Effect of Feeding Whole Soybeans, Roasted Soybeans, or Distillers Grains in Silage-Based Growing Beef Diets

Authors: Melissa K. Bausch, Graduate Student; Rebecca L. McDermott, Research Technician; Jim C. MacDonald, Professor, Animal Science, Lincoln; Pablo L. Loza, Former Assistant Professor, PHREEC (Scottsbluff); Galen E. Erickson, Professor, Animal Science, Lincoln. 

Summary with Implications

An individual feeding experiment was conducted to evaluate the effect of feeding raw whole soybeans (WSB), roasted whole (RSB) soybeans or distillers grains (MDGS) at three inclusions (7%, 14%, or 21% of diet dry matter) on growing performance, compared to a common control diet (0%) with urea. The greater inclusions of roasted soybeans or distillers grains increased gain and efficiency in growing cattle. Cattle fed the 21% inclusion of roasted soybeans were the most efficient, likely due to the protected protein increasing rumen undegradable protein content, and the additional energy from the higher levels of fat and protein. The 21% modified distillers grains diet resulted in the greatest intakes and gain, however efficiency was not improved when compared to the 21% raw whole soybean diet. These data suggest that soybeans can be fed to growing cattle to provide fat and protein, but roasting enhances the response in performance compared to raw soybeans and may be a suitable alternative to distillers grains without impacting performance.

Introduction

Diets used for growing cattle in the feedlot typically include a significant proportion of ingredients such as corn silage, which provides both protein and energy. Previous research has shown that the rumen undegradable protein (RUP) of corn silage is estimated to be low, around 16% of crude protein, with only 40% of the RUP being digestible. (2022 Nebraska Beef Report pp. 22-25). In order to meet the metabolizable protein requirements of the animal, RUP has been supplemented in the form of distillers grains, which has an RUP content of 63% (% of CP). Previous work has shown that supplementing distillers grains in silage-based growing diets improved cattle performance (2011 Nebraska Beef Report pp. 20-21). Soybeans are higher in crude protein, around 40%. Raw soybeans still have a high proportion of rumen degradable protein, roasting soybeans can protect the protein and increase the RUP to 50% or more. The objective of this study was to evaluate the effect of feeding whole raw or roasted soybeans and modified distillers grains as a supplemental protein source in silage-based growing diets on growing cattle performance.

Procedure

A growing study was conducted at the Eastern Nebraska Research, Extension, and Education Center (ENREEC) near Ithaca, NE utilizing crossbred heifers (n = 119; initial BW = 684 lb) in a 3 x 3 + 1 factorial treatment design and were individually fed using the Calan gate system. Before trial initiation, heifers were limit-fed at approximately 2% of body weight (BW) for five consecutive days to minimize weight variation due to gut fill. Heifers were weighed on three consecutive days to establish initial body weights. After the second day weight, cattle were blocked by weight (3 blocks) and stratified by weight within block. Heifers were then assigned randomly to treatment to ensure equal weight per treatment by block. To establish the intercept, 20 heifers were assigned to the control diet and 11 heifers were assigned to each of the experimental diets. The control diet was designed to set a baseline as the intercept for impact of increasing inclusion of each protein type. 

All heifers were implanted on the third day of weighing with Ralgro (Merck Animal Health). There were ten dietary treatments used in this study and treatment diets are summarized in Table 1. All diets were formulated to meet or exceed the metabolizable protein requirements of the animals using the beef NASEM model (2016). Urea was added to the supplement at 1.4% of the total diet DM in the diet containing only dry-rolled corn (DRC) as the grain source, 0.8% of the diet in the 7% MDGS diet, at 0.6% of the diet in 7% WSB and 7% RSB treatments, and 0.25% of the diet in the 14% distillers grains treatment to meet RDP requirements. Each diet contained 5% supplement and 74% corn silage on a dry-matter basis. The control diet only also included  21% (of diet DM) DRC. As this experiment was a factorial design, the 7% diets contained the ingredient of interest at 7% diet DM and DRC at 14% DM. The 14% diets contained 7% DRC, and the 21% diets contained no additional DRC. The roasted and raw soybeans were fed whole.

Melengestrol Acetate was added to all diets at 0.5mg/heifer/day (MGA; Zoetis Animal Health) for suppression of estrus. Monensin (Rumensin; Elanco Animal Health) was also supplied over the duration of the feeding period at 20 grams/ton. Treatment diets were fed a total of 84 days, and cattle were limit-fed at the end of the feeding period for 5 days before another 3-day weigh period to evaluate performance for the growing period.

Performance data were analyzed using the MIXED procedure of SAS and analyzed with the individual animal as the experimental unit and block as a fixed effect. Linear, quadratic, and cubic contrasts were developed to evaluate the effect of inclusion level by separated by protein type utilizing the CON diet as the common intercept. Main effects are presented as no interactions between protein type and inclusion level were observed in the 3×3 factorial (P > 0.10). A P-value of less than 0.10 was considered significant. 

Results

Effect of Protein Source 

Including MDGS in the diet resulted in greater (P < 0.01) dry matter intake (DMI) than the soybean diets (Table 2). For gain (ADG), a protein source effect (P = 0.02) was observed with the MDGS treatment resulting in increased gain compared to the WSB treatment with RSB intermediate. Cattle fed diets containing RSB had improved feed conversion (P = 0.01) compared to cattle fed the diets with MDGS and WSB. No protein source effects were observed for ending weight (P = 0.22).

Effect of Inclusion

An inclusion effect for ADG was observed, with the greatest gain associated with the 21% inclusions (P = 0.01). An inclusion effect for feed conversion was observed, with the 21% inclusion resulting in improved feed conversion over the 14% inclusion (P = 0.08). When performance responses were evaluated using the common intercept (CON), a linear increase in ending BW (P = 0.01) was observed for cattle fed increasing inclusions of MDGS. Similarly, a linear increase in ending BW was observed for cattle fed increasing inclusions of WSB (P = 0.05). A linear increase in DMI was observed for cattle fed increasing inclusion of MDGS (P  <0.01), whereas a quadratic decrease was observed as RSB inclusion increased (P = 0.05). ADG increased linearly for the WSB diets by inclusion rate (P < 0.01), however, a cubic response was observed for MDGS (P = 0.08) and RSB (P = 0.04). Cubic responses were observed for feed conversion in the MDGS (P = 0.04), WSB (P = 0.10), and RSB (P = 0.03) treatments due to a decrease from 0 to 7% inclusion, then no further improvement when 14% was fed, and then decreased again with a 21% inclusion. In general, there appears to be a quadratic and linear improvement in performance but the response at 14% inclusion is unclear and resulted in the statistical response to be cubic. One explanation is that any one of the protein sources met the protein requirement at the 14% inclusion, but the response at 21% was due to the protein being utilized as an energy source and having greater energy than corn it displaced at 21% inclusion. 

Conclusions

Based on feed conversion and ADG, feeding raw whole soybeans in silage growing diets performs similar to supplementing modified distillers grains, whereas feeding roasted soybeans is slightly better than both. Roasted soybeans have greater rumen undegradable protein than raw soybeans and provide a response in silage growing diets. Therefore, if economical, raw or roasted soybeans may be an appropriate alternative protein source to distillers grains for growing cattle.

Acknowledgment

Funding was provided by the Nebraska Soybean Board. Products were provided by Elanco Animal Health, Zoetis Animal Health, and Merck Animal Health. 

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