Killing-out percentage

Killing-out percentage explained

KO% is expressed as the weight of the carcase in relation to the weight of the live pig immediately before slaughter.

The most valuable part of the pig is the meat contained in the carcase. Producers are paid on the weight of the carcase and an assessment of its leanness, rather than the weight of the live animal.

Normally, the KO% ranges from 72–80%. In the UK, the average reported killing-out value in the last decade was 75–76%.

The EU definition of the carcase is ‘the body of a slaughtered pig, bled and eviscerated, whole or divided down the midline, without tongue, bristles, hooves and genital organs, but with flare fat, kidneys and diaphragm’.

Muscle and fat are the most important components of a carcase. In the UK, the flare fat, kidneys and diaphragm may be removed and the tongue may be left in, with the application of approved adjustments to the weight, then reflected in price paid.

The time of measuring liveweight greatly affects the KO%. If the pigs are weighed after feeding or before despatch from the farm, the liveweight will be about 5 kg greater than if the pigs are weighed after 24 hours without food or just before slaughter. So if you are comparing feeds or genotypes, weigh at a consistent time

Additional trimming in the abattoir for health reasons, e.g. abscesses and pleurisy, will reduce carcase weight and, therefore, KO%.

In some cases, the carcase weight is measured after cooling, rather than before cooling. In these cases, the KO% will also be affected, as a hot carcase will weigh 1.5–2% more than a cool carcase because of the evaporative weight loss during chilling.

A standard adjustment of 2% is applied to convert hot weight to cold weight under EU legislation.

The main pre-slaughter factors contributing to KO% are those that affect the pigs' liveweight at the moment of slaughter. There is no universal combination of factors at farm level that will enhance KO% on every farm. Each farm should work out where it stands, and possible areas for improvement should be identified.

Ways to maximise carcase weight in relation to liveweight

Breed, sex and liveweight are important, but, if these are constants, the major influence is the amount of feed in the gut, and whether the pig loses carcase weight due to stress before slaughter. Ensuring a correct period without feed (8–12 hours) and minimising pre-slaughter stress are the most straightforward ways to enhance KO%.

Gain as accurate a weight as possible both for the live pig and for the carcase – service and calibrate your weigh crate.

Well-muscled meat type breeds have proportionally heavier carcases, so will have a better KO%.

Normally, the heavier the pig, the better the KO%. This is because the main components of the pig carcase, muscle and fat, are later developing than the parts of the pig that constitute the offal.

As Large White pigs increase in weight from 70–120 kg, the KO% increases by 5% – a 1% increase in KO% per 10 kg liveweight.

Both the level of feeding and the composition of the diet have an effect on KO%. Diets with high levels of fibre, which are relatively indigestible, reduce KO%, while diets with a high nutrient density increase it.

Pigs housed on straw have a lower KO% than those in fully slatted systems.

If a pig is deprived of food, it will mobilise body tissues to provide energy for maintaining the vital functions of the body. It also has a negative effect on welfare and increases stress.

Fasting pigs for 24 hours can result in a loss of 3.8% of their initial liveweight and 2.1% of carcase weight in comparison with a fasting period of only four hours. An optimal fasting period would be 8–12 hours. 

Take steps to ensure loading, transport and lairage time do not result in excessive fasting.

A major pre-slaughter stress is the transport of animals from the farm to the abattoir. It has been found that the carcase weight of pigs transported for six hours can be reduced by 1 kg, corresponding to a 2% reduction in KO%. You should consider the following:

• Ensure haulier knows precise number to be transported before the vehicle is dispatched to the farm
• Avoid ramps at loading
• Aim to maintain pigs in stable social groups
• Minimise transit time to the abattoir
• Avoid use of goads
• Consider use of toys during transport