Review on Beef Cattle Pre-slaughter Stress and Its Effect on Meat and Carcass Quality

Pre-slaughter stress includes all the conditions and practices that apply during the period when the animal is moved from source or market to entry into the stunning box at the abattoir. Cattle can be stressed during transportation, marketing and handling at abattoirs. During such condition physiological changes (increased heart rate, respiratory rate, body temperature, activity of enzymes, stress hormones (cachecholamine, cortisol) and glycolysis) has been occur which used to measure stress before cattle slaughter. Such changes affect the meat quality by depleting muscle glycogen which result in lower rate of post-mortem lactic acid synthesis, high ultimate pH, tough meat, abnormal muscle color and high water retention capacity.

affects the animal's ability to cope, reduce its fitness and has negative implications on animal welfare. During stress animals are prone to weight loss, produce poor meat quality and considerably reduced profit of the producer (Adzitey, 2011).

Stress Associated with Marketing and Transportation
Animals are either sold at the markets or sent directly from farms to abattoirs for slaughter. Loading, transport and unloading conditions depend on the facilities on the farm, market and at the abattoir, and on the layout of the truck, the driving condition and distance travelled. Transporting and marketing process are stressful to animals which involves removal from their home environment, loading and unloading onto vehicles, often long journeys and holding in unfamiliar surroundings. These results in their being potentially exposed to physical stresses such as extremes of temperature, humidity, vehicle vibration and changes in acceleration, noise, and confinement and crowding. There are also psychological or emotional stresses such as handling, breakdown of social groups and mixing with unfamiliar animals, unfamiliar or noxious smells and novel environments (Adzitey, 2011). Animals may suffer from hunger, thirst and fatigue because they are not usually fed before and during transport, and water may not be available. Other conditions such as injury, suffocation and death may prevail in transportation (Warriss, 2000).
Livestock transport in Ethiopia done either by trekking, ordinary truck and combination of both. In all method of transportation animals are exposed to different stress (Dirbaba and Hurrissa, 2009). Many studies have shown that loading and unloading are the most stressful part of transport. The stress associated with handling at the time of loading and unloading can vary according to factors such as the quality of handling (gentle vs rough), experience of the handler, the temperament and condition of the animals and the quality of the handling facilities (Hall and Bradshaw, 1998). Loading is the most stressful operation than unloading because loading requires close proximity to humans and this can cause fear in animals that are not habituated to human contact and finally, pain may result from mishandling of animals (beating or poking animals with a stick, especially in sensitive areas like the eyes, mouth, ano-genital regions or belly): (Knowles et al., 1994).
Transportation stress has shown to cause suppression of the immune system, making animals more vulnerable to disease. Cattle have been observed to have higher heart rates during transportation, which may indicate higher levels of stress, but may have also been due to increased activity during loading and unloading and from movement and exertion to maintain balance on the truck. Transportation has been also shown to cause elevated body temperature, which may have been due to psychological stress, physical activity or the increased internal temperature of the truck (Ishiwata et al., 2008). Cattle have exhibited other physiological indicators of stress during transit including increased creatine kinase concentrations indicating possible muscle damage and poor meat quality caused by stress markers such as high glucose and lactate concentrations (Sporer et al., 2008).
Factors such as transportation time, stocking density, standard of driving , road condition and design of the vehicle (size, space, surface) are important in inducing pre slaughter stress (Ruizdela et al , 2001: Nijsane andMuchenje, 2017).) During transportation, animals can do little to help themselves when they are in danger or discomfort due to confinement. In farms, markets and lairage, animals needs much freedom of movement and could avoid certain uncomfortable conditions (Ohl & Van der Staay, 2012). Over speeding, sudden stops, rapid acceleration and long journey times without appropriate rest should be avoided during transportation as these will increase carcass and meat quality defects. Careful loading, unloading needed to be practice and transportation to be done in a gentle manner under a quieter environmental condition to ensure the safety of animals in transportation to reduce stress to its minimum (Adzitey and Nurul, 2011).

Stress at Abattoirs
At arrival at the slaughterhouse animals are unloaded, may moved for weighing, hold in reception pen until transferred to lariage. Grandin (2008) reported that moving cattle in abattoirs exposes the animals to a different structural design. The main purpose of lairage is to maintain a reservoir of animals so that the processing line in the abattoir can operate at a more or less constant speed irrespective of variations in the delivery of livestock. The second function is to allow the animal sufficient time to recover from the stressful effects of transport in order to restore their muscle glycogen levels, thereby allowing normal anaerobic muscle metabolism after slaughter that ensures good quality meat and better animal welfare (Terlouw et al., 2012). However, lairage may be characterized by unfamiliar conditions, such as concrete floors as opposed to the natural grass farm, rough handling procedures, feed restriction, overcrowding, changes in social structure (through separation and mixing), and the presence of unfamiliar animals which leads to stress condition (Ferguson & Warner, 2008).
High stocking density in lairage pens may promote fighting behavior in animals. Careless and improper handling of animals in the lairage such as the use of electrical goads, beating by sticks or rope and tail twisting are stressful to animas (Terlouw et al., 2012). In addition improper stunning can also be stressful in which stunning tools do not functioned properly and/or poorly trained operator (Mareko, 2005). Abattoirs may have inappropriate lighting and many of them are very noisy (Adzitey and Nurul, 2011). Therefore providing cattle Advances in Life Science and Technology www.iiste.org ISSN 2224-7181 (Paper) ISSN 2225-062X (Online) Vol.78, 2020 3 with adequate amount of suitable feed and water if they will be kept longer than expected to promote glycogen accumulation, hydration, and calm behavior. Cattle should not be mixed with other unfamiliar cattle so that fighting does not occur (Warriss, 2003). Currently, different technologies such as ventilation equipment in lairage, appropriate lighting, limited use of electric goads and appropriate passageways for animals to walk have been used in abattoirs to reduce the stress in animals (Ponnampalam et al., 2017).

The Nature of Stress Response
Animal normally responds to stress with physiological and behavioral changes in a characteristic way. This stress response has two components. The first is a rapid short term alarm' response (defensive response). The acute stress response activates when the animal is exposed to a stress-stimuli for a short time. It contains either the flight or fight response. The preparations response involve the secretion of catecholamine hormones, adrenaline and noradrenalin (epinephrine and norepinephrine) and enzymes into blood circulatory system and eliciting a sequence of physiological responses, including increased heart and respiration rates, elevated body temperature and decrease protein degradation (Warris, 2000). The second component of the stress response occurs after the 'alarm' response and over a longer time period (adaptive response). Its role is to allow the animal to recover from the alarm response or to 'adapt' to the new situation. This component of the animal's response to stress mainly involves the Hypothalamic-pituitary-adreno-cortical axis. (Armario, 2006;Warris, 2000). During stressful episodes the hypothalamus secretes a hormone, corticotrophin-releasing factor (CRF). This stimulates the pituitary gland to secrete adrenocorticotrophic hormone (ACTH) into the blood. ACTH in the blood stimulates the cortex of the adrenal gland to secrete corticosteroid hormones. The release of the corticosteroid hormones (cortisol) is a characteristic response of an animal to stressors. (Armario, 2006;warris 2000. Age, sex, health status, breed, and previous experiences of animals can influence the way they cope with stress (Grandin, 1999).

Measuring Pre-slaughter Stress
When animals are exposed to pre slaughter stress condition such as handling, transportation and environmental stressors (climate, temperature and nutrition), they react by eliciting certain physiological and behavioral changes in order to cope with the situation. These changes can be measured pre-slaughter to indicate how much stressed animals are suffering. Physiological changes such as increased heart rate, respiratory rate, body temperature activity of enzymes, stress hormones (cachecholamine, cortisol), body temperature and glycolysis had been observed (Mader, 2003). Enzymatic secretions which are released into the serum through leakage arising from altered membrane permeability include alkaline phosphate, acid phosphate, aspartate aminotransferase, creatine kinase and Lactate dehydrogenase (Sattler and Furll, 2004). These changes of enzymes and hormones indicate the level of stress created and reducing the quality of meat and its products. Hormone such as catecholamines (epinephrine and norepinephrine) are difficult and expensive to measure, not reliable as their concentration shows wide variation and their effects last only for a few minutes and only useful as indices of acute stress where samples can be taken very soon after the stress. Hence it is not the best indicators of stress (Warris, 2000).

Creatine kinase and lactate dehydrogenase
Creatine Kinase (CK) is an enzyme found in the skeletal muscles of animals, responsible for maintaining energy homeostasis at the sites of high ATP (Dieni and Storey, 2009). This enzyme appear to be the most widely accepted and more generally used measures of stress sensitivity and the magnitude of stress associated with most systems of animal husbandry and pre-slaughter animal handling (Okeudo and Moss, 2005). Rupture of muscles causes the release of CK which is deposited into the blood. The increased levels of CK in the blood (plasma or serum) are an indication of how stressful the handling was before the animal were slaughtered and the extent of muscular damage during handling and transportation in many species ( Minka and Ayo, 2010). Moreover, the presence of this enzyme in the blood is due to breed temperament, excitability and fighting (Chulayo & Muchenje, 2017).
Lactate dehydrogenase (LDH) is an enzyme found in almost all body tissues. It plays an important role in cellular respiration, the process by which glucose (sugar) from food is converted into usable energy for cells. This enzyme also increases in the blood after muscle and tissue damage (Knowles and Warris, 2007). Both CK and LDH have been used as indicator of trauma, high levels of physical activity or other damages during handling and transport in farm animals. According to Jones and Price (1992) an increase of LDH had been also observed in deer frightened by capture whose muscles are not damaged.

Cortisol
Cortisol is steroid hormone (glucocorticoid) released from the adrenal glands of cattle in to blood during periods of stress and measurement of its concentration in blood had been reliable and widely used as a good indicator of