The feeding, economics and environmental impact of heavy pigs

By Mick Hazzledine, Premier Nutrition Products Ltd - This is a report from The 14th Annual JSR Technical Conference held on the 16 September 2003 which examines the feeding of heavy pigs, the economics of production and environmental impact.
calendar icon 8 March 2004
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JSR 14th Annual
Technical Conference

The conference entitled "Connecting our customers to create the value Chain" held on September the 16th 2003 and was a huge success attracting over 150 delegates and a range of well respected inductry speakers.


Increasing slaughter weight reduces the cost of production of pigmeat. The savings are farm specific but are generally of the order of a 3p/kg DW saving for each 10kg increase in slaughter weight. Where growth rate can be improved, or feed is relatively cheap, these savings can be substantially higher. It is worth considering heavier slaughter weights alongside measures to improve health such as de-stocking. Improved health gives the benefits of improved growth and feed conversion although the effects on grading are inconsistent.

At least 2 feeds and preferably 3 feeds are required from 30kg liveweight. Accurate farm records are essential if feed specifications are to accurately meet the pigs’ requirement.

The genotype of pig is important as the differences between genotypes increase at higher weights. Early maturing genotypes can see a marked fall in growth rate at higher weights, together with a rapid increase in P2, and thus are less suitable.

Abattoir contracts are complex and computer models are extremely useful to determine optimum weight and contract. Weighing of pigs can dramatically increase returns, particularly at heavier weights, as penalties for over-weights can be severe.

Increasing slaughter weight increases the nitrogen output from the finishing farm per unit of pigmeat produced. However less weaners are required and thus savings are evident on the breeding farm. Overall, providing that low protein feeds are used in late finishing stage, the effects on N output per kilo of pigmeat produced are negligible.


The UK has increased its pig slaughter weight from 63.7kg in 1989 to over 73kg today. Despite this slaughter weights remain low compared to international competitors. For example the Danes are at 80kg, Dutch at 93kg whilst the French are averaging 88kg. Canada average 89kg whilst top of the list comes the USA with a hefty 98kg.

The economics of pig production have changed markedly in recent years. Feed, as a percentage of total costs, has fallen. The costs of weaner production have risen in part due to PMWS and reproductive problems. Genetically our pigs continue to improve, with a greater potential for lean growth at higher weights. Such factors mitigate towards heavier carcase weights.


The BSAS Nutrient Requirements Standards for Pigs has recently been published. This publication gives guideline feed specifications for pigs of various ages and has been used as a reference point in this article. It should be noted that the requirements are given in terms of net energy and digestible amino acids. These are recommended for commercial use. Within this article, however, I refer to digestible energy and total amino acid levels simply because the numbers are more familiar.

Adequate amino acid levels in the feed are crucial if lean growth is to be optimised. To determine the amino acid levels in feeds for any age of pig requires knowledge of both the potential lean growth of the pig at the weight in question and its feed intake. Both lean growth and feed intake are genetically determined but commercially compromised, usually primarily by disease.

As weight increases the genetic differences in lean growth diverge. Some genotypes are relatively early maturing; they show a more marked decline in lean growth as weight increases. As most commercial breeding companies test their lines up to 90kg there is a lack of good data, on modern UK genotypes, at heavier weights. Such information is required.

Feed intake is of particular interest. The BSAS nutrient requirements gives a feed intake curve derived largely from academic data, and thus, by definition, relatively healthy pigs. Comparing this to Pigfacts costings, intakes on commercial farms in the UK are some 8% below this curve on average. In contrast data from Denmark and the USA suggest intakes about 18% higher than the BSAS standard. Such differences in intake are fundamental. Put simply if we are examining the lysine concentration in the feed then we have to have to allow an extra 26% in the UK just to account for lower appetite. This is the major reason why finishing feeds are cheaper in many competitor countries. It also helps to explain why the Danes are now rapidly approaching 900g/day as the average growth rate in finishing, whilst in the UK we are struggling closer to 700g/day.

For an “intermediate” pig type (one growing around 795g/day from 20-90kg) the BSAS Nutrient Requirements suggests a total lysine level of 0.84% from 60-90kg and 0.73% from 90-120kg (the ideal balance of amino acids is described in the standards; in the following text it is assumed that amino acids are balanced).

There are a number of further commercial considerations.

As previously discussed feed intake is lower than that in the standards, raising the total lysine required, for the 60-90 and 90-120kg periods, by 8% to 0.91 and 0.79%.

The standards are modelled on an individual pig; the commercial reality is that we are feeding a population. In you feed the average pig then the best boars will not perform to their maximum ability. What percentage of the population do we want growing flat-out?

Finally we don’t have pens of pigs all weighing for example, 90kg. Some pigs in the pen may well be 75kg. Do we feed a better feed to look after these lighter pigs? Or are they lighter pigs because they have previously been damaged and therefore cannot respond to better feeds?

There are then a large number of considerations before specifying feeds for finishing pigs, particularly at heavy weights. The following specifications are for an “intermediate” pig type and take account of the factors discussed above. The lysine levels include a degree of “safety margin”. In the light of achieved farm results it may be that these can be removed.

Table 1. Feed specifications for finishing pigs

How many feeds should be fed in the finishing period? Amino acid requirements fall with age and pigs are more able to cope with fibrous feed ingredients. Bulky feeds help reduce energy intake and thus give a modicum of control on grading. Three feeds are probably a good commercial compromise, although on farms where feed intake is unknown this degree of sophistication may be unwarranted.

Other aspects of feed specifications for finishing pigs, such as minerals and vitamins, are given in the BSAS document.

Typical feed formulations, based upon the specifications in Table 1, are shown in Table 2. These are derived using raw material costs from August 2003.

Table 2. Example feed formulations (abbreviated)

Allowing £25/t to cover feed manufacture and delivery gives a feed price of £117.72/t delivered for the final finisher. Using typical performance data the terminal deadweight FCR is around 4.8. Thus the feed cost of an extra 1kg of carcase is 57p.

Production costs

Where is this extra weight going to come from? There are obviously many ways to tackle this and each offers a unique solution.

  • Grow the pigs faster. If extra slaughter weight can be achieved through faster growth then there is only the extra feed to pay for. On most commercial farms in the UK growth rate is more limited by health than by genetics, nutrition and management. Restocking can provide huge improvements in growth.

  • Produce fewer pigs either by purchasing less weaners or reducing sow numbers.
  • Build or rent more finishing accommodation.

As a simple example MLC, in their “industry guide to the production of heavier pigs”, cite a 1000 place batch finishing operation, which has fixed and variable costs, excluding feed, of £30,356/annum (equivalent to £9.20 for a 100kg gilt). Vaccination costs were taken as an addition £1/pig. Annual liveweight sales increased slightly as the heavier pigs grew marginally faster. In this analysis increasing liveweight from 100 to 110kg reduced production cost from 91.2 to 87.5p/kg DW, and at 120kg to 84.5p/kg DW giving savings of 3.7p/kg and 3.0p/kg for the respective 10kg increases.

Pen utilisation and stocking density must be considered. If there were no mixing of pigs in the above example, and all pigs were sold at heavier weights, then pigs sold are reduced further as the stocking density of the pen becomes the limiting factor. In this case though reductions in production cost are still around 3p/kgDW for each 10kg liveweight increase.

Where feed is cheaper, for example with co-products, then the economics of heavy pig production improve further. In the above example a 20% reduction in feed price increases the production cost saving, from an increase of 10kg liveweight, up to 4.7p/kg on average.

Carcase return

For the majority of producers increasing slaughter weight reduces production costs. But for this to be economically viable this reduction must exceed any reductions in abattoir returns. Consideration must be given to the abattoir contract itself, and to how well the pigs fit the contract.

Abattoir contracts are complex, employing as many as 35 weight/P2 classifications. Describing a contract as “paying base for a 13mm pig up to 90kg deadweight” says very little; the devil is in the detail. In particular on heavy pig contracts the penalties for over- weight pigs can be punitive. In one case for example a 90kg DW boar was worth £90 and a £91 kg boar £69! It doesn’t take many such pigs to destroy the economics of heavy pig production.

Pig selection for the abattoir is crucial. This is particularly the case the closer the average slaughter weight comes to the abattoir overweight classifications carrying the bigger penalties. It is also the case where the population of pigs is relatively fat, and where the rate of increase in P2 with weight is high. For most producers weighing of at least a proportion of the pigs is necessary to maximise returns.

What increase in P2 should you expect? On an ad lib-feeding system then about 0.15mm/kg DW is typical with values of 0.1-0.2mm not uncommon. Values much greater than 0.2mm/kg DW are worthy of investigation as it may be, for example, that amino acid supply is sub optimal or that the genotype matures too early.

To evaluate abattoir contracts, slaughter weight optima, pig variability etc is a complex, and specialised operation. Fortunately computer models exist for this purpose. Meadow Quality have recently produced an excellent model, Premier Income Grading Systems (P.I.G.S), looks at historic grading and farm data, remodels the pigs at higher slaughter weights, and offers this new population of pigs to the various abattoir contracts. Net margins are calculated and “what-ifs” can be performed.

As an example the PIGS programme was used to look at a producers returns at various slaughter weights on a heavy pig contract. Returns increased up to about 76kg DW, as fewer pigs were hitting the lightweight pig penalties. The return/kg remained little altered up to 81kg DW but then fell by 4p/kg by the time pigs reached 86kg DW. Had the pigs been weighed then the fall in carcase return at 86kg DW was only 1p/kg compared to pigs of 76kg DW.

It is again reiterated that each farm situation is unique


Does heavy pig production increase or decrease nitrogen output from the farm?

Two points in particular are of relevance. Despite the use of low protein finishing feeds nitrogen excretion in the finishing herd, per kilo of pigmeat produced, rises with increases in slaughter weight. However less weaners are required. Thus the contribution from the sow and growers is reduced.

Overall, in an exercise using a 15% crude protein feed from 100kg BW, the savings in nitrogen output from the sow and weaners matched the increase from the finishing pig. Under such circumstances heavy pig production has a negligible effect on nitrogen output.

If however a 19% protein feed was fed throughout finishing the combined nitrogen output of the farm increases by some 3% for each 10kg increase in liveweight.


An industry guide to the production of heavy pigs. - MLC, PO Box 44, Winterhill House, Snowdon Drive, Milton Keynes. MK6 1AX.

Source: JSR - 16th September 2003

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