.
In all stages of loading, unloading and waiting in the slaughterhouse, injuries and wounds occur, and, on average, 34% of pigs have some type of skin lesion before slaughter (8). The occurrence of bruising in swine carcasses is mainly caused by high density during transport, a fact not found in this present study.
In waiting areas inside slaughterhouses, facilities that have very large pens favor the occurrence of animal skin lesions, as they shelter several animals from different lots, thus, fights for hierarchal reasons may occur more frequently (9). According Guardia et al (10), high density of animals during transportation or accommodation may also favor the appearance of damage to the skin.
In a study of Souza et al (5), when evaluating different levels of vitamin E in the diet of pigs in the growing and termination phases, was found a linear increase in carcass yield with supplementation of up to 400 mg of vitamin E per kg of feed.
Mota-Rojas et al (11) indicated that the duration of transport affects the occurrence of lesions on the skin of animals. The longer the time of transport the greater amount of lacerations they will have in the slaughterhouse. The ideal would be to slaughter animals near the sites of breeding and production, so that the stress of transport could be minimized. Also, they stated that short-distance transport does not exert negative effects on the quality of meat, and it is a suitable practice to be implemented in slaughterhouse management.
High densities (above 0.6m2/100kg) will increase the occurrence of injuries and lacerations in animals (12). High accommodation and transport densities provide less space for animals, generating greater physical contact, trampling of animals in case of falls and possible confrontations, resulting in higher occurrences of bruises on carcasses.
Greenish hematomas indicate that the animal got hit over 24 hours ago, when the animals are still on the farm, and no greenish hematomas means that animals were properly handled by the producer. The presence of purple-blue hematomas indicate that the animal got hit less than 24 hours ago, thus it happened during transport and handling of animals in the resting area of the slaughterhouse. Between five and 10 days, the hematoma is yellow, and after 14 days, on average, it disappears.
Carcass yield may be affected by other factors, such as genotype, gender, nutrition, temperature and weight at slaughter, in which the heavier the animal at slaughter, the greater the carcass yield. The values found for carcass yield in present study were similar to those found in by Oliveira et al (13), testing different levels of crude protein in feed for barrows. Carcass yield values found by these authors were between 76% and 78%.
Also, no significant differences were found by Oliveira et al (13) in heart weight of pigs in a work that evaluated different protein levels in animal ration. Kerr et al (14) have described no differences in heart weight of pigs also when working with different protein levels in the diet. They have found no variations in liver weight, when evaluating animals slaughtered at 36 kg bodyweight, after being kept in different thermal environments. No differences were described for the values of liver weight in pigs, when evaluating different levels of crude protein in feed.
Oliveira et al (13) and Kerr et al (14) have found no significant differences in kidney weight and on the performance of pigs.
Final pH of meat below 5.8 can indicate occurrence of PSE meat (15), and above 6.2 may indicate the occurrence of DFD meat (16). Thus, animals of all treatments had pH values within the desired range for the quality aspects of meat.
Guo et al (17) and Janz (18) have found no differences were detected in L* when adding vitamin E in the diet of pigs). The larger the L* value of the parameter the paler are the meat (19) and meat with L* values above 53 are considered PSE (15, 20).
The addition of vitamin E was inefficient in promoting improvements in the coloring of meat, which is consistent with several studies that have found no effects of vitamin E on meat color (17, 18, 21, 22). No difference are reported by Caldara et al (15) between the values of a* and b* of meat considered normal and PSE meat, finding values between 8 and 11 for the parameter a* and 6-9 for the parameter b*, similar to the rates determined in this present study.
The addition of glucose was also not effective in promoting changes in the parameters L*, a* and b*. However, adding carbohydrate sources that can rapidly be absorbed and digested can manipulate the reserves of muscle glycogen, avoiding its depletion at the moment of slaughtering (23), and promoting adequate production of lactate, keeping final pH (pH 24 hours after slaughter) in proper levels.
In conclusion, the occurrences of injuries to the skin and carcass of pigs are due to animal fights during their stay at the waiting area of the slaughterhouse. Contusions in back and limbs are also a critical occurrence during animal stay at this area. Adding glucose, sodium bicarbonate, and vitamin E to diet did not affect the yield of carcass, viscera and stomach contents of pigs given the normal patterns of pre-slaughter, but has affected pH and red pigment intensity of pork meat.
This article was originally published in Rev.MVZ Córdoba 22(1):5619-5630, 2017. ISSN: 0122-0268. DOI:dx.doi.org/10.21897/rmvz.922. This is an Open Access article under a Creative Commons Attribution License.