Soy Isoflavones and Swine Nutrition

Two experiments were conducted at Louisiana State University to determine the effects of soy isoflavones on growth, meat quality and carcass traits of growing-finishing pigs. In the first experiment three dietary treatments were fed to four pens of three pigs weighting 26 kgs. The treatments consisted of a corn-soybean meal diet, a corn-soy protein diet with reduced isoflavones level and a corn-soy protein with added isoflavones to equal the corn-soybean meal diet. The results indicated that growth performance, longissimus muscle area, 10th-rib fat depth, percentage of muscling, and various carcass quality measurements were not significant (P>0.10) by dietary treatment. Dressing percentage, carcass length, weight and percentage of fat-free lean in the ham and carcass, lean-gain per day, lean:fat and ham weight were decreased (P>0.10) and ham fat and the percentage of fat in the ham and carcass were decreased (P>0.10) in the pigs fed the corn-soy protein-isoflavone supplemented diet compared to the pigs fed the corn-soy protein diet. The pigs fed the corn-soy protein isoflavone supplement diet had similar carcass traits as the pigs fed the corn-soybean meal diet, except the carcass length, percent ham lean were greater (P<0.01) and total ham fat was less (P<0.01 in the pigs fed the corn-soy protein-isoflavone supplement diet.

In the second experiment, gilts(four pigs per treatment, five replicates) were fed a corn-soybean meal diet, or diets with 2X or 5X levels of supplemented isoflavone compared to the basal corn-soybean meal treatment. Treatment did not affect growth performance or carcass traits with the exception of color scores and drip loss that were reduced as isoflavone levels in the diet were increased.

These results indicate that soy isoflavones decrease fat and increase lean in growing-finishing barrows, but not at levels above those normally expected for standard corn-soybean meal diets. These results suggest that adding higher levels of the soy isoflavones to swine growing-finishing diets will not improve performance, carcass or meat quality. Conversely, feeding up to five times the normal level of soy isoflavones to growing –finishing pigs did not reduce growth performance or carcass value. The normal levels of isoflavones in soybean meal are without major impact on swine feeding

Payne, R.L., and co-workers. 2001. Effects of dietary soy isoflavone on growth, carcass traits, and meal quality in growing-finishing pigs. J. Animal Sci. 79(5):1230-1239.