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The rumen microbial ecosystem provides ruminants a selective advantage, the ability to utilize forages, allowing them to flourish worldwide in various environments. For many years, our understanding of the ruminal microbial ecosystem was limited to understanding the microbes (usually only laboratory-amenable bacteria) grown in pure culture, meaning that much of our understanding of ruminal function remained a “black box.” However, the ruminal degradation of plant cell walls is performed by a consortium of bacteria, archaea, protozoa, and fungi that produces a wide variety of carbohydrate active enzymes (CAZymes) that are responsible for the catabolism of cellulose, hemicellulose, and pectin. The past 15 years have seen the development and implementation of numerous next-generation sequencing (NGS) approaches (e.g., pyrosequencing, Illumina, and shotgun sequencing), which have contributed significantly to a greater level of insight regarding the microbial ecology of ruminants fed a variety of forages. There has also been an increase in the utilization of liquid chromatography (LC) and mass spectrometry (MS) that revolutionized transcriptomic approaches, and further improvements in the measurement of fermentation intermediates and end products have advanced with metabolomics. These advanced NGS techniques along with other analytic approaches, such as metaproteomics, have been utilized to elucidate the specific role of microbial CAZymes in forage degradation. Other methods have provided new insights into dynamic changes in the ruminal microbial population fed different diets and how these changes impact the assortment of products presented to the host animal. As more omics-based data has accumulated on forage-fed ruminants, the sequence of events that occur during fiber colonization by the microbial consortium has become more apparent, with fungal populations and fibrolytic bacterial populations working in conjunction, as well as expanding understanding of the individual microbial contributions to degradation of plant cell walls and polysaccharide components. In the future, the ability to predict microbial population and enzymatic activity and end products will be able to support the development of dynamic predictive models of rumen forage degradation and fermentation. Consequently, it is imperative to understand the rumen’s microbial population better to improve fiber degradation in ruminants and, thus, stimulate more sustainable production systems.

This article provides a science-based, data-driven perspective on the relevance of the beef herd in the U.S. to our society and greenhouse gas (GHG) contribution to climate change. Cattle operations are subject to criticism for their environmental burden, often based on incomplete information disseminated about their social, economic, nutritional, and ecological benefits and detriments. The 2019 data published by the U.S. Environmental Protection Agency reported that U.S. beef cattle emitted 22.6% of the total agricultural emissions, representing about 2.2% of the total anthropogenic emissions of CO2 equivalent (CO2e). Simulations from a computer model developed to address global energy and climate challenges, set to use extreme improvements in livestock and crop production systems, indicated a potential reduction in global CO2e emissions of 4.6% but without significant enhancement in the temperature change by 2030. There are many natural and anthropogenic sources of CH4 emissions. Contrary to the increased contribution of peatlands and water reservoirs to atmospheric CO2e, the steady decrease in the U.S. cattle population is estimated to have reduced its methane (CH4) emissions by about 30% from 1975 to 2021. This CH4 emission deacceleration of 2.46 Mt CO2e/yr2 might be even more significant than reported. Many opportunities exist to mitigate CH4 emissions of beef production, leading to a realistic prospect of a 5% to 15% reduction in the short term after considering the overlapping impacts of combined strategies. Reduction strategies include feeding synthetic chemicals that inactivate the methyl-coenzyme M reductase (the enzyme that catalyzes the last step of methanogenesis in the rumen), red seaweed or algae extracts, ionophore antibiotics, phytochemicals (e.g., condensed tannins and essential oils), and other nutritional manipulations. The proposed net-zero concept might not solve the global warming problem because it will only balance future anthropogenic GHG emissions with anthropogenic removals, leaving global warming on a standby state. Recommendations for consuming red meat products should consider human nutrition, health, and disease and remain independent of controversial evidence of causational relationships with perceived negative environmental impacts of beef production that are not based on scientific data.

The objective of this trial was to determine the influence of live yeast supplementation (LY), environmental condition (ENV), and their interaction (TRT) on energy partitioning, nitrogen metabolism, and ruminal fermentation dynamics of steers receiving a grower-type diet. The effects of LY and ENV were investigated using a 2 × 2 crossover design that spanned five periods. Eight Angus-crossbred steers were randomly split into pairs and housed in four outdoor pens outfitted with an individualized feeding system. Animals were limit-fed a grower diet (DIET) at 1.2% shrunk body weight (SBW) with no live yeast supplementation (NOY) or a grower diet top-dressed with 10 g LY/d for 14 d (1.2 × 1012 CFU/d). On days 13 and 14, animals were subjected to one of two ENV conditions, thermoneutral (TN; 18.4 ± 1.1 °C, 57.6 ± 2.8% relative humidity [RH]) or heat stress (HS; 33.8 ± 0.6 °C, 55.7 ± 2.7% RH), in two side-by-side, single-stall open-circuit, indirect respiration calorimetry chambers. Data were analyzed using a random coefficients model. Carryover effects were examined and removed from the model if not significant. Gross (GE), digestible, metabolizable, heat, and retained energies were not influenced by DIET, ENV, or TRT (P ≥ 0.202). Gaseous energy, as a percentage of GE, tended to increase during HS (P = 0.097). The only carryover effect in the study was for oxygen consumption (P = 0.031), which could be attributed to the tendency of NOY (P = 0.068) to have greater oxygen consumption. DIET, ENV, or TRT (P ≥ 0.154) had no effects on total animal methane or carbon dioxide emissions. Similarly, DIET, ENV, or TRT (P ≥ 0.157) did not affect ruminal pH, redox, protozoa enumeration, ruminal ammonia concentrations, and acetate-to-propionate ratio. Propionate concentrations were the greatest in animals in TN conditions receiving LY (P = 0.034) compared to the other TRT. This effect is mirrored by TN-LY tending to have greater acetate concentrations (P = 0.076) and total VFA concentrations (P = 0.065). Butyrate concentrations tended to be greater for animals fed LY (P = 0.09). There was a tendency for LY to have elevated numbers of Fusobacterium necrophorum (P = 0.053). Although this study lacked effects of LY on energy partitioning, nitrogen metabolism, and some ruminal parameters during HS, further research should be completed to understand if LY is a plausible mitigation technique to enhance beef animals' performance in tropical and sub-tropical regions of the world.About 70% of global beef production is located in tropical and sub-tropical regions. With elevated temperatures and significant humidity, these regions impose heat stress on beef animals. Heat stress is the main antagonist to ruminant production as it decreases dry matter intake and digestion and increases energy expenditure due to the animal’s need for thermoregulation. Supplementation of live yeast products has proven efficacious at improving ruminal fermentation dynamics. This study sets out to determine if live yeast supplementation to animals in heat stress conditions can positively affect energy partitioning, nitrogen metabolism, and ruminal parameters. Additionally, this study models the ruminal performance after exposure to heat stress or live yeast supplementation. This study identified several interesting in vitro dynamics of previously stressed- or supplemented rumen fluid. Although there were a lack of effects for live yeast supplementation on energy partitioning, nitrogen metabolism, and some ruminal parameters during heat stress, further research should be completed in order to understand if live yeast supplementation is a plausible mitigation technique to enhance the performance of beef animals reared in tropical and sub-tropical regions of the world.

The objectives of this multipart study were 1) to assess the efficacy of sampling methods of methane concentration ([CH4]) of headspace gas produced during in vitro gas production (IVGP) fermentation, 2) to verify whether headspace [CH4] sampled from an exetainer has the same [CH4] as the headspace of IVGP bottles, 3) to measure relative humidity (RH) within an IVGP bottle, and 4) to compare [CH4] on a dry-gas (DG) basis when accounting for water vapor pressure (Pw). The original IVGP protocol recommends placing bottles on ice (0 °C) for 30 min to stop fermentation (ICE). A laboratory protocol recommends placing the bottles in the refrigerator (4 to 6 °C) to slow fermentation for 48 h and subsequently allowing the bottles to return to ambient temperature before sampling (FRIDGE). This study evaluated the previous methods against a direct sampling of the headspace gas after incubation (DIRECT). Rumen inoculum from four rumen-cannulated beef steers was combined and homogenized before incubating the fermentable substrate of ground alfalfa hay. After 48 h of IVGP incubation, each bottle was randomly assigned to a treatment protocol. The pressure (P), volume (V), and temperature (T) of headspace gas in each bottle were recorded. Headspace gas was then thoroughly mixed, and 12 mL gas was removed into an evacuated exetainer for [CH4] sampling via gas chromatography (EXET; Objective 1). Eight bottles from ICE and FRIDGE were randomly selected to follow EXET, whereas the remaining bottles had [CH4] directly measured from their headspace (BOTT; Objective 2). Five diets of differing feed composition and nutrient densities were used with a blank to test the RH of the IVGP slurry (Objective 3). Using RH, [CH4] was transformed to a DG basis to account for Pw (Objective 4). Statistical analysis was completed using a random coefficients model. There were no differences between EXET and BOTT (P = 0.28). The RH of the IVGP slurry was 100% (P = 1.00), confirming that IVGP gas is saturated with water vapor. The P, V, and T differed among treatments (P 0.01). The [CH4] of DIRECT, ICE, and FRIDGE were different (P 0.01). Dry-gas P, V, and [CH4] differed among treatments (P 0.01). As the methods differ in their assessment of [CH4], there is no clear recommendation. Instead, to present a more accurate [CH4], P, V, and T should be measured when sampling headspace gas and equations presented should be used to remove volume inflation due to water vapor and present [CH4] on a DG basis.Greenhouse gas emissions (GHG) from ruminant production equate to 81% of total global livestock supply chain emissions, with 51% originating from beef cattle production. Traditional in vivo estimation methods of methane (CH4), a highly scrutinized greenhouse gas, are timely and costly. In vitro gas production (IVGP) methods can accurately describe CH4 emission patterns from the rumen but tend to overestimate quantities. Additionally, in vivo estimation methods present CH4 on a dry-gas basis, whereas in vitro do not. In vitro methods utilize a gas chromatography machine to estimate CH4. Laboratory constraints can impose deviations to a strict IVGP protocol. This multi-objective study evaluates three treatment methods of IVGP bottles to understand whether discrepancies exist in CH4 estimation when deviating from the published protocol. To estimate CH4 from IVGP more accurately and provide a more comparable number to in vivo methods, this study also evaluates environmental conditions within an IVGP bottle to formulate a system of equations to calculate CH4 on a dry-gas basis. This study found that the treatment method of the IVGP bottle had an impact on CH4 estimation, and the developed equations should be utilized to produce more comparable estimates.

This study determined the energy requirement for maintenance of purebred Nellore cattle and its crossbreds using data from a comparative slaughter trial in which animals were raised under the same plane of nutrition from birth through slaughter and born from a single commercial Nellore cowherd. A total of 79 castrated steers (361 ± 54 kg initial body weight [BW]) were used in a completely randomized design by age (22 mo ± 23 d of age) with four genetic groups (GG): Nellore (NL), ½ Angus × ½ Nellore (AN), ½ Canchim × ½ Nellore (CN), and ½ Simmental × ½ Nellore (SN). The experimental design provided ranges in metabolizable energy (ME) intake (MEI), BW, and average daily gain needed to develop regression equations to predict net energy for maintenance (NEm) requirements. Four steers of each GG were slaughtered to determine the initial body composition. The remaining 63 steers were assigned to different nutritional treatments (NT) by GG; ad libitum or limit-fed treatments (receiving 70% of the daily feed of the ad libitum treatment of the same GG). Full BW was recorded at birth, weaning, 12, 18, and 22 mo. In the feedlot, steers were fed for 101 d a diet containing (DM basis) 60% corn silage and 40% concentrate. No difference in age at weaning (P = 0.534) and slaughter (P = 0.179 and P = 0.896, for GG and NT, respectively) were observed. AN steers were heavier at weaning weight, yearling weight and had higher empty BW (EBW; P = 0.007, P = 0.014, and P0.001, respectively) in comparison to NL, CN, and SN. There were no interactions (P0.05) between GG and NT for any variable evaluated. When fed ad libitum, AN steers had higher daily MEI (Mcal/d; P0.001) in comparison to NL, CN, and SN. On a constant age basis, differences were observed on body composition (P0.05) between GG. The slope (P = 0.600) and intercept (P = 0.702) of the regression of log heat production on MEI were similar among GG. Evaluating at the same age and the same frame size, there were no differences in NEm requirement between Nellore and AN (P = 0.528), CN (P = 0.671), and SN (P = 0.706). The combined data indicated a NEm requirement of 86.8 kcal/d/kg0.75 EBW and a ME required for maintenance requirement had a common value of 137.53 kcal/d/kg0.75 EBW. The efficiency of energy utilization for maintenance and the efficiency of energy utilization for growth values were similar among GG (P0.05 and P0.05, respectively) and were on average 63.2% and 26.0%, respectively. However, although not statistically different, the NEm values from NL showed a decrease in NEm of 5.76% compared with AN steers.Although several studies have shown that the maintenance energy expenditures vary with breeds, there has been no available data comparing the energy requirements of different genetic groups of beef cattle determined during the finishing phase when raised under the same plane of nutrition from birth through slaughter born from a single cowherd. This study evaluated the influence of purebred Nellore and its crosses with Simmental, Angus, and Canchim slaughtered at the same age and body composition on their net energy requirement for maintenance (NEm). Animals were reared in tropical conditions, receiving only free-choice minerals from birth through the beginning of the feedlot phase, potentially altering the intake, carcass composition, mature weight, and consequently, affecting the energy requirement for maintenance during the finishing period. The pooled data analysis for Nellore and its crosses resulted in common NEm requirement of 86.9 kcal/d/kg0.75 of empty body weight (EBW). However, although not statistically different, the NEm values from Nellore (NL) and Angus × Nellore (AN) were 85.5 and 90.8 kcal/d/kg0.75 EBW, respectively, showing a decrease in NEm of 5.76% for NL in comparison with AN steers.

A renewed interest in data analytics and decision support systems in developing automated computer systems is facilitating the emergence of hybrid intelligent systems by combining artificial intelligence (AI) algorithms with classical modeling paradigms such as mechanistic modeling (HIMM) and agent-based models (iABM). Data analytics have evolved remarkably, and the scientific community may not yet fully grasp the power and limitations of some tools. Existing statistical assumptions might need to be re-assessed to provide a more thorough competitive advantage in animal production systems towards sustainability. This paper discussed the evolution of data analytics from a competitive advantage perspective within academia and illustrated the combination of different advanced technological systems in developing HIMM. The progress of analytical tools was divided into three stages: collect and respond, predict and prescribe, and smart learning and policy making, depending on the level of their sophistication (simple to complicated analysis). The collect and respond stage is responsible for ensuring the data is correct and free of influential data points, and it represents the data and information phases for which data are cataloged and organized. The predict and prescribe stage results in gained knowledge from the data and comprises most predictive modeling paradigms, and optimization and risk assessment tools are used to prescribe future decision-making opportunities. The third stage aims to apply the information obtained in the previous stages to foment knowledge and use it for rational decisions. This stage represents the pinnacle of acquired knowledge that leads to wisdom, and AI technology is intrinsic. Although still incipient, HIMM and iABM form the forthcoming stage of competitive advantage. HIMM may not increase our ability to understand the underlying mechanisms controlling the outcomes of a system, but it may increase the predictive ability of existing models by helping the analyst explain more of the data variation. The scientific community still has some issues to be resolved, including the lack of transparency and reporting of AI that might limit code reproducibility. It might be prudent for the scientific community to avoid the shiny object syndrome (i.e., AI) and look beyond the current knowledge to understand the mechanisms that might improve productivity and efficiency to lead agriculture towards sustainable and responsible achievements.Data analytics have evolved remarkably. This paper discussed the evolution of data analytics from a competitive advantage perspective within academia and illustrated the combination of different advanced technological systems in developing hybrid intelligent mechanistic models (HIMM). Data analytics tools are divided into 3 stages. The first stage (collect and respond) ensures that data are correct and free of influential data points, and it represents the data and information phases for which data are cataloged and organized. The second stage (predict and prescribe) results in gained knowledge from the data and comprises most predictive modeling paradigms, and optimization and risk assessment tools are used to prescribe future decision-making opportunities. The third stage (smart learning and policy making) aims to apply the information obtained in the previous stages to foment knowledge and use it for rational decisions. Although still incipient, HIMM form the forthcoming stage of competitive advantage. HIMM may not increase our ability to understand the underlying mechanisms controlling the outcomes of a system, but it may increase the predictive ability of existing models by helping the analyst explain more of the data variation. The scientific community needs to resolve the lack of transparency and reporting of artificial intelligence for code reproducibility.

Our objectives were to 1) investigate the difference in chemical composition and disappearance kinetics between loose dried distillers' grains (DDG) and extruded DDG cubes and 2) evaluate the effects of supplementation rate of extruded DDG cubes on voluntary dry matter intake (DMI), rate and extent of digestibility, and blood parameters of growing beef heifers offered ad libitum bermudagrass (Cynodon dactylon) hay. To characterize the changes in chemical composition during the extrusion process, loose and extruded DDG were evaluated via near-infrared reflectance spectroscopy, and dry matter (DM) disappearance kinetics were evaluated via time point in situ incubations. Extruded DDG cubes had greater (P ≤ 0.01) contents of fat, neutral detergent insoluble crude protein, and total digestible nutrients, but lower (P ≤ 0.01) neutral and acid detergent fiber than loose DDG. Additionally, the DM of extruded DDG cubes was more immediately soluble (P0.01), had greater (P0.01) effective degradability and lag time, and tended (P = 0.07) to have a greater disappearance rate than loose DDG. In the 29-d supplementation rate study, 23 Charolais-cross heifers were randomly assigned to one of four supplemental treatments: 1) control, no supplement; 2) low, 0.90 kg DDG cubes per d; 3) intermediate, 1.81 kg DDG cubes per d; or 4) high, 3.62 kg DDG cubes per d. Titanium dioxide was used as an external marker to estimate fecal output and particulate passage rate (Kp). Blood was collected from each animal to determine supplementation effects on blood metabolites. Indigestible neutral detergent fiber was used as an internal marker to assess the rate and extent of hay and diet DM digestibility (DMD). Increasing supplementation rate increased Kp and total diet DMI linearly (P0.01), yet linearly decreased (P0.01) hay DMI. Hay DMD decreased quadratically (P0.01), while total diet DMD increased linearly (P0.01) with increased DDG cube inclusion. Supplemented heifers had greater (P = 0.07) blood urea nitrogen concentrations than control animals 4 h post-supplementation. Intermediate and high rates of supplementation resulted in lower (P0.01) serum nonesterified fatty acid concentrations post-supplementation than control heifers. Concentrations of serum glucose and lactate were greatest (P ≤ 0.06) 8 h post-supplementation. Our results suggest that extruded DDG cubes may be an adequate supplement for cattle consuming moderate-quality forage, and further research is warranted.Growing cattle are oftentimes provided supplemental concentrate as a source of protein and energy in order to meet performance goals when consuming low-quality forages. The effects of supplemental concentrate on forage intake vary, which may be related to the quality of forage and the characteristics of the supplement being evaluated. Dried distillers’ grains (DDG) are a by-product of ethanol production and have become a common supplement for growing cattle due to the increased energy and rumen undegradable protein content. A stable DDG cube made via a novel extrusion process may be advantageous for pasture supplementation due to the reduced risk of loss of product from wind and soil mixing that is common with loose DDG. The effects of supplementation rate of traditional concentrate sources on forage intake are abundant, but research regarding extruded DDG cubes is almost nonexistent. Thus, our objective was to evaluate extruded DDG cube supplementation rate (0, 0.90, 1.81, or 3.62 kg DDG cubes per d) for growing cattle on voluntary intake and digestibility of moderate-quality forage. Although increasing supplementation rate reduced forage intake and digestibility, total diet intake and digestibility were increased. Our results suggested that extruded DDG cubes have potential as a supplement for cattle consuming moderate-quality forage.

This research evaluated the effects of supplementing extruded dried distillers’ grains (DDG) cubes to grazing steers on subsequent finishing performance and carcass characteristics. Steers (n = 140) grazed tall fescue (Festuca arundinacea)/bermudagrass (Cynodon dactylon) pastures from 14 April to 17 September 2020 with supplementation treatments (n = 3 pastures/treatment) that included: 1) Fertilized Control (FC), no supplementation on N fertilized pastures (112 kg N/ha); 2) Fertilized Supplement (FS), supplemented DDG cubes at 2.9 kg/d prorated for 3-d/wk feeding on N fertilized pastures; and 3) Supplement (S), supplemented DDG cubes at 0.75% of BW/d prorated for 5-d/wk feeding on unfertilized pastures. All animals were followed through the finishing phase in a commercial feedyard to investigate carryover effects on feedlot performance in 2 pens comingled across supplemental treatment. Carcass characteristics were evaluated via ultrasonography on d0 and d84 of finishing, and measurements were obtained at harvest. Feed DMI were segregated to individual animals according to Guiroy et al. (2001) and Tedeschi and Fox (2020b). Supplemented animals were heavier (P < 0.01) at feedlot entry than FC, but harvest BW did not differ (P = 0.23). However, S and FS required 37 fewer days on feed (P = 0.01) than FC. Supplementation on pasture reduced total feed required (P = 0.02) and feed costs (P = 0.01) relative to FC. Gains were greater (P = 0.02) for FC and FS than S from d0 to d84, but did not differ thereafter (P ≥ 0.15). At harvest, FC had the greatest dressing percent (P < 0.01) and lower yielding carcasses than FS (P = 0.01), but did not differ (P = 0.11) from S. Overall, extruded DDG cube supplementation during grazing did not negatively affect subsequent feedlot performance or carcass characteristics, but reduced the total feed required for finishing.

Intelligent societies are built through education. Wisdom gained through scientific knowledge and discourse is necessary for spreading reliable information and building consensus among citizens of the six continents on earth. Internationalization empowers the fostering and discovery of novel techniques and resources that could solve contemporary issues assailing humankind’s prosperity, including sustainability, environmental pollution, and hunger. A community might have found solutions to problems other communities face; however, our failures of globalization postpone their resolution. Animal science is not immune to these failures. Livestock production could incorporate know-how from other communities, borrowing from experiences of student and faculty exchange and study abroad programs. The tremendous evolutionary aspects of ruminants’ digestive system allow them to thrive in diverse and sometimes inhospitable ecosystems and convert human-inedible resources into high-quality animal products for human consumption. Humankind relies on ruminants for energy and protein consumption, wool, and draft power. This symbiotic relationship has led to extreme production systems due to economy-of-scale factors and the availability of resources in some countries. But, other countries have relied on rustic, low-intrusive production systems that are more amenable to the environment and more conducive to sustainability. Therefore, breaking the boundaries across nations through international partnership programs will lead to sharing scientific knowledge and enhancing management programs essential to the long-term continuation of this human-ruminant symbiotic relationship within responsible animal welfare programs. Besides improving the communication among societies and spreading scientific advancements, such internationalization programs will shape students, i.e., the workforce of the future, into citizens of the world with accurate and helpful information about the language, culture, problems, and needs of other civilizations and how to enrich our likelihood and theirs. As a result, leaders of the many different nations worldwide can, once again, expand the frontiers of scientific knowledge in seeking sustainable, responsible, and affordable animal agriculture activities.

Nutritional grouping (NG) strategies have been proposed mainly in dairy cattle to improve economic efficiency (30-60$/cow per year) of dairy farmers. In dairy cattle, NG is made according to net energy (NE) requirements estimated from some animal variables (i.e., milk yield and dairy merit). However, NG has not been evaluated for beef cattle, likely because data are not readily available and existing protocols have been fixed for decades by the beef industry, such as allotting by body weight (BW): growing diet for 180 to 400-kg animals, and finishing diet for 400 to 550-kg animals. Therefore, we investigated an unsupervised machine learning (ML) technique in R to sort animals at the arrival according to their DM intake (DMI), NE and metabolizable protein (MP) requirements, estimated through INRA from BW and average daily gain. We utilized data from 77 growing Friesian steers allotted conventionally by BW (139±21.6 kg) in 4 pens, weighed every 3 weeks (n=9 weighings) during 190 days, and fed a high-energy diet (1.59 Mcal NE/kg DM and 89 g MP/kg DM). Results identified that estimated performances were significantly (P< 0.002) different between 3 groups made from ML and between 4 pens made from BW; however, ML groups presented a minor within-group variability of NE and MP requirements (-25%CV) than pens. We also regressed energy and protein intake minus their respective requirements by the duration of the experiment observing a better fitting (R2= 0.93 vs 0.80) when allotting animals by groups than by pens, which implicates better feed efficiency if diets were formulated according to requirements established by ML groups. We demonstrated that ML techniques could help the decision-making of beef farmers to better sort animals according to their requirements and not only by BW. The next step is to formulate rations according to animal requirements to improve efficiency.

The study aimed to investigate the effects of two feeding times and two sources of energy supplementation on pH, short-chain fatty acids (SCFA), and in vitro gas production (IVGP) of beef cattle reared in Urochloa brizantha cv. Marandu pastures. We used eight rumen-cannulated ½ Aberdeen Angus x ½ Nellore young bulls (280±7 kg) distributed in a double 4x4 Latin square design. Treatments consisted of supplementation at 0.3% of body weight with corn or citrus pulp, supplied at 0900 or 1700. Ruminal fluid pH was measured with a digital pH analyzer and SCFA was analyzed on a Shimadzu HPLC. The IVGP was determined using a transducer and a data logger for 48 h after incubation of samples combining forage and supplement in real intake proportion (88% forage, 12% supplement). Considering the rapid fermentation of sugars, animals supplemented with pectin maintained higher pH (P = 0.021) due to changes in bacterial populations to digest the pectic substances (Table 1). Lactate production after starch digestion caused lower pH. Despite the differences in evaluated energy substrates, there was no effect on the primary SCFA concentration (P > 0.05). Citrus pulp provided greater formic (P = 0.005) and valeric (P = 0.042) acids concentrations compared with corn, but there was no influence of formic acid in lactic acid production (Table 1). The greater IVGP by citrus pulp (P = 0.0140; Figure 1) may be related to its greater carbohydrate fraction A, soluble with a rapid rate of rumen degradation, and also because its ruminal fermentation results in greater acetic acid production, which provides more ruminal H2 and CO2, favoring the CH4 production. The citrus pulp can be used as an alternative source to corn because it might prevent acidosis, does not affect the main SCFA production, and is a non-human edible feed.