Can we tell if an animal was stressed by the taste of its meat?
Stressed animals on their way to the slaughterhouse often produce lower-quality meat.
Published
Sick animals are not suitable for human consumption and are removed during inspections.
Live animal transport drivers and farmers determine if the animals are healthy enough to be transported to the slaughterhouse.
Slaughterhouses inspect each individual animal for disease and injury, says Gry M. Holmbakken, a specialist in food safety at Nortura farmers’ cooperative, one of Norway’s largest food producers.
Additionally, the Norwegian Food Safety Authority inspects all animals before and after slaughter.
An animal that cannot walk without assistance is not allowed to be taken to the slaughterhouse. Animals with serious, open wounds are also exluded, according to Norwegian regulations on the transport of animals (link in Norwegian).
If the wounds and injuries are minor, however, the animals can become food. For example, pigs can develop shoulder sores from lying on hard concrete, similar to bedsores in humans, according to Svineportalen, Norway’s pig industry portal.
If the wound has healed, the pig can become food. The same applies to animals with minor hernias and healed tail wounds.
Such injuries and wounds can cause stress in animals. Poor conditions in barns and pens can also lead to stress.
And stress affects the meat.
Tough meat and an unpleasant smell
Meat from stressed animals can be of lower quality.
Hunters are familiar with this.
“A moose that is wounded and chased becomes very stressed. Its meat becomes tough, flavourless, and quickly develops an unpleasant odour," says Tom Johannessen, a butcher and sausage maker at the Norwegian Food Research Institute (Nofima).
Livestock are vulnerable on the way from the barn to the slaughterhouse.
'Transport exposes animals to a range of events and experiences that often trigger a stress reaction, both physical and psychological,' writes Animalia, the meat industry’s primary knowledge and development centre in Norway (link in Norwegian).
Uncomfortable in livestock transport trucks
In Norway, the maximum allowed travel time to the slaughterhouse is eight hours.
Pigs and chickens live indoors in the same environment their entire lives. The journey to the slaughterhouse can be especially stressful for them.
“For instance, pigs may encounter unfamiliar pigs in the slaughter truck. They then need to establish a new social hierarchy in a very short time, which can lead to stress,” says Rune Rødbotten.
He is a researcher at Nofima.
“Pigs can react differently, and stress affects them and their meat differently,” he says.
Efforts to calm chickens
Chickens are also uncomfortable on the way to the slaughterhouse. The Norwegian poultry company Norsk Kylling has implemented various measures to help with this.
“Norsk Kylling systematically works on measures to minimise stress for chickens during collection, transport, and reception at the slaughterhouse,” quality manager Solfrid Bjørkøy writes in an email to sciencenorway.no.
The slaughterhouse controls temperature, humidity, and light to calm the chickens, according to Bjørkøy.
Employees also work as quietly as possible and use electric forklifts.
“We are the only slaughterhouse that uses a method where the tray the chicken is sitting on is moved directly into the gas anaesthetic without tipping the bird or doing anything else that could contribute to stress beforehand,” writes Bjørkøy.
Poor bleeding reduces shelf life
Stress-reducing measures have also been implemented for other livestock.
“Animals should avoid unnecessary stress on the way to the slaughterhouse and while being housed there,” Holmbakken writes in an email to sciencenorway.no.
The animals should have access to food and water and be allowed to move around.
It is crucial for both animal welfare and meat quality that the animals are properly anaesthetised and that the blood is drained well during slaughter. If this does not happen, it can reduce the shelf life of the meat, according to Holmbakken.
Stress meat
When stress manifests in meat, it is referred to as stress meat.
“In stressful situations, the body secretes signalling substances and hormones like cortisol. Most consumers likely cannot taste these compounds in stress meat, but many can recognise reduced juiciness,” says Rune Rødbotten.
In the 1990s, selective breeding removed a specific gene in pigs thought to eliminate stress meat. However, the problem persisted.
“Even though that particular gene was removed, stress meat cannot be entirely avoided. There are many other forms of stress that affect the meat,” explains Rødbotten.
Pale and crumbly meat
In recent years, new quality issues have been observed in ham.
The meat has an unusually pale colour, looks boiled, and has loose muscle fibres. This is called PSE meat.
In products like cooked or cured ham, the texture becomes crumbly, the meat feels dry, lacks flavour, and slices fall apart, according to Animalia’s the State of Meat 2023 status report (link in Norwegian).
A research project investigated the issue, discovering that up to 30 per cent of round steak from seven slaughterhouses showed quality deveiations. This meat is either thrown away or used in cheaper products.
Stress increases lactic acid
“In pigs, stress just before slaughter can cause the meat to release an abnormal amount of fluid during storage, making it seem dry when eaten,” says Rødbotten.
This occurs because the pH level drops rapidly in the warm muscles immediately after slaughter, causing muscle proteins to denature, change form, lighten in colour, and lose liquid.
“If your pork chops seem less juicy, it could be because the pig was stressed before slaughter – or simply because the chef overcooked them,” says Rødbotten.
He notes that most livestock in Norway are well cared for, even at the slaughterhouse, and the occurence of stress meat is relatively low in this country.
Less tender steak
Beef quality can also be impacted by stress, as shown in a study from the Norwegian University of Life Sciences (NMBU) mentioned in the farming magazine Bondevennen (link in Norwegian). Stress during transport, at the slaughterhouse, or during the actual slaughter can reduce beef tenderness.
For cattle and sheep, stress before slaughter can affect meat quality differently. Stress in these animals leads to a smaller drop in pH than usual,” says Rødbotten.
This results in darker meat with a dry surface, even though it retains more water than normal. This is called DFD (Dark, Firm, Dry) meat.
“Meat having a relatively high pH is unsuitable for storage and develops an unpleasant bacterial odour after a short time,” says Rødbotten.
Stress not visible in chicken meat
“Stress before slaughter can impact meat quality in all species, but the effects differ. For pigs, the meat becomes less juicy, though storage life isn’t affected. For cattle and sheep, the meat retains more moisture but is unsuitable for storage,” Rødbotten explains.
Stress meat can also occur in chickens.
Norsk Kylling reports that researchers in Brazil found stress-related PSE and DFD meat in chicken. However, such findings have not been documented in Norway.
“We continuously test the meat, but unlike red meat and pork, we can’t document a difference in taste due to stress in white meat,” says Bjørkøy from Norsk Kylling.
Stress is simply not visible in white meat, she says.
More space in barns
Nevertheless, living conditions and the environment affect meat quality.
Norsk Kylling uses a chicken breed that grows more slowly. The birds are given more space in barns and more opportunities to be active.
“We have data showing that this gives the muscles and meat a clearer structure,” writes Bjørkøy.
While they regularly test the meat, they have not found other health and welfare factors significantly affecting its taste.
Rancid taste
In addition to health and welfare, animal feed plays a critical role in meat quality, according to Holmbakken from Nortura.
A few years ago, fish oil in pig feed was found to cause a rancid taste in pork, leading to reduced use of fish oil in feed.
“Different types of feed affect meat flavour, particularly in pigs and poultry,” writes Holmbakken, emphasising that robust standards are in place to prevent negative deviations.
The taste of mountain pastures
But can feed improve meat flavour?
This is often claimed in advertising by meat producers and farmers.
“Both the fish and animals on our farms or in mountain pastures live well and eat natural feed. This gives delicious flavour and healthy food!” Uvdalsbonden writes on their online farm store website.
Nortura advertises Gilde Gourmet lamb as tasting of mountain pastures, herbs, and fresh grass.
Both yes and no
A study from NIBIO showed that animals grazing near farms grew larger and heavier than those grazing in the wild. However, researchers found little difference in the quality of the meat.
Tom Johannessen from Nofima is on the jury for the Spesialist label, an award for the best Norwegian meat.
He answers both yes and no to the question of whether outdoor grazing improves meat flavour.
“There can be differences, such as animals grazing on seaweed in coastal pastures or heather in mountain pastures. But size, weight, and fat marbling matter most for flavour,” says Johannessen.
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Translated by Ingrid P. Nuse
Read the Norwegian version of this article on forskning.no
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