Dietary Needs of Pigs and Poultry
The dietary nutrient needs of pigs and how well those needs are met by conventional corn are shown in Figure 3. Caloric requirements vary according to pig age and phase of production, i.e., growth vs. reproduction. In general, corn can supply all the calories pigs require. In contrast, broilers have such a high lean growth rate and therefore a high dietary amino acid requirement, that diet is often too low in energy for optimum growth performance. Thus, conventional corn only sometimes meets the caloric needs of poultry. The sole fatty acid requirement (linoleic acid) can easily be met by corn. In contrast, corn supplies only a portion of the pig’s need for amino acids, minerals and vitamins.
Amino acids are building blocks of protein. Twenty-two amino acids comprise body protein. Ten amino acids are essential (indispensable), i.e., they must be supplied in the diet, and 12 are nonessential (dispensable). The essential amino acids are listed in Figure 4. Pigs require specific amounts of these amino acids in their diet rather than a certain amount of protein. Therefore, pigs do not have a dietary protein requirement, per se. While nutritionists distinguish between essential and nonessential amino acids, all 22 amino acids are equally important for protein (muscle) deposition.
Optimum growth and reproductive performance are possible only if the diet contains the proper amount of each of 10 essential amino acids. It any one of the 10 essential amino acids is not supplied in the proper quantity, performance will be impaired.
In order to illustrate the link between amino acid essentially and animal performance, consider a barrel that has 10 staves. Each stave represents one of the 10 essential amino acids. The height of each stave is proportional to the extent that the animal’s requirement for each amino acid is met (Figure 5). All the staves in this barrel are high enough; therefore, it can be filled completely with water indicating the animal can respond to its genetic capacity (Figure 6). However, if the lysine stave was broken off at 80% of its required height (Figure 7) the barrel could only be partially filled (Figure 8). Therefore, the animal could perform at only 80% of its genetic capacity even though the supply of the other nine amino acids is adequate.
The nutritional value (quality) of proteins in feed ingredients varies considerably. Proteins are rated according to their quality. Protein quality is primarily dependent on the amino acid content of the protein and the bioavailability of amino acids in the protein.
A protein that provides a perfect pattern of essential and nonessential amino acids in the diet without any excesses or deficiencies is called an “ideal protein”. This pattern is supposed to reflect the exact amino acid requirements of the pig for maintenance, growth and reproduction. Therefore, an ideal protein provides exactly 100% of the recommended level of each amino acid (Figure 9).
How ideal are proteins in corn for pigs? Compare the requirement for four essential amino acids by a 90 lb pig to the amount of these amino acids in corn (Figure 10). For lysine, tryptophan, and threonine, a significant disparity exists between the required level and the amount in corn. A good match is observed for arginine, however. Therefore, corn proteins in addition to those found in most feeds, are not very ideal for pigs. Information on how nutritionists overcome this problem is presented later in this lesson.
The amino acid present in the least amount relative to its requirement is termed the first-limiting amino acid. The extent to which it is adequate in the diet will determine the level of animal performance. Figures 11 and 12 show the limiting amino acids in corn and sorghum for pigs and poultry, respectively.