Nutrient to Calorie Ratio
Nutrient to calorie ratios must be considered when setting the energy level in diet formulation. This is because the energy content of the diet will dictate the amount of feed consumed by growing-finishing pigs. In general, increasing energy concentration of growing-finishing pigs diets will result in reductions in voluntary feed intake. The reductions are the results of pigs adjusting their voluntary feed intake to meet their daily nutrient demands while maintaining a constant energy intake (Nyachoti et al., 2004). But it should be understood that essential nutrients such as amino acids and phosphorous in the diet must be adjusted with this increasing energy concentration of the diet. Because voluntary feed intake will be reduced, daily intake of these essential nutrients will also be decreased. This decrease in nutrient intake may limit growth performance and thus the nutrient:calorie ratio must be adjusted accordingly. Therefore, to maintain a constant level of intake of these essential nutrients, the concentrations of these nutrients must be increased simultaneously with increased energy concentration in the diet.
The importance of this nutrient to calorie ratio can be observed when determining the lysine level in diet formulation. It is well established that lysine is the first limiting amino acid in swine diets as it is the most important substrate for generating body protein (Liao et al., 2015). This relationship shows that increasing lysine intake with energy intake will improve protein deposition and weight gain (Chiba et al., 1991; Marcal et al., 2017).