Effects of dried distillers grains inclusion in supplements on intake, digestibility, metabolism, and performance of suckling beef calves on pasture

EdinaelRodrigues

Almeida1✉Emailedinaelr.a@gmail.comEmailjohnnatan.goncalves@ufv.brEmailjeanmarcelo97@hotmail.comEmailluannacoelhozoo@gmail.comEmailpatricia.leite@ufv.brEmaillilian.toma@ufv.brEmailjose.godinho@ufv.brEmaillaura.ricardo@ufv.brEmailjulia.vieira@ufv.brEmailclaudiabsampaio@ufv.brEmaildetmann@ufv.brEmaileritonvalente@yahoo.com.brEmailsidnei.lopes@ufv.br

1de ZootecniaUniversidade Federal de Viçosa36570-900ViçosaMG

2Brasil. ²Departamento de AgronomiaUniversidade Federal de Viçosa36570-900ViçosaMGBrasil

3Departamento de ZootecniaUniversidade Estadual do Oeste do Paraná85960-000ToledoBrasil

Edinael Rodrigues de Almeida (0000-0002-0160-0329)¹, Johnnatan Castro Cabral Gonçalves (0009-0008-9852-6540)¹, Jean Marcelo Albuquerque (0009-0004-3728-3240)¹, Luanna Carla Coelho (0009-0008-1468-1501)¹, Patrícia Siqueira Leite (0000-0002-5537-8831)¹, Lilian Yukie Pacheco Toma (0009-0003-5573-0473)¹, José Augusto Moura Godinho (0009-0003-9503-2733)¹, Laura Ferrarez Ricardo (0009-0007-8308-7015)¹, Julia Liliane Vieira (0009-0003-9043-9016)², Cláudia Batista Sampaio (0000-0002-7761-0232)¹, Edenio Detmann (0000-0001-5708-4987)¹, Ériton Egídio Lisboa Valente (0000-0001-6551-1790)³, Sidnei Antônio Lopes (0000-0002-0333-3797)¹.

¹Departamento de Zootecnia, Universidade Federal de Viçosa, Viçosa 36570-900, MG, Brasil. ²Departamento de Agronomia, Universidade Federal de Viçosa, Viçosa 36570-900, MG, Brasil. ³Departamento de Zootecnia, Universidade Estadual do Oeste do Paraná, Toledo, 85960-000, Brasil.

edinaelr.a@gmail.com, johnnatan.goncalves@ufv.br, jeanmarcelo97@hotmail.com, luannacoelhozoo@gmail.com, patricia.leite@ufv.br, lilian.toma@ufv.br, jose.godinho@ufv.br, laura.ricardo@ufv.br, julia.vieira@ufv.br, claudiabsampaio@ufv.br, detmann@ufv.br, eritonvalente@yahoo.com.br, sidnei.lopes@ufv.br.

Abstract

The supply of metabolizable nutrients to suckling beef calves on pasture can improve their performance, increasing weaning weight and productivity in cow–calf systems. The objective was to evaluate the effects of dried distillers grains (DDG) inclusion on intake, digestibility, metabolism, and performance of suckling beef calves grazing tropical pastures. Forty-eight Nellore calves, 120 ± 35 days of age and 135 ± 23.4 kg of body weight (BW), were used. Calves received one of the following treatments under a creep-feeding strategy: mineral mixture only, provided ad libitum (CONTROL); or concentrate supplementation (SUP, 6 g/kg BW, containing 225 g/kg crude protein) with 0% (SUP0), 48.4% (SUP48), or 96.8% (SUP96) DDG inclusion. Concentrate supplementation increased intake of dry matter (DM), crude protein (CP), non-fibrous carbohydrates (NFC), total digestible nutrients (TDN), and the CP/digestible organic matter ratio (P < 0.10). Digestibility of DM, CP, and NFC decreased linearly with increasing DDG inclusion. Serum glucose, insulin-like growth factor 1, and blood urea nitrogen concentrations were greater in calves receiving concentrate supplementation (P < 0.10). Concentrate supplementation increased average daily gain, weaning BW, and ribeye area (P < 0.10), with no differences related to DDG inclusion (P > 0.10). DDG can be included in supplements for suckling beef calves grazing tropical pastures, with potential to replace traditional feedstuffs such as corn and soybean meal, without negatively affecting weight gain.

Keywords:

animal development

metabolizable protein

tropical pastures

cow-calf beef systems

creep-feeding

Introduction

In intensive systems of beef cattle production, calf supplementation is essential to obtain heavier animals, thereby enabling early slaughter of males and early breeding of females (Paulino et al., 2012; Lima et al., 2016). During the first weeks of life of beef calves in tropical systems under balanced forage supply, maternal milk is the main nutrient source, being sufficient to meet nutritional requirements for optimized gains close to 1 kg/animal/day. However, as lactation progresses, milk production decreases while the calf’s nutritional requirements increase, making milk insufficient to sustain this target from the 12th–14th week onward (Lopes et al., 2023).

Previous studies have demonstrated that creep-feeding supplementation of suckling calves effectively increases body weight at weaning (Valente et al., 2013; Lopes et al., 2016; Carvalho et al., 2019), as nutrients derived from grains are more digestible than those from pasture, particularly for calves whose fermentative capacity is still developing. Nevertheless, the adoption of supplementation may lead to increased production costs, potentially limiting the implementation of this strategy, since the cost of feed ingredients is a critical factor in strategic decision-making. Therefore, the use of alternative feed ingredients may reduce supplementation costs and enhance the feasibility of its application in tropical beef production systems.

With the expansion of ethanol plants producing corn-based ethanol, the availability of dried distillers grains (DDG) have increased (Conab, 2024). DDG are rich in digestible fiber and protein, particularly the rumen-undegradable fraction (Buttrey et al., 2012). In addition to supplying nitrogen to ruminal microorganisms, supplementing grazing cattle with DDG is a strategy to increase the flow of amino acids to the intestine, thereby improving nitrogen use efficiency (Ferrari et al., 2021) and increasing metabolizable protein supply. Due to its nutritional value and relatively low cost, DDG has been widely used in Brazilian feedlot systems (Alhadas et al., 2023; Bremer et al., 2011; Depenbusch et al., 2009), primarily to replace feedstuffs with protein or energy profiles like traditional ingredients. However, there is a lack of studies evaluating its use in supplementation of grazing cattle, especially suckling calves.

Our hypothesis is that supplementation improves intake, digestibility, and metabolism and, consequently, increases weaning weight of suckling beef calves. Additionally, we hypothesize that DDG can be included in these supplements without impairing the performance and metabolism of these animals. Therefore, the objective of this study was to evaluate the effects of supplementation, as well as the inclusion of DDG in supplements-replacing soybean meal and corn while maintaining isoproteic content-on productive performance, metabolism, and nutritional characteristics of suckling beef calves grazing tropical pastures.

Material and methods

All procedures conducted during the experiment were approved by the Animal Ethics Committee for the Use of Production Animals at the Federal University of Viçosa, Brazil (CEUAP-UFV, protocol 011/2022). The study was carried out at the Beef Cattle Teaching, Research, and Extension Unit of the Department of Animal Science, Federal University of Viçosa, located in Viçosa, Minas Gerais, Brazil, from February to May 2023, covering both the rainy and the rainy-to-dry transition seasons.

A total of 48 suckling Nellore calves (30 males and 18 females), with an average age of 120 ± 35 days and an initial body weight (BW) of 135 ± 23.4 kg, born to multiparous cows (average 5 years of age and 480 kg BW), were used. Cow–calf pairs were randomly allocated to 12 paddocks of approximately 3.8 ha each, uniformly covered with Urochloa decumbens, and equipped with water troughs and covered feed bunks. Calves had restricted access to the feeding bunks through a creep-feeding system.

The experimental design was completely randomized, with four treatments, four replicates per treatment (experimental units), and 12 observational units per treatment, ensuring balanced distribution of male and female calves within each group. The treatments consisted of mineral mixture only, provided ad libitum (CONTROL); or concentrate supplementation (SUP) with 0% (SUP0), 48.4% (SUP48), or 96.8% (SUP96) DDG. Supplements were formulated to provide 6 g/kg BW, with 22.5% crude protein (CP), and were offered daily at 11:00 a.m. (Carvalho et al., 2019), with supplement allowance adjusted every 30 days according to intermediate BW measurements of the animals (Table 1).

Table 1
Composition of supplements (g/kg), based on natural matter.
Ingredient	Treatment
Ingredient	CONTROL	SUP0	SUP48	SUP96
g/kg
Ground Corn Grain	-	564	283	0
Soybean Meal	-	404	201	0
DDG	-	0	484	968
Pro-molasses	-	2	2	2
Mineral Mixture¹	1000	30	30	30

¹Percent composition: manganese sulfate 0.5; magnesium oxide 1.60; cobalt sulfate 0.05; copper sulfate 0.70; zinc sulfate 1.50; dicalcium phosphate 50.00; sodium selenite 0.09; potassium iodate 0.05; flower of sulfur 3.31 and sodium chloride 42.20.

The experimental period lasted 127 days, consisting of a 10-day adaptation phase to the supplements and paddocks, followed by 117 days of evaluation. During the adaptation phase, the dams were fed 100 g/animal/day of ground corn to stimulate bunk attendance and increase the time spent near the feed bunks, thereby promoting greater supplement intake by the calves. After this period, cows received only mineral mixture ad libitum.

Experimental procedures and sampling

For forage characterization, samples were collected every 30 days to determine dry matter (DM) and potentially digestible dry matter (pdDM) per hectare. Each paddock was sampled at five random points using pruning shears and 0.5 × 0.5 m metal frames. For qualitative evaluation of the pasture, samples were obtained every 15 days through hand-plucking to simulate grazing. After collecting, forage samples were weighed and dried in a forced-air oven at 55°C for 72 h and subsequently ground in Wiley-type knife mills using 1- and 2-mm mesh screens.

To evaluate intake and digestibility, a 9-day trial was conducted. Fecal excretion was estimated using the external marker chromium oxide (Cr₂O₃), provided in paper cartridges at a dose of 10 g/calf/day. The marker was administered to all 48 calves through a metal probe, directly into the esophagus, always at 10:00 a.m. Titanium dioxide (TiO₂) was used to estimate individual supplement intake, incorporated into the supplement and supplied at 10 g/calf/day. The first five days of the trial were allocated to animal adaptation to the markers. From the sixth day onward, fecal samples were collected at different times (06h00, 10h00, 14h00, and 18h00) to obtain representative samples from each animal (Sampaio et al., 2011). On the fifth day of the digestibility trial, a hand-plucked forage sample was collected from each paddock to evaluate the nutritive value of the forage consumed by the animals. Individual fecal samples (~ 200 g) were collected immediately after defecation, dried, and processed as described for forage samples. After grinding, a composite sample per animal was formed from the four collection days and used for chemical analyses. Indigestible neutral detergent fiber (iNDF) was used to estimate forage intake.

To estimate milk production of the dams, two collections were performed at 40 and 90 days after the start of the experiment. Calves were separated from their mothers at 16:00 h on the day before milk collection. At 18h00, calves were returned to their dams to allow suckling, aiming to completely empty the udder. Calves were then separated again at 19h00 and remained in a pen with access to water for a 12-hour period. The cows were allowed to graze in a nearby paddock, and on the following morning at 07h00, mechanical milking was performed after intravenous administration of 0.5 mL of oxytocin (10 IU/mL, Ocitovet®, Brazil) into the mammary vein. Daily milk yield for each cow was estimated as the production during the milking period (considering the time of calf separation and the time of milking) and adjusted to a 24-hour period Lopes et al. (2022).

For performance evaluation and determination of shrunk average daily gain (ADG), animals were weighed after a 14-hour solid feed fast at the beginning and end of the experiment. Additionally, body condition score (BCS) of the cows, on a scale from 1 to 9 NRC (1996), was assessed by five trained technicians at the start and end of the trial. Ribeye area (REA) and subcutaneous back fat thickness (SFT) were evaluated by ultrasound immediately after blood sampling. Ultrasound images were collected transversely across the Longissimus dorsi muscle between the 12th and 13th ribs and the rump. SFT was measured at the mid-distal portion of the Ribeye area (LSFT). Additional images were obtained at the P8 site, measured at the intersection between the Gluteus medius and Biceps femoris muscles, located between the ischial and ilial tuberosities, where rump fat thickness (RSFT) was assessed. Ultrasound images were collected using an Aloka ultrasound machine (model SSD 500V, Aloka Co., Ltd., Tokyo, Japan) with a 17.2-cm linear carcass transducer at 3.5 MHz, coupled with acoustic gel. Vegetable oil was applied as a coupling medium to ensure adequate contact between the probe and the animal’s body. Images for REA and SFT measurements were analyzed using BioSoft Toolbox® II for Beef (Biotronics Inc., Ames, Iowa, USA).

Chemical analysis

Forage, feces, and supplement samples were subjected to chemical analyses following the standard analytical procedures of the Brazilian National Institute of Science and Technology in Animal Science (INCT-CA) (Detmann et al., 2021). Samples ground to pass through a 1-mm sieve were analyzed for DM (INCT-CA method G-003/1), ash (INCT-CA method M-001/2), CP (INCT-CA method N-001/2), and ether extract (EE; INCT-CA method G-005/2). Neutral detergent fiber corrected for ash and protein (apNDF; INCT-CA method F-013/1) was determined using thermostable α-amylase without sodium sulfite, and insoluble protein in neutral detergent (NDIP; INCT-CA method N-004/2) was also quantified. iNDF of forage, feces, and supplement was estimated from samples ground to 2 mm and incubated in situ for 288 h using F57 bags (Ankom®) (INCT-CA method F-009/1). Additionally, fecal samples were analyzed for chromium (INCT-CA method M-005/2) and titanium (INCT-CA method M-007/2) contents. Organic matter (OM) was defined as 100 minus ash percentage.

Milk samples were analyzed for protein, fat, lactose, and total solids using infrared spectroscopy (Lactoscan SLP, Ultrasonic Milk Analyzer). Serum concentrations of total protein (biuret method, Bioclin® K031), albumin (bromocresol green method, Bioclin® K040), glucose (enzymatic colorimetric method, Bioclin® K082), and urea (enzymatic colorimetric method, Bioclin® K056) were quantified using an automated biochemical analyzer (Mindray BS200E, Shenzhen, China). Insulin-like growth factor type 1 (IGF-1) was measured using Siemens® kits (Berlin, Germany) on an automated chemiluminescence analyzer at a commercial laboratory. Globulins were calculated as the difference between total protein and albumin. Serum urea nitrogen (SUN) was estimated as 46.67% of the urea concentration.

Equations

Forage samples collected at ground level were used to estimate pdDM, according to the equation proposed by Paulino et al. (2008):

$\:pdDM=0.98\:x\:\left(100-\text{N}\text{D}\text{F}\right)+\:(\text{N}\text{D}\text{F}-\text{i}\text{N}\text{D}\text{F})$

where: pdDM = potentially digestible dry matter (%); 0.98 = true digestibility of intracellular content; NDF = neutral detergent fiber (%); iNDF = indigestible neutral detergent fiber.

Fecal dry matter excretion was estimated as the ratio between the amount of chromium oxide administered and its concentration in the feces. Individual supplement intake (ISI) was calculated using the following equation:

$\:ISI\:\left(g/day\right)=\frac{FExIFc}{IGs}\:x\:SupG$

where: ISI = individual supplement intake (g/day); FE = fecal excretion (g/day); IFc = indicator concentration in the animal’s feces (g/g); IGs = indicator provided in the supplement offered to the group (g/day); SupG = amount of supplement offered to the group of animals (g/day).

Individual forage dry matter intake (IFDMI) was estimated using the internal marker iNDF according to the equation proposed by Detmann et al. (2001):

$\:IFDMI=\frac{[\left(FE\:x\:iNDFfeces\right)-SDMI\:x\:iNDFsup]}{iNDFforage}\:$

where: IFDMI = individual forage dry matter intake (kg/day); FE = fecal excretion (kg/day); iNDFfeces = concentration of iNDF in the feces (kg/kg); SDMI = supplement dry matter intake (kg/day); iNDFsup = concentration of iNDF in the supplement (kg/kg); and iNDFforage = concentration of iNDF in the forage (kg/kg). Total dry matter intake (TDMI) was calculated as the sum of forage and supplement intake.

Statistical analysis

The experiment was conducted using a completely randomized design with four treatments and four experimental units per treatment (i.e., group of animals/paddock). Data was analyzed according to the following model:

$\:Y\:ijkl=\:\mu\:+Ti+G\left(i\right)j+Sk+\:\epsilon\:ijkl$

Where: Y_ijkl = observation recorded on the animal l, of sex k, belonging to the group j and submitted to treatment i; µ = overall mean; T_i = effect of treatment i (fixed); G_(i)j = effect of animal group j nested within treatment i (random); S_{k =} effect of calf sex k (fixed); and ε_ijkl = random error, unobservable and assumed to be NIID (0, σ_ɛ²).

Treatment sum of squares was further decomposed into orthogonal contrasts to evaluate the overall effect of supplementation (CONTROL vs. SUP) and the linear and quadratic effects of DDG inclusion in the supplement. All statistical analyses were performed using the MIXED procedure of the Statistical Analysis System (SAS, version 9.4), with a significance level of α = 0.10.

Results

The average availability of DM and pdDM during the experimental period was 2.85 and 1.96 t/ha, respectively, which resulted in an average availability of 174 g/kg and 117 g/kg BW (Fig. 1). The forage collected through simulated grazing had an average CP content of 75.7 g/kg DM (Table 2).

Fig. 1

- Average over the months of dry matter (DM) availability, potentially digestible dry matter (pdDM) in kg/ha and crude protein in g/kg in DM.

Table 2
Chemical composition of supplements and Urochloa decumbens throughout the experiment.
Item	Supplement			Months¹
Item	SUP0	SUP48	SUP96	February	March	April	May
g/kg DM
DM	891	904	913	281 ± 2.7	319 ± 19.5	324 ± 16.4	269 ± 28.6
OM	41.0	40.4	43.0	907 ± 4.2	908 ± 3.7	905 ± 4.5	904 ± 4.0
CP	224	224	224	66,7 ± 6.6	69,6 ± 10.6	85,7 ± 6.1	80,9 ± 15.3
EE	43.2	42.5	43.6	13,5 ± 0.2	13,5 ± 0.3	13,4 ± 0.7	14,0 ± 0.8
apNDF	147	333	537	658 ± 0.7	662 ± 1.1	648 ± 6.7	611 ± 8.8
NFC	510	341	146	169 ± 4.9	163 ± 11.1	158 ± 7.8	198 ± 12.8
iNDF	43.4	64.4	80.8	226 ± 1.1	275 ± 2.5	272 ± 15.9	303 ± 72.0
g/kg in CP
NDIP	27.6	52.3	74.3	122 ± 12.2	171 ± 22.7	167 ± 18.7	184 ± 33.0

DM = dry matter; OM = organic matter; CP = crude protein; EE = ether extract; apNDF = neutral detergent fiber corrected for ash and protein; NFC = non-fibrous carbohydrate; iNDF = indigestible neutral detergent fiber; NDIP = neutral detergent insoluble protein. ¹Mean ± standard deviation of the mean (samples collected manually during the study).

Milk production and composition of the cows were not affected by calf supplementation (P > 0.10). On average, milk production was 6.3 kg/day (Table 3). This reflected the absence of a supplementation effect on milk dry matter intake by calves (P = 0.12) (Table 4).

Table 3
Effect of supplementation and inclusion of distiller's grains in calf supplements on milk production and composition of Nellore cows. Milk production; FCM = 4% fat-corrected milk yield; ¹CONTROL: not supplemented, SUP supplemented with 0%, 48.4%, or 96.8% DDG inclusion in the supplement; ²SEM: Standard error of the mean. ³ CONTROL × SUP, contrast between supplemented and non-supplemented calves. L and Q = linear and quadratic effects of treatments. Significative when P < 0.10.
Item	Treatment ¹
Item	CONTROL	SUP0	SUP48	SUP96	SEM²	CONTROL × SUP	L	Q
kg/day
Milk	6.01	6.48	6.27	6.52	0.386	0.38	0.93	0.63
FCM	7.02	7.55	7.59	7.34	0.390	0.32	0.71	0.77
g/kg
Protein	33.4	33.4	33.2	34.0	0.286	0.60	0.16	0.23
Fat	52.9	51.1	54.2	49.3	1.91	0.56	0.52	0.12
Lactose	50.1	50.1	49.9	51.1	0.423	0.60	0.16	0.22
Total solids	146	143	146	143	1.67	0.54	0.90	0.16

Table 4
Effects of supplementation and inclusion of distillers' dried grains on voluntary intake of suckling calves on tropical pasture.
Item	Treatment ¹					P value³
Item	CONTROL	SUP0	SUP48	SUP96	SEM²	CONTROL × SUP	L	Q
kg/day
DM	2.41	3.31	3.13	2.96	0.101	< 0.001	0.043	0.99
DMF	1.47	1.23	1.11	0.94	0.141	0.051	0.19	0.88
DMS	-	1.13	1.02	1.01	0.102	-	0.45	0.72
DMM	0.88	0.98	0.96	0.99	0.047	0.12	0.85	0.69
OM	2.22	3.07	2.91	2.75	0.091	< 0.001	0.042	0.97
CP	0.35	0.56	0.54	0.54	0.008	< 0.001	0.15	0.85
EE	0.34	0.40	0.41	0.40	0.022	0.036	0.94	0.69
apNDF	0.94	0.96	1.06	1.15	0.076	0.22	0.11	0.95
NFC	0.25	0.80	0.53	0.30	0.040	< 0.001	< 0.001	0.74
iNDF	0.48	0.44	0.43	0.39	0.021	0.036	0.17	0.58
dOM	1.35	2.18	1.96	1.80	0.100	< 0.001	0.032	0.84
TDN	1.38	2.26	2.07	1.88	0.112	< 0.001	0.043	0.97
g/kg
CP/dOM	254	265	282	301	11.4	0.062	0.054	0.94

DM = dry matter; DMF = forage dry matter; DMS: supplement dry matter; DMM: milk dry matter; OM = organic matter; CP = crude protein; EE = ether extract; apNDF = neutral detergent fiber corrected for ash and protein; NFC = non-fibrous carbohydrate; iNDF = indigestible neutral detergent fiber; dOM: digestible organic matter; TDN: total digestible nutrients; CP/dOM: crude protein to digestible organic matter ratio; ¹CONTROL: unsupplemented – or SUP: supplemented with 0%, 48.4%, or 96.8% DDG inclusion in the supplement; ²SEM: Standard error of the mean. ³ CONTROL × SUP, contrast between supplemented and non-supplemented calves. L and Q = linear and quadratic effects of treatments. Significative when P < 0.10.

Supplementation increased total DM, OM, CP (P < 0.001), EE (P = 0.036), and the crude protein/digestible organic matter (PB/dOM) ratio (P = 0.062) intake. On the other hand, IFDMI was higher for CONTROL animals (P = 0.051). There was no effect of supplementation on apNDF intake (P = 0.22) (Table 4). Supplementation linearly increased (P < 0.001) NFC intake. However, a decrease in NFC (P < 0.001) and iNDF intake (P = 0.036) was observed with the increasing inclusion of DDG in the supplement.

SUP calves had greater dOM and TDN intake (P < 0.001). However, among supplemented animals, a negative linear effect was observed for dOM (P = 0.032) and TDN (P = 0.043) with the inclusion of DDG in the supplement. Also, SUP increased digestibility of DM, OM, CP, NFC, TDN, and dOM (P < 0.10). However, among SUP animals, a reduction in digestibility of DM, OM, CP, NFC, and dOM was observed with the inclusion of DDG in the supplement (Table 5).

Table 5
Effects of supplementation and inclusion of distillers dried grains on the digestibility of suckling calves on tropical pasture.
Item	Treatment ¹					P value³
Item	CONTROL	SUP0	SUP48	SUP96	SEM²	CONTROL × SUP	L	Q
g/g
DM	0.557	0.675	0.634	0.614	0.016	0.002	0.035	0.60
OM	0.603	0.707	0.673	0.652	0.018	0.007	0.067	0.78
CP	0.634	0.737	0.688	0.672	0.023	0.046	0.094	0.58
EE	0.820	0.854	0.861	0.846	0.016	0.107	0.73	0.60
apNDF	0.407	0.437	0.443	0.462	0.053	0.53	0.74	0.92
NFC	0.437	0.799	0.745	0.656	0.029	< 0.001	0.010	0.64
g/kg MS
dOM	556	656	625	607	16.1	0.004	0.067	0.74
TDN	570	682	660	634	22.0	0.008	0.15	0.93

DM = dry matter; OM = organic matter; CP = crude protein; EE = ether extract; apNDF = neutral detergent fiber corrected for ash and protein; NFC = non-fibrous carbohydrate; dOM: digestible organic matter; TDN: total digestible nutrients; ¹CONTROL: not supplemented - or SUP: supplemented with 0%, 48.4%, or 96.8% inclusion of DDG in the supplement; ²SEM: Standard error of the mean. ³ CONTROL × SUP, contrast between supplemented and non-supplemented calves. L and Q = linear and quadratic effects of treatments. Significative when P < 0.10.

Calves SUP had higher blood concentrations of IGF-1 (P = 0.010), glucose (P = 0.048), and SUN (P < 0.001). Albumin showed a quadratic effect (P = 0.061), and Globulins showed a positive linear effect (P = 0.067) with increasing DDG inclusion in the supplement (Table 6).

Supplementation increased (P < 0.001) weaning body weight (WBW), ADG, REA, and LSFT of calves (P = 0.075). A quadratic effect of supplementation was observed for RSFT (P = 0.014), but not for other performance variables related to calves (WBW, ADG, REA, LSFT) (Table 7). The BCS of the cows was not influenced by treatments (P > 0.10) (Table 7).

Table 6
Effects of supplementation and inclusion of dried distiller's grains on the metabolic profile of suckling calves. ¹Insulin-like Growth Factor 1 and Serum urea nitrogen; ²CONTROL: not supplemented - or SUP: supplemented with 0%, 48.4%, or 96.8% DDG inclusion in the supplement; ³SEM: Standard error of the mean. ⁴CONTROL × SUP, contrast between supplemented and non-supplemented calves. L and Q = linear and quadratic effects of treatments. Significative when P < 0.10.
Item¹	Treatment ²					P value⁴
Item¹	CONTROL	SUP0	SUP48	SUP96	SEM³	CONTROL × SUP	L	Q
Total Proteins, g/dL	5.43	5.36	5.63	5.69	0.146	0.45	0.15	0.57
Albumin, g/dL	2.92	2.91	3.11	2.98	0.063	0.28	0.48	0.061
Globulins, g/dL	2.48	2.46	2.50	2.74	0.092	0.45	0.067	0.37
Glucose, mg/dL	78.4	83.9	86.3	83.3	2.261	0.048	0.86	0.36
IGF-1, ng/mL	275	363	377	339	21.99	0.010	0.46	0.35
SUN, mg/dL	7.99	12.2	12.8	11.1	0.667	< 0.001	0.25	0.18

Table 7
Effects of supplementation and inclusion of distillers dried grains on the performance of suckling calves and cows on tropical pasture.
Item¹	Treatment ²					P value⁴
Item¹	CONTROL	SUP0	SUP48	SUP96	SEM³	CONTROL × SUP	L	Q
BCS	5.20	5.38	5.30	5.26	0.172	0.59	0.63	0.93
WBW, kg	223	251	246	242	3.985	< 0.001	0.17	0.83
ADG, kg	0.75	0.99	0.94	0.91	0.034	< 0.001	0.18	0.83
REA, cm²	39.8	44.2	46.4	46.1	1.010	< 0.001	0.24	0.35
RSFT, mm	2.28	2.41	2.92	2.31	0.144	0.14	0.64	0.014
LSFT, mm	2.83	3.57	3.60	3.05	0.243	0.075	0.18	0.36

¹BCS: final cow body condition score; WBW: calf weaning weight; ADG: average daily gain of calves; REA: calf ribeye area; RSFT: calf subcutaneous fat thickness at the rump; LSFT: calf loin subcutaneous fat thickness. ²CONTROL: not supplemented - or SUP: supplemented with 0%, 48.4%, or 96.8% DDG inclusion in the supplement. ³SEM: standard error of the mean. ⁴CONTROL × SUP: contrast between supplemented and non-supplemented calves. L and Q: linear and quadratic effects of treatments. Significant when P < 0.10.

Discussion

The average availability of pdDM was 117 g/kg BW, a value above the recommended Paulino et al. (2008), demonstrating that forage availability was not limiting during the study, allowing animals to exercise selective grazing. Additionally, the average content of 75.7 g CP/kg DM was close to the minimum recommended value of 80 g CP/kg DM for ruminal microorganisms to optimize the use of low-quality fiber (Lazzarini et al., 2009; Detmann et al., 2010). Under these circumstances, supplementation increased nutrient supply, mainly rumen protein, optimizing forage utilization and the availability of metabolizable nutrients for continuous animal growth.

Supplemented calves had greater total DM intake but lower forage intake. This may be associated with the carbohydrate effect, which leads to the substitution of forage intake by concentrate (Carvalho et al., 2019, Almeida et al., 2018, Lopes et al., 2016, Souza et al., 2010). In this condition, the use of non-fibrous carbohydrates as an energy substrate in the ruminal environment becomes preferential for non-fibrolytic microorganisms (Costa et al., 2009). Fibrolytic species have a slower growth rate and tend to be less competitive when compared to non-fibrolytic species (Detmann et al., 2024). Regarding milk intake, the similar consumption between SUP and CONTROL animals indicates the calf’s preference, as it does not replace milk intake with other feed sources. Therefore, calf supplementation with grains does not alter suckling behavior and, consequently, cow milk production, corroborating other studies Lopes et al. (2016).

The linear reduction in NFC intake, as DDG inclusion levels increased in the supplement, may have been caused by the variation in supplement composition, which showed a decrease in NFC levels as DDG was included, since DDG has a low NFC content because starch is removed during ethanol production (Adams et al., 2022). Despite the similarity in NDF intake between SUP and CONTROL calves, CONTROL animals had higher iNDF intake. Distillers dried grains contain large amounts of NDF, but with low lignin content, making them sources of potentially digestible fiber (Schingoethe, 2006). The higher iNDF intake by CONTROL calves simply indicates higher forage intake, which has a higher concentration of iNDF in its composition.

The CP/dOM ratio indicates the protein-energy balance of the diet (Detmann et al., 2014), which is necessary for ruminants to optimize productive processes on pasture. Maximum pasture intake is observed when the CP/dOM ratio is approximately 216 g/kg Reis et al. (2016). Thus, maximum fiber utilization occurred for SUP and CONTROL animals, since the CP/dOM ratio was above 216 g/kg DM in both treatments.

The higher digestibility of DM, OM, CP, and NFC in SUP calves was the result of the higher concentration of easily fermentable and digestible components present in the grains (Almeida et al., 2018). Thus, the better nutritional value of the SUP calves’ diet led to greater intake of digestible components, increasing TDN and dOM intake. On the other hand, supplementation did not improve NDF digestibility, which may be related to the higher presence of non-fibrolytic microbiota compared to fibrolytic, potentially impacting fiber digestibility negatively (Detmann et al., 2024).

Due to the higher energy intake in SUP calves, higher glucose levels were reflected in the serum of these animals. IGF-1, in turn, is an endocrine regulator of muscle growth in cattle, acting on glucose and amino acid metabolism (Santos, 2014) and having a strong correlation with nutritional status. Due to the higher nutritional supply in SUP animals, confirmed by higher glucose levels, IGF-1 levels were also higher in these calves. Additionally, SUN was higher in SUP calves compared to CONTROL, which occurred due to the greater protein, and consequently nitrogen, availability in the rumen of these animals. Other studies corroborate our findings, confirming that SUN is considered a sensitive marker of protein balance in ruminant diets, including suckling calves Batista et al. (2016) e Moreira (2022).

SUP calves performed better compared to CONTROL. On average, supplementation provided an additional 200 g/day of weight gain, resulting in 23.3 kg more body weight at weaning. As demonstrated by our results, supplementation for suckling calves improves nutrient intake and digestibility. Consequently, it also increases the supply of metabolizable protein and energy, allowing greater deposition of muscle and adipose tissue by the animal, directly impacting performance (Valente et al., 2014, Valente et al., 2012). Thus, in our study, SUP calves also showed greater REA and LSFT.

Supplementation improves intake, nutrient digestibility, and metabolism of suckling beef calves under tropical conditions, leading to better performance during the cow-calf phase and higher weaning weight. Additionally, when economically feasible, DDG can be used as an alternative feed option for these animals, replacing traditional ingredients such as corn meal and soybean meal, without negatively affecting weight gain of suckling beef calves on tropical pastures.

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Declarations

and Assertions:

Financing.

We would like to thank the Coordination for the Improvement of Higher Education Personnel (CAPES) - Financing Code 001, for the financial support.

Conflict of interest

The authors declare that they have no conflicts of interest.

Author Contributions

“Edinael Rodrigues de Almeida (Conceptualization, Investigation, Visualization, Supervision, Writing – original draft and corresponding author)”, Johnnatan Castro Cabral Gonçalves, Jean Marcelo Albuquerque, Luanna Carla Coelho, Patrícia Siqueira Leite, Lilian Yukie Pacheco Toma, José Augusto Moura Godinho, Laura Ferrarez Ricardo, Julia Liliane Vieira (Writing – review & editing), Cláudia Batista Sampaio (Data curation, Methodology, Validation, Writing – review & editing), Edenio Detmann (Formal analysis, Methodology, Validation, and Writing – review & editing), Ériton Lisboa Valente (Data curation, Methodology, Validation, Writing – review & editing), Sidnei Antônio Lopes (Conceptualization, Data curation, Methodology, Project administration, Resources, Supervision, Validation, Visualization, Writing – review & editing).

Data availability:

The datasets generated and/or analyzed during the current study are available from the manuscript and also from the corresponding author upon reasonable request.