Effects of Feeding Raw Soybeans or Roasted Soybeans to Feedlot Steers

Authors: Melissa K. Bausch, Graduate Student; 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 

A feedlot study compared feeding raw or roasted soybeans, soybean meal, or distillers grains to a dry-rolled corn with urea control on finishing cattle performance and carcass traits. Cattle fed roasted soybeans had improved marbling and gained more weight over the feeding period than cattle fed whole soybeans. Feed conversion was improved in the steers fed the roasted and whole soybean containing diets over steers that consumed the distillers grains diet. Cattle fed soybean meal and distillers grains had similar performance and carcass characteristics in this experiment. Cattle fed soybeans, soybean meal, or distillers had better gains and conversions than those fed the urea control diet. These data suggest that soybeans may be fed to finishing cattle to supplement fat and protein and may be an option to displace corn or distillers grains in finishing diets when soybeans are readily available or economical. 

Introduction

Supply of distillers grains and price has been variable resulting in feedyards feeding lower inclusion levels in recent times. In addition, less traditional distillers are available as more processing plants continue to lower the fat content or change the process to fractionation. Concurrently, demand for fats and oils is increasing the availability of soybean products. Soybeans have a crude protein content of 40%, which is mostly comprised of rumen degradable protein (RDP) that is utilized by the microbial population within the rumen. The protein content of soybean meal remaining after oil extraction is approximately 50%, with measured RDP content of about 30% but varies depending on the heating process. Roasting soybeans can increase the amount of protein that is rumen undegradable to 50% or more, which is available for absorption in the small intestine and more direct utilization by the animal. The objective of this study was to evaluate the effect of using whole or roasted soybeans, soybean meal, distillers grains or a dry-rolled corn control in finishing cattle diets on performance and carcass characteristics. 

Procedure

A finishing study was conducted at the Panhandle Research Extension and Education Center (PREEC) near Scottsbluff, NE utilizing crossbred yearling steers (n = 400; initial BW = 950 lb) in a generalized, randomized block design. Before trial initiation, steers were limit-fed at approximately 2% of body weight (BW) for five consecutive days to minimize weight variation due to gut fill. Steers were weighed on two consecutive days to establish initial body weights. Cattle were assigned to pens based on the first day weight and sorted into pens from one of two weight blocks on the second day of obtaining weights: light (4 replications) and heavy (4 replications). Steers were stratified by weight within block and assigned randomly to pens to ensure equal initial pen weights by block. Pens were assigned randomly to treatment within each block with 8 pens per treatment and 10 steers per pen. 

All steers were implanted on the first day of weighing with Revalor-XS (Merck Animal Health) at weighing. Cattle were stepped up onto their respective finishing diets utilizing a 28-day step-up period where the alfalfa hay was replaced with dry-rolled corn in four steps (8, 7, 6, and 7 days). The alfalfa was stepped down at 50%, 40%, 30%, 19%, and 0% (DM basis) and silage was stepped up over steps 1-2 from 16% to 20% (DM basis) with all soybean products being fed at their final inclusion beginning day 1. The diet containing distillers grains contained the same roughage steps as the soybean diets, with distillers grains stepped down at 28%, 24%, 20%, 15%, 12%. The control diet hay inclusion was stepped down at 50%, 40%, 25%, 10%, and 0%.  There were five dietary treatments used in this study and the finishing 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 included at 1.5% of the total diet DM in the diet containing only dry-rolled corn (DRC) as the grain source, 1% of the diet in the distillers grains, roasted soybeans, and raw soybeans treatments, and at 0.5% of the diet in the soybean meal treatment to meet RDP requirements. Urea was supplied through the liquid supplement. Each final diet contained either 9% (control diet) or 6% supplement (all other diets) and 20% corn silage on a dry-matter basis. The control diet only had the addition of DRC to the diet (71% of diet DM). The rest of the treatments contained the ingredient of interest with DRC making up the remainder. The soybean meal diet contained 9% (DM basis) soybean meal and 65% (DM basis) DRC. The soybean treatments contained raw or roasted soybeans at 10% of diet DM and 64% DRC. The raw soybeans were stored unprocessed and rolled before feeding. The roasted soybeans were rolled before undergoing the roasting process. The wet distillers grains (WDGS) diet contained 12% (diet DM) WDGS and 62% (DM basis) DRC. Monensin (Rumensin, Elanco Animal Health) and tylosin (Tylan, Elanco Animal Health) were fed for the duration of the feeding period at 30g/ton DM and 8.8 g/ton DM, respectively.

A beta-agonist was added to all diets (Optaflexx; Elanco Animal Health) for 28 days at the end of the feeding period and removed 2 days before harvest. Steers were fed trial diets for 132 days including the step-up period and harvested at a commercial abattoir (Cargill, Fort Morgan, CO). Liver abscess scores and hot carcass weights (HCW) were collected on the day of harvest. Final BW was calculated from HCW using a common 63% dressing percentage. Average daily gain (ADG) and feed efficiency were calculated based on carcass-adjusted final BW. Feed efficiency (G:F) was analyzed, but data are reported as feed conversion (F:G). Carcass characteristics such as 12th rib fat thickness, USDA marbling score, and longissimus muscle (LM) area were collected after a 48-hour chill. 

Carcass and performance data were analyzed using the MIXED procedure of SAS and analyzed with pen as the experimental unit and block as a fixed effect. Liver abscess presence data were analyzed as a binomial distribution using the PROC GLIMMIX procedure of SAS. 

Results

Cattle fed control (CON), distillers grains, and roasted soybean diets had greater (P < 0.01) dry matter intake (DMI) than cattle fed the raw soybean diet, with the soybean meal treatment being intermediate between the two groups (Table 2). Cattle fed the diet containing roasted soybeans had the greatest ADG at 4.20 lb/d, which was greater than (P < 0.01) the control (3.47 lb/d) and raw soybean (3.92 lb/d) diets, with distillers grains (3.96 lb/d) and soybean meal (3.93 lb/d) being intermediate between roasted and whole soybeans. Steers fed the raw and roasted soybeans diets had the best conversions, which was significantly (P < 0.01) better than steers fed the control and distillers diets, with the soybean meal diet intermediate.

Feeding roasted soybeans resulted in a greater HCW (P < 0.01), marbling score (P = 0.01), and 12th rib fat coverage (P < 0.01) compared to the control and raw soybean diets. There were no differences between the distillers grains and soybean meal treatments for carcass characteristics. Cattle fed raw soybeans had a larger LM area (P = 0.03) than the control with no other significant LM area differences between treatments. Dietary treatment had no impact on the occurrence of liver abscesses (P = 0.56).

Conclusions

Feeding roasted soybeans to finishing cattle increased carcass weight and average daily gain, as well as marbling score compared to feeding raw soybeans. Cattle fed soybean meal and distillers grains had similar performance and carcass characteristics but all of the natural protein diets outperformed the control diet. These data suggest that raw or roasted soybeans may be an option to displace corn or distillers grains in finishing diets when soybeans are readily available or economical. Roasting soybeans leads to cattle being able to eat and gain more with no impact on feed conversion compared to raw soybeans. 

Acknowledgment

Funding provided by the Nebraska Soybean Board; Products provided by Elanco Animal Health and Merck Animal Health.

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