Raw vs Roasted Soybeans – Feeding roasted high oleic soybeans to high producing cows

Soybeans are a common oilseed used in dairy rations as a source of both protein and energy. Recently high oleic soybeans (HOSB) have been developed due to interest from the human food industry to have an increase in oleic acid compared to linoleic acid. This shift in fatty acid profile makes HOSB of interest for dairy producers since oleic acid lowers the risk of milk fat depression and offers a potential tool for increasing milk fat.

Even at very high levels (~24% diet DM), HOSB are shown to increase milk and milk fat yields. As they have grown in popularity, more questions have been raised about implementation strategies in dairy diets, especially relating to how HOSB work as a protein source. A recent study from Michigan State University investigated the effects of feeding raw or roasted HOSB
to high-producing cows.

Thirty-six multiparous Holstein cows (45.6 kg ± 6.22 kg/d of milk yield) were used in a 4 x 2 truncated Latin square design with 35 d periods to enable evaluation of longer-term effects of feeding HOSB. Cows were fed either a control diet with no HOSB (CON); 16% DM roasted and ground HOSB (RST); 16% raw and ground HOSB (RAW-D); or 16% raw and ground HOSB bypass protein (RAW-U). The CON treatment represented a low-fat diet, while all HOSB treatments were balanced for fatty acids. When comparing roasted versus raw HOSB, the primary difference between treatments was in the protein fractions. The RUP fraction in the roasted soybean diet was the highest (45.2% of CP) due to the heat treatment, followed by CON and RAW-D treatments (35.4% and 34.6% respectively). Finally, RAW-U had added by-pass protein which made it higher than RAW-D (39.9%).

Figure 1 highlights the difference in the fatty acid profile between conventional soybeans and HOSB. Table 1 presents overall intake and lactation performance data while Figure 2 presents the weekly milk and milk fat yields.

Figure 1. Comparison of the fatty acid profile of conventional and high oleic soybeans.

Table 2. Feed intake and lactation performance parameters from multiparous cows fed raw or roasted high oleic soybeans.

¹CON = control diet with no HOSB supplementation; RST = 16% DM roasted and ground HOSB; RAW-D = 16% raw and ground HOSB; RAW-U = 16% raw and ground HOSB + bypass protein
²CON vs. HOSB = CON vs RST + RAW-D + RAW-U
³RST vs. raw = RST vs RAW-D + RAW-U
⁴PRTN = RAW-D + RAW-U
*Significance was declared at P-value ≤ 0.05; tendency was declared at 0.10 ≥ P-value > 0.05.

SUMMARY:

Cows fed any HOSB treatment increased DMI and milk and milk component yields compared to control cows.
Roasting HOSB increased yields of milk and milk components compared to both raw HOSB treatments.
Cows fed roasted HOSB had increased yields of preformed FA compared to those fed raw HOSB which was primarily driven by an increase in milk oleic acid yield.
The addition of a bypass protein source increased milk and milk protein yields, though it resulted in a decrease in milk fat concentration which led to no difference in milk fat yield.
De novo fatty acid (< 16C) yield was not affected by treatment though feeding any HOSB treatment reduced mixed fatty acid (= 16C) yield and increased preformed fatty acid (> 16C) yield. Roasting HOSB increased preformed fatty acid yield compared to raw HOSB treatments.