The objective of this Utilization of High-Oleic Soybeans study was to investigate the effect of three soybean sources differing in fatty acid profile and processing method on productivity and milk composition in lactating dairy cows. The soybean sources were: 1) an extruded conventional soybean meal (SBM; 48% CP and 8.7% ether extract; 22% oleic acid), 2) an extruded Plenish® (DuPont Pioneer, Johnston, IA) high-oleic acid variety SBM (51.4% and 8.4%, respectively; 75% oleic acid), and 3) whole, heated Plenish® soybeans (40.0% and 20.2%, respectively). The study involved 15 Holstein cows in a replicated 3 × 3 Latin square design experiment with three 28-d periods. The inclusion rate of the three soybean sources in the diet was (all data are on DM basis): 17.1, 17.1, and 7.4%, diets CESBM, PESBM, and WHPSB, respectively, providing 1.4 to 1.5% soybean oil. The rest of the dietary ingredients were: corn silage, 41%; alfalfa haylage, 16%; grass hay/straw mix, 4%; ground corn grain, 10%; cottonseed hulls, 4%; molasses, 4.9%; and a mineral/vitamin premix, 3%. The WHPSB diet also contained 9.7% solvent-extracted SBM. The diets had similar content of CP (17.0 and 17.6%), NDF (31.0 and 32.0%), ether extract (3.8 and 4.0%), and NEl (1.53 and 1.54 Mcal/kg).

The results indicated, compared with control extruded SBM diet, the Plenish® diets tended to increase (P = 0.09) DMI (27.1, 27.8, and 27.8 kg/d, CESBM, PESBM, and WHPSB, respectively Milk yield was not affected by treatment (average of 42.2 kg/d; SEM = 1.41). The Plenish® diets increased (P ‹ 0.01) milk fat content (3.55, 3.74, and 3.76%, respectively). Feed efficiency was decreased (P ‹ 0.001) by the Plenish® diets, compared with CESBM (1.50 and 1.51 vs. 1.57 kg/kg, respectively). Diets had a marked effect on milk fatty acid profile; the Plenish® diets increased (P ‹ 0.01) mono-unsaturated and cis-9 18:1 and decreased (P ‹ 0.01) poly-unsaturated, total trans-, and conjugated linoleic fatty acids concentrations in milk fat. The researchers concluded that in this study the Plenish® soybean treatments compared with conventional extruded SBM had no effect on milk yield, increased milk fat concentration, decreased feed efficiency, and modified milk fatty acid profile in a manner expected from the greater concentration of oleic acid in Plenish® soybean oil.