Bridging the Gap Between Genetic Potential and On-Farm Performance in Commercial Pigs

By Aedmund J. McClure, Courtesy of Alltech Inc. Commercial hybrid pigs as found on farms throughout the world today have a much improved potential for growth and a much better ability to convert feed to liveweight gain than their counterparts in the late 1950s.
calendar icon 21 December 2007
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Continuous genetic selection since the early 1960s has been aimed primarily at reducing body fat content to provide the consumer with leaner pig meat in line with changing eating patterns, and more recently in improving the litter size at farrowing.

Given this change in the type of animals being supplied by the breeding companies, have the necessary changes to nutrition, management (including hygiene) and environmental inputs been implemented to allow performance expressed at farm level to move more in line with the true genetic potential? Or, is there a need for more detailed and serious action to quantify and change the various inputs in order to narrow the gap between actual and potential performance? This paper examines the current situation and looks beyond this point as to likely changes required to bring commercial pig farmingmuch closer to true least-cost pig meat production for the future.


Ameasure of the progress made from ongoing genetic selection programmes and the sale of improved breeding stock to commercial producers in the UK can be gained by examining the change in backfat measurement inUK slaughter pigs. Meat and Livestock Commission (MLC) values (1991a) indicate the progress made in reducing carcass fat in pigs (Figure 1). This reduction in body fat implies needed changes in other nutritional inputs. Modern pigs, by virtue of lower fat insulation, lose heat more easily. As a result closer attention to housing temperature at each stage in the nursing, growing and finishing stages is required. Increased lean tissue deposition (and decreased fat deposition) potential makes it necessary to supply feedswith higher levels of essential amino acids, particularly for the early growing stages, if the improved growth of lean tissue is to be expressed in practice.

A measure of the progress in breeding pig performance over time can be gained from examination of on-farmrecording schemes. Evaluation by the Meat and Livestock Commission (1991b, 1998) of breeding herd performance in theUKreveals the performance averages given in Table 1. The recent emphasis on genetic selection programmes to increase numbers of pigs born alive is reflected in commercial herd averages and is a very positive aspect of improving lifetime productivity of the breeding sow. However, increased numbers of pigs born alive are only of real value provided that the pigs can be successfully weaned. Additionally, increasing the numbers born alive has resulted in two practical changes, namely:

  • Reduced average piglet birth weight.
  • Increased spread in birth weights between the lightest and heaviest littermates.

Major changes at farm level, particularly in the areas of early piglet management and supplementary feeding, are required in order that extra piglets born alive are saved and not accounted for as increased pre-weaning mortality percentages.



The introduction of improved pig breeding stock into commercial pig farms requires capital investment. If that investment is to be realized, i.e. more live pigs born with higher growth potential, then standards of feeding and management must be adjusted.

Figure 1. Change in backfat (P2) measurements for 60-80 kg deadweight pigs (MLC, 1991a)

Table 1. Trends in breeding pig performance1

1MLC/Signet, 1998.

First, what levels of performance are possible given good management and nutrition frommodern suckling, growing and finishing pigs at commercial farmlevel and how does current performance measure up to the potential? Some indications of performance potential may be gained by examining piglet growth trials where intake of highly digestible supplementary feeds are maximised under excellent standards of management and feeding techniques (Table 2). Using these data as a comparison point, pre-weaning piglet performance, both on average and for the better commercial piglet producers in the UK, currently falls short of genetic growth potential by 20-25%. There is clearly a need to re-examine the current management and feeding practices for pigs in the farrowing house.

Table 2. Potential versus actual piglet pre-weaning growth performance1

1MLC/Signet, 1998.

The weight-for-age at weaning has a large impact on post-weaning growth performance. Again, examination of post-weaning growth rates in commercial practice as compared to the genetic potential (MLC/Signet, 1998) (Table 3) indicates a widening of the weight-for-age relationship as the growth cycle progresses. It becomes evident from these performance comparisons that maximising early growth rate is critical to controlling the feed cost involved in pig meat production. Higher early growth rate reduces the number of expensive feeding days pre-slaughter (at maximum daily intake and poorer feed efficiency) on ad libitum feeding systems employed on most commercial farms.

Table 3. Potential versus actual piglet post-weaning growth performance1

1MLC/Signet, Farm Busuness Consultancy UK data- 12 months ending 30/09/1998

Further information as to the genetic potential for growth of pigs in the later stages of finishing may be gained from carrying out computer growth simulations using feeds of known nutrient density in conjunction with known management and environmental controls at farm level (MLC/Signet, 1998, Table 4). These studies indicate the potential savings in feeding days under typical UK conditions on many commercial farms. The extent of the growth performance gap to be bridged with the finishing pig would appear to be greater than for younger pigs.

Some degree of caution is necessary here since the performance and growing time required during this stage is influenced by early piglet growth performance. Thus poorer growth in young pigs results in extended feeding time to reach the final slaughter weight. The changes needed are increases in nutrition and management inputs to bring about higher nutrient intake between birth and 50-60 kg liveweight. The goal is to accelerate early performance when pigs are more efficient followed by closer control of nutrient inputs between 60 kg and slaughter to reduce nutrient wastage.

Table 4. Growth potential versus actual commercial performance in finishing pigs (genetic potential - by growth model prediction1)

1MLC/Signet, 1998.


In the overall context of pig meat production it is also necessary to maximise the lifetime productivity of pig breeding stock. Replacement breeding stock represent a major investment in commercial pig production and replacement costs have increased in line with animal potential to produce increased litter numbers born alive and increased carcass leanness. Examination of annual female breeding stock replacement rates within UK herds indicates a continuous and high level of replacement (MLC, 1991b; Table 5). To what extent this is due to a desire to improve carcass quality or output is unclear; however evidence in the field would tend to suggest that the more likely reasons are due to on-farmnutritional shortfalls which adversely affect fertility and/or skeletal defects such as leg problems.

Whatever the reason(s), the inescapable fact is that in practical terms lifetime productivity today is the same as it was a decade and a half ago. The key to progress in this area given larger litter numbers born alive must be improved early piglet management with supplementary feeding to reduce pre-weaning mortality coupled with improved nutrition and management of sows to extend the breeding lifetime within the herd.

Table 5. Female breeding herd replacement rates and their effects upon lifetime productivity of the herd1)

1MLC/Signet, 1991b.

As a guideline, suggested lifetime productivity targets for female replacement breeding stock are given in Table 6. Achievement of these targets in commercial production is vital for a future in pig meat production and will only be possible provided a much more disciplined approach is taken in terms of:

  • Adequate nutrition of gilts pre-breeding to maximise backfat reserves.
  • Careful heat detection and natural service or artificial insemination techniques.
  • Phase feeding of sows during pregnancy to maximise implantation and foetal growth.
  • Adequate trace mineral nutrition during pregnancy and lactation for improved sow fertility and piglet vitality at birth.
  • Step feeding to maximise lactation feed intake, milk production and mimimise body weight loss.
  • Supplementary feeding of piglets from day 1 with highly digestible dry feed to maximise intake, promote early digestive system development and increase growth rate.
Table 6. Female breeding stock: lifetime productivity targets for 1999 and beyond.


Pig producers and those involved directly in giving nutritional and management advice on all aspects of pig production need to clearly focus on the objectives of the commercial exercise. In the case of the breeding female the objective should very clearly be to maximise lifetime productivity as measured by the number of piglets weaned at maximum weight for age. Practically this implies following a management and feeding strategy that results in:

  • Production of the maximum number of litters (minimum 7) before culling from herd.
  • Maximising piglet numbers born alive.
  • Maximising live piglet birth weights.
  • Management and feeding of suckling piglets to minimise pre-weaning mortality and maximise dry matter intake both from sow’s milk (number 1 priority) and solid creep feed (number 2 priority).

In the case of the growing pig the objectives may be summarised as follows:

  • To produce pig meat at minimum total cost.
  • To maximise lean tissue deposition from birth to slaughter.
  • To minimise fat deposition from 50-55 kg to slaughter.



Laying the foundation for a long and productive breeding life begins at final selection at 80-90 kg (if not before) by feeding to maximise body fat deposition (minimum 20mmbackfat at P2 position) before first service at 130-140 kg and expression of third oestrus. This is best achieved by ad libitum feeding of a high energy/low essential amino acid pre-breeder diet to discourage lean tissue growth and maximise fat deposition. Avoid overfeeding of the gestation diet for the first 28 days post-service as this causes rapid body gain leading to increased hepatic blood flow and increased metabolic clearance of progesterone. A decrease in the plasma progesterone concentration will reduce the production of uterine secretory proteins that play an important role in successful attachment of fertilised ova to the wall of the uterus.

Piglet birth weight is influenced by nutrient intake level from day 85 of gestation through to farrowing. Increasing the level of nutrients consumed by the gilt or sow on a daily basis at this stage will have a positive effect on piglet birth weights and will also condition the breeding animal for maximum daily feed intakes during the following lactation. The form of trace mineral supplements during this period will also have a beneficial effect on both breeding female mineral status and piglet viability at birth. Minerals in the organic or Bioplex form are more readily available for absorption and better able to cross the placenta to increase the mineral status of the neonate and thereby improve livability.

The aim in the farrowing house should be to feed the nursing sow in such a way that nutrient intakes increase daily to reach 7 kg of a high density lactation diet by day 10, with further gradual increases to maximise daily intake and milk production by day 21. The overall aim is maximum milk production coupled with minimum weight loss during the nursing period.


Piglets have the potential for fast lean tissue growth from day 1 provided that sufficient nutrients are consumed on a daily basis. Intake of sow’s milk is the number 1 priority. It is ‘rocket fuel’ in terms of digestibility and nutrient availability for the newborn piglet. However during the course of lactation with larger litter sizes, the problem is that sow’s milk as a sole source of nutrition limits individual piglet growth owing to the finite amount of milk available and the dry matter which it contributes. Piglet growth rate is governed by dry matter intake and the digestibility (i.e., available nutrient content) of that dry matter. It is essential that daily dry matter intake is maximised by the suckling piglet from day 1 for a number of very important commercial reasons:

  • To minimise early mortality of healthy but low birth weight piglets.
  • To stimulate early development of the digestive system.
  • To maximise availability of nutrients to fuel growth at the genetic potential of the animal.

Sow’s milk, being low in dry matter, expands stomach volume in the piglet fairly rapidly. Meeting the commercial objective, genetic growth potential, requires occupation of this expanded stomach capacity with increased intakes of the highest quality dry matter in the form of solid feed. The commercial practice of giving small quantities of digestible, highly palatable solid feed in meal form on day 1 and ‘nose dipping’ of the smallest piglets a few hours post-farrowing will result in increased dry matter intake, reduced early mortality and earlier development of the digestive system. This may be followed after a few days by mixing in increasing quantities of pelleted piglet starter feed and phasing out of the original starter meal by 7-10 days of age. Careful and sensible adoption of this approach increases consumption of high quality piglet feeds between birth and weaning. The earlier the weaning age, the earlier solid feeding should be offered to suckling piglets, otherwise the more severe the growth check post-weaning.

The priority for selection of the raw materials for piglet feeds must be maximum dry matter digestibility of the final feed mix if genetic growth potential is to be achieved from the earliest possible age. Formulation of diets to the highest quality standards (ie., digestibility) is the requirement, not formulation to a cost standard as diet cost in piglet feeds is purely a reflection of raw material quality and nutrient density. Specially selected quality protein sources (such as milk products, fishmeals, biopeptides), cereal sources (cooked to rupture starch grains) and vegetable oils are the basis of successful early piglet feeds (birth to 12-15 kg) to maximise growth rates both pre- and post-weaning.


Highly consistent protein sources of animal origin such as low temperature dried fishmeals may be difficult to obtain on a regular basis in many areas of the world where direct early piglet feeding is practised. A new alternative to solve this problem is now available in the form of Alltech Ultimate Protein Biopeptides. Peptides consist of variable length chains of linked amino acid (typically 2-50 amino acid units) which result from the hydrolysis of proteins. Wheat gluten and brewer’s yeast are blended and subjected to controlled enzyme hydrolysis to produce a consistent highly digestible product containing biologically active peptides targeted to easily cross the intestinal brush border, accelerate intestinal maturation and crypt depth, encourage development of beneficial intestinal flora and contain glutamic acid to improve feed flavor.

The inclusion of Ultimate Protein 1672 to replace more conventional protein sources in piglet feeds fed both before and after weaning has been shown to improve growth performance. In a post-weaning trial in the UK, piglets weaned at 21 days were used to compare a control feed with one in which some of the protein was replaced with Ultimate Protein 1672. There were 65 piglets per treatment. The control group received a feed containing skim milk, fish meal and potato protein sources. The test feed contained 5% Ultimate Protein 1672 as partial replacement for the protein. The feeds had equal energy, protein and essential amino acid levels. Pigs given the feed including Ultimate Protein 1672 had 6.5% higher average daily liveweight gain and 6% higher daily intake (Table 7).

Table 7. Effect of Ultimate Protein 1672 on piglet performance.

Use of a highly digestible piglet feed ingredient such as Ultimate Protein 1672 during the period from birth to 20+ kg will enable improved growth rates in commercial pigs and allow the producer to take advantage of the reduction in feeding days to slaughter.

Whilst the foregoing briefly outlines the basics of providing quality nutrient sources for the young piglet, maximising growth rates is not just a matter of nutrient supply and consumption per se.What is required is adherence to sound nutritional principles coupled with the discipline of ensuring only the highest standards of daily piglet management including animal comfort, temperature levels and control, and hygiene. The gastrointestinal tract of the piglet at birth is sterile and the farrowing house environment influences the pattern of development of the bacterial flora in the gut.

Maintenance of strict farrowing pen hygiene standards allied to control of the development of the bacterial flora in the gut of the piglet via the solid feed route eliminates piglet scouring problems, an essential requirement if genetic growth potential is to be achieved. Bacterial scouring in piglets must be avoided as it causes permanent damage to the lining of the intestine resulting in decreased ability to absorb nutrients. Since the ability to absorb nutrients is fundamental to rate of growth, the scouring piglet never catches up and has poorer growth rate and feed conversion efficiency from the point at which scouring occurs to slaughter weight.


A brief examination of the feed consumption pattern of the pig from birth through to slaughter at 90 kg illustrates the importance of maximising growth, particularly in the early stages (Figure 2). The important factors to appreciate are:

  • 66% of the total feed requirement from birth to slaughter at 90 kg is consumed during the final 33% of the total weight gain.
  • Pigs growing from birth to 60 kg are much more efficient than pigs beyond 60 kg.
  • Rapid growth from birth to 30 kg has a major effect in the reduction of feeding days at maximum feed intake pre-slaughter, thereby lowering overall feed production cost.
  • In order to bring pig meat production more into line with least cost, a change in feeding systems and management is needed. Nutrient intake (and lean tissue deposition) must be maximised from birth to approximately 50-60 kg for maximum weight for age followed by a restriction in energy intake to avoid excessive production of carcass fat. This must be done while supplying sufficient intake of energy and essential amino acids to continue to maximise lean tissue deposition through to the desired slaughter point.
  • As illustrated in Table 4, the time difference in feeding days between estimated genetic growth potential and actual performance as recorded for the top third of UK pig producers is some 35 days (155 minus 120 = 35 days). With improved piglet management in the farrowing house and increased supplementary feed consumption from day 1 it should be feasible to increase weaning weights by some 500-1000 g. When this is achieved it represents a savings of about seven days feeding at the slaughter end of the production cycle.
  • Increased intakes of feed by weaned piglets with more enhanced digestive capability (by virtue of increased feed intake pre-weaning) over the weight range of 10-30 kg will result in further improvements in weight gain, feed conversion efficiency and final feeding days pre-slaughter (Table 8). Cumulatively the effect of improved management and feed intakes pre-and post-weaning can represent 14-21 days savings in feed usage at maximum intake levels pre-slaughter - equivalent to some 35-50 kg of finishing feed.
  • Prevention of early piglet scouring and/or looseness can be worth up to 7-10 days reduction in time to slaughter at approximately 90 kg.Again this represents a feed savings of 15-25 kg. Taken overall, the combined effect of improved early feed intake and scour prevention can amount to a time saving of 21-31 days and a saving in feed requirement of some 50-75 kg finishing feed. This is what current pig genetics are capable of delivering at unit level provided improvements can be made in early management, hygiene, feed quality and feeding techniques.
Figure 2. Distribution of weight gain and feed intake between birth and slaughter at 90 kg.

Table 8. Effect of increasing feed intake on post-weaning piglet performance from 10-30 kg liveweight (growth model predictions).


Current feeding systems for finishing pigs based on ad libitum feeding of a given feed nutrient specification over a wide weight range (eg., 5-90 kg) result in the production of surplus carcass fat due to over-consumption of energy. This is to be avoided as it usually leads to:

  • Increased costs of production since fat is more expensive to produce than lean meat.
  • Reduced sale value due to downgrading.

Controlling the daily energy intake to supply amounts required for body maintenance and lean tissue deposition from 50-55 kg onwards will result in decreased carcass fat content. This may be achieved in practice by:

  • Restricted daily feeding to a pre-determined maximum level.
  • Frequent and progressive changes in energy density of feed with increasing liveweight when feeding ad libitum.
  • Continuous blending of two feeds with different nutrient densities i.e., ratio feeding.

Using the last technique, pigs may be taken from 10-15 kg through to slaughter by the blending in two stages of a total of three feed specifications (Table 9). Based upon the genetics of the pigs, a computerised programme may be used to select the appropriate ratios for each stage in the growth cycle. In practical terms the feed ratios for individual groups of pigs may be changed on a weekly basis. Depending upon the feed blends used, pigs may be grown as fast or as slowly as required according to the market requirements at a given time. In an increasingly diverse marketplace this feeding system is likely to assume increased relevance and become more widespread in the future as a means of achieving carcass uniformity.


Advances in genetics have currently provided commercial producers around the world with pigs of production potential far in excess of the current performance levels being achieved. Bridging this gap in performance will only become possible for the future by appreciation of true production potential followed by marked improvements in standards of management, hygiene, environment and feeding. Where this can be achieved in practice, great progress can be made towards true least-cost pig meat production and the necessary return on extra investment involved in the purchase of genetically improved pig breeding stock.

Table 9. General feed specifications for continuous blending of feeds with different nutrient densities.


Meat and Livestock Commission. 1991a. In: Pig Yearbook 1991. Meat& Livestock Commission, Milton Keynes, UK. pg.75.

Meat and Livestock Commission. 1991b. In: Pig Yearbook 1991. Meat& Livestock Commission, Milton Keynes, UK Pg. 13.

MLC/Signet Farm Business Consultancy. 1998. 12 Months ending 30/09/1998. Published jointly by MLC, Milton Keynes, UK and SAC COSAS, Ltd. Edinburgh, UK.

December 2007
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