Effects of raw and roasted high oleic soybeans on milk production of high-producing dairy cows; Economic analysis of high-oleic soybeans in dairy rations.

Oilseeds are a good source of fat and protein and often increase milk fat yield. Soybeans are a commonly used oilseed that can increase FCM and increase milk component yields at higher inclusion levels. Although soybeans can increase milk fat yield, they contain high levels of linoleic acid (C18:2), a fatty acid (FA) that can increase the risk of milk fat depression. It is known that dietary oils high in oleic acid (cis-9 C18:1) have less of a negative influence on milk fat secretion compared with oils high in. Recently, novel varieties of soybeans have been developed that are enriched in cis-9 C18:1, at the expense of C18:2. High oleic soybeans (HOSB) contain >70% cis-9 C18:1 and <10% C18:2, which is vastly different than conventional soybeans, which contain ~50% C18:2. Based on the increased content of cis-9 C18:1 and lower content of C18:2, HOSB are an attractive alternative to conventional soybeans for dairy cows, as cis-9 C18:1 has been found to increase milk production of high-yielding cows and reduce loss of BW. Also, some previous studies have indicated that the use of HOSB in various forms can have benefits as a component of dairy rations, but the economic implications of HOSB use have not been previously evaluated. To investigate further, the studies cited were (1) designed to evaluate the effects of raw and roasted HOSB on milk production responses of high-producing dairy cows, and (2) evaluate the economic incentives for HOSB use in dairy rations and quantifying the potential use by US dairy farms.

In the first study, 36 multi-lactation Holstein cows (45.6 ± 6.22 kg milk per day; 110 ± 61 days in milk [[DIM]) were randomly assigned to treatment sequences in a 4 × 2 truncated Latin square design with 35-day periods. Treatments were as follows: (1) control diet, containing soybean meal and soybean hulls (CON); (2) 16% roasted and ground HOSB (RST); (3) 16% raw and ground HOSB (RAW-D); and (4) 16% raw and ground HOSB, plus additional rumen bypass protein (RAW-U). The HOSB replaced conventional soybean meal and hulls in the control diet, and rumen bypass protein replaced soybean meal in RAW-U to maintain dietary nutrient composition (% DM) of ~28.0% NDF, 21.3% forage NDF, 27.3% starch, and 17.8% CP. Fatty acid contents of CON, RST, RAW-D, and RAW-U were 1.60, 4.30, 4.36, and 4.34% DM, respectively. In the second study, the potential economic impact of using HOSB

in dairy rations was evaluated based on a synthesis of results from five prior feeding trials. Milk income less feed costs (MILFC) per cow per day was calculated based on assumed increases in milkfat production and increased cost of rations including HOSB. The effects of changes in MILFC are evaluated for herds with different numbers of lactating cows, and the total volume of HOSB required to support different proportions of US dairy cows was calculated.

Results in the first study showed that, for most variables tested, significant interactions between treatment and week occurred, as HOSB increased production variables compared with CON, and RST increased production responses compared with the raw treatments, with only the magnitude of difference varying between weeks. Overall, HOSB increased DMI and yields of milk, 3.5% FCM, ECM, and milk fat, but did not affect milk protein yield. The RST treatment did not affect DMI but increased milk yield, 3.5% FCM, ECM, milk fat, and milk protein. Compared with RAW-D, RAW-U increased milk yield and milk protein and tended to increase ECM. Overall, HOSB inclusion at 16% of DM increased production responses in these high-producing dairy cows, but the roasted HOSB had a greater effect than the raw HOSB, and the addition of rumen bypass protein positively affected the milk protein response.

The economic results of the second study were based on the assumption that 5% of the dietary DM was substituted for HOSB. The increase in the assumed milkfat of 1.4 kg per cow per day had the potential to increase MILFC by up to $0.27 per cow per day or increase the average value of milk by $0.64 per 100 kg for a cow producing 41 kg milk per day. Changes in MILFC will be highly correlated with the price of butter but the results were positive for an extended period. The effects of HOSB on MILFC suggest the potential for increasing farm profitability could be $33,000 per year for a dairy farm of 500 lactating dairy cows.

Interpretation and implications: The use of high oleic acid soybeans in SA rations are limited because of availability and price, but the results do show the importance of the roasted product, the possible advantage of supplementing with products containing oleic acid and the addition of bypass protein, if soybean is the only supplementary protein (which it is normally not in SA rations). This advantage will only realize in TMR cows producing in access of 40kg milk per day and where milkfat depression is experienced. In most cases, milk buyers do not pay on a milkfat basis, and therefore milk volume is targeted, but from an efficiency point of view (kg milk per kg DM), milkfat levels in association with milk volume are important, as has been shown in a previous article:

        GFE (kg/kg) = 1.881 + 1.344MFY −0.003LW, R² = 0.91.                                                                                                                            

where: GFE = gross feed efficiency, MFY = milkfat yield (milkfat % x milk yield), and LW = live weight.

The relationship of GFE with milkfat is explained by better energy mobilization in more efficient cows. Utilizing this equation in selection will enhance both milkfat and milk yield which is beneficial.