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Solubles Syrup from Microbially-Enhanced Soy Protein Processing: A potential protein supplement

Written collaboratively by Chelsea R. Schossow, Jill Anderson, and William R. Gibbons.

Project Overview

The South Dakota State University (SDSU) Dairy and Food Science department recently conducted some initial preliminary research on feeding dairy heifers soluble syrup residues resulting from a microbial (fungal) treatment process of soybean meal. This fungal treatment process was originally developed for manufacturing Aquaculture feeds. The protein in the by-product solubles syrup is highly rumen degradable and the syrup is thought to also contain prebiotic compounds. This combination of nutrients could stimulate rumen fermentation, fiber utilization, and efficiency of heifers fed high forage diets.

The syrup contains 39.73% crude protein (CP) on a dry matter (DM) basis. Due to its similar protein content to soybean meal (43-44% CP) there is potential for partial replacement in cattle diets. The purpose of this experiment was to create a baseline for future research on feeding this solubles syrup to heifers and mature cattle. There was uncertainty as to how the syrup would impact heifer intakes, nutrient utilization, or growth performance. The hypothesis was that feeding the solubles syrup would increase heifer utilization of highly fibrous forages due to its potential benefits to rumen fermentation.


To test this hypothesis an experiment was conducted in fall of 2016 at the SDSU Dairy Research and Training facility. A total of 18 growing dairy heifers of approximately 9-10 months of age, were used in a 6 week feeding study to analyze the effects of partially replacing soybean meal and corn in the ration with the solubles syrup. Heifers were assigned to one of two treatments: 1) a control (CON) total mixed ration (TMR) or 2) a TMR with 6.5% microbially-enhanced soy protein solubles syrup (SYP) (Table 1). Diets had similar crude protein (14.6 and 13.9 % CP on DM basis for CON and SYP, respectively) and metabolizable energy (ME) was 2.36 and 2.33 Mcal/Kg of DM. Heifers were individually fed and had access to water at all times. Evaluation of growth performance was achieved by weighing, measuring skeletal frame size, and recording body condition scores (1=emaciated, 5=obese) every two weeks. Fecal grab samples were collected during week 6 to determine total tract nutrient digestibility.

Table 1. Experimental diets

Ingredients, % DM CON SYP
Grass Hay 34.91 34.91
Corn Silage 33.96 33.96
Corn, ground 10.01 8.52
Soybean meal 13.53 8.52
MSP - Syrup 0.00 6.50
DDGS 5.01 5.01
Vit & Min Pre mix 2.31 2.31
Energy booster 0.27 0.27



Heifers fed the SYP treatment had similar dry matter intakes (DMI), body weights, average daily gain (ADG), gain:feed (or feed efficiency), and frame growth (data not shown) compared to the controls. Overall growth performances were similar between treatments (Table 2).

As hypothesized heifers on SYP had greater total tract digestibility of dry matter (DM), organic matter (OM) and neutral detergent fiber (NDF). There was a tendency for increased crude protein (CP) and acid detergent fiber (ADF) total tract digestibility for SYP compared with CON. (Figure 1).

Table 2. Heifer Growth Performance

  CON SYP SEM Treatment week Treatment × week
DMI, kg/d 9.87 9.68 0.489 0.79 <0.01 0.01
Gain:Feed 0.115 0.125 0.0168 0.58 <0.01 0.39
Body Weight, kg
Mean 366.2 365.3 2.73 0.82 <0.01 0.96
Week 0 367.1 365.8 10.21 0.87    
Week 6 379.8 378.4 3.06 0.75    
ADG, kg/d 1.00 0.97 0.089 0.83 0.01 0.97

*Reminder there are 2.2 lbs per kg.

Bar graph showing total tract digestibility of dry matter. For a complete descpription, contact SDSU Extension at 605-688-6729
Figure 1. Total tract digestibility of dry matter.


In this initial study, the new solubles syrup effectively replaced a portion of corn and soybean meal. Result demonstrated this product is viable and has potential in the dairy and livestock industry as an alternative protein feed additive. Heifers maintained intakes and had increased nutrient digestibility, it was speculated that if fed over a longer feeding period the increased nutrient digestibility may translate in better feed efficiency or growth performance. However, this was a preliminary study and more research is necessary to optimize its use particularly assessing different dietary inclusion amounts and in different feeding scenarios.


This research was funded by a Griffiths Undergraduate Research Award through the College of Ag and Biological Sciences at SDSU with additional support by the SDSU Ag Experiment Station. The solubles syrup test product was donated by Prairie AquaTech, Brookings SD.