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John Maltman, Swine Specialist
The process of growth generally has several identifiable components. Hair, skin, bone, internal organs lean and fat. The two which interest us most are lean and fat. Overall growth can roughly be divided into two sections. The first part is energy driven; the second part is protein driven as is illustrated in Figure 1.
This distinction has to do with the pig's physical capacity. Its stomach is small to start with so we need to formulate rations using ingredients which are high in digestible energy. Most often these are wheat, hulless barley and corn. Each of these ingredients have different amino acid profiles but are used initially for their high digestible energy content and low fibre levels. Amino acids (protein) can be adjusted through addition of common high protein ingredients such as soybean meal, canola meal or peas. Further refinements to the ration can be made using synthetic amino acids. Lysine and methionine will be familiar to most pig producers.
Proceeding through their growth curve the components of gain change from high levels of lean tissue and low levels of fat to high levels of fat and lower levels of lean tissue.
The genetic code of the pig will dictate where this change begins and also the degree of change. Our job is to feed the pig appropriately to maximize lean tissue deposition and minimize fat. To accomplish this it is helpful to know the potential growth curve of the pigs on the farm. This growth curve is very similar for all genetics and both sexes in early life. Small differences between sexes begin to emerge at about 45 Kg live weight .The full impact of genetics is experienced after phase two . If split sex feeding is practiced then this is the point where barrows will go on a new ration and gilts will remain on the first stage ration to a heavier weight, switching later than barrows.
Phase two of a mixed sex group often runs between 45 and 75 Kg. for a rapid growing genotype. For some genetics the change point will come earlier at 60 or 70 Kg.. This point in the growth curve represents a significant physiological change for the pig. Fat is easily deposited at this age as the animal is beginning to reach maturity and growth slows.
Phase three begins about 100 Kg live weight. We have begun to substantially reduce the energy level of the ration. The pig has a large capacity to eat and can usually consume three kilograms of feed daily, with little trouble. This volume of feed makes it easy for the pig to consume more digestible energy and amino acids than are needed for maximum lean tissue deposition. For some genotypes wheat will still be in the ration at this stage. Other genetics will grow too fat and do best with an all barley ration from 75 kg. to market weight.