I have been often asked whether pig formulas should be formulated with the minimum or maximum crude protein concentration possible. Assuming cost is about the same, I have always favoured low-protein diets. Nevertheless, this should not be taken as a universal statement, because there are conditions, mainly economical, under which a low-protein diet is not profitable. But, let's see first, why low-protein diets are beneficial from a biological point of view and how this translates into more money for the producer!
To begin with, a low-protein diet is one that provides all required amino acids without excesses. To lower the protein concentration of a diet, the use of synthetic amino acids is of paramount importance, and here is where economics must play in favour of the lower-protein diet. As of today, only crystalline lysine, methionine, threonine, and tryptophan are commercially available. As such, we must continue to provide some excess protein in order to cover the needs of other essential amino acids, such as valine and isoleucine. Thus, the question becomes, how much can we lower crude protein?
The answer is rather easy but it has taken many years of research to find out! Under most conditions, a 2% points reduction in crude protein by using crystalline amino acids (for example, from 18% to 16% crude protein in the diet) creates no problems in animal performance or carcass characteristics. A 4% points reduction requires a bit more work. For this, other amino acids, such as valine and isoleucine must be well balanced. And in addition, all amino acids should be expressed on a true ileal digestible basis, whereas the energy of the diet should be expressed using a (good) net energy system.
But, let's get back to why low-protein diets are beneficial. First, the animal benefits from less excess protein (nitrogen) that has to deaminate (detoxify) as free nitrogen in the blood system is toxic and must be excreted (via urine). This brings us to another benefit, namely less urine production and consequently lower demand for water. This translates to less manure volume! In addition, what manure is produced is lower in nitrogen, not only because of less nitrogen in urine, but also because with lower-protein diets, protein digestibility is increased and as such less nitrogen is excreted in faecal matter. A good way to protect that environment of ours! Not to mention the less land needed to dispose the manure, which is a constant headache in many parts of this world.
Now, as the animal has less excess protein to get rid off (an energy consuming process), it is left with some spare energy and here we run the risk of increasing carcass lipid concentration if we are not vigilant. This becomes especially tricky as we go from 2 to 4% points reduction in dietary crude protein concentration. And, here is where the use of the net energy system is of most importance. As net energy is expressed independently of dietary crude protein (a problem inherent in the metabolisable energy system), we can formulate low-protein diets without increasing carcass fatness! As such, we can take advantage of the energy 'surplus' and direct it to lean tissue deposition. This means, lower feed/gain ratio, a good thing always, and of course, lower cost of production.
In conclusion, low-protein diets are good for the animal, the environment, and the producer. All these, assuming the cost of crystalline amino acids does not rob us of all these benefits! But, this is something you should take up with your amino acid supplier!