ABSTRACT We investigated the impact of weaning at 30, 75, and 180 days of age on performance, body measurements, and rumen development (using the β-hydroxybutyrate biomarker) of beef calves until 190 days of age. A total of 64 Brangus calves were assigned to three treatments: hyper-early (W30), weaned at 32±0.89 days of age (n = 22, 10 males and 12 females); early (W75), weaned at 77±0.95 days of age (n = 20, 12 males and eight females); and conventional (W180), weaned at 183±0.82 days of age (n = 22, 13 males and nine females). Body weight (BW), average daily gain (ADG), β-hydroxybutyrate (βHBA), and morphometric measurements were evaluated. These variables were influenced by an interaction between treatment and days and were not affected by the sex of calves. The W30 calves experienced weight loss from 30 to 40 days of age compared with the W75 and W180 calves. Consequently, at day 75, W30 animals were lighter and had lower body length, thoracic circumference, withers height, and croup height compared with the W75 and W180 calves. However, no significant differences in BW were observed among treatments at 85 days of age. Additionally, W30 calves exhibited higher ADG and a moderate correlation with βHBA levels. Weaning calves at 30 days of age may negatively affect their performance until the sixth week after weaning, but there is no impairment in performance at 190 days of age. 75 18 using βhydroxybutyrate β hydroxybutyrate biomarker 19 6 hyperearly hyper W30, W , (W30) 32089 32 0 89 32±0.8 n 22 1 females females) W75, (W75) 77095 77 95 77±0.9 20 W180, (W180) 183082 183 82 183±0.8 females. . BW, (BW) ADG, (ADG) βHBA, (βHBA) evaluated W3 3 4 W7 W18 Consequently length circumference However 8 Additionally levels 7 (W30 3208 32±0. 2 (W75 7709 9 77±0. (W180 18308 183±0. (BW (ADG (βHBA W1 (W3 320 32±0 (W7 770 77±0 (W18 1830 183±0 (W 32± 77± (W1 183±

ABSTRACT The main objective of this study was to evaluate the effects of phenotypic, genotypic, and auction characteristics that may influence the selling prices of bulls. Data from 1,540 Braford and 1,179 Brangus bulls sold at auctions in the state of Rio Grande do Sul, Brazil, were collected and evaluated individually. Body condition score (BCS), muscularity, frame, foreskin size, presence or absence of horns, and data regarding the auction such as name/venue, event edition, forms of payment, among others, were considered. Information such as weight at the time of sale, scrotal circumference (SC), expected profit differences, selection indexes, and date of birth were collected from the catalogs supplied at the auctions. To obtain the influence of the selected explanatory variables throughout the conditional distribution of bull prices, a quantile regression was used, and the quantiles were established as follows: 10th, 25th, 50th, 75th, and 90th. The buyers of Braford and Brangus bulls valued characteristics such as age, weight, and SC in relation to frame, muscularity, BCS, and foreskin size. In addition, the price behavior at different auctions was positively related to the operation time of the auction in this market and with the reputation of the seller. Regarding genetic variables of Brangus bulls, these had little or no influence on the selling price. There was a positive influence on the weaning index in the 90th quantile and on the final index in the 50th and 75th quantiles. Buyers of synthetic bull breeds at auctions value the phenotypic characteristics of bulls more than they do genetic characteristics, which may not reflect permanent gains in the cattle herd. genotypic 1540 1 540 1,54 1179 179 1,17 Sul Brazil individually BCS , (BCS) muscularity frame size horns namevenue name venue name/venue edition payment others considered sale SC, (SC) differences indexes used follows 10th th 25th age addition seller herd 154 54 1,5 117 17 1,1 (BCS (SC 15 5 1, 11

Resumen Este estudio compara el desempeño técnico y financiero de diferentes sistemas de producción de ganado para carne y evalúa la comercialización oportunista practicada en estos sistemas. Se evaluaron datos de cuatro unidades de producción ubicadas en el sur de Brasil: vaca-cría en pastos nativos (VCPN; 1,155 ha; 1,529 animales); vaca-cría con agricultura (VCA; 1,008 ha; 1,313 animales); recría-engorda (URE; 360 ha; 435 animales); y engorda (UE; 205 ha; 168 animales) así como un sistema integrado que simula los parámetros físicos y económicos de las cuatro unidades (SIA; 2,728 ha; 3,445 animales). Las cuatro unidades independientes fueron consideradas como de comercialización oportunista y el SIA como no oportunistas. El mayor rendimiento se obtuvo para URE (297 kg/ha), seguido de SIA (114 kg/ha), UE (98 kg/ha), VCPN (87 kg/ha) y VCA (83 kg/ha). La VCPN fue la más económicamente eficiente, considerando el margen bruto por kilogramo (MB/kg) (US$ 0.93). El valor del MB/kg del SIA (US$ 0.74) fue un 37 % superior en comparación con la suma del promedio de las cuatro unidades (US$ 0.54), y el SIA tuvo los costos totales de producción por kg más bajos (22.5 %). Se llegó a la conclusión de que cada unidad independiente podría aumentar el MB/kg (37 %) y el MB/ha (3.8 %) y utilizar crías en una unidad de recría-engorda para su posterior venta. Por lo tanto, la integración de los sistemas de producción de carne de res aumenta el margen bruto de las empresas, presentando una ventaja comercial rentable para los empresarios rurales a través de la comercialización no oportunista.

Abstract This study compares the technical and financial performance of different beef cattle production systems and assesses the opportunistic commercialization practiced in these systems. It was evaluated data from four production units located in southern Brazil: cow-calf in native pastures (CCNP; 1,155 ha; 1,529 animals); cow-calf with agriculture (CCA; 1,008 ha; 1,313 animals); rearing-fattening (RFU; 360 ha; 435 animals); and fattening (FU; 205 ha; 168 animals) as well as an integrated system simulating the physical and economic parameters of the four units (IAS; 2,728 ha; 3,445 animals). The four independent units were considered as opportunistic commercialization and IAS as non-opportunistic. The highest yield was obtained for RFU (297 kg/ha), followed by IAS (114 kg/ha), FU (98 kg/ha), CCNP (87 kg/ha), and CCA (83 kg/ha). The CCNP was the most economically efficient, considering the gross margin per kilogram (GM/kg) (US$ 0.93). The GM/kg value of IAS (US$ 0.74) was 37 % higher compared to the sum of the average of the four units (US$ 0.54), and IAS had the lowest total production costs per kg (22.5 %). It was concluded that each independent unit could increase GM/kg (37 %) and GM/ha (3.8 %) and use calves in a rearing-fattening unit for further sale. Hence, the integration of beef production systems increases the gross margin of firms, presenting a profitable business advantage to rural entrepreneurs through non-opportunistic commercialization.

ABSTRACT This study was performed to evaluate the efficiency index of cow-calf systems, based on different feed technologies commonly employed in the Rio Grande do Sul state, southern Brazil. Hence, the efficiency of 35 cow-calf herds was evaluated by Data Envelopment Analysis (DEA). Data was collected by online survey and in-depth interviews, as well as data registers from the cow-calf systems, located in 31 municipalities. The analyzed indicators included rates of mortality, pregnancy, birth, and productivity. The feed technologies evaluated were the use of cultivated pastures during winter and summer, supplementation during winter and summer, creep feeding, deferral of natural pasture, use of grazing systems, and employee's capacitation. Approximately 80% of the evaluated farms showed low-to-medium Efficiency Index (EI; up to 0.79 in a scale of 0 to 1), 13% presented high EI, and only 7% had very high EI (above 0.95). The use of cultivated pastures with the inclusion of protein supplementation and employees’ capacitation were highlighted as the main practices to increase efficiency of cow-calf systems in Rio Grande do Sul. The technologies identified as most impactful raise the EI of production systems from low to medium. Our results assist in decision-making in the use of feed technologies, pointing out a direction for the use of technologies that make breeding systems more efficient from a productive point of view.

ABSTRACT With the objective of identifying the concerns, attitudes, and opinions of meat buyers and their relationship with their choice of place of purchase (supermarkets, free fair, or butchers), 381 consumers in the city of Garanhuns, Brazil, were interviewed. Data analysis was performed using descriptive statistics and discriminant analysis, complemented by stepwise regression, Wilks’ Lambda test, and Fisher’s linear test. Most of the respondents expressed that inadequate commercialization of meat occurred in free fairs, and the lack of hygiene and the fact that meat was exposed in the environment without refrigeration were the main preoccupations. They also reported that meat consumption without inspection could lead to disease transmission, with pork being considered the most dangerous. Based on the theory of planned behavior, buyers agreed that their attitudes toward the purchase of meat (concern with food safety, price, animal welfare, environment, and slave labor) influenced their purchasing decisions. Regarding the subjective norms, the results indicated that purchase intention could be modulated by the opinion and judgment that other people exercise on the buyer’s choice decision. Regarding perceived control, the respondents said that they were confused at the time of purchase and got irritated after making a purchase that did not satisfy their desires. The factors that differentiated consumers who prefer to buy meat in supermarkets from those who prefer butchers and free fairs are mainly the price of the product, custom/tradition, customer service, and hygiene of the establishment. Buyers who have a lower level of schooling and live in rural areas also tended to buy meat in free fairs.

ABSTRACT The objective of this study was to verify the association of improved native grassland and winter and summer pastures on the weaning rate in beef cattle production. Subsequently, we also verified the socioeconomic and productive characteristics related to the adoption of technologies to increase the weaning rate of the farmers. The survey was conducted with 73 producers of Hereford and Braford cattle in the state of Rio Grande do Sul, Brazil. A data analysis was performed using the minimum ordinal squares method and the regression analysis (Tobit). The results showed that cattle farmers who adopt winter pastures have greater weaning rates, and the factors that influence this adoption are related to a greater number of employees on the farm and the use of a crop-livestock production system. In addition, farmers who receive a greater number of technical assistance visits per year are more likely to adopt winter pastures and improved native grassland. This information can be useful in the formulation of technological dissemination programs that aim at a sustainable production of beef cattle.

ABSTRACT Traditional livestock productivity is hard to estimate, since it depends on a gamut of animal production indicators that are difficult to measure for many farms. Thus, we propose an analytical method for estimating productivity and understanding the importance of animal production indicators under different full-cycle cattle production systems in Brazil. To evaluate the impact of these indicators, equations were derived from a comutational model of herd evolution for estimating the output parameters of the system as follows: productivity per hectare (PH) and offtake rate (COR), as a function of the indicators; calving rate (CR), mating age (AM), age of slaughter (AS) and stocking rate (SR). For this analysis, twenty-seven scenarios (simulation data) of low to high productivity were used, resulting from the combination of the following factors and levels: 1) calving rate of 50, 65 and 80 %; 2) mating age of heifers of one, two and three, years of age; and 3) age at slaughter of one, two and three year old steers. The scenario with the highest impact for each parameter and the indicator of highest impact for each scenario were identified for the production conditions in the region. Under most scenarios, a reduction in mating age had a greater impact on the productivity indexes compared to a reduction in slaughter age. Appropriate management of available technologies enables farmers to compare the marginal impacts of specific indicators on full-cycle production systems for beef cattle.

Abstract This research determines which factors most influence the purchase price of bulls in livestock auctions in the State of Rio Grande do Sul, Southern Brazil. Hence, 760 beef bulls sold in eleven different auctions between August and November 2013 were analysed. The data consists of: breed, muscularity (MUSC), frame (FRAME), body condition score (BCS), scrotal circumference (SC) and body weight (BW). Other data such as the animal entry order and the purchase price of the bulls was collected during the auction. A linear generalized model was used to evaluate the interaction of each variable with the purchase price of the bulls. An ANOVA with Tukey post-hoc was used to compare the differences between the categories that influenced the purchase price of bulls and were realized in the software SPSS 20.0. All breeds presented declining prices from the first to the second entry order and increasing purchase prices from the order third to forth. Bulls with large frame received higher purchase prices independent of the auction order, except for the second order of entry, in which medium and small animals were more valued. Angus bulls obtained the highest prices in relation to the breeds Brangus and Hereford. The frame and breed constituted the main phenotypic characteristics that influence in price. In addition, the order of entry of bulls in the ring influence the purchase price.

Resumen Esta investigación determina qué factores influyen más en el precio de compra de los toros en las subastas de ganado en el estado de Rio Grande do Sul, en el sur de Brasil. Por lo tanto, se analizaron 760 toros de carne que se vendieron en 11 subastas diferentes entre agosto y noviembre de 2013. Los datos consisten en: raza, musculatura (MUSC), marco (MARCO), puntaje de condición corporal (PCC), circunferencia escrotal (CE) y peso corporal (PC). Otros datos, como la orden de entrada de animales y el precio de compra de los toros, se recopilaron durante la subasta. Se utilizó un modelo lineal generalizado para evaluar la interacción de cada variable con el precio de compra de los toros. Se aplicó un ANOVA con Tukey post-hoc para comparar las diferencias entre las categorías que afectaron el precio de compra de los toros y se utilizó el software SPSS 20.0. Todas las razas registraron precios decrecientes desde el primer al segundo orden de entrada, y los precios de compra aumentaron desde el tercer orden al siguiente. Los toros con constitución grande recibieron precios de compra más altos independientemente del orden de entrada en la subasta, a excepción del segundo, en el que los animales medianos y pequeños fueron más valorados. Los toros Angus obtuvieron los precios más altos en relación con las razas Brangus y Hereford. La constitución y la raza constituyeron las principales características fenotípicas que inciden en el precio. Además, el orden de entrada de los toros en la pista influye en el precio de compra.

ABSTRACT This study was intended to estimate the genetic associations between growth traits and visual scores with possible changes in mature weight (MW) in 397,900 Nellore animals. A bi-character analysis was performed to estimate the (co)variances and genetic parameters for MW, which comprises the following traits: conformation, finishing precocity, musculature at weaning (WC, WP, and WM) and yearling (YC, YP, and YM), birth weight (BW), weight from birth to weaning (WG), weight from weaning to yearling (YG), and final index (FIND). The observed mean MW was 417.6±56.2 kg, and the direct genetic effect mean estimated heritability ( h 2 a 1) of MW was 0.45. Overall, the BW was 31.0±3.7 kg, and the estimated h² was 0.34. The heritability estimate of the maternal additive genetic component ( h 2 m 2) of BW was 0.07. We calculated the mean WG to be 144.1±26.3 and estimated the h 2 a 2 as 0.18 and h 2 m 2 as 0.07. The value for h 2 a YG (0.17) and YW (0.26) were also estimated. The heritability of the weaning WC (0.17), WP (0.19), and WM (0.17) and yearling YC (0.25), YP (0.27), and YM (0.25) were estimated using visual scores. The h 2 m values for weaning WC, WP, and WM (0.06) with visual scores were estimated. The genetic correlations between body weight (BoW) at YC and WC (0.62) were considered moderately high and positive. In addition, YP (0.18), YM (0.15), WP (0.13), and WM (0.14) were considered moderately low compared with MW. The genetic correlation between BW and FIND (0.38) was considered positive and moderate. The heritability estimation indicates that growth traits, visual scores, and weight of adult cows could be changed by selection. Cows that presented the highest h 2 a values for live weight responded rapidly to selection based on growth characteristics, visual scores, and FIND and might result in increased final MW.

RESUMO: O objetivo deste estudo foi avaliar a eficiência bioeconômica em sistemas de produção de bovinos de corte no sul do Brasil. A pesquisa foi realizada com 33 pecuaristas que operam com sistemas de produção baseado em ciclo completo, em áreas maiores ou iguais a 900 hectares. As respostas foram classificadas em dois fatores: tecnologia (TEC) e gestão (GES), os quais foram separados em subfatores com seus respectivos componentes. A análise de correspondência múltipla, teste de Tukey, análise de cluster e correlação de Pearson foram os procedimentos estatísticos. Os componentes do TEC estavam acima do normal para os pecuaristas brasileiros, mas a margem bruta ainda é menor do que a necessária para gerar recursos financeiros para uma remuneração adequada ao pecuarista. Os pecuaristas foram classificados em três grupos de acordo com a eficiência bioeconômica: baixo (BNE), intermediário (INE) ou alto nível de eficiência (ANE). O driver TEC diferenciou os clusters BNE x ANE e o GES, expresso principalmente em custos, o INE x ANE. A correlação positiva entre a idade no primeiro acasalamento e a idade ao abate no agrupamento ANE explica os custos mais elevados quando comparados aos INE, devido ao uso de recursos alimentares diferenciados. Os investimentos em tecnologias relacionadas à alimentação de rebanho no agrupamento ANE melhoraram a produtividade em apenas 20% e o custo por hectare em 95 USD ha-1 em comparação ao cluster INE. As principais diferenças entre os pecuaristas se devem ao uso de tecnologias relacionadas à alimentação e ao gerenciamento de custos. Portanto, antes de implementar uma nova tecnologia, uma avaliação econômica é necessária.

ABSTRACT: The objective of this study was to evaluate the bioeconomic efficiency of beef cattle production systems in the south of Brazil. A survey was conducted with 33 beef cattle farmers operating with complete cycle production systems in areas larger or equal to 900 ha. Answers were classified in two drivers, technology (TEC) and management (MAN), which were separated into subfactors with their respective components. Multiple correspondence analysis, Tukey test, cluster analysis, and Pearson correlation were the statistics procedures. The TEC components were above normal for Brazilian farmers, but the gross margin is still lower than that needed to generate financial resources for a proper remuneration of cattle farmer. Farmers were classified into three clusters according to bioeconomic efficiency: low (LEL), intermediate (IEL), or high-efficiency level (HEL). The TEC driver differentiated the LEL x HEL clusters and the MAN, mainly expressed in costs, the IEL x HEL. Positive correlation between age at first mating and age at slaughter in the HEL cluster explains the higher costs when compared to IEL because of the use of differentiated feed resources. Investments in technologies related to herd feeding in HEL cluster improved the productivity by only 20% and the cost per hectare by 95 USD ha-1 in comparison to IEL cluster. The main differences between farmers are because of the use of technologies related to feeding and cost management. Therefore, before implementing a new technology, an economic evaluation is necessary.

RESUMO: A busca por animais com características específicas é evidenciada na comercialização em leilões, em que, ao analisar os animais, compradores consideram as características individuais (musculosidade, frame, composição racial, peso) como preditor de qualidade e ajustam seus lances conforme suas preferências. Dessa forma, o presente estudo buscou avaliar o impacto de características fenotípicas e de padrão racial na composição do preço final de venda de bezerros comercializados em feiras oficiais na fronteira oeste do Rio Grande do Sul. Foram avaliados 507 lotes de bezerros comercializados nas feiras de terneiros de cinco municípios da região da Fronteira Oeste do estado do Rio Grande do Sul. Para a atribuição de escores visuais, considerou-se grupo genético, frame, musculosidade e pelagem dos animais. Foi realizada a análise de variância e a comparação dos preços finais médios pelo teste de Tukey a 5% de significância. As variáveis de maior impacto no preço foram grupo genético e tamanho dos animais. Animais de raças sintéticas obtiveram valorização superior nos três anos Estudados, considerável desvalorização e queda na oferta de animais sem definição racial. Os menores valores foram atribuídos a animais de tamanho grande.

ABSTRACT: The demand for beef cattle with specific traits is evident from sales in auctions. While purchasing, buyers consider individual traits (e.g., muscularity, frame, racial composition, and weight) as predictors of quality, and adjust their bids according to their preferences. The present study aimed to evaluate the effect of phenotypic and racial characteristics in determining the final sale price of calves of beef cattle in official auctions at the western border of the state of Rio Grande do Sul, Brazil. Five-hundred and seven lots of calves sold in calf auctions from five cities on the western border of Rio Grande do Sul were evaluated. The assignment of visual scores was based on their genetic group, frame, muscularity, and coat. Analysis of variance and the Tukey test at 5% significance level were performed for comparing the final average prices. Variables with the greatest impact on price were the genetic group and the size of the animals. Animals of synthetic breeds obtained higher value in the three years studied and animals without racial definition showed considerable devaluation and a decrease in supply. Larger animals had less value.

ABSTRACT This study assessed the risks of different management practices to increase pregnancy rate in beef cow-calf systems, aiming at assisting decision-making. The perception of 18 experts on animal sciences regarding the risks of 32 nutritional, breeding, and general management practices applied to increase pregnancy rate were evaluated through questionnaires. The experts were selected by a non-probability sampling of researchers on veterinary and animal sciences. In addition, five farmers and eight technical consultants were also selected. The questionnaire was applied during a face-to-face meeting. The risk of each practice was assessed according to four factors, namely, cost, technical knowledge, operational complexity, and flexibility, and an equation was developed to calculate this risk. The applied method allowed to determine the risk of each practice, obtaining results similar to those previously perceived by the experts. Operational complexity and cost had greater influence on the estimated risks compared with the other factors. Moreover, the increase of one unit in operational complexity and cost increased the perceived risk and the estimated risk scores in 0.43 and 0.28 points, respectively. Overall, the application of general management practices presented lower risk score compared with nutritional and breeding practices, which were not different from which other. Equations to estimate the risks of farm managers should routinely apply management practices to increase the efficiency of cow-calf production systems.

ABSTRACT This study was intended to evaluate body size structure and growth parameters of crossbred heifers fed at four nutritional levels to achieve puberty earlier. Animals were classified depending on their level of crossing between Nelore and Hereford and subjected to four nutritional levels (kg day−1) as follows: 0.5 (light; n = 32), 0.75 (medium; n = 32), 1.00 (high; n = 29), and 1.25 (very high; n = 27). Heifers at puberty and at weaning were individually classified for growth parameters. The fat thickness and longissimus muscle area throughout the experimental period were determined by ultrasonography. The height, heart girth, frame, and weight:height ratio were variables used to evaluate body traits. Univariate analysis of variance using the GLIM MIXED procedure os SPSS was performed and the significance level was set at 0.05. Age and body weight at puberty were 388±1.9 days and 331.4±1.3 kg, respectively. Body condition score demonstrated an interaction between nutritional level and crossbred degree. Heifers with the highest degree of Nelore had higher fat thickness and lower weight:height ratio compared with other racial groups at puberty. Pearson correlation coefficient showed a negative association for body condition score (−0.34) and fat thickness (−0.58) compared with age at puberty. The increased fat thickness at younger ages at puberty was observed in all racial groups. The increased weight:height ratio at younger ages at puberty was observed in all racial groups. We observed higher values for a frame in animals at the higher level of supplementation. There is a greater correlation between live weight gain and phenotypic traits during weaning to achieve puberty at an earlier age in crossbred heifers.

ABSTRACT This study aimed at estimating the heritability of age at first calving and of performance traits included in the selection index and the genetic correlations between age at first calving and these performance traits. Data were extracted from the Conexão Delta G database and only data from herds in which heifers were bred younger than 24 months of age were used, resulting in a file with 331,310 evaluated animals. The following traits were included in the analyses: age at first calving, birth to weaning gain, post-weaning weight gain, visual scores of conformation, precocity, and muscling evaluated at weaning and in yearling heifers. Covariance components were obtained by bi-character analyses between traits. An alternative age at first calving was also taken into account, in which all heifers were used, including those that were mated and did not calve. Covariance components and estimates of the effects included in the model were obtained using the software program DMU. Heritability estimates were 0.11 and 0.13 for age at first calving and alternative age at first calving, 0.38 for birth to weaning gain, and 0.13 for post-weaning weight gain. Visual score estimates ranged between 0.16 and 0.18 at weaning and 0.19 and 0.29 in yearlings. Genetic correlation estimates of the traits were low, but in the desirable direction. Selection for birth to weaning gain and visual scores does not have a negative effect on age at first calving or alternative age at first calving.

ABSTRACT The objective of this study was to evaluate the effects of mineral and protein-energy (MPES), exogenous fibrolytic enzyme supplements (ES), combination of MPES + ES, and straw without supplement (WS) on digestibility, fermentation kinetic parameters, cumulative gas production, methane, CO2 production, and volatile fatty acid concentration of rice straw of low and high nutritional value, estimated by in vitro techniques. The experimental design was randomized and factorial 2 × 4: two straws (low and high nutritional value) incubated with four supplements (MPES, ES, MPES + ES, and WS) and their interactions. Four experimental periods were used, totaling four replications per treatment over time. Data were analyzed by PROC MIXED of SAS. The in vitro dry matter and organic matter digestibilities of the rice straw with high nutritional value was improved by MPES, while the combination of MPES + ES supplements inhibited the digestibility of this straw. Dietary carbohydrate and nitrogen increased through MPES and MPES + ES supplements resulted in an increase in NH3-N concentration and a decrease in CO2 production due to the microbial mass formation. However, this increase was not enough to improve organic matter degradability parameters, cummulative gas production, gas production kinetics, and acetate:propionate ratio and reduce methane emissions. The straw with high nutritional value showed greater content of nitrogen fraction a, effective degradability, cummulative gas production, and methane and CO2 productions comparing with low-nutritional value straw. The use of MPES and MPES + ES supplements can be used as strategy to mitigate CO2 in ruminant production systems that use rice straw.