Soybean Hulls and White Oat Grains in Steer Finishing

Abstract

This study aimed to investigate the feasibility of using ground soybean hulls and white oat grains to finish steers reared exclusively on concentrated feed. We used 33 steers, predominantly of Charolais or Nellore breeds, and randomly assigned the animals to the treatments, blocking them according to genetic predominance. The diets were isonitrogenous, and the treatments consisted of soybean hulls, white oats, and mix these in equal parts, supplemented with calcitic limestone and a protein nucleus. The study measured variables related to the dry matter intake (DMI) and bromatological fractions of diets, as well as performance of steers. No significant differences were observed between treatments in terms of DMI during the experimental period. Although DMI intake was similar across treatments, steers receiving the mixed diet exhibited significantly higher weight gain than those on the soybean hull diet (1.300 vs. 0.972 kg day^-1). However, both these treatments showed comparable results to the white oat grain diet (1.203 kg day^-1), achieving a similar final weight (387.22 kg). Implementing 100% concentrate diets is technically feasible for steers fed with white oat grain and the mixture of soybean hull and white oat grain, which also demonstrated superior performance compared to the soybean hull treatment.

Key words
subclinical acidosis; high grain; average daily gain; neutral detergent fiber

INTRODUCTION

Greater animal performance is not always synonymous with economic feasibility in beef cattle rearing. Thus, integrating alternative techniques into the production system can be beneficial. In this context, high-grain diets present higher feed efficiency and weight gain, as well as operational benefits such as higher energy density, ease of daily feed management, labor reduction, and the possibility of fewer feedings (Mendes 2023). These advantages make it possible to balance technical efficiency with profitability (Karpinski 2017, Mendes 2023).

High-grain feeds require additives to maintain rumen physiology and prevent a drop in ruminal pH, which could limit animal performance. This is also true for high-concentrate diets where growth-promoting additives, often included in protein cores, are used to prevent metabolic disorders.

Soybean hulls can serve as both roughage and concentrate, enabling performance similar to corn-based diets (Cattelam et al. 2018, Argenta et al. 2019). Similarly, white oat grain can be used in ruminant diets as a “bulk-concentrate” because it is a cereal with a sufficient neutral detergent fiber (NDF) content to promote rumination in beef cattle on high-concentrate diets (Argenta et al. 2019, Callegaro et al. 2020). White oat grain also offers high digestible energy, making it suitable for finishing animals that require more energy-dense diets. Diets must contain a minimum of 6 to 9% neutral detergent fiber to ensure adequate dry matter intake and prevent metabolic issues (Grandini 2012).

Previous research has suggested that soybean hulls and white oat grains can be included in ruminant diets, yet there is a knowledge gap regarding their use in exclusively concentrate-based diets for confined finishing steers. According to the NRC (2016), beef cattle require 8% physically effective NDF to maximize feed efficiency and manage feeding well, alongside the use of ionophores in high-concentrate diets. The primary hypothesis of this research is that steers could perform optimally due to the nutritional composition of the investigated feeds. A secondary hypothesis is that comparing animal performance across diets could yield comparable results. Therefore, this study aims to explore the feasibility of using soybean hulls and white oats in high-concentrate diets for confined finishing steers.

MATERIALS AND METHODS

The experiment took place at the Cattle Breeding Laboratory of the Department of Animal Science at the Universidade Federal de Santa Maria (UFSM). Thirty-three steers, predominantly of the Charolais or Nellore breeds, were used. At the start of the adaptation period, these steers were 20 months old and had an average live weight (LW) of 270 (±29.57) kg. The animals were randomly assigned to treatments, with the groups being organized based on their genetic predominance and initial weight.

Before the start of the experimental period, the steers were subjected to a 16-day adaptation phase. During this period, each steer was housed in an individual 12-m² stall that was paved and covered, equipped with feeders and water dispensers (Figures 1 and 2). The steers were gradually transitioned through three roughage-to-concentrate ratios based on dry matter (DM): 50:50 for the first four days, 30:70 for the next four days, and 0:100 for the final eight days. The concentrate provided during the adaptation phase was identical to that used in the experimental phase. Feed offerings and residuals were meticulously recorded, with leftovers kept between 5% and 8% of the total feed provided. The steers had ad libitum access to feed, which was supplied twice daily. Leftovers were removed daily before the morning feeding to assess the previous day’s intake and adjust the next day’s feed quantity. Additionally, endoparasites were controlled during this phase with the subcutaneous administration of 10% albendazole sulfoxide.

Figure 1
Experimental animals facilities.

Figure 2
Experimental animals facilities.

The diet consisted entirely of concentrate, formulated based on the bromatological composition of the ingredients and calculated following the NRC (2000) guidelines to ensure an isonitrogenous nutrient profile. The dietary treatments were as follows: a soybean hull-based concentrate, a white oat grain-based concentrate, and a mixed concentrate composed of equal parts soybean hulls and white oat grains, supplemented with calcitic limestone and a protein core that included the virginiamycin growth promoter (Table II).

Table I
Participation of the ingredients (Natural Matter) and the bromatological composition of the offered diets (Dry Matter).

Concentrate ingredients, g kg-1	Treatments
	Soybean husk	Mixture	White oat grain
White oat grain	-	418.0	840.0
Soybean husk	834.0	418.0	-
Calcitic limestone	41.0	47.0	52.0
Protein nucleus	125.0	117.0	108.0
g kg-1 Dry Matter	Bromatological Composition
Dry Matter (g/kg Natural Matter)	901.18	906.49	911.75
Crude Protein	154.35	154.32	154.16
Ethereal Extract	13.48	31.12	48.73
Mineral Matter	103.56	101.83	98.90
Acid Detergent Fiber	407.64	278.09	149.63
Neutral Detergent Fiber	593.80	424.63	256.93
ADIP	5.11	2.97	0.86
NDIP	9.57	6.88	4.21
Hemicellulose	186.16	146.54	107.30
Cellulose	355.11	221.15	88.22
Lignin	20.10	30.80	41.40
Calcium	20.48	20.55	20.24
Phosphorus	2.21	2.66	3.11
Total Digestive Nutrients	612.11	662.89	724.16
OMIVD	781.65	724.34	668.54

• N/ADIP=neutral/acid detergent insoluble protein; OMIVD=organic matter in vitro digestibility.

Table II
Ruminal pH and bacteria activity values (time at the reduction of the methylene blue in seconds) according to the treatments and collection times.

Sampling times	Treatments
	Soybean husk		Mixture		White oat grain
Hours	pH	Time (s)	pH	Time (s)	pH	Time (s)
08:00	5.69	19	5.92	17	6.11	40
09:00	5.47	12	5.86	16	6.17	36
10;00	5.46	15	5.89	17	5.79	33
12:00	5.38	20	6.01	15	6.14	61
14:00	5.46	37	5.97	23	6.33	33
15:00	5.37	25	5.69	27	6.60	31
16:00	5.29	20	5.85	20	6.05	27
18:00	5.56	17	5.82	38	6.43	35
20:00	5.56	17	6.22	26	6.07	50
22:00	5.55	17	6.09	23	5.70	65
00:00	5.54	19	6.07	30	5.49	91
02:00	5.60	23	6.13	40	5.51	107
04:00	5.58	16	5.96	21	5.40	101
06:00	5.63	15	6.05	21	5.63	100
Mean	5.51	19	5.96	24	5.95	58

During the experiment, the animals were fed twice daily, at 8:00 AM and 2:00 PM. Protein nucleus and calcitic limestone were added to the feeders and thoroughly mixed with the base ingredient being tested. The voluntary dry matter intake (DMI) and bromatological constituents of diets were determined by calculating the difference between the amount of feed supplied and the leftovers. We calculated feed conversion by dividing the total DMI (kg) by the total LW gain (kg) for the entire experiment. Feed efficiency was determined by dividing the total LW gain (kg) by the total DMI (kg) over the whole experimental period.

We calculated the daily LW gain by subtracting the initial weight from the final weight and dividing the result by the number of days between weighings. The weighings were conducted after a 14-hour fast from solids and liquids. Body condition was assessed based on visual observation, using a scoring system ranging from 1 to 5, where 1=very thin, 2=thin, 3=intermediate, 4=fat, and 5=very fat. Body condition score changes were determined as the difference between the initial and final scores. The animals were sent to the slaughterhouse when they reached a suitable slaughter condition, identified by a visual body condition score of 3.5. The first steers from the mixture and white oat grain treatments were sent for slaughter after 92 days, while animals from the soybean hull treatment were sent after 109 days of the experiment.

Samples of the diet ingredients and feed leftovers were collected twice a week. These samples were homogenized for consistent sampling. They were then pre-dried in a forced-air oven at a temperature of 55°C for 72 hours. Afterward, the samples were ground in a “Willey” type mill with a 1 mm sieve and stored in plastic containers for subsequent chemical analysis.

We determined DM content by oven drying at 105°C until constant weight was achieved, and ash content was determined by incineration in a muffle furnace at 550°C until constant weight. Organic matter (OM) content was calculated by subtracting the ash value from the DM value. Total nitrogen (N) content was determined using the Kjeldahl method (AOAC 1995), modified to use a 4% weight/volume (w/v) boric acid solution as the receiver of free ammonia during distillation, a 0.2% w/v bromocresol green and 0.1% w/v methyl red solution as the indicator, and a standard sulfuric acid solution for titration.

Ether extract (EE) was measured by treating the samples with ether in a reflux system at 180°C for 2 hours. Contents of neutral detergent fiber (NDF) and acid detergent fiber (ADF), as well as acid detergent lignin (ADL), were determined according to Van Soest et al. (1991). Contents of soluble nitrogen (N), neutral detergent insoluble nitrogen (NDIN), and acid detergent insoluble nitrogen (ADIN) were determined following the methods described by Licitra et al. (1996).

Total digestible nutrient (TDN) was quantified according to the method described by Weiss et al. (1992). Digestible energy (DE) was calculated based on the NRC (2000) guidelines, where 1 kg of TDN equals 4.4 Mcal of DE, and metabolizable energy (ME) is calculated as 0.82 times the DE. In vitro organic matter degradability of ingredients was determined at the laboratory of the National Institute of Agricultural Technology (INTA) in Argentina.

Parallel to the main experiment, we collected rumen fluid from three steers in the white oat grain treatment group and two from each of the soybean hulls and mixture treatment groups. Minami et al. (2021) also used a similar number of experimental units to assess the effects of experimentally induced subacute ruminal acidosis. Prior to each collection, the animals were adapted to their diets for 15 days. Subsequently, ruminal fluid was collected using a 60 ml disposable syringe and a hand pump, through a Foley catheter, at 14 different times throughout the day (08:00, 09:00, 10:00, 12:00, 14:00, 15:00, 16:00, 18:00, 20:00, 22:00, 00:00, 02:00, 04:00, and 06:00). This process allowed us to gather data on hydrogen ion concentration (pH) and bacterial activity in the rumen. The pH of the ruminal fluid was determined immediately after collection using a digital potentiometer.

Bacterial activity was assessed by measuring the reduction of methylene blue, following the method described by Dirksen (1981). We transferred 19 mL of ruminal fluid, maintained at a temperature between 38 and 42°C, into a test tube. Then, we added 1 mL of 0.03% methylene blue solution to the tube and thoroughly mixed the sample. The reduction time was recorded using a timer, comparing the sample tube against a control tube containing 20 mL of ruminal fluid. The timer was started immediately after mixing the ruminal fluid with methylene blue, and the endpoint was noted when both tubes exhibited similar coloration.

We employed a randomized block design, considering the predominance of Charolais or Nellore breeds, with three treatments and a variable number of samples per treatment. This design comprised eleven animals during the adaptation period and, during the experimental phase, ten animals for the soybean hulls treatment and eleven animals for the white oat grain and mixture treatments. During the experimental period, one of the animals refused to eat and subsequently died.

The data analyzed from each experimental unit correspond to the means of the evaluations of each animal in the experimental period. We tested the variables for normality using the Shapiro-Wilk test. The data were then subjected to analysis of variance and F-test using PROC GLM. The means were compared using the “t” test at a significance level of 5%. The mathematical model of the analysis of variance corresponds to the general linear model:

$$Yij=\mu +\tau i+\beta j+(\tau i\ast \beta j)+\epsilon ij$$

Where: Yij represents the dependent variables, μ is the mean of all observations, τi corresponds to the treatment effect, βj corresponds to the breed predominance effect, τi * βj is the effect of the interaction between the treatment i and the breed predominance j (error a), and εij corresponds to the residual experimental error.

We also conducted Pearson’s correlation test using the PROC CORR procedure. The data were analyzed using the SAS (2001) statistical package.

The study was approved by the Committee on Ethics in the Use of Animals of UFSM (Protocol No. 066/2012).

RESULTS AND DISCUSSION

Adaptation period

During the adaptation period, the treatments influenced the steers’ daily dry matter intake (DMI) (P<0.05, Table III). Animals consuming a diet based on white oat grain showed lower intake compared to those in the mixture treatment (6.13 vs. 7.02 kg day^-1), while intake in the soybean hulls treatment was similar to that in the white oat grain and mixture treatments (P>0.05). The white oat grain treatment offers more energy due to its higher TDN (72.41%), resulting in higher intake per unit of weight by the steers and, consequently, a lower amount of dry matter (DM) required. With the increase in the proportion of concentrate during the adaptation period, there was an increase in TND consumption. According to Brown & Millen (2009), when the roughage ratio is between 40 and 60%, and subsequently changes to 91% concentrate during the adaptation period, DMI is reduced. Animals subjected to diets with a high percentage of concentrate typically exhibit limited consumption due to energy density rather than physical limitations, as is usually the case with diets containing a high percentage of roughage.

Table III
Body weights and initial and final scores, daily live weight gain, and dry matter consumption of steers fed diets with a high percentage of concentrate during the adaptation period.

Variables	Treatments			CV	P
	Soybean husk	Mixture	White oat grain
Intake of dry matter (kg day-1)	6.79ab	7.02a	6.13b	142.70	0.0319
Initial weight (kg)	266.00	271.63	271.54	11.50	0.8766
Final weight (kg)	271.86	275.77	280.59	11.02	0.7765
Daily live weight gain (kg)	0.202	0.142	0.312	11.85	0.4489
Initial body condition score, points	2.61	2.65	2.68	2.79	0.1398
Final body condition score, points	2.67	2.69	2.71	2.89	0.4444

• CV = Coefficient of Variation / P = Probability / Distinct letters in the line differ between each other (P<0.05).

During the adaptation period, the diets did not influence the initial and final weights (P>0.05). Similarly, the mean weight gain did not differ, with a mean value of 0.218 kg day^-1 (Table III). This relatively low performance is attributed to the changes occurring in the ruminal environment during the adaptation period. The increase in the amount of concentrate during adaptation leads to a higher proportion of rapidly fermentable carbohydrates, thereby reducing the proportion of fibrinolytic bacteria and promoting the rapid growth of amylolytic bacteria. According to Owens et al. (1998), diets containing a high proportion of starch increase the availability of free glucose, stimulating the growth of various bacteria, which, in turn, increases the production of volatile fatty acids (VFAs) and decreases ruminal pH (Table II). This pH reduction may lead to ruminal health issues such as subclinical acidosis, consequently affecting animal performance. Brown et al. (2006) reported problems in animals when the adaptation period is shorter than 14 days until the cattle begin to receive the definitive diet with 92 to 95% of the concentrate.

Experimental period

During the experimental period, we observed no difference (P>0.05) in DMI for steers fed exclusively concentrate diets (Table IV). The average values were expressed as follows: 7.42 kg day^-1, 2.23% of live weight (LW), and 95.50 g per unit of metabolic size. However, this similar DMI did not result in similar animal performance (P<0.05), although they presented similar initial weight (275.09 kg) and final weight (387.22 kg). These results stem from the non-isoenergetic nature of the diets (Table I). Consequently, the steers from the soybean hull treatment remained in confinement for 109 days, while those from the other treatments remained for 92 days. The animals from the mixture treatment exhibited a more significant weight gain than those from the soybean hull treatment (1.300 vs. 0.972 kg day^-1). However, both treatments were similar to the white oat grain treatment (1.203 kg day^-1). One of the main contributing factors to this result was the lack of physically effective fiber present in the soybean hull, which did not promote sufficient rumination and, therefore, the production of bicarbonate by saliva (Callegaro et al. 2020), known for its buffering properties. According to Mertens (1999), soybean hulls contain only 2% of physically effective fiber, making them inferior to ground corn, which contains 4.3%. Thus, cattle fed soybean hulls may exhibit lower rumination time and, consequently, produce less bicarbonate.

Table IV
Consumption of dry matter (DM), body weight and initial and final body condition scores, daily live weight gain, total body condition score gain, conversion, and feed efficiency (FC; FE) of finished steers exclusively fed concentrate.

Variable	Treatments			CV	P
	Soybean husk	Mixture	White oat grain
Cons. DM (kg day-1)	6.83	8.00	7.44	16.63	0.1223
Cons. DM (kg 100 kg-1 of LW)	2.12	2.38	2.21	12.90	0.1374
Cons. DM (g unit of metabolic size)	90.06	101.90	94.56	13.35	0.1215
Initial weight (kg)	269.16	275.63	280.5	11.02	0.7036
Final weight (kg)	375.22	395.30	391.15	9.71	0.4600
Daily live weight gain (kg)	0.972b	1.300a	1.203ab	23.02	0.0291
Initial body condition score (points)	2.67	2.69	2.72	2.89	0.3761
Final body condition score (points)	3.45	3.67	3.52	5.85	0.0666
Total body condition score gain (points)	0.77	0.98	0.80	23.05	0.0521
FC (kg DM kg-1 LW)	7.35	6.22	6.42	16.25	0.0650
Feed efficiency (kg LW kg-1 DM)	0.142	0.163	0.161	17.38	0.1686

• CV = Coefficient of variation / P = Probability / Distinct letters in the line differ between each other (P<0.05).

The aforementioned characteristic of the soybean hulls contributed to maintaining the ruminal pH below 5.7 during the 24 hours of ruminal fluid collection (Table II). According to Berchielli et al. (2011), a ruminal pH below 5.5 suggests subclinical ruminal acidosis, as animals may experience acute acidosis at a pH below 5.0. These authors suggested that the pH should be below 5.5 for one hour a day rather than below 5.8 for several hours, as a pH below 5.5 results in a small number of protozoa and a predominance of gram-positive bacteria that produce lactic acid. In diets with a higher concentrate proportion, the rumen hosts amylolytic bacteria, which thrive at a lower pH of around 5.8.

One factor that could have contributed to the higher weight gain of the steers in the mixture treatment compared to those in the soybean hull treatment is the fractioning of carbohydrates and proteins. The combination of soybean hulls and white oat grain likely optimized microbial growth efficiency by synchronizing the degradation of carbohydrates and proteins, thereby maximizing microbial performance and reducing losses in the rumen.

Given this, synchronization likely occurred between carbohydrates and protein in the rumen of these animals, providing both energy and protein to rumen microorganisms throughout the day. This synchronization occurred due to the different degradation rates of the ingredients (soybean hull and white oat grain) in the diet, resulting in similar performance among the animals from the white oat grain and mixture treatments. This theory is widely used to support the synchronism of fractions containing carbohydrates and proteins in feed (Mizubuti et al. 2014, Santo et al. 2017, Magalhães et al. 2021, Poveda-Parra et al. 2021).

According to the theory of metabolic feedback, cattle possess a capacity for maximum productivity in which nutrients can be used to meet their productive demands (Illius & Jessop 1996). When nutrients, particularly protein and energy, are absorbed in excess, or when the nutrient ratio is incorrect (energy in the case of the study), negative metabolic feedback impacts DMI (Nascimento et al. 2009). The energy balance is regulated by a metabolic product present in the bloodstream that interacts with receptors associated with the central nervous system. Consequently, when energy reserves (adipose tissue) increase, the satiety center in the hypothalamus is stimulated, leading to a reduction in food intake.

In this context, animals typically fed high-concentrate diets, as in our study, exhibit a lower DMI per unit of metabolic size compared to diets with roughage: concentrate, owing to the high energy density of high-concentrate diets. Similarly, DMI as a percentage of LW is lower for animals fed these diets.

Body condition scores also remained unchanged, as did the initial and final weights (Table IV). Notably, in this study, the final body condition score correlated positively with the final weight (r = 0.5947, P<0.003), indicating consistency in the assessments made by the evaluators.

Feed conversion and efficiency did not exhibit differences between treatments, with mean values of 6.66 kg of DM kg LW^-1 and 0.155 kg of LW kg DM^-1 (Table IV). It is worth noting that diets with 100% concentrate do not necessarily lead to higher production efficiency due to potential inadequacies in the ruminal environment.

The consumption of crude protein remained unaffected by the treatments (P>0.05), with a mean of 1.20 kg day^-1 and 0.364% of LW (Table V). This result was expected since the diets were isonitrogenous. Similarly, the daily intake of calcium was consistent across all treatments. However, phosphorus intake differed, with higher levels observed in the mixture and white oat grain treatments compared to the soybean hull treatment (23.24 vs. 14.62 g day^-1). This discrepancy in phosphorus intake may have arisen due to a numerically lower DMI (11.5%) observed in the animals treated with soybean hulls (P = 0.123).

Table V
Consumption of crude protein, calcium and phosphorus day, and of fibrous components (kg day^-1 and kg 100 kg^-1 of live weight) of the feed by finished steer fed exclusively concentrate.

Consumption	Treatments			CV	P
	Soybean husk	Mixture	White oat grain
Crude Protein (kg)	1.107	1.297	1.215	15.04	0.0769
Crude Protein (kg 100 kg-1 of LW)	0.346	0.386	0.361	22.25	0.0965
Calcium (g)	170.91	190.98	183.20	12.03	0.1331
Phosphorus (g)	14.62b	22.48a	24.00a	16.97	0.0001
Neutral detergent fiber (kg day-1)	4.09a	3.44b	1.99c	16.97	0.0001
Neutral detergent fiber (kg 100 kg-1 LW)	1.27a	1.02b	0.59c	13.47	0.0001
Acid detergent fiber (kg day-1)	2.49a	2.14b	1.08c	18.05	0.0001
Acid detergent fiber (kg 100 kg-1 LW)	0.77a	0.63b	0.32c	15.83	0.0001
Hemicellulose (kg dia-1)	1.60a	1.29b	0.91c	18.80	0.0001
Hemicellulose (kg 100 kg-1 LW)	0.501a	0.387b	0.270c	17.06	0.0001
Cellulose (kg dia-1)	2.16a	1.72b	0.60c	12.40	0.0001
Cellulose (kg 100 kg-1 LW)	0.673a	0.514b	0.177c	4.60	0.0001

• CV = Coefficient of variation / P = Probability / Distinct letters in the line differ from each other (P<0.05).

Due to the higher concentration of neutral detergent fiber in the diet containing soybean hulls (Table I) and the similar DMI observed across treatments (Table II), we noted that neutral detergent fiber intake (both in kg day^-1 and kg per 100 kg of LW) was elevated in the animals fed soybean hulls (Table V). This consumption was notably higher than that observed in the mixture and white oat grain treatments (P<0.05).

When the DMI of beef cattle is constrained by their physical capacity to eat, neutral detergent fiber consumption should ideally not exceed 12.7 g kg^-1 of LW (Resende et al. 1994, Faturi et al. 2006). Thus, none of the treatments in our study were limited by the fibrous component of the diet, with an average neutral detergent fiber consumption of 12.7, 10.2, and 5.9 g kg^-1 of LW for the steers receiving the soybean hull, mixture, and white oat grain treatments, respectively (P<0.05). However, Faturi et al. (2006) suggested that neutral detergent fiber consumption alone does not entirely explain DMI variations. They observed higher intake in cattle fed diets containing higher levels of neutral detergent fiber (48%), corresponding to 1.28% of LW for the starch diet and 1.25% for the soluble fiber diet. Conversely, the consumption of this fibrous fraction by animals fed starch and diets low in neutral detergent fiber (39.8%) was only 0.99% of LW. The upper or lower limits in the consumption of soluble fiber within the neutral detergent should be related to the quality of the fiber in the diets, as well as the characteristics of the animals (Faturi et al. 2006).

In diets high in concentrate and offered ad libitum, cattle may overeat, leading to a drop in ruminal pH. Consequently, intake decreases as pH levels drop. This reduction in consumption acts as an internal mechanism to limit excessive fermentation, allowing pH levels to return to normal. Once pH stabilizes, cattle resume eating more, leading to another cycle of excessive acid production (Schwartzkopf et al. 2003). As a result, DMI often oscillates in diets consisting solely of concentrate, with leftovers exceeding recommendations on some days and none on others.

The consumption of acid detergent fiber exhibited a similar pattern to that of neutral detergent fiber (P<0.05, Table V). The acid detergent fiber fraction in feed primarily comprises cellulose and lignin, along with variable amounts of ash and nitrogen compounds, representing the less soluble constituents of the cell wall. However, this fraction is negatively correlated with food digestibility.

Cell wall components, namely hemicellulose and cellulose, were consumed to a lesser extent (in terms of both kg day^-1 and % of LW) by the steers from the white oat grain treatment (Table V) while presenting intermediate consumption for the mixture treatment and higher consumption for the soybean hull treatment (P<0.05). These findings correlate with neutral detergent fiber intake, as hemicellulose and cellulose exhibited a significant positive correlation with neutral detergent fiber intake (P<0.0001). Hemicellulose and cellulose are constituents of fibrous carbohydrates, which occupy space in the digestive tract and require chewing for particle size reduction and passage through the digestive tract. Therefore, neutral detergent fiber holds similar nutritional significance as it represents the same carbohydrate fraction in feedstuffs (Berchielli et al. 2011).

Steers fed diets containing white oat grain exhibited higher intake values of ethereal extract (0.405 kg, 0.120% of LW, P<0.05), whereas those consuming the mixture showed intermediate values (0.274 kg, 0.081% of LW). Conversely, consumption was lower for steers receiving soybean hulls (0.102 kg, 0.032% of LW) (Table VI). Intake of ethereal extract and other bromatological components was computed based on the fraction’s composition in the diet, as DMI did not differ (Table III). Therefore, the lipid content in the diet influenced the observed result.

Table VI
Daily consumption (kg day^-1 and kg 100 kg^-1 of live weight) of ethereal extract (EE), total digestible nutrients (TDN), digestible (DE) and metabolizable energy (ME) of finished steers fed exclusively concentrate.

Consumption	Treatments			CV	P
	Soybean husk	Mixture	White oat grain
EE (kg day-1)	0.102c	0.274b	0.405a	16.07	0.0001
EE (kg 100 kg LW)	0.032c	0.081b	0.120a	10.71	0.0001
TDN (kg day-1)	4.59b	5.69a	5.97a	14.38	0.0012
TDN (kg 100 kg-1 LW)	1.42b	1.69a	1.77a	20.14	0.0003
DE (Mcal day-1)	20.19b	25.04a	26.28a	14.40	0.0012
DE (Mcal 100 kg-1 LW)	6.28b	7.46a	7.81a	20.17	0.0003
ME (Mcal day-1)	16.56b	20.53a	21.55a	14.40	0.0012
ME (Mcal 100 kg-1 LW)	5.15b	6.11a	6.40a	20.10	0.0001

• CV = Coefficient of variation / P = Probability / Distinct letters in the line differ between each other (P<0.05).

On the other hand, TDN intake (kg day^-1, % of LW) as well as digestible and ME (Mcal day^-1, Mcal 100 kg^-1 of LW) was comparable among steers receiving the white oat grain and mixture treatments (P>0.05), but higher than that of animals treated with soybean hulls (P<0.05). It also elucidates the similar weight gain observed in steers from the mixture and white oat grain treatments (Table III), while steers from the soybean hull treatment did not ingest sufficient nutrients to achieve the performance levels attained by their counterparts. This discrepancy is likely linked to the metabolic disturbance due to subclinical ruminal acidosis, which hindered nutrient intake.

CONCLUSIONS

Our research hypotheses regarding steers fed exclusively concentrate diets, being able to exhibit their performance normally, as well as demonstrating similar performance across the treatments studied, were partially confirmed. Specifically, this was observed in the white oat grain and the mixture of soybean hulls plus white oat grain treatments.

Hence, implementing exclusively concentrate diets is technically feasible for steers fed white oat grain and a mixture of soybean hull and white oat grain, supplemented with protein nucleus. This implementation does not compromise the animal performance and allows for a shorter confinement period compared to steers fed soybean hulls.

ACKNOWLEDGMENTS

The authors express their gratitude to the Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq) for providing the fellowship for the PhD student, as well as to the team at the Cattle Breeding Laboratory for their dedication and commitment to conducting this research.

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Publication Dates

• Publication in this collection
  25 Nov 2024
• Date of issue
  2024

History

• Received
  14 Mar 2024
• Accepted
  8 Sept 2024