Impact of Grain Characteristics on Diet Formulation
It should be apparent that grain cannot comprise the sole ingredient in the diet of swine. Therefore, nutritionists must include additional ingredients in the diet of swine to ensure optimum performance. A typical Midwest swine diet is shown in Figure 17. Soybean meal and L-lysine•HCL are added to supply sufficient qualities of essential amino acids. Phytase and dicalcium phosphate are added to compensate for the poor phosphorous digestibility of grain. The remaining ingredients are added to satisfy the pig’s requirement for vitamins and other minerals.
Let’s compare the total dietary levels of lysine, tryptophan, threonine, and arginine in the diet shown in Figure 17 to the pig’s requirement for these amino acids (Figure 18). Because lysine is the most limiting amino acid for swine, the diet was formulated to meet the lysine requirement. Thus, the quantity of lysine in the diet and the amount required by the pig, match. However, there is a slight excess of tryptophan and threonine and a significant excess of arginine. These excesses will not typically impair pig performance. However, much of the nitrogen provided via the oversupply of amino acids will be excreted in the urine. Recent evidence suggests that many volatile compounds that comprise odor from livestock operations originate from excess amino acids in the diet.
The lysine in corn is contained in protein. The protein content of corn is variable, and is influenced by soil type, hybrid and level of fertilization. Is protein content of corn a good indicator of its lysine level? Data in Figure
19 indicate a poor relationship exists between corn protein and lysine concentration. Corn containing 9.5 % crude protein could have the same amount of lysine as 7.8% protein corn. The lack of a good correlation between crude protein and lysine content indicates that efforts to improve the lysine content of corn are not simply a matter of increasing its protein content. For the nutritionist the implication is to not automatically decrease the amount of supplemental protein (i.e., soybean meal) in the diet when using high protein corn. Otherwise, the diet could be low in lysine.