3 Ways to Increase Lean Growth – Reducing Backfat in Pigs

3 Ways to Increase Lean Growth - Reducing Backfat in PigsThere is a range of methods to increase lean growth and reduce back fat, the most important  methods being:

  • genetic selection (long term)
  • nutrition (medium term)
  • products/feed additives.

Diets need to be balanced for protein (amino acids) and energy, and suit the genetics of your herd, but there are other items to check such as feed intake, feed separation, sufficient water supply and health. Products such as ractopamine and porcine somatotropin (pST) need to be applied in a planned and strategic way.

It is recommended that these strategies be discussed with specialist consultants to determine the best course of action. Before this, monitor and analyse your herd’s performance to know what is actually happening and how to make improvements to optimise return. For example, know feed intakes and the average and range of slaughter weights and fats.


Increasing growth and reducing back fat by genetic selection is a long-term strategy. Choose a breeding stock supplier that uses a genetic improvement program over the long term, not just the closest supplier. Sires can be selected to provide what your herd requires e.g. to reduce fat or to concentrate on growth rate.

Bringing pigs into your herd can be a health risk as diseases may also be brought in. If these diseases or strains of organism are new to your herd they can cause a costly outbreak so consult a veterinarian about the health status of both herds. A safer alternative to purchasing pigs is to purchase semen.

Selecting for low P2 reduces fat at other sites

Contrary to some suggestions in the field, selecting pigs over generations for lower P2 does not shift the fat to other sites but does reduce overall carcase fat, and P2 is a good indicator of carcase lean. This fat reduction has been shown by our researchers in two trials 10 years apart with different genetics. The result of P2 selection was less fat depth at all sites measured although there were variations. The greatest reduction in fat depth was at the end of the eye muscle before the streak begins, and the least was at the mid-back site.

Selecting on P2 is the best single indicator of carcase lean. Measuring other sites as well increases the accuracy by only a very small amount. Many studies over the last 20 years on many breeds have shown that reducing P2 by 1 mm increases carcase lean by about 0.5%.

A trial also showed that changing the carcase fat by nutrition, reduced fat at all sites by similar amounts (the depths at different sites were not significantly different). The difference between males and females in fat depth varied between sites.


Nutrition is a faster way than genetics to increase growth and reduce back fat but can still take a few months to have an effect. Consider getting a second opinion on your piggery diets. The diets need to suit the pigs’ genetic capability. Additional diets may be needed to more closely match the pigs’ requirements as they grow, to ensure they are not over or under supplied with nutrients. AUSPIG is a good method to check the nutrition and management of your herd.

Checking the herd’s nutrition is more than just having balanced diets (e.g. lysine: energy) that best suit your pigs. In the feed mixing area, check items such as the quality of ingredients (e.g. that the actual protein level of the ingredient is the same as that being used in formulating the diets), and whether the ingredients are included by weight and not volume.

Feed management also must be considered. Bins must be cleaned out to reduce moulds. Ensure that the correct feed is going into the correct bin. Check if ingredients in the diet are separating, e.g. in the bin or through the feed lines, with the result that the pigs are not getting the whole diet but only an unbalanced part of it such as more of the fibrous or the heavier sections.

Know the intake of your pigs, and how it changes with the season, so that diets can be adjusted to provide the required amount of nutrients each day. Check that the pigs have regular access to feed and that feed distribution within a group is even. Irregular intake leads to distorted growth patterns, which compromises lean growth and results in fatter pigs.

Products and additives

Specific products and feed additives can change the way pigs use nutrients. For example, ractopamine (Paylean) and porcine somatotropin or pST (Reporcin). Ractopamine improves lean tissue growth and feed efficiency with little effect on P2 while pST improves lean tissue growth and feed efficiency and decreases P2.

Ractopamine directs nutrients to increase production of muscle rather than fat – it increases the size of muscle fibres and thus muscle mass. To support this protein synthesis, finisher diets need to contain sufficient lysine with other amino acids in balance. Ractopamine is fed for between two to a maximum of four weeks immediately prior to slaughter of finisher pigs; it is only of limited benefit to pigs for a pork market (e.g. 65 kg liveweight).

The greatest benefits are when fed to females and castrates. It is not of greater benefit if fed for longer than four weeks (response declines and can be negative) and the pig needs to keep being fed the additive once begun otherwise the growth rate rapidly decreases and fat levels rapidly increase.

Porcine somatotropin (pST) is a protein naturally produced by the pig and is the main factor controlling growth and metabolism. Administering pST during the finishing phase assists the pig to continue to deposit muscle tissue and reduce the amount of fat in the carcass.

Thus growth rate, feed efficiency and lean meat content are improved when it is given for 28-42 days before slaughter. The currently available product needs to be injected daily or every two days.

As using pST normally reduces voluntary feed intake and increases the maintenance requirements of the animal as well as increasing protein deposition, the diets need to contain enough protein, energy and minerals to maximise growth.

Recent research reports that using both ractopamine and pST (pST given daily or twice/three times a week) in the last two weeks of production resulted in greater production efficiency than using either of the products singly.

What else can be done.

You can also:

  • check and where necessary improve health, environment, stocking rates.
  • check the water supply (lean meat is made of protein and water). Water restriction can lead to lower feed intake and slower growth, and if erratic can tend to distort growth patterns.
  • ensure no post-weaning set backs.
  • use consultants to check management.