1. Introduction
The finishing of cattle in feedlot or pasture is a strategy that allows intensive meat production through the exploitation of maximum biological efficiency, combined with the rapid deposition of muscle and fat tissue, which determine greater system productivity [
1]. The finishing system, however, can be compromised by the inadequate nutrition of the animal in the growth phase, since the type and quality of the diet determine the supply of the animal’s requirements, which directly reflects on the performance and carcass quality [
2]. Furthermore, the proportion of tissues in the carcass represents the most important aspect of animal composition, as it determines a large part of its economic value and influences the efficiency and cost of meat production [
3]. Non edible byproducts from human feed are desirable to replace conventional sources of animal supplements to improve the sustainability of beef cattle production in tropical regions while maintaining productivity.
The diet quality also plays an essential role during the finishing phase in both systems, pasture or feedlot, as it determines the gains obtained by the animals. During the dry season, tropical grasses have low crude protein, higher fiber content and low forage allowance due to the seasonality of production, not providing the nutritional requirements to the animals [
4]. In feedlot there is no such limitation, since feed is offered in quantity and quality according to the purpose of gain. In both systems, the productive response of animals occurs due to the intake, digestibility and metabolism of nutrients directly influenced by the type and quality of the ingredients used [
5].
The use of less costly products that are not consumed by humans in animal feed has gained increasing attention in the context of sustainable production [
6]. Cottonseed meal is a by-product of the oil industry and relatively rich sources of protein (30% to 50%) and amino acids [
7]. Traditionally, it is used as a protein source in the ruminant nutrition as they tolerate well the presence of gossypol in the diet [
8].
Alternatively, the dried distiller’s grains (DDG), a by-product of the ethanol production from corn or sorghum, stands out for being efficient in the nutrition of ruminants, meeting both the energy and protein demands of the diets, when the cattle are kept in the pasture or feedlot [
9]. Although DDG are corn substitutes, the inclusion of this by-product is limited by seasonal availability and by negative impacts of excess N and sulfuric acid, which can affect animal performance, carcass quality and the environment [
10].
In Brazil, most of the industries produce DDG without solubles, resulting in the dry grind processing of corn for ethanol production. The use of DDG can improve ruminal health due to its highly fermentable fiber, and low starch content, reducing the acidosis risk occurrence of cattle finished in feedlot with high proportion of grains [
11]. DDG, moreover, consists of a source of minerals and has a high value of non-degradable protein, increasing the metabolizable protein supply [
12]. However, although DDG have been used in temperate regions in
Bos taurus animals’ diet, mainly in feedlots [
10], there are few studies providing information about use of this by-product in tropical regions and comparing finishing systems in feedlot or pasture.
The study aimed to evaluate the efficiency of replacing cottonseed meal by DDG on intake, digestibility, daily weight gain, carcass gain and yield of Nellore cattle finished in pasture or feedlot. We hypothesized that DDG can replace cottonseed meal without compromises the productivity in both finishing systems (pasture or feedlot).
2. Materials and Methods
2.1. Location and Experimental Area
The study was conducted during the animal finishing phase, at the Forage and Grasslands sector of the Sao Paulo State University “Julio de Mesquita Filho” (FCAV/UNESP), Jaboticabal, SP, located at 21º15′22′′ South, 48º18′58″ West, at 595 m of altitude, climate is subtropical of the AW type according to the Köppen classification, characterized by warmer and rainfall summer, and dry winters.
Climate data was daily determined by the Department of Exact Sciences of FCAV/UNESP. During the experiment period, from April to August/2016, average of temperature was 20.6 °C, with a minimum of 12.6 °C and a maximum of 31.0 °C, and the average precipitation was 93 mm, totalizing 28 rainy days.
This experiment was conducted during the dry season, in which animals that came from the post weaning phase in pasture were finished in two different systems: pasture or conventional feedlot.
The finishing phase experiment was conducted after the post weaning phase in order to evaluate the nutritional history of Nellore bulls raised in pastures of
Urochloa brizantha (Hochst ex A. Rich) Stapf cv Marandu (Marandu grass). During the post weaning phase, pastures of Marandu grass were managed at 25 cm height in continuous grazing and variable stocking rate, using put and take stocking technique [
13].
Animals from the pasture finishing system were kept in the original paddock to minimize possible environment and stress effects and were adapted to finishing diet for 18 days, increasing 0.3% to 0.3% BW of the supplement amount until established its intake. After adaptation period, supplement was offered ad libitum once a day and a leftover of 3% to 5% was allowed.
At the beginning of the experiment, all animals were submitted to the control of endo and ectoparasites, using albendazole sulfoxide as vermifuge and fluazuron pour-on for cattle tick control. The experimental period was 117 days, from May to July 2016, with the first 18 days of adaptation to the diets, and three evaluation periods of 33 days each, for the pasture and feedlot systems.
All animals were submitted to three treatments in a completely randomized design in a 2 × 3 factorial arrangement, with two production systems (pasture versus feedlot) and three supplements: CM, conventional supplement with corn as an energy source and cottonseed meal (CM) as a protein source; 50DDG, supplement with replacement of 50% of the CM protein source by DDG; and 100DDG, supplement with 100% replacement of the CM protein source by DDG. The inclusion of corn DGG was determined on crude protein basis and its chemical composition is presented in
Table 1.
2.2. Feedlot System
In the feedlot system, the effect of replacing cottonseed meals was studied using 3 pens per treatment, which was considered the experimental unit. Animals were allocated in collective pens of 60 m
2, with concrete floor, and covered feeder area, totalizing 4 animals/pen. We used 36 Nellore bulls (
Bos indicus), with an average of initial body weight (BW) of 409 ± 40 kg, distributed in three treatments (
Table 2), receiving a diet with roughage:concentrate (R:C) ratio of 30:70 respectively, with corn silage being the source of roughage.
The diets were formulated for a gain of 1.5 kg/d, according to NRC [
14]. The adaptation of the animals in the feedlot followed a stair-step protocol with variation in the R:C ratio, being five days with 65:35, five days with 50:50, five days with 40:60, and three days with 30:70, totaling 18 days of adaptation. Final diet was 30:70 of R:C and was offered ad libitum at 6 am and 3 pm. In the morning, leftovers were removed and weighted in order to adjust the quantity to allow daily leftovers of 3% to 5%.
In the feedlot system, feed intake was measured daily in each pen composed of 4 bulls by determining the difference between what was supplied and what was left over. In each experimental period, samples of leftovers were collected during 5 days, and later a composite sample was made for chemical analysis.
2.3. Pasture System
In the pasture system, the effect of replacing cottonseed meals was assed using 3 paddocks per treatment. The experimental area for evaluation of grazing animals was formed with
Urochloa brizantha cv. Marandu (palisade grass), divided in 9 experimental paddocks, being three of 0.7 ha (3 animals) and six of 1.3 ha (4 animals). The stocking rate was kept the same (2.5 animal unit/ha; animal unit = 450 kg of BW) in all paddocks using additional animals, according to put and take stocking technique [
13], in a continuous stocking system.
In this system, 33 Nellore bulls were used, with average of initial BW of 407 ± 33 kg and 24 months of age. Animals were distributed in three treatments (
Table 3), receiving forage ad libitum and supplementation of 1.5% BW at 8 am, in open trough, with at least 0.5 linear meters per animal.
Animals adaptation to the supplement followed a stair-step protocol, changing the amount of concentrate, which the first five days was 0.7% BW, five days with 1% BW, five days with 1.3% BW and three days with 1.5% BW, totaling 18 days of adaptation.
2.4. Forage Samples, Leftovers and Roughage from Pasture Finishing System
Forage mass was measured every 28 days; 80 points of height of palisade grass were taken randomly in the paddock with the aid of a graduated ruler [
15]. From the average height, three representative samples of grass per paddock were collected, by cutting 5 cm from the soil of all forage contained in a 0.25 m
2 metallic frame [
15].
The samples were initially weighed, then sub-sampled in 2 parts, one for determining the pasture morphological composition, manually separated into senescent material (leaf and stem), green stem (leaf sheath and stem) and green leaf blades, and one for green leaves to estimate of total dry matter (TDM, kg MS/ha) availability of forage from each paddock. The samples were dried in an oven with air circulation at 55 °C for 72 h and weighed.
Weekly composed samples of leftovers and roughage at the end of feedlot were taken to a forced ventilation oven at 55 °C for 72 h and then ground in a Wiley mill, with a 2 mm sieve, for sample removal for incubation and determination of indigestible neutral detergent fiber (iNDF) [
16], and then ground to 1 mm for chemical composition analyses. The concentrate ingredients were sampled once in each experimental period, being stored in a freezer (−20 °C) for further laboratory analysis.
2.5. Analysis of Feed Samples, Leftovers and Feces
The feed, leftover and feces samples were quantified in terms of dry matter (DM, method 934.01), organic matter (OM, method 942.05), and ether extract (EE, method 954.02), according to [
16]. Crude protein (CP) was obtained by thermal conductivity using the Leco
® equipment (model FP-528, Leco Corporation, St. Joseph, MI, USA). The neutral detergent fiber (NDF) and acid detergent fiber (ADF) evaluations were performed on the Ankom
® 2000 (Ankom Technologies, Macedon, NY, USA). The NDF of the concentrates, treated with thermostable amylase, the NDF, ADF, NDF corrected for ash and protein (NDFap), lignin (H
2SO
4 72%), neutral detergent insoluble nitrogen (NDIN) and acid detergent insoluble nitrogen (ADIN) of forage were analyzed according to AOAC methodologies [
17].
Non-fibrous carbohydrates (NFC) were determined according to [
18].
2.6. Nutrients Intake and Digestibility in Pasture System
To estimate fecal production, we used chromium oxide (Cr
2O
3) as an external marker, the usual inert marker in research in Brazil and approved by local and national Ethics Committee on the Use of Animals. For this assay, 10 g/animal/d was provided at 9 am for 10 days via the esophagus with the aid of an applicator. The first 7 days were used for adaptation and the last 3 for collection of feces [
19], which were collected at 7 am and 1 pm; 9 am and 3 pm; and 11 am and 5 pm, respectively, immediately after spontaneous defecation. For this evaluation, eighteen animals were used (BW = 500 kg), with 6/treatment and 2/paddock.
Fecal recovery of Cr
2O
3 was determined following the methodology of atomic absorption spectrophotometry [
20]. From these data, fecal excretion (FE) was determined through the equation below [
21] (Equation (1)):
Concomitantly to the feces collection, simulated grazing collections were performed by the hand plucking method [
22] to evaluate the chemical composition of the forage consumed by the animals.
Forage intake was estimated based on fecal production data and iNDF as an internal marker. A sample composed of feces was made based on the dry weight in air, per animal, of the three days of collection, identified and subsequently analyzed for chromium contents, by atomic absorption spectrophotometry [
23], and quantity of nutrients as previously described.
The individual intake of the supplements was estimated according to the average supply of supplements for each animal in the paddock (1.5% BW).
From the intake of nutrients by forage and supplements and their excretion in feces, the total apparent digestibility was calculated through the calculation: DDM = (TDMI − FE)/TDMI where, DDM = total apparent digestibility of dry matter (%); TDMI = total dry matter intake (kg/d); FE = fecal excretion (kg/d).
The intake of total dry matter (TDMI), organic matter (OMI), crude protein (CPI), neutral detergent fiber (NDFI), indigestible neutral detergent fiber (iNDFI), non-fibrous carbohydrates (NFCI) and ether extract (EEI) were determined. Likewise, the digestibility values of total dry matter (TDMD), organic matter (OMD), crude protein (CPD), neutral detergent fiber (NDFD), non-fibrous carbohydrates (NFCD) and ether extract (EED) were determined.
2.7. Nutrients Intake and Digestibility in Feedlot System
The intake of animals from the feedlot was measured daily by the difference between the supply and the leftovers of each pen. The diet and orts of each pen were sampled weekly, making a composite sample at the end of the experimental period. The samples were dried in an oven at 55 °C for 72 h and then ground in a Wiley mill (Wiley Mill, Thomas Scientific, Swedesboro, NJ, USA), with 2 and 1 mm sieves.
At the end of each experimental period, feces were collected from the animals immediately after defecation to determine digestibility. The samples were collected at alternate times, 4 pm and 11 am, 3 pm and 09 am and 2 pm and 7 am on the first, second and third days of collection, respectively.
A sample composed of feces based on dry weight in air was constituted, through samples collected over the days and times of collection, identified and subsequently analyzed for the contents of iNDF [
15], to determine the fecal excretion through an internal marker [
24], and other bromatological analyzes.
2.8. Animal Performance
In order to determine the average daily gain (ADG) of the animals, weighing was performed at the beginning (initial body weight (IBW)) and end (final body weight (FBW)) of the experimental period, after a 12-h feed and water fasting. The same procedure was taken at the beginning and end of the adaptation period, in order to estimate its ADG (ADGadap). Intermediate weighing every 33 days, without fasting, was also conducted to adjust the supplement supply.
All animals were slaughtered in a commercial slaughterhouse. The carcass of each animal was divided into two half-carcasses, which were weighed to obtain the hot carcass weight (HCW). After weighing, carcass yield (CY) was determined as a function of fasting live weight and HCW.
The daily carcass gain (ADGc) was estimated according to the following equation (Equation (2)), considering the initial carcass weight (ICW) as 50% of the IBW fasting for 12 h.
2.9. Statistical Analysis
Animals were distributed in a completely randomized design, in a 2 × 3 factorial arrangement, with two production systems (pasture versus feedlot) and three supplements (CM, 50DDG, 100DDG). Supplements and the finishing system were considered fixed effects and pens and paddocks were considered random effects. The paddock was considered the experimental unit for finishing in pasture, and the pen for feedlot. Data analysis was performed using the statistical package SAS (2008), version 9.2, using mixed models by PROC MIXED. The averages generated were compared with the Tukey test using the PDIFF option in the LSMEANS command, when significant. The level of significance used to assess the differences between the means was α = 0.05.
3. Results
The finishing system affected the intake of TDMI, CPI, NDFI and iNDFI (
p < 0.05), which averages were higher in the pasture finishing system compared to feedlot. The OMI, NFCI and EEI were higher in the feedlot compared to pasture system (
p < 0.05) (
Table 4).
The TDMI in % BW was higher in animals supplemented with 50DDG (
p < 0.05). The intake of DM, OM, CP, NDF, iNDF and EE were similar among feedlot diets (
p > 0.05). In the pasture finishing system, the animals had lower TDMI in the CM (10.04 kg/d) in detriment to the 50DDG (12.08 kg/d). The OMI in the pasture system was lower in the CM (8.15 kg/d) compared to 50DDG and 100DDG, with averages of 10.24 and 9.54 kg/d, respectively. The CPI in the pasture system was lower in the CM (1.5 kg/d) compared to 1.74 and 1.66 kg/d of the 50DDG and 100DDG, respectively. The NDFI in the pasture system was lower in the CM (3.34 kg/d) compared to the 50DDG and 100DDG, whose averages were 4.92 and 4.43 kg/d, respectively. The iNDFI in the pasture system was higher in 50DDG (1.94 kg/d) compared to the CM and 100DDG, which averaged 1.36 and 1.44 kg/d, respectively. Metabolizable energy intake was higher in pasture compared to feedlot (
p = 0.0409), besides being higher in the 50DDG diet than the other treatments (
p = 0.0252) (
Table 4).
Nutrient digestibility was influenced by finishing systems (
Table 5). TDMD, OMD, CPD, NFCD and EED were higher in feedlot when compared to pasture finishing (
p < 0.05). On the other hand, NDFD was lower in feedlot than in pasture, whose averages were 468.5 and 523.1 g/kg, respectively (
p < 0.05). There was no difference among diets in both finishing systems for nutrient digestibility (
p > 0.05) (
Table 5).
Animal performance was higher in the feedlot finishing system (
p < 0.0001) compared to pasture, with averages of 1.57 kg/d and 0.99 kg/d, respectively (
Table 6). The FBW of animals finished in feedlot was higher (
p < 0.0001) than animals finished in pasture, with averages of 566 kg and 504 kg, respectively. ADGc was also higher in feedlot (
p < 0.0001) when compared to the pasture system, whose averages were 1.09 kg/d and 0.78 kg/d, respectively. Among diets, there was no difference for ADG (
p = 0.3698) and ADGc (
p = 0.2665). The ADG during the adaptation (ADGadap) was not influenced by finishing systems (
p = 0.1571) and diets (
p = 0.0661) (
Table 6).
In the pasture finishing system, there were no differences in forage mass, forage allowance and morphological composition among treatments (
p > 0.05), which averaged 6.0 t DM/ha of FM; 3.2 kg DM/ha of forage allowance; 8.0% of green leaf; 13.3% of green stem; 26.9% of senescent leaf and 26.3% of senescent stem, during dry season experiment (
Table 7).
5. Conclusions
The effect of replacing levels of cottonseed meal with DDG is the same for beef cattle finished in conventional feedlot or in pasture.
In the feedlot system, the beef cattle performance is better than in the grazing system. Nonetheless, there is no difference in animal performance during the adaptation period or finishing phase in both systems.
Although DDG can be an alternative to replace cottonseed meal, further studies should consider an economic analysis in feedlot or pasture system, including its market availability.