Researchers at the University of Nebraska conducted research to investigate methods to reduce the nitrogen excretion in growing and finishing pigs.

A number of studies have shown no difference in growth, nitrogen retention and/or carcass quality when pigs were fed reduced protein, amino acid supplemented diets; however, other studies have shown reduced performance with low crude protein, amino acid supplemented diets compared to intact corn-soybean meal diets.

The Nebraska researchers conducted two experiments to test why low crude protein, amino acid supplemented diets do not always produce the same performance as standard corn-soybean diets. The results of the experiments were not consistent.

In the growth trial, the researchers were able to reduce the crude protein percentage by four units, with appropriate amino acid supplementation, and maintain performance. However, in the nitrogen balance experiment, the low-protein, amino acid supplemented diets supported less nitrogen retention, regardless of the initial protein percentage (14, 16 or 18%).

The researchers relate that the reasons for the inconsistent results are unknown and note that the starting weights and duration of the experiments differed and may play a role in the pig's sensitivity to low-protein, amino acid-supplemented diets. Additional experiments are currently being conducted to investigate those issues.

In a nitrogen balance study, 12, 90-lb. crossbred gilts were fitted with urinary catheters one week before the beginning of the experiment. The gilts were penned individually in metabolism crates and fed a specific sequence of diets during three periods of seven days. The diets were three, standard corn-soybean diets with 14, 16 and 18% crude protein (CP). Each of the corn-soybean diets also had a low CP, amino acid supplemented counterpart with 4% less CP (10, 12 and 14% CP, respectively). Crystalline amino acids were added to restore the formulated total concentration to that in the standard corn-soybean diet.

The results of the first experiment showed no effect of dietary concentration of crude protein on average daily feed intake (ADFI), average daily gain (ADG) and feed-to-gain ratio (F/G), although the intact diets had numerically greater performance (Table 1).

Nitrogen intake, nitrogen retention, apparent nitrogen digestibility, nitrogen excretion in feces and urine, and concentration of urea in urine increased as dietary protein concentration increased. The research also showed that additions of the four crystalline amino acids were not as effective in increasing nitrogen retention, compared to gilts fed the corresponding standard intact diets.

In the second experiment, a growth performance trial, 36 crossbred gilts were individually penned and fed one of six diets for 35 days. The starting weight was 43 lb. and finishing weight was 103 lb. The diets fed included: a control, standard corn-soybean meal diet; 16% CP diet and five, reduced CP, amino acid supplemented diets with 11, 12, 13, 14 and 15% CP. The reduced CP diets included crystalline amino acids added to equal the total amino acid concentrations in the 16% CP diet. The added amino acids included lysine, tryptophan, threonine and methionine.

The researchers found no differences among gilts fed 12, 13, 14, 15 or 16% CP diets in ADG, F/G, loin eye muscle area or average daily lean gain. They found a reduction in the responses to these variables in gilts fed the 11% CP diet as compared to the other five treatments. ADFI and backfat thickness were not affected by diet, the researchers report, but there was a tendency for feed intake to increase as the crude protein increased from 11% to 14% and decrease above this concentration (Table 2).

Researchers: Jose Figueroa, Austin Lewis and Phillip Miller, University of Nebraska. Phone Lewis at (402) 472-6421 or e-mail alewis2@unl.edu.