Effect Of Stress On Meat Quality Of Cattle Biology Essay

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Within this report I am going to investigate the effect of stress on the meat quality of cattle, and outline possible solutions to this issue.

What are the effects of stress on meat quality?

Stress has a major impact on meat significantly decreasing the quality of it. Energy required for muscle activity is obtained from glycogen in the muscle. Once the animal has been slaughtered the glycogen is converted into lactic acid. Lactic acid is required to produce meat, which is tender and tasteful, with a longer shelf life and good aesthetics. When the animal becomes stressed before and/ or during slaughter, the glycogen is used up quicker and the lactic acid which develops in the meat after slaughter is reduced. A major impact of this includes 'Dark, firm and dry (DFD) meat' This is when the carcass of the slaughtered animal is much darker, drier and firmer than normal. The meat is then of inferior quality, as it has less taste and a lower aesthetic value as well as a shorter shelf life due to the abnormally high pH value (6.4 - 6.8). [i] 

Stress can be induced by cattle in several ways. Initially transportation is a major cause of stress for cattle. This is an unnatural and uncertain process to cattle, which contributing to the increase of stress on the cattle. Traditional methods of movement has been via foot, however expansion for demand has meant that more easier and efficient methods of transport are required to transport the animals from farm to slaughterhouse. Transportation is about getting as many cattle from one place to another as quickly and easily as possible.

Another contributing factor that causes stress in cattle is how they are handled prior to slaughter within the slaughterhouse. This is again unknown territory to cattle, remembering that once the cattle have reached the slaughterhouse, they have previously been transported. How the cattle are handled from birth to death can be another factor that affects the amount of stress induced by cattle. The stress levels are dependent on the exposure to things during the animal's life. For example if the cattle have been transported previously, when the cattle are transported again it will be a less stressful experience, as it won't be so unfamiliar to them.

How are the cattle biologicallly effected?

Glycogen is an energy store in animals. It is made by the liver and the muscle, however can be produced by glycogenesis in the brain and stomach. Glycogen is an energy reserve which can quickly be obtained to meet a sudden need for glucose, an energy source. The glycogen found in muscles is found in low concentration, therfore can quickly be used up during increased activity. [ii] 

Cortisol is a glucocorticoid, which is produced by the adrenal gland, and release in response to stress. Its main funtions are to increase blood sugar levels through glucocorticoids. Glucorticoids are steroid hormones which bind to the glucocordicoid receptor, which is found in almost every vertebrate animal cell. Glucocorticoid(glucose + cortex + steroid), which comes from the role in regulation of glucose. [iii] 

When an animal is exposed to induced activity for example prior to slaughter, muscle glycogen is used, as the glycogen get used up and the animal becomes stressed in reponse cortisol is produced, increasing the blood sugar levels through glucocorticoids, and regulation of glucose.

How is the effect measured?

The effect of stress on meat quality can be measured in several ways, which is both qualitative and quantative. An animal requires energy from glycogen, for muscle activity. An animal should have a high glycogen content in the muscle; once the animal has been slaughtered the glycogen in the muscle converts to lactic acid. The lactic acid makes the meat more tasteful and tender, with a longer shelf life and more aesthetically pleasing.

The ph levels, shelf life, cortisol hormone levels are methods of meat quality measurements that are based on numerical data. The pH level of the meat is measured it should be ideally 6.2 or lower. Spoilage, is when the meat is considered unfit for human consumption, a few factors that can cause the spoilage are; micro-organisms, improper freezing and the exposure to air. The meat is deemed spoilt if it has an unpleasant taste and/ or odour, this also decreases the shelf life of the meat. [iv] The aesthetics of the meat, taste and tenderness is another measurement, however this is based on opinion, and the opinion of the customer purchasing the meat. The bruising of the meat affects the aesthetics of the meat, for the consumer.

An experiment has been carried out by ' Nebraska Beef cattle reports' surrounding the topic of the effect of stress on cattle. The experiment carried out was generalised, stating just the effect, not the cause of the stress and ultimately the effect. Their experiment being 'The effects of induced stress and supplemental Chromium on Meat quality of Finishing Heifers'. [v] 

'The cooperative Research centre (CRC) have carried out extensive research about how pre-slaughter treatment affects meat quality. The CRC have summarised the factors relating to pre-slaughter handling being;

Cattle being susceptible to stress resulting in dark cutting (high PH) meat.

The stress is cumulative (e.g. time of feed + weather +mixing with other cattle) - This implies that the stress is caused colectivly by different factors, in this case it is suggesting that the change in feed times, the weather and the company can have an effect on cattle.

Mixing cattle with strangers 1 week before slaughter results in tougher meat.

Purchasing then slaughtering cattle directly from the market results in tougher meat than if they were sent directly to the slaughterhouse.

Overall they concluded that pre-slaughter stress causes tougher beef, even when its PH and colour is normal. However these factors haven't been quantified.' [vi] 

What is the main solution?

My main solution to this issue is to reduce transportation distances. However there are implications to this solution. The implications include ethical and economic, ethically the animal should be treated carefully anyway in order to reduce the stressed caused to the animal. It shouldn't require an issue such as reduction in meat quality to indicate a requirement to change how the animal is handled. Economically time scale and demand, means that cattle have to be transported quickly and efficiently to keep up with the demand and also the cattle have to be transported wherever they are required, to supply the supplier for the consumer's consumption. However reducing transportation distances will have environmental applications because environmentally; a global move towards change to tackle climate change; reduction in transportation distances which is directly linked to transportation time for cattle. By reducing transportation distances, will cut pollution and help to reduce the effects of climate change, this solution will have more backing from people because tackling climate change is a global issue.

A study was carried out evaluating the effect of transportation time and vehicle design on stress levels of cattle and meat quality. The experiment that was conducted involved 18 transports (six short, six medium, six long) involving 118 sample animals including both heifers and bulls. 'The stress levels were evaluated by blood serum parameters, heart rate monitoring, behavioural recording and the occurrence of carcass bruising.' The quality of the meat was evaluated by measuring muscle glycogen content, pH value, temperature, drip loss, colour and tenderness. The heart rate of heifers (95bmp) was lower in comparison to the heart rate of the bulls (114bmp), however during transportation the average heart rate was 100 bmp. When being unloaded the heart rate of the heifers increased (109bmp) whereas the heart rate for the bulls remained at the average (100bmp). The reason that their heart rate may of increased because of blood sampling occurring whilst the animals were being unloaded. The heart rate lowered during medium and long transportation distances compared to the heart rate of cattle travelling short distances. Cattle who were transported singly or in pairs, for medium or long distances, seemed less stressed and nervous, which was more evident in the animals transported in large groups over short distances.

'The results indicate that larger pens of three or four animals may increase stress during transportation. When being loaded, animals loaded singly or in twos had significantly lower blood cortisol content than those loaded in larger groups. Bruising was more severe in carcasses that had been transported short distances and loaded in larger groups. The severe damage was evident on the perennial and hipbone area. Muscle glycogen levels were highest after long distances.' [vii] 

Overall this source suggests that transportation distances have an effect on the stress induced by the cattle, the longer the distance the less stress caused. This could be because the animals get use to it as time goes on, so the experience becomes less stressful for the animal. Also the number of animals transported seemed to make a difference, the less animals being transported, the less stress the animals became, perhaps because they had more room and less animals to have an influence upon each other. Therefore these two factors, less cattle transported over a longer distance, seems to be a less stressful experience for the animal, in accordance to this experiment carried out. However again there are implications to these factors being the least stressful. Transporting fewer cattle at a time isn't economical, with a fast growing demand for beef(figure 1).


Figure 1


This graph illustrates that on average there is an increasing demand, though it indicates a decline at first in also shows a steady increase in latter years, customers want a quantity of meat sometimes over quality, therefore cheaper cuts are often preferred as they don't cost as much, to be able to obtain each cut and as much as possible a lot of cattle are required daily to support the demand. Thus more cattle need to be transported at one time to produce enough of each cut to supply everyone's needs and requirements. Travelling further distances isn't environmentally friendly or economically viable, environmentally travelling further would cause more pollution, thus contributing to global warming, economically travelling further will cost more in fuel, with increasing fuel prices, taking less cattle further just isn't a viable option for transporting cattle to the slaughter house. However though putting more cattle in with each other increases the amount of meat spoilage, increases wastage however this percentage is considerably lower in comparison to the amount of meat obtained by more cattle being transported at one time. Thus it is more viable to transport more cattle over a long distance, because though travelling further has implications, more meat will be obtained, to provide the customer and ultimately the consumer with a quantity of varying priced cuts and less stressed animals based on the results of this experiment.

What are the alternative solutions?

Two alternative solutions for reducing stress in cattle would be sympathetic handling prior to slaughter and sympathetic handling from birth to death. By quietly handling cattle prior to slaughter will reduce stress. Prior slaughter handling includes design, construction and operation of the slaughterhouse and handling immediately before slaughter. These are requirements stated by Defra (Department for environment, food and rural affairs) in the 'FAWC Report on the welfare of farmed animals at slaughter or killing - part 1: Red meat animals'. [x] 


This graph illustrates the importance of reducing transportation distances and implementing more sympathetic handling prior to slaughter. Though this graph shows that the highest percentage of mortality is during transportation, which coincides with my main solution it also supports the need to be more sympathetic with pre-slaughter handling of cattle. This is clearly shown on this graph that there is a fairly high percentage mortality of lairage mortality; lairage is where the cattle are held prior to slaughter. Sympathetic handling from birth to death is the overall handling of the cattle, limiting the exposure to stressful situations, such as weaning calves too early and transporting cattle often. In some situations the calves have to be weaned at an early age to be able to obtain the by product of milk, the calves are then artificially reared, though this would initially seem stressful for the animal the operation is carried out at a very young age so there is less stress as the calf has no emotional attachment to its mother. Transporting cattle isn't a singular occurrence, many cattle are reared on one farm and slaughtered on another, because most people specialise in an area of cattle production, some calf rearing, some suckler cows and others fattening cattle. Therefore reducing the number of transports isn't viable in most situations. Overall sympathetic handling from birth to death should be implicated anyway from an ethical point of view.