Rethinking the corn-soy diet

Supplementing L-Lysine is about as common in swine diets as supplementing with salt.

A common rule of thumb when formulating swine diets is that 3 lb. of L-Lysine plus 97 lb. of corn can substitute for 100 lb. of soybean meal. This substitution has generally reduced diet costs because of economically priced L-Lysine and $2/bu. ($0.036/lb.) or less for corn.

As the price of corn jumped approximately $1.50/bu. ($0.027/lb.), the cost of a grower-finisher diet increased over $35/ton of complete feed while reducing the opportunity price of L-Lysine.

Before the price increase, swine diet formulation centered on minimum protein (or amino acid) levels and the maximum use of synthetic amino acids — primarily L-Lysine. This thinking needs to be reevaluated with $3.50/bu. ($0.063/lb.) corn, because the higher cost may delete synthetic L-Lysine from the diet in favor of soybean meal.

In Table 1, a typical 0.9% total lysine (0.74% digestible lysine) corn-soybean meal diet containing 3 lb./ton of L-Lysine was used as a base diet to evaluate “what if” comparisons for various corn and soybean meal prices and to determine the resultant opportunity price for L-Lysine. The opportunity price suggests the maximum price one can afford to pay for L-Lysine before being rejected from the formulation in favor of soybean meal.

Cost analysis

At what price does 46% soybean meal become competitive with corn?

The answer is $4/bushel ($0.072/lb.) for corn and $7.21 ($144.20/ton) for 46% soybean meal, when using the same minimum nutrient restrictions used for determining the opportunity price for L-Lysine in Table 1.

If soybean meal would ever become competitive with corn (replacing it in the diet), the resultant diet would contain excess protein and amino acids.

The scenario would necessitate that swine researchers and nutritionists consider maximum nutrient restrictions for protein (and amino acids), in light of higher corn prices and limited supply, with lower soybean meal prices.

If higher soybean meal usage and no synthetic amino acids are used in swine diets, the nitrogen excretion in the manure will increase — a plus for the value of hog manure as fertilizer.

Energy from corn has been a very economical source for swine diets. However, with limited corn supplies and high prices, producers are evaluating alternative sources of energy for swine diets, including other grains, by-products of the feed and food industry, and dried distiller's grains with solubles.

Economics of animal fat

Another alternative would be to increase the energy density of diets by adding supplemental animal fat to improve feed efficiency. Determining the economics of animal fat supplementation for the finisher pig requires a few assumptions:

• Estimated feed consumption (50 lb. to market) is approximately 400 lb.

• Improved feed efficiency is the primary benefit of supplemental animal fat in a finisher diet (1% supplemental animal fat improves feed efficiency approximately 2%).

• Adding 60 lb./ton of animal fat increases metabolizable energy approximately 60 Kcal/lb. of complete feed. Therefore, the amount of feed consumed by a finisher pig (150 lb. to market) would be approximately 376 lb.

• The same corn, 46% soybean meal and L-Lysine prices as used in Table 1.

In Table 2, nutrient restrictions, ingredient prices and the opportunity price for L-Lysine from Table 1 were used to determine the opportunity price for animal fat.

The opportunity price suggests the maximum price that one can pay for animal fat, based on improved feed efficiency and the assumptions indicated.

Ingredient price relationships have changed, which could result in changes in swine diet composition and nutrient restrictions; this may be different than we have been accustomed to.