Experts in the UK have suggested that a 10% increase in pig carcass weight could potentially cut production costs by up to £0.04 per kg (MLC Report 2003). Although this figure is based on experience from a non-castrating market with relatively low slaughter weights, the same principle applies to other pig rearing systems.

Some significant costs are incurred on a per pig basis, so the heavier pigs at slaughter the more these particular costs can be diluted. A simple example is sow feed: A typical sow might produce 20 slaughter pigs and eat 1,200 kg of feed per year (60 kg per pig). At a slaughter weight of 105 kg, each kilogram of pig produced has ‘cost’ the equivalent of 0.57 kg of sow feed (60/105), in addition to what the pig ate itself. At a slaughter weight of 145 kg, this figure is reduced to 0.41 kg.

Higher weight production

From the pig processor’s point of view, increasing carcass weight can have similar financial benefits because, depending on equipment, the cost of processing a heavier carcass may be no higher but would provide a greater yield of saleable meat.

However, before switching to higher weight pig production there are a number of factors that have to be taken into consideration, if the change is to yield the expected results. With greater maturity, there is a tendency for fat deposition to increase and feed conversion efficiency to get worse.

Excess backfat is a particular problem in castrated male pigs that do not benefit from superior feed conversion rates and lean tissue gains that are typical of intact boars. If castrates grow too heavy, then the increase in P2 may reach a level that is less desirable to processors. For example, castrates slaughtered at 130 kg may have a P2 of 18mm (MLC figure).

An answer to the problem of maintaining acceptable productivity at higher slaughter weights would be to raise entire boars. However, in non-castrating markets, heavier weights are associated with different meat quality problems – principally the higher risk of boar taint – and behavioural issues associated with boar behavioural patterns.

These heavyweight factors can be put in two broad categories: those affecting the farm, and those affecting the supply chain.

On-farm factors

Bigger pigs need more room. This isn’t just a result of the increasing interest in animal welfare by consumers and legislators: It’s necessary if pigs are to achieve their full growth potential. Pushing up slaughter weights also means keeping pigs longer in the finishing barn and coping with larger variations between individuals.

Depending on the pig production system being used, this has implications for the management of animal throughput and stocking levels. Physically housing, feeding and moving larger pigs may require an investment in farm infrastructure. EU animal welfare legislation, for example, stipulates that pigs with an average weight above 110 kg should each have a minimum of 1m2 floor area per animal; that’s nearly double the minimum for pigs in the 50-85 kg bracket.

Single sex groups are highly desirable to minimize the difference in performance within the group as weight increases and to avoid unwanted sexual activity. Transport to the abattoir may have to be adjusted to make sure pigs have sufficient room. Larger pigs are also likely to exert more wear and tear on the farm environment – especially non-castrated boars.

Even in single sex groups, sexual and aggressive behaviour between non-castrated males can become a management problem, leading to injuries, leg problems and in some cases a significant animal welfare issue. In well-managed units, the risk period is at the end of fattening—removing heavier animals from pens can disrupt established social hierarchies and lead to fighting between those remaining.

Similarly, mixing with unfamiliar animals, for example, during transport or at the slaughterhouse, can lead to stress and fighting between entire males, which in turn can lead to carcass damage and meat quality defects. Depending on the timing, pigs that are stressed before slaughter are more likely to produce Pale Soft and Exudative or Dark Firm and Dry meat, both of which are undesirable.

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Although attempts are being made to reduce these problems, particularly the risk of boar taint by genetic improvement, an anti-taint vaccine Improvac from Pfizer Animal Health may reduce boar-like behaviour in the late fattening stage.

In addition to sex differences, genetics are important when considering slaughter weights. Both lean growth and feed intake are partially genetically determined and differences in performance between genotypes can increase at higher weights. Early maturing genotypes, for example, may show a significant fall in growth rate at higher weights and a rapid increase in P2.

Optimal feeding regimens and slaughter weights for heavy pigs have been the subject of much research. The ideal feeding regimen will vary from herd to herd and even between individual pigs: If you feed to suit the average pig, then by definition some will underperform.

Computer modelling programmes can assess the effect of different variables on production costs and output; remember that every farm and herd is different and you should find out what works best for you.

External factors

Bigger carcasses present a number of value opportunities for the pig processor. Seam butchery becomes easier, cutting along and between muscles and removing unwanted fat and gristle, to produce lean, well-trimmed cuts that are attractive to consumers. New cutting techniques allow a wider and more diverse range of products to be produced, and increased muscle bulk also facilitates the production of larger boneless joints and steaks. Meat tends to become more tender and juicier as the animal gets older, principally as a result of increased intramuscular fat deposits.

On the downside, castrates tend to lay down more fat as they get older. Unless the excess fat is trimmed, the result could be a less appealing product for consumers in many markets. Fat deposition can be limited by restricting feed intake, but this needs to be done with care as it can also affect other aspects of growth performance and meat quality.

In cases where pigs are sold to a buyer contract, the specifications will have to be re-defined if carcass size is increased. Likewise, the slaughterhouse needs to be equipped to accept bigger animals. If vaccination is used to facilitate the production of larger boars, the abattoir staff must be prepared to see pigs that behave like castrates but with testicles that will need to be removed on the line. It is essential to check that heavier animals are acceptable to the abattoir before implementing any changes.

Legislators and consumers are increasingly aware of environmental issues and in some markets these are being actively targeted for control. Several EU states have already introduced legislation to limit the amount of pig manure used per hectare of land – although these vary considerably.

Raising heavier weight pigs also has implications for waste handling. Heavier pigs eat more feed and create more waste, but this can be balanced by the reduced number of pigs required to produce a given amount of meat and the fact that the environmental impact is spread over more meat production. The particularly poor feed conversion rates of castrates means that the amount of waste that has to be dealt with per kg increases even more if such animals are reared. Waste management and the environmental impact need to be considered on a broad basis if pigs are to be raised to higher finishing weights.

Another problem attracting attention from both consumers and governments is animal welfare. In terms of heavier pig production, stocking levels, transport and castration are key areas of concern. In some markets, physical castration is being phased out and in others the compulsory use of anaesthesia is a possibility.