Performance, Metabolism, and Economic Implications of Replacing Soybean Meal with Dried Distillers Grains with Solubles in Feedlot Cattle Diets

Abstract

The growing demand for biofuels, especially ethanol produced from corn, has driven the production of co-products such as dried distillers grains with solubles (DDGS). With a high protein content (around 30%), fiber, and minerals, DDGS presents an economical alternative for animal nutrition, replacing traditional sources like soybean meal while maintaining productive performance and reducing costs. This study evaluated the total replacement of soybean meal with DDGS in the diet of confined Holstein cattle, focusing on weight gain, feed intake, digestibility, feed efficiency, animal health, meat quality, and economic viability. The 24 animals received diets with 80% concentrate, containing either DDGS or soybean meal, and no significant differences were observed in terms of body weight (p = 0.92), feed intake (p = 0.98), or feed efficiency (p = 0.97) between the two treatments. The average daily gain was 1.25 and 1.28 kg for cattle in the DDGS and soybean meal groups, respectively (p = 0.92). Regarding metabolic and digestive parameters, no relevant changes were found in blood levels, except for higher serum cholesterol (p = 0.03) levels in animals fed DDGS. The digestibility of neutral detergent fiber (NDF) (p = 0.03) and acid detergent fiber (ADF) (p = 0.05) was lower in the DDGS group, while the digestibility of ether extract was higher (p = 0.02). Rumen fluid analysis revealed an increase in the production of short-chain fatty acids (p = 0.01), such as acetic and butyric acids (p = 0.01), in the DDG-fed animals. In terms of meat quality, animals fed DDGS produced meat with lower levels of saturated fatty acids (SFA) (p = 0.05) and higher levels of unsaturated fatty acids (UFA) (p = 0.02), especially oleic acid (p = 0.05). This resulted in a healthier lipid profile, with a higher UFA/SFA ratio (p = 0.01). In terms of economic viability, DDGS-based diets were 10.5% cheaper, reducing the cost of production per animal by 7.67%. Profitability increased by 110% with DDGS compared to soybean meal, despite the high transportation costs. Therefore, replacing soybean meal with DDGS is an efficient and economical alternative for feeding confined cattle, maintaining zootechnical performance, increasing meat lipid content and improving fatty acid profile, and promoting higher profitability. This alternative is particularly advantageous in regions with easy access to the product.

1. Introduction

The growing global demand for biofuels and the considerable increase in industries specialized in producing ethanol from cereals, especially corn, produce renewable compounds that seek to reduce environmental damage compared to the production and use of fossil fuels [1]. Corn is one of the most produced cereals in the world, especially in countries such as the United States and Brazil, where the production of biofuels from this cereal is increasing due to the excellent availability of the raw material. To produce ethanol, corn is subjected to fermentation and high temperatures, where sugars present in the grains, including starch, are used by yeast, transforming glucose into alcohol, resulting in its production [2].

After drying the residue, we have the dried distiller’s grain (DDG), where proteins, fibers, and minerals are retained [1]. DDG is the solid part obtained in this process, to which vinasse or syrup, rich in amino acids and lipids, also received in the fermentation process, can be added, giving rise to the DDGS, dried distillers grains with solubles. This coproduct has proteins, fats, fibers, and minerals with great potential in animal nutrition, providing carbon and nitrogen for microbial fermentation [3]. It is considered a protein food used in the diet of both monogastric and ruminant animals, presenting approximately 30% crude protein [4]. In animal nutrition, protein components and non-voluminous energy increase feed costs when added to diets [5]. The search for economically viable alternatives, reducing costs, such as using coproducts, which allow maintaining performance and productivity, such as DDGS, is constantly growing.

The protein source typically used in ruminant feed is soybean meal, which has good levels of rumen-degradable protein and provides essential amino acids for the animal, such as lysine [6]. However, a limitation on the use of this product is its high demand, which increases its market value and production costs. DDGS appear as an interesting source of protein, containing amino acids in its composition, especially methionine, allowing its inclusion in animal feed, reducing costs, and maintaining productive performance [7]. The search for levels of inclusion of this coproduct in ruminant feed is the focus of many studies, aiming at safe levels at which DDGS can be included in the diet without harming performance or causing problems in the animal or the products derived from it due to its lower starch concentration. In addition, this research aims to verify whether DDGS is a viable feed in the diet of male Holstein calves in feedlots, animals that are usually discarded at birth due to high production costs and low carcass yield, which makes their breeding unfeasible from an economic point of view. Thus, it is important to know whether the use of co-products can be effective for performance, and allow a profitable activity that farmers seek to consider this breed as a market niche.

As a hypothesis of our study, we expected that the replacement of soybean meal by DDGS would maintain the growth performance of animals without causing significant changes in ruminal parameters and their products, despite the differences in the composition between the feeds, promoting economic gain due to the lower cost of the diet. Among the implications of this research with DDGS, it is important to highlight the focus on environmental sustainability and diversification of feed resources, providing more scientific support for the use of industrial waste to feed ruminants.

As already mentioned, there are many justifications for this research, from reducing production costs while maintaining productivity, a lower-cost feed source for Holstein cattle that are discarded at birth on many dairy farms, but mainly for the valorization of Bioresources from agri-food waste for sustainable cattle feeding, as is the case with DDGS. Therefore, the objective of the study was to evaluate whether the total replacement of soybean meal by DDGS in the diet of Holstein steers in the finishing phase under confinement conditions is an advantageous option considering weight gain, feed intake, dry matter digestibility, feed efficiency, animal health, meat quality, and economic viability.

2. Materials and Methods

2.1. DDGS and Soybean Meal

The DDGS used in the experiment was acquired from Cooperativa Cooper A1 (Palmitos, Santa Catarina, Brazil), presenting the following composition data, % (Dry matter (DM): 90.82; total digestible nutrients (TDN): 75.70; crude protein (CP): 34.71; neutral detergent fiber (NDF): 33.48; Starch: 7.36; ether extract (EE): 7.28; ash: 9.37), where the proportion of inclusion of the same in the concentrate was 23.75%. The soybean meal used was produced and supplied by Cooperativa Agroindustrial Alfa (Cooperalfa, Chpaecó, Santa Catarina, Brazil), with the following composition, % (DM: 93.20; TDN: 77.33; CP: 48.13; NDF: 14.32; EE: 2.33; ash: 7.29) corresponding to 12.50% inclusion in the concentrate.

2.2. Animals and Installations

Twenty-four intact male Holstein calves, 10 months old, weighing 345.6 ± 3.84 kg, were used in this study. The animals were housed in a barn with individual stalls measuring 15 m², partially covered and equipped with feeders and drinkers. The study lasted 90 days, with the first 21 days spent adapting to the facility and diet.

2.3. Experimental Design and Diets

The cattle were divided into two groups in a completely randomized design with 12 replicates per group. The diet provided (

Table 1. Chemical composition and fatty acid profile in Total Mixed Ration (TMR).

Variables	TMR: DDGS	TMR: Soybean Meal
Dry matter 1, %	52.0	52.1
Mineral matter, %	6.15	5.79
Crude protein, %	14.2	13.9
NDF, %	22.4	24.0
ADF, %	11.2	14.3
Ash, %	3.53	3.29
Fatty acid, %
C8:0 (Caprylic)	0.02	0.03
C12:0 (Lauric)	0.07	0.05
C14:0 (Myristic)	0.20	0.18
C15:0 (Pentadecanoic)	0.07	0.10
C16:0 (Palmitic)	19.2	21.4
C16:1 (Palmitoleic)	0.21	0.23
C17:0 (Heptadecanoic)	0.14	0.17
C17:1 (cis-10-Heptadecenoic)	0.05	0.05
C18:0 (Stearic)	3.04	3.46
C18:1n9t (Elaidic)	0.09	0.11
C18:1n9c (Oleic)	28.8	26.5
C18:2n6c (Linoleic)	43.7	42.5
C20:0 (Arachidic)	0.52	0.50
C20:1n9 (cis-11-Eicosenoic)	0.22	0.28
C18:3n3 (a-Linolenic)	2.54	3.28
C20:2 (cis-11,14-Eicosadienoic)	0.12	0.10
C22:0 (Behenic)	0.34	0.38
C24:0 (Lignoceric)	0.46	0.48
∑ Saturated fatty acids (SFA), %	24.1	26.8
∑ Unsaturated fatty acids (UFA), %	75.8	73.1
∑ Monounsaturated fatty acids (MUFA), %	29.4	27.2
∑ Polyunsaturated fatty acids (PUFA), %	46.3	45.9
UFA/SFA	3.16	2.73

The diet (TMR) of the DDGS group was formulated based on corn silage (30.0%), ground corn (40.1%) soybean hulls (3.3%), DDGS (23.6%), and mineral core (3.0%). The diet (TMR) of the soybean meal group was based on corn silage (30.0%), ground corn (41.2%), soybean hulls (12.4%), soybean meal (13.4%), and mineral core (3.0%). The mineral supplement used had the following micro-ingredients and their guaranteed levels: calcium (g/kg) (min 231.4); phosphorus (g/kg) (min 40.0); sulfur (g/kg) (min 40.0); magnesium (g/kg) (min 25.0); potassium (g/kg) (min 10.0); sodium (g/kg) (min 70.0); cobalt (mg/kg) (min 15.0); copper (mg/kg) (min 750.0); chromium (mg/kg) (min 20.0); iron (mg/kg) (min 700.0). ¹: Dry matter content (DM%), crude protein (CP%), neutral detergent fiber (NDF%), acid detergent fiber (ADF%), and ether extract (EE).

), formulated based on the nutritional requirements, provided 2.4% DM in relation to their live weight, in a concentrate/forage ratio (80:20). It was offered three times a day, at 8:00 a.m., 10:15 a.m., and 5:00 p.m., weighed and supplied individually directly into the feeder. Differences in the diet consisted of protein sources, soybean meal, and DDGS. The diets formulated for both groups were isoenergetic and isonitrogenous.

2.4. Data and Sample Collection

At all times of data and sample collection, the cattle had been without food for approximately 14 h, but had free access to water. The collections occurred in the morning period between 07:00 and 08:30 h, considering the same feeding order of the animals as on the previous day. This practice was used to standardize the animals and thus have less fluctuation in the parameters of body weight, blood, and ruminal fluid due to feeding.

Weight was measured on days 1, 21, 55, and 90 of the experiment, using a digital scale before the morning feeding to monitor performance. From this data, weight gain and average daily weight gain were calculated. Based on the assessment of consumption, feed efficiency was measured.

Blood collections were performed on the same days as the weighing, with 8 mL collected per animal from the coccygeal vein and divided into two tubes: a vacuolated tube with anticoagulant (EDTA) for blood count analysis and a vacuolated tube without anticoagulant for subsequent centrifugation and serum collection for serum biochemistry analysis. The tubes were refrigerated at 10 °C in an isothermal box until they arrived at the laboratory. To separate the serum, the tubes were centrifuged without anticoagulant (7500 RPM for 10 min). The serum was transferred to microtubes, labeled, and stored at −20 °C until analysis.

The ruminal fluid collection was performed on days 55, and 90 of the experiment, with the aid of an esophageal probe and vacuum pump, instantaneous pH measurement with the help of a pH meter (Testo 0563 2051, Campinas, SP, Brazil) and freezing of samples at −20 °C for analysis of volatile fatty acid profile. Feces, diet, and respective leftovers for analysis of apparent digestibility were collected once a day for three consecutive days at different times, on days 78, 79, and 80 of the experiment.

After 90 days of experimentation, the animals were slaughtered at a local slaughterhouse, following the procedures described in the legislation, with a state inspection system. After fasting, with access only to water, the animals were stunned with a pneumatic pistol, followed by bleeding and skinning. A portion of the longissimus dorsi muscle was removed and stored under refrigeration (6 °C) in non-vacuum plastic bags for 24 h to transform the muscle into meat (rigor mortis) for further analysis. After this process, the samples were refrigerated at −20 °C until analysis.

2.5. Zootechnical Performance

From the measurement of body weight (BW), it was possible to calculate the other variables. Weight gain (WG) was calculated from the data from the last weighing by subtracting the weight from the previous weighing (final weight−initial weight); daily weight gain (ADG) was calculated from the weight gain divided by the period in days (WG/time (days)); feed intake (dry matter intake—DMI) was calculated from the weighing of the amount of feed provided and subtracting its respective leftovers later. The leftovers were weighed daily in the morning individually. To calculate feed efficiency, the equation was used: feed efficiency = ADG/DMI.

2.6. Laboratory Analysis

2.6.1. Chemical Composition of Diet and Feces

Samples of the feed provided and their respective leftovers were collected and subsequently dried in a forced ventilation oven for 72 h at a temperature of 55 °C, after which they were ground in a knife mill to a size of 1 mm and submitted to analyses to determine the dry matter content (DM%), crude protein (CP%), neutral detergent fiber (NDF%), acid detergent fiber (ADF%) ether extract (EE), and mineral matter (MM%) according to the methodology of literature [8,9,10], as described by Brunetto et al. [11].

2.6.2. Hemogram

Blood with an anticoagulant was used to evaluate the total blood count. An automatic blood cell counter (EQUIP VET 3000^®, Equip, Itatiba, SP, Brazil) quantified the number of leukocytes, platelets, and erythrocytes, hemoglobin concentrations, hematocrit percentage, and the leukocyte differential. The results were extracted from the equipment and then tabulated for analysis.

2.6.3. Metabolic Biochemistry

Serum levels of total proteins, albumin, globulins, glucose, amylase, gamma-glutamyl transferase (GGT), aspartate aminotransferase (AST), cholesterol, triglycerides, fructosamine, urea, calcium, phosphorus, magnesium, and iron were measured using commercial kits (Analisa^®, Gold Analisa Diagnóstica Ltd.a, Belo Horizonte, MG, Brazil) following the manufacturer’s recommendations, and using automatic equipment (Zybio EXC 200^®, Equip, Itatiba, SP, Brazil).

2.6.4. pH and Volatile Fatty Acids in Ruminal Fluid

The ruminal fluid underwent a slow thawing process at 5 °C, and then the sample was homogenized manually. A volume of 1 mL of the supernatant from the ruminal fluid samples was placed in polypropylene microtubes and then centrifuged for 5 min (12,300× g). An aliquot of 250 μL of the supernatant was transferred to a new microtube containing formic acid (250 μL), following the same protocol recently published [11]. Fatty acid quantification was performed using a gas chromatograph equipped with a flame ionization detector (GC-FID; Varian Star 3400, Palo Alto, CA, USA) and an autosampler (Varian 8200CX, Palo Alto, CA, USA) in split mode (1:10) up to 250 °C. Acetic, propionic, butyric, valeric, and isovaleric acids were separated by a CP-Wax 52CB capillary column (50 m × 0.32 mm; stationary phase thickness of 0.20 μm), according to standard methodology [11]. Method validation was performed, and the standardization results were presented in Table S1. The results were expressed as 100 mol/L of each short-chain fatty acid (SCFA) in the ruminal fluid.

2.6.5. Digestibility Coefficient

For the analysis of apparent digestibility, individual fecal samples were collected once a day, for a period of three consecutive days, at different times each day (08:00 h, 13:00 h, and 18:00 h). To measure daily fecal excretion, the internal indicator indigestible neutral detergent fiber (NDF) was used, estimated from the feed provided, daily leftovers, and feces, using the in situ digestibility technique [12], adapted for an incubation period of 240 h [13]. Then, the percentage of DM and NDF was measured [9]. The final residue of the NDF analysis was incubated in fistulated animals. With these data, fecal excretion was estimated by the difference between the ingested NDF and the iNDF excreted in feces (kg DM/day). Subsequently, the apparent digestibility coefficient (ADC) of DM was determined by the difference between the amount consumed and that obtained in feces; the same methodology was used to determine the ADC of other nutrients.

2.7. Meat Analysis

We used a portion of the collected sample to analyze the meat’s composition. Meat was processed, and the subcutaneous fat and connective tissue fragments were removed. The sample was then placed in a device, near-infrared reflection spectrometer, model Spectra Star 2600 XT series of near-infrared analyzers (Unity Scientific^®, Jakarta, Indonesia), where data on the percentage of DM, fat, and protein were obtained.

We used the Bligh and Dyer method [10] for lipid extraction, with some modifications previously published by Brunetto et al. [11]; then, fatty acid methylation was performed by the transesterification method [14]. The extracted lipids were mixed with 1 mL of 0.4 M KOH methanolic solution, and the test tubes were vortexed for 1 min. Then, the sample aliquots were kept in a water bath for 10 min at boiling point, followed by cooling to room temperature, following a methodology previously published by the research group [11]. Using a TRACE 1310 gas chromatograph with a flame ionization detector, fatty acid methyl esters (FAME) were measured. An aliquot of 1 μL of the prepared sample was injected into a splitless injector operated in 1:10 split mode at 250 °C, with hydrogen used as carrier gas [11]. The separation of FAMEs was performed with an RT 2560 chromatographic column (film thickness of 100 m × 0.25 mm × 0.20 μm, Restek, Bellefonte, PA, USA), following standard analysis methodology [11]. The FAMEs were identified based on the experimental retention time, when compared to the authentic standard (FAME Mix-37, Sigma Aldrich, St. Louis, MO, USA). Results are shown as a percentage of each FA identified in the lipid fraction, according to Visentainer and Franco [15].

2.8. Cost Analysis

The cost analysis was calculated using dry matter intake (DMI) data [16]. Knowing the cost/kg of DM of the diet consumed, it was possible to calculate the total feeding costs during the experimental period, adding a percentage of 20% to this value, such as extra expenses related to facilities, electricity, medicines, and labor. With the commercialization of the carcasses, a value of US$ 3.13 per kg was collected; thus, we discounted the total production cost, obtaining the profit (US$/animal).

2.9. Statistical Analysis

All data were analyzed using the “MIXED procedure” of SAS (SAS Inst. Inc., Cary, NC, USA; version 9.4), with Satterthwaite approximation to determine degrees of freedom for the fixed effects test. Growth performance (except for BW), meat, and production costs data were tested for treatment fixed effects using animal (treatment) as a random effect. BW, blood count, biochemistry, and serum ruminal biomarker data were analyzed as repeated measures and tested for treatment, day, and treatment × day fixed effects using animal (treatment) as a random effect. The d1 results were included as an independent covariate because they reflect different results prior to the start of the experiment, without any influence from DDGS, indicating an individual effect of each animal. Day 1 results were removed from the data set to generate the treatment mean but were retained as a covariate. In order to construct the first-order autoregressive covariance structure, we used the Akaike information criterion. The means were separated using the PDIFF method (t-test), and all results were reported as LSMEANS followed by SEM. Significance was defined when p ≤ 0.05, and trend when p > 0.05 and ≤0.10.

3. Results

3.1. Performance and Clinical Changes

During the experimental period, there were a few days in which some animals (between 4 to 7 days) presented leftover feed, the vast majority without any other clinical changes. However, during the study, five cattle reduced their consumption and presented altered fecal consistency (diarrhea) (two in the DDGS group and three in the soybean meal group); it was necessary to intervene with oral bicarbonate and injectable dipyrone for 3 days at 24-h intervals. Within 48 h after the drug intervention, the animals resumed consuming all the feed provided.

Table 2. Body weight, weight gain, daily weight gain, feed intake, and feed efficiency of cattle fed DDGS replacing soybean meal under confinement conditions.

Variables	DDGS	Soybean Meal	SEM	P-Treat 1	P-Day 1	P-Treat × Day 1
Body Weight. kg				0.92	0.01	0.88
d1	345.9	345.3	3.84
d21	374.3	371.3	3.56
d90	458.9	460.9	3.51
Average daily gain (ADG). kg/day
d1-90	1.25	1.28	0.05	0.92	-	-
d21-90	1.22	1.29	0.04	0.86	-	-
Dry matter intake (DMI). kg/day
d1-90	8.77	8.80	0.02	0.98	-	-
d21-90	8.83	8.87	0.03	0.97	-	-
Feed efficiency 2. kg/kg
d1-90	0.142	0.145	0.01	0.97	-	-
d21-90	0.138	0.145	0.02	0.81	-	-

¹: no statistical difference between groups and interaction treatment vs. day (p > 0.05). ²: Feed efficiency = ADG/DMI.

presents the results for body weight, daily weight gain, daily feed intake, and feed efficiency; all of these variables had no effect of treatment and/or treatment × day interaction (p > 0.05). Only a day effect was observed for body weight in both groups, which is expected in animals in the growth and fattening phase.

3.2. Hematology and Serum Biochemistry

Hematology and biochemistry results are presented in

Table 3. Serum hematological and biochemical biomarkers (days 1, 21, 55, and 90) of cattle fed DDGS as a substitute for soybean meal under confinement conditions.

Variables	DDGS	Soybean Meal	SEM	P-Treat	P-Treat × Day
Hemogram
Total leukocyte (×103/µL)	6.90	7.71	0.34	0.51	0.28
Lymphocyte (×103/µL)	4.06	4.62	0.23	0.64	0.37
Granulocytes (×103/µL)	1.79	1.96	0.12	0.82	0.70
Monocyte (×103/µL)	1.05	1.12	0.06	0.75	0.86
Erythrocytes (×106/µL)	7.60	7.33	0.07	0.92	0.88
Hemoglobin (mg/dL)	12.1	11.9	0.13	0.94	0.93
Hematocrit (%)	32.9	32.7	0.26	0.91	0.96
Platelets (×103 µL)	294	216	22.6	0.11	0.16
Serum biochemistry
Albumin (g/dL)	3.01	3.05	0.02	0.96	0.98
Total protein (g/dL)	7.41	7.51	0.06	0.89	0.91
Globulin (g/dL)	4.40	4.46	0.07	0.93	0.96
Amylase (U/L)	124	122	6.42	0.88	0.91
GGT (U/L)	28.3	29.0	0.78	0.94	0.87
AST (U/L)	123	121	4.57	0.92	0.83
Cholesterol (mg/dL)	93.0 a	84.7 b	2.37	0.03	0.18
Triglycerides (mg/dL)	14.8	15.5	0.37	0.84	0.89
Fructosamine (mg/dL)	2.80	2.77	0.02	0.95	0.97
Urea (mg/dL)	16.9	20.4	1.02	0.22	0.11
Calcium (mcg/dL)	8.87	8.83	0.06	0.96	0.97
Phosphorus (mcg/dL)	9.69	9.98	0.11	0.95	0.92
Magnesium (mcg/dL)	2.64	2.82	0.05	0.76	0.65
Iron (mcg/dL)	207	215	4.64	0.81	0.55

Note: When p ≤ 0.05, there was a treatment effect, illustrated by different letters on the same line; there was no treatment × day interaction for serum biomarkers of biochemistry and hematology.

. There was no treatment effect or treatment × day interaction for all hematologic variables (erythrocytes, hematocrit, hemoglobin, platelets, total leukocytes, granulocytes, lymphocytes, and monocytes). Among the biochemical variables, there was only a treatment effect for cholesterol levels, which was higher in the cattle serum that consumed DDGS (p = 0.03). There was no treatment effect or treatment × day interaction for albumin, total protein, globulin, triglycerides, fructosamine, urea, calcium, phosphorus, magnesium, and iron levels, as well as amylase, GGT, and AST activity (p > 0.05).

3.3. Short-Chain Fatty Acids in Ruminal Fluid

Table 4. Fatty acid profile in ruminal fluid of cattle fed DDGS as a replacement for soybean meal under confinement conditions.

Variables	DDGS	Soybean Meal	SEM	P-Treat	P-Treat × Day
pH	6.68	6.64	0.04	0.92	0.73
Total SCFA (mmol L−1)				0.26	0.01
d55	81.3 a	67.4 b	1.52
d90	71.6	69.5	1.32
Acetic acid (mmol L−1)				0.05	0.01
d55	58.7 a	48.0 b	1.24
d90	46.5 a	42.6 b	1.03
Butyric acid (mmol L−1)				0.24	0.01
d55	9.25 a	6.39 b	0.85
d90	8.04	9.41	0.97
Propionic acid (mmol L−1)	12.2	12.2	0.51	0.92	0.95
Isovaleric acid (mmol L−1)	1.84	1.76	0.22	0.75	0.84
Valeric acid (mmol L−1)	1.14	1.19	0.08	0.96	0.92

Note: When p ≤ 0.05, there was a treatment effect or treatment × day interaction, illustrated by different letters on the same line.

presents the results of pH and SCFA in the ruminal fluid. There was no effect of treatment or interaction for pH (p > 0.05). There was a treatment × day interaction for levels of total SCFA and butyric acids, which were higher in cattle that consumed DDGS than the other group on day 55. Treatment effect and treatment × day interaction for levels of acetic acid in the rumen, being higher on both collection days (d55 and d90) in cattle that consumed DDGS. No treatment effect or interaction existed for propionic, isovaleric, and valeric acid levels.

3.4. Digestibility

Table 5. Apparent digestibility coefficient (ADC) in confined cattle fed with DDGS as a replacement for soybean meal.

Variable	DDGS	Soybean Meal	SEM	p-Value
ADC—Dry material	0.68	0.70	0.01	0.62
ADC—Organic material	0.71	0.73	0.01	0.56
ADC—Crude protein	0.64	0.71	0.03	0.25
ADC—Neutral detergent fiber	0.38 b	0.50 a	0.02	0.03
ADC—Acid detergent fiber	0.44 b	0.52 a	0.02	0.05
ADC—Ether extract	0.70 a	0.63 b	0.01	0.02

Note: When p ≤ 0.05, there was a treatment effect or treatment × day interaction, illustrated by different letters on the same line.

presents the apparent digestibility coefficient (ADC) of nutrients. Cattle that consumed DDGS had lower ADCs of NDF and ADF than those fed soybean meal; conversely, the ADC of ether extract was higher in cattle fed DDGS than in the other group. No effect of treatment was observed for the ADC of DM, organic matter, and crude protein.

3.5. Total Lipids and Fatty Acid Profile in Meat

Table 6. Total lipids and fatty acid profile in meat from cattle fed DDGS as a replacement for soybean meal under confinement conditions.

Variables	DDGS	Soybean Meal	SEM	p-Value
Total lipids %	2.44	2.08	0.07	0.03
C8:0 (Caprylic) %	0.01	0.02	0.01	0.95
C12:0 (Lauric) %	0.04	0.06	0.02	0.51
C14:0 (Myristic) %	1.55	1.65	0.31	0.34
C14:1 (Myristoleic) %	0.32	0.53	0.31	0.05
C15:0 (Pentadecanoic) %	0.23	0.35	0.22	0.41
C16:0 (Palmitic) %	25.06	26.85	0.34	0.05
C16:1 (Palmitoleic) %	3.16	3.14	0.58	0.95
C17:0 (Heptadecanoic) %	0.38	0.42	0.07	0.86
C18:0 (Stearic) %	12.97	14.09	0.27	0.02
C18:1n9t (Elaidic) %	1.63	1.65	0.12	0.96
C18:1n9c (Oleic) %	36.58	34.97	0.42	0.05
C18:2n6c (Linoleic) %	12.61	11.09	0.19	0.11
C20:0 (Arachidic) %	0.10	0.09	0.01	0.95
C18:3n6 (γ-Linolenic) %	0.07	0.07	0.01	0.98
C20:1n9 (cis-11-Eicosenoic) %	0.16	0.18	0.02	0.95
C18:3n3 (Linolenic) %	0.24	0.34	0.03	0.02
C21:0 (Henicosanoic) %	0.26	0.26	0.08	0.92
C20:2 (cis-11.14-Eicosadienoic) %	0.14	0.14	0.03	0.95
C22:0 (Behenic) %	0.04	0.04	0.02	0.98
C20:3n6 (cis-8.11.14-Eicosatrienoic) %	0.70	0.64	0.03	0.78
C20:4n6 (Arachidonic) %	3.52	3.17	0.15	0.91
C22:2 (cis-13.16-Docosadienoic) %	0.02	0.03	0.70	0.98
C24:0 (Lignoceric) %	0.05	0.04	0.01	0.97
C20:5n3 (cis-5.8.11.14.17-Eicosapentaenoic) %	0.11	0.12	0.01	0.98
C24:1n9 (Nervonic) %	0.02	0.02	0.03	0.99
C22:6n3 (cis-4.7.10.13.16.19-Docosahexaenoic) %	0.04	0.04	0.00	0.99
Other variables
∑ Saturated fatty acids (SFA) %	40.69	43.87	0.71	0.05
∑ Unsaturated fatty acids (UFA) %	59.31	56.13	0.65	0.02
∑ Monounsaturated fatty acids (MUFA) %	41.87	40.49	0.48	0.25
∑ Polyunsaturated fatty acids (PUFA) %	17.44	15.64	0.32	0.01
UFA/SFA	1.46	1.28	0.06	0.01

presents the meat results. A higher percentage of fat was observed in the meat of cattle that consumed DDGS. In the meat of cattle that consumed DDGS, a lower rate of myristoleic, palmitic, stearic, and linolenic acids was observed compared to animals that consumed soybean meal, as well as a higher percentage of oleic acid in the DDGS group. The sum of SFA was lower in animals that consumed DDGS than in the other group, and these animals had a higher sum of UFA in the meat. PUFA was higher in the DDGS group meat than in the control (soybean meal). A higher UFA/SFA ratio was also observed in cattle that consumed DDGS than in those that consumed soybean meal.

3.6. Economic Viability

Table 7. Production costs, revenues, and profits from the confinement of cattle fed DDGS as a replacement for soybean meal.

Variables	DDGS	Soybean Meal	SEM	p-Value	Difference (%) 2
Diet costs (US$ animal/day)	2.37	2.65	-	-	10.57 ↓
Total production cost considering consumption (US$/animal) 1	680	698	3.78	0.31	7.67 ↓
Carcass weight, kg	228.1	228.1	6.32	0.97	0.02 ↑
Amount paid per carcass (US$ 3.13 per kg)	714	714	3.27	0.92	0.02 ↑
Profit (US$/animal)	34.44	16.34	2.52	0.02	110.7 ↑

¹: value refers to the costs of cattle (US$ 6.50 kg BW), feed and 20% added to feed for other expenses. According to the literature [16], these expenses would be related to electricity, installation wear and tear, medications/vaccines and daily labor. ²: The difference between the groups for each of the variables was presented as a percentage, with the DDGS group always being compared to the control (soybean meal).

presents the economic viability results. The addition of DDGS reduced the cost of the diet by 10.5%. Considering the intake, the cost of producing each steer fed with DDGS was 7.67% lower than that of soybean meal. This situation resulted in a profit of 110% when DDGS were used in the cattle diet instead of soybean meal.

4. Discussion

The use of unconventional feeds or coproducts in animal feed, such as DDGS, has gained prominence due to its nutritional composition, which includes good protein and energy levels, high fiber percentage, and lower cost, encouraging its use. Including DDGS in the diet of confined cattle has proven to be an effective alternative for maintaining animal performance when used as a substitute for soybean meal in the diet, focusing on protein replacement. As shown in Table 2, the replacement did not change the parameters of weight gain, DM intake, and feed efficiency in isoenergetic and isoprotein diets. This high replacement power is due to the high protein content present in DDGS (above 30%), its relevant fiber fraction (approximately 33%), and the considerable amount of lipids originating from soluble fats [17], essential components for animals in growth and finishing conditions. However, it is important to highlight that the composition of DDGS may vary depending on the raw material used in its production, impacting its effects on animal metabolism and formulation [18], which may result in non-compliance with nutritional requirements according to the animal category.

In addition to the crude protein content, the fiber percentage is the main difference between soybean meal and DDGS, as soybean meal has lower levels of NDF compared to DDGS [19]. This difference can influence the precision profile in the rumen, promoting more stable productivity and a lower risk of metabolic problems in animals fed DDGS. As shown, the use of DDGS was proven in changes in the profile of fatty acids produced during ruminal fermentation, with an increase in the concentrations of short-chain fatty acids (SCFA). According to Shen et al. [19], changes in the ruminal microbiota, such as changes in the population of protozoa and bacteria, can alter the concentrations of SCFA caused by different feed compositions when this substitution is performed. This increase was attributed to the higher concentrations of acetic and butyric acid in the ruminal fluid of animals that consumed DDGS. The higher amount of fiber in DDGS stimulates the patent of bacteria specialized in fiber fermentation [20], resulting in a more significant production of acetate, a two-carbon SCFA, and an essential energy source for ruminants associated with the formation of fatty acids. Knowing the ruminal microbiota may be a possibility to understand the mechanism involved in the increase in volatile fatty acids, such as acetic and propionic.

Regarding the digestibility coefficient of the fibrous portion, a reduction was observed in the group fed DDGS. This is due, in part, to the lower availability of protein at the ruminal level for the proliferation of microorganisms and aid in the digestion and fermentation of this fiber when compared to soybean meal. The reduced digestibility of fiber is related to the fact that this process occurs predominantly in the rumen, where the interaction between microorganisms, nutrients, especially protein, and environmental conditions determines the efficiency of fibrous fermentation. DDGS has a high concentration of UFA in the ether extract (EE), which can be associated with increased serum cholesterol levels in animals. This effect is explained by the more significant digestibility of EE in animals that received DDGS, indicating more substantial absorption and availability of these compounds for the tissues. This more considerable digestibility contributes to a higher percentage of intramuscular fat, increasing the fat content in the meat of animals treated with DDGS [21].

The inclusion of DDGS also influences the fatty acid profile of meat. Due to the high concentration of UFA in the coproduct, including oleic acid and linoleic acid, there is a modulation in the processes of lipolysis, biohydrogenation, and ruminal synthesis [22], resulting in a greater flow of unsaturated compounds to the intestine, where they are absorbed. This process alters the lipid profile of meat, favoring a composition with a higher proportion of UFA, such as oleic acid, which can bring nutritional and sensory benefits to the final product. This interference in the biohydrogenation process causes the conversion of PUFA into saturated fatty acids (SFA) to be reduced, resulting in a lower concentration of palmitic (C16:0) and stearic (C18:0) acid and causing changes in the ratio of unsaturated/saturated fatty acids [22]. Dietary sulfur levels can promote changes in the fatty acid profile of meat from animals receiving DDGS, as this mineral is present in good quantities in this residue. This can promote changes in the populations of microorganisms present in the ruminal environment and alter fatty acid biohydrogenation processes [23].

Regardless of the protein source used in the diet, the blood count, serum biochemistry, and metabolic parameters were similar, except for total cholesterol levels, which were higher in cattle that consumed DDGS. This effect on serum lipids is probably related to the more substantial digestibility of the EE, which allowed greater availability of fat to be absorbed by the intestine, resulting in this higher cholesterol concentration. Still, it is worth noting that the values were within the normal range for adult cattle in both groups [24].

The cost of producing confined cattle is high in Brazil, mainly due to the cost of concentrate, which has ingredients that suffer from price fluctuations throughout the year due to the effects of the harvest (law of supply and demand) but are also impacted by weather conditions, which have resulted in extreme conditions in recent years, from a brief drought to severe dry seasons or floods. This situation has significantly influenced the use of industry coproducts in animal feed, emphasizing DDG and DDGS. The diet that replaced soybean meal with DGGS had a lower daily animal cost and, as it did not affect performance, resulted in a higher profit per animal. It is essential to clarify that the cost of DDGS used in this experiment was high due to the costs of the product and the freight of over 900 km. When we consider the cost of this coproduct in regions where it is available in the industry, the value of DDGS can be up to 30% lower during the harvest period compared to the cost in our research.

The diet was formulated for the cattle to gain 1.5 kg per day, but this did not happen, with the maximum average daily gain in this experiment being 1.28 kg and 1.25 kg (soybean meal and DDGS, respectively). This is due to the diet used in the study, composed of 80% concentrate and 20% corn silage, which presents positive results for beef cattle. However, when used in cattle of breeds suitable for milk production, such as the Holstein, the animals did not respond in weight gain due to a condition of subclinical and/or clinical acidosis (three animals: two in the DDGS group and one in the soybean meal group), similar to the ADG of 1.32 kg detected in a diet with a greater inclusion of concentrate (70%) and (30%) silage [25]. However, it is much lower than what occurred in colder diets, that is, with a lower proportion of concentrate or fast-fermenting carbohydrates in the diet, with (55%) concentrate and (45%) silage, where the ADG was 1.62 kg [26]. This is the explanation for the low profitability of the confinement system here; the animals did not gain the projected body weight, reducing feed efficiency. In addition to these studies by our research group, others not yet published show that Holstein cattle respond positively to ADG formulated in cold diets, with a maximum of 65% concentrate.

According to the literature, there are benefits to cattle performance when DDGS is used in the diet; however, it can result in operational difficulties [27]. As practical implications of these results with DDGS, we highlight the lower production cost, which allows for greater profit; in addition, this study shows that DDGS can be used as a substitute for a higher-cost protein source, providing an alternative byproduct as feed for confinement. Having a sustainable destination for the residue is valuable, especially because the number of ethanol-producing plants is growing in Brazil, which prevents the residue from being disposed of inappropriately, leading to environmental contamination.

5. Conclusions

Replacing soybean meal with DDGS in the diet of Holstein cattle in confinement is an advantageous option because the animals maintain similar weight gain and feed efficiency between treatments without causing any harm to animal health and metabolism. In addition, the use of DDGS was able to improve the digestibility of EE, increase serum cholesterol levels, and modulate the fatty acid profile in the meat, with emphasis on a lower amount of SFA and a higher amount of UFA, resulting in meat that is more desirable to the consumer from a health point of view. Furthermore, the diet with DDGS has a lower cost, and consequently results in greater profitability in the production system, providing economic and environmental sustainability.