In 1989, our average carcase weight was 63.7kg and P2 was 11.8mm. Only 3.4% of pigs averaged over 80kg carcase weight and these were 16.1mm at 84.6kg carcase weight.  In less than twenty years, progress has been dramatic with average carcase weight today approaching 84kg, an increase of over 30%, and P2 down to 11.3mm.  Carcase weight recently has increased annually by around 1kg.

Clean pig carcase weight

Abattoir contracts have changed markedly during this period too. In 1989, back fat was a major determinant of pig price and most contracts were based upon <12mm for the top grade. Recognising the economic importance of back fat, we had low appetite genotypes with average feed intakes of less than 1.8kg/day from 28-85kg and growth rates of only 628g/day. Abattoir contracts today are very different, with most being 14mm, and so are our pigs with much healthier appetites and growth rates averaging 838g/day (albeit over a higher weight range, 36 to 109kg) according to the latest AHDB figures.

Statements such as “I want 90% of pigs in the top grade” or “I don’t want more than one overweight per load” or “I want to be within 3p/kg DW of the top price” are still uttered in our industry. They are old “rules of thumb” which may have had merit in 1989, but have little place in 2018. Abattoir contracts are increasingly complex and need proper interrogation if farm profit is to be maximised.


There are four major factors which influence the payment on a particular contract:

  1. Average weight
  2. Variation in weight (standard deviation, SD)
  3. Average back fat
  4. Variation in back fat (standard deviation, SD)

For the majority of producers P2 is no longer a major concern; compared with weight, rarely does P2 have a major influence on the optimum slaughter weight.  Further, P2 is not an “easy fix” for the producer. It is predominately determined by genetics and unless pigs can be restrict fed, then nutrition has only a limited influence on P2 and nutritional interventions are rarely cost-effective.  

In determining profitability, carcase weight is crucial – not just average weight but the spread in that weight as financial penalties on over-weights are often severe


cold carcase weight (kg) and backfat (P2mm)

Initially, as we increase weight, carcase return improves as we have fewer under-weights, but when a specific weight is reached return starts to decline as pigs are harshly penalised for being over-weight and fat – and it is galling to see a pig losing up to £70 for gaining an extra kilogram!

The importance of weight variation cannot be over-emphasised. The following graph shows the carcase value (p/kg DW) of three batches of pigs from the same farm sent to the same abattoir.

Dw (kg) by p/kg DW

When the variation in weight (known as the standard deviation or S.D.) was high (SD = 7.9), the optimum carcase value (p/kg DW) was at a weight of almost 84kg. However reducing variation (SD = 5.7) increased the price received by 1.4p/kg DW and increased the carcase weight at which this was achieved to 88kg. This equates to an extra gross income of over £7/pig or around £125k for a 700 sow farm and net profit after feed and overheads of around £58k/annum.

The weight variation described of 5.7-7.9 is not particularly extreme. We have seen values approaching 4 where producers weigh their pigs and as high as 9 where pens are being cleared or a lorry being filled for example.

Maximising profitability is not the same as maximising pence per kilo carcase

On most contracts the optimum slaughter weight for maximum profit is higher than that which results in the maximum pence per kilo carcase weight. We need to think population. The overweight pigs “catch the eye” because of the very obvious penalties, but we must remember that the majority of the other pigs supplied were within the less punitive parts of the contract and many could show a healthy return from higher weights.

The following table illustrates marginal carcase income and associated costs – i.e. the costs associated with each extra 1kg DW. Pence per kilo was maximised at around 81kg. However additional feed and overhead costs did not exceed the increases in carcase value until the carcase was 86kg so, in this example, profit was maximised at a carcase weight 5kg heavier than the maximum pence per kilo. This is not atypical.

Carcase weight table

The above table does not include any additional mortality which, even when very low, would marginally reduce the optimum carcass weight. Overhead costs also require debate as a fixed daily rate does not consider the reduced number of batches of pigs that can be reduced annually, but it does focus the mind on production logistics – if we could get an extra day’s growth it’d be worth between 56p and £1/pig.

Over the last few months, we have analysed thousands of pigs using a new online data analysis programme called BaconCheck. The results have been enlightening as the following table illustrates.

Comparison of 5 farm data

Farm A is selling well selected, light-weight pigs as accommodation is limiting, although for some reason they were sold on a heavy contract so underweights were a problem. Hence, a huge £8.46/pig potential increase in value on the existing contract moving from 77kg to nearly 89kg. Alternatively, a more appropriate contract could be considered.

Farm B can achieve an extra £6.53/pig by moving carcase weight up by 12 kg; Farm C, an extra £2.66 from an increase of 8kg. Farm D selects the pigs very well but they are fat, as the sire was selected for a particular retailer contract, and there is only a small potential increase in profit from increasing weight.

Farm E was a pen clearance from one of our trials and thus had a high weight variation (SD 8.7) and a relatively low optimum weight as discussed earlier. Finally farm F selected pigs well and the carcase weight is “spot-on”. However, the pigs are very lean; energy intake must have been low and growth rate potential lost, opening up further avenues for investigation.

Such methodology allows us to determine the optimum carcass weight on differing contracts, the accuracy of pig selection and rewards for improving this. It also assists in decisions to extend  accommodation, with projected payback of less than 5 years seen on new buildings. Alternatively, another option is to achieve the higher carcase weight by reducing sow numbers, selling some weaners or reviewing turnaround processes on farm.

Optimum carcase weight is generally higher for boars than gilts, being leaner and converting much better at higher weights, unless of course there are additional weight penalties. Now that split sexing is becoming more common, determining optimum slaughter weight by sex is a further refinement. Using 3 rather than 2 finishing feeds also increases optimum carcase weight as the final finisher feed is often £8-10/t cheaper, reducing the costs of these extra kilos.

The optimum average carcase weight on average in our analysis to date?  88kg.

BUT this average value is about as much use as buying new shoes knowing that on average men take a size 10 and women a size 6 but not knowing your own size. You might be lucky……….but the odds are you will be less than comfortable!

Determining optimum carcase weight is complex, and producers have all the information required in their abattoir returns, so why guess?


For further information please contact the authors:

Mick Hazzledine - Premier Nutrition (

James Christian - BaconCheck Ltd (