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The aim of this work was to optimize the process of elaborating liver pâtés and omental lamb fat and to evaluate the quality of the products. Livers and fats were obtained from lambs fed with diets composed of corn and soybean meal that were partially replaced by cupuaçu, tucumã and palm kernel cake. To prepare the pâtés, livers were baked for 20 minutes at 100°C, weighed, seasoned, crushed, packaged and pasteurized. The best formulation of the pâté was with 40% liver, 10% fat, 35% water, and pasteurized for 20 minutes at 65°C. The pâté from the livers of lambs fed with palm kernel cake obtained a higher caloric value of 193.05 kcal/100 g and all pâtés met the recommended microbiological quality. There was a significant effect (p< 0.05) of the diets on the aroma and texture of the liver pâtés of lambs fed corn and soybean meal and palm kernel cake, and these were 6.38 and 3.37, respectively. Thus, the pâtés can be considered an alternative to increase the options for consumption of liver from lambs, and also for adding commercial value to lamb viscera. [ABSTRACT FROM AUTHOR]

The nutritional composition of bovine liver, particularly in terms of vitamins E, β-carotene, and cholesterol concentration, is significantly influenced by the cattle-rearing system and diet. This study aimed to elucidate the impact of four predominant cattle-rearing systems in the Eastern Amazon region on the vitamin E, β-carotene content, and cholesterol levels in bovine liver during the rainy season. Liver-tissue samples were collected from 48 cattle, with twelve specimens representing each rearing system. The systems encompassed two native pastures located in flood-prone areas, cultivated pastures on upland terrain and a confinement-rearing system. Our findings indicate that, when considering all rearing systems collectively, there were no significant differences in the levels of vitamins and cholesterol in the liver tissues (p > 0.05). However, a marked disparity in cholesterol levels emerged when comparing intensive rearing systems to extensive ones, with the former demonstrating notably higher concentrations (p = 0.01). Additionally, the intensive rearing system was associated with elevated levels of β-carotene (p < 0.01), α-tocopherol (p = 0.01), and β-tocopherol (p = 0.01) relative to the extensive systems. No significant variations were observed amongst the different extensive systems (p > 0.05). These results suggest that, while all rearing systems yielded liver tissues with typical concentrations of vitamins and cholesterol, the intensive rearing system led to a higher accumulation of certain vitamin compounds. This study highlights the substantial nutritional implications of different cattle-rearing systems in the Eastern Amazon and provides valuable insights for developing dietary strategies to optimize the nutritional quality of bovine liver. Therefore, the generated results are groundbreaking in the Eastern Amazon, Brazil, and inspire the development of new research projects to address other demands in this field and achieve additional outcomes. [ABSTRACT FROM AUTHOR]

Simple Summary: This review aims to deepen the understanding of buffalo farming in the Amazon, presenting the quality and nutritional value of buffalo meat and liver. We will explore the characteristics of nutrients and their influence on human health, with a special focus and particular emphasis in vitamins, minerals, and lipids. By investigating fatty acids and cholesterol, we seek to understand the complexity of lipids and their contribution to nutritional quality. The main objective of this study was to provide subsidies to improve buffalo farming practices, promote a healthier human diet and contribute to environmental sustainability in the Amazon region. Thus, this review aims to deepen the understanding of buffalo farming in the Amazon, presenting the quality and nutritional value of buffalo meat and liver. This information serves as a subsidy to improve practices related to the breeding system, nutrition, health and sustainability associated with aquatic buffaloes. For this, a review of the databases was carried out using the descriptors "nutritional value of buffalo meat", "nutritional value of buffalo liver" and "buffalo breeding in the Amazon". Thus, the consumption of foods derived from aquatic buffaloes has important nutritional value for human consumption. In view of this, it is possible to conclude that the nutrition of these animals is influenced by the biodiversity of the Amazon, giving unique characteristics to its products, also highlighting the importance of carrying out research that aims to value the potential use of this species and strengthen the economy of the region. [ABSTRACT FROM AUTHOR]

Simple Summary: Environmental factors like climate, diet, and farming methods significantly affect microbial activity and composition. Understanding these adjustments is crucial for improving ruminant nutrition and production. This review summarizes research on rumen microbiota and molecular methods for microbial identification in ruminant rumen fluid. Analyzing rumen microbiology in various ruminants is challenging due to environmental and nutritional influences on microbial interactions. Key genera include Entodinium spp. and Aspergillus spp. for protozoa and fungi, respectively, with Fibrobacter spp. prevalent among bacteria. Major techniques involve DNA extraction, amplification, and sequencing. In conclusion, this review highlights the knowledge in the literature about rumen microorganisms and the associated molecular approaches. Variations in environments, including climate, diet, and agricultural practices, significantly impact the composition and microbial activity. A profound understanding of these adaptations allows for the improvement of nutrition and ruminant production. Therefore, this review aims to compile data from the literature on the rumen microbiota and molecular techniques for identifying the different types of microorganisms from the rumen fluid of ruminants. Analyzing the literature on rumen microbiology in different ruminants is complex due to microbial interactions, influenced by the environment and nutrition of these animals. In addition, it is worth noting that the genera of protozoa and fungi most evident in the studies used in this review on the microbiology of rumen fluid were Entodinium spp. and Aspergillus spp., respectively, and Fibrobacter spp. for bacteria. About the techniques used, it can be seen that DNA extraction, amplification, and sequencing were the most cited in the studies evaluated. Therefore, this review describes what is present in the literature and provides an overview of the main microbial agents in the rumen and the molecular techniques used. [ABSTRACT FROM AUTHOR]

Simple Summary: The El Niño presents itself as a serious problem in the pastures of the northern region of Brazil, as it compromises the availability and quality of forage and water. Therefore, the objective of this study was to characterize the thermographic profile of three production systems in the Eastern Amazon, Brazil. The results show significant differences between areas with and without chestnut tree shade. Between August and November, the highest temperatures were recorded in full sun pastures, contrasting with lower temperatures in shaded areas. The interaction between the systems revealed significant thermal variations, highlighting the positive impact of native trees on thermal regulation and indicating possible strategies to mitigate the adverse effects of El Niño. The El Niño represents a substantial threat to pastures, affecting the availability of water, forage and compromising the sustainability of grazing areas, especially in the northern region of Brazil. Therefore, the objective of this study was to characterize the thermographic profile of three production systems in the Eastern Amazon, Brazil. The study was conducted on a rural cattle farm in Mojuí dos Campos, Pará, Brazil, between August and November 2023. The experiment involved livestock production systems, including traditional, silvopastoral and integrated, with different conditions of shade and access to the bathing area. An infrared thermographic (IRT) camera was used, recording temperatures in different zones, such as areas with trees, pastures with forage and exposed pastures. The highest mean temperatures (p = 0.02) were observed in pastures with full sun from August to November. On the other hand, the lowest average temperatures were recorded in areas shaded by chestnut trees (Bertholletia excelsa). The highest temperature ranges were found in sunny areas and the lowest were recorded in shaded areas. The highest temperatures were observed in the pasture in full sun, while the lowest were recorded in areas shaded by chestnut trees (p < 0.0001). The interaction between the systems and treatments revealed significant temperature differences (p < 0.0001), with the native trees showing an average temperature of 35.9 °C, lower than the grasses and soil, which reached 61.2 °C. This research concludes that, under El Niño in the Eastern Amazon, areas shaded by Brazil nut trees had lower temperatures, demonstrating the effectiveness of shade. Native trees, compared to grasses and soil, showed the ability to create cooler environments, highlighting the positive influence on different species such as sheep, goats and cattle. [ABSTRACT FROM AUTHOR]

Simple Summary: The objective was to characterize the pastures by grazing cycle, as well as to evaluate the performance of buffaloes in intensive rotational grazing in a silvopastoral system in the eastern Amazon supplemented with agro-industry co-products in order to characterize the grazing cycles, the composition of the fractions and the carcass yield. Fifteen non-castrated, crossbred water buffaloes (Murrah × Mediterranean) were used. Forage protein varied: leaves contained 11.4% protein in the leaves and 50% FDA in the stems. The grass had higher amounts of B3/B2 proteins, which are less indigestible in leaves (17.16%). Forage production varied; the second cycle was better (leaf/stem 2.11). Despite a varied supplement intake, daily weight gain (1 kg/day) and carcass yield (49.23%) showed no differences, ensuring cost-effective, sustainable production. Incorporating supplements derived from coconut and palm kernel co-products enhances performance and carcass yield, comparable to standard supplements. This practice lowers production expenses, optimizes forage utilization, and enhances production chain sustainability, making it a recommended approach. The objective was to characterize the pastures by grazing cycle, as well as to evaluate the performance of buffaloes in intensive rotational grazing in a silvopastoral system in the eastern Amazon supplemented with agro-industry co-products in order to characterize the grazing cycles, the composition of the fractions, and the carcass yield. Fifteen non-castrated, crossbred water buffaloes (Murrah × Mediterranean) were used. All animals used in the study were clinically healthy and weighed approximately 458 kg. The animals were grazed in a single group, and supplementation (1% of live weight—LW/day) was divided into three treatments: control (control—conventional ingredients); Cocos nucifera coconut cake (Cocos nucifera) (coconut cake—70%); and palm kernel cake (Guinean elaeis) (palm kernel cake—70% palm kernel cake). The chemical composition of the forage is different in each part of the plant, with higher protein values in the leaves (11.40%) and higher acid detergent fiber (ADF) values in the stems (50.03%). Among the ingredients of the supplement, corn has the highest percentage of indigestible protein (35.57%), most of the protein in palm kernel cake is B3 (49.11%), and in Coco, B2 (51.52%). Mombasa grass has a higher percentage of B3 and B2 proteins; the indigestible fraction is lower in the leaves (17.16%). The leaf/stem ratio also varied between grazing cycles, being better in the second cycle (2.11%) and with an overall average of 1.71. Supplement consumption varied between cycles and was higher in the control treatment, with an overall mean of 4.74. There was no difference in daily weight gain and carcass yield, with an average of 1 kg/day and 49.23%, respectively. Therefore, it can be concluded that including supplements based on by-products from the coconut and palm oil agro-industries promotes performance and carcass yields compatible with conventional supplements. Their use reduces production costs, optimizes the utilization of forage mass, enhances the sustainability of the production chain, and, therefore, is recommended. [ABSTRACT FROM AUTHOR]

Simple Summary: The objective of this work was to evaluate the effects of climatic conditions and supplementation based on palm kernel cake, on the thermoregulation of crossbred buffaloes in the eastern Amazon. Over a 12-month period, 24 female buffaloes with an initial age of 54 ± 7 months and an average weight of 503.1 ± 23 kg were divided into four groups with different levels of palm kernel cake supplementation relative to body weight. The animals were kept in Brachiaria brizantha pastures with access to water and mineral salt. Supplementation did not influence the physiological variables of thermoregulation. Throughout the year, mean values of rectal temperature, respiratory rate and body surface temperature were higher in the afternoon (p > 0.05). Supplementation with palm cake did not result in influences on the thermoregulation of buffaloes in the study region. The respiratory rate showed an association with the annual seasonality of temperatures, with higher averages in the afternoons of the rainy season. The positive correlation between the rectal temperature, respiratory rate, and body surface temperature indicates that buffaloes respond to atmospheric thermal elevations (afternoon period), which is reflected in increasing thermal indices. In ruminants, diet composition has a positive correlation with heat production, which can influence thermoregulation, energy expenditure and, consequently, animal performance. The objective of this work was to evaluate the effects of climatic conditions and supplementation based on palm kernel cake, on the thermoregulation of crossbred buffaloes in the eastern Amazon. The research was carried out at Embrapa Amazônia Oriental (01°26′ S and 48°24′ W), Belém, Pará, and lasted 12 months (representing the entire year). Twenty-four buffaloes, females, with initial age and an average weight of 54 ± 7 months and 503.1 ± 23 kg, respectively, non-pregnant, non-lactating and clinically healthy were used, divided into four treatments based on the supplementation content of the palm cake (%DM) in relation to their body weight (%): 0, 0.25, 0.50 and 1.0. The animals were kept in paddocks with Brachiaria brizantha (cv. Marandu), in a rotating system, with water to drink and mineral salt ad libitum. Equipment was installed to record environmental data (temperature and relative humidity, dew point temperature, wet bulb and black globe) and physiological data: rectal temperature (RT); respiratory rate (RR); and body surface temperature (BST), recorded twice a day, always in the morning (6:00 a.m. to 7:00 a.m.) and afternoon (12:00 p.m. to 1:00 p.m.) shifts, and were used to calculate the Globe Temperature and Humidity Index (GTHI). Supplementation did not influence the physiological variables of thermoregulation (p > 0.05). However, there were differences in the GTHI between the shifts, with higher means in the afternoon shift, especially in the less rainy period of the year, where the GTHI reached 92.06 ± 2.74 (p < 0.05). In all periods of the year, the mean values of RT, RR and BST were higher in the afternoon shift (p > 0.05). The respiratory rate (RR) is associated with the annual seasonality of the thermal waters, with higher averages in the afternoons of the rainy season. The positive correlation for rectal temperature, respiratory rate and body surface temperature indicated that buffaloes respond to thermal elevations in the atmosphere (afternoon period) and, consequently, reflect on the GTHI. Supplementation does not influence thermoregulation; the changes observed occurred in response to the region's thermal and rainfall conditions (mainly in the afternoon shift), with higher GTHI values. [ABSTRACT FROM AUTHOR]

The characterization of dairy farming is fundamental for the sector, as the information obtained directs institutional and public policy actions, which contribute to the development of the milk production chain. The objective of this research was to highlight and analyze two points: identify the spatial concentration of production and investigate the existence of centers specializing in milk production; evaluate the sources of growth in dairy farming in micro-regions of Pará and verify their participation in the growth and productivity of the herd. Regarding specialization in milk production, in the initial year of the study, there were nine specialized micro-regions; however, in the final year, only six fell into this classification, being Parauapebas, Marabá, Tucuruí, Redenção, São Félix do Xingu, and Altamira. Southeastern Pará stands out as the main dairy hub in the state, which encompasses municipalities with a tradition in dairy farming, such as Água Azul do Norte, the largest state producer since 2012. The effective growth in milk production from the 1990s to 2020 showed an increase in state production of 3.23% per year, with a greater contribution to this growth in herd productivity gains than in relation to the expansion of the herd; however, ten micro-regions presented a negative average annual growth rate, being located in the Northeast of Pará, Marajó, and the Metropolitan Region of Belém, a result resulting from the reduction of the herd expansion effect, as the productivity effect of all micro-regions exhibited positive rates, with the exception of Cametá and Arari. The sharpest decline occurred in Arari, with a sharp drop in milk production, number of animals milked, and cow yield. The twelve micro-regions with positive annual rates are located in the mesoregions of Southeast Pará, Southwest Pará, and Baixo Amazonas, nine associated with intensive growth and three more linked to extensive growth. In general, the results show that the regions specialized in the activity are more articulated, presenting the highest percentages in terms of quantity produced, herd milked, and financial movement, compared to non-specialized locations. Through analyses, it is possible to obtain a better understanding of the regional growth process, with a focus on dairy activity, as the information and particularities of properties are fundamental to guide public and private institutions on the reality and existing problems, enabling readjustment and new policy formulations with the aim of alleviating producers' limitations, as well as enhancing growth and reducing intra- and inter-regional imbalances. [ABSTRACT FROM AUTHOR]

Simple Summary: This study evaluated the influence of Amazonian ecosystems, during the dry and rainy seasons, on the composition of the livers of water buffaloes (Bubalus bubalis) raised in the Eastern Amazon in extensive and intensive systems. The results showed that the total lipid content was affected by location and season. Total cholesterol, α-tocopherol and γ-tocopherol were influenced by the interaction between ecosystems, location and seasonal periods. Animals raised in pastures had higher levels of omega-3, while those in confinement had higher levels of omega-6. Amazonian ecosystems influenced the nutritional values of buffalo livers, with better results in the extensive system. The diet offered to animals has a great influence on the composition of tissues and, consequently, the quality. The objective of this study was to evaluate the influence of Amazonian ecosystems, in the dry and rainy periods of the year, on the composition of cholesterol, tocopherols, β-carotene and the fatty acid profile of the livers of water buffaloes (Bubalus bubalis) reared in the Eastern Amazon, in an extensive or intensive system. Total lipid content was influenced by the location and time of year (p < 0.05). Ninety-six male water buffaloes were used (12 per sampling period), aged between 24 and 36 months, with average weights of 432 kg (end of the rainy season) and 409 kg (end of the dry season). Total cholesterol, α-tocopherol and γ-tocopherol influenced the relationship between extensive vs intensive ecosystems, location, periods and the interaction between the location and period of the year (p < 0.05). Animals raised in a pasture ecosystem had the highest values of omega-3, and those raised in confinement, the highest values of omega-6 (p < 0.05). The proportions of n-6/n-3 and hypocholesterolemia (7.14) and hypercholesterolemia (3.08%) (h/H) were found in greater amounts in animals raised in confinement (p < 0.05). The atherogenic index (AI) had a higher value in the rainy season, in animals raised in Santarém (2.37%), with no difference between pasture and feedlot ecosystems, except in animals raised in the rainy season in Nova Timboteua, with a lower AI (1.53%). The thrombogenicity index (TI) was higher in the livers of confined animals (0.32%) and lower (0.18%) in those raised in Nova Timboteua (rainy season). Amazonian ecosystems influence the nutritional values of buffalo liver, with the best nutritional values in animals in the extensive system. [ABSTRACT FROM AUTHOR]

Simple Summary: This study aimed to characterize the thermal patterns of cattle raised in three different production systems during the transition period in the eastern Amazon, Brazil, using infrared thermography and by evaluating thermolytic responses. The evaluated systems were silvopastoral (with shade and no access to the bathing area), traditional (without shade and with no access to the bathing area), and integrated (with access to the shade and the bathing area). The thermographic images showed that the silvopastoral system, with shading, provided more favorable thermal conditions compared to the other systems. Physiological analyses revealed that the cattle maintained a rectal temperature within normal ranges in all systems. However, the respiratory rate was higher in the traditional system, indicating possible thermal stress in this environment. The thermal comfort indices indicated moderate stress conditions at times of greater solar intensity in all systems. In general, the results suggest that the silvopastoral system offers better thermal conditions for cattle, providing shade and reducing thermal stress. Thus, management practices aimed at animal welfare and productivity in production systems in the eastern Amazon region can be adopted by ranchers. In the Lower Amazon mesoregion, there are basically three types of production systems: the traditional (without shade and no bathing area), the silvopastoral (with shade and no bathing area), and the integrated (with shade and bathing area). It is considered that the type of production system influences the thermal comfort and productivity of cattle, so this research aims to evaluate the influence of these three types of production systems on the thermoregulation of Nellore cattle. The experiment was carried out on a rural property for raising cattle, located in Mojuí dos Campos, Pará, Brazil, during the transition period (June/July). Thirty bovine males (not castrated, aged between 18 and 20 months, average weight of 250 ± 36 kg, body condition score of 3.5, clinically healthy) were randomly divided into three groups: Silvopastoral System—SS (n = 10), Traditional System—TS (n = 10), and Integrated System—IS (n = 10). Climate variables were collected (air temperature (AT °C), relative humidity (RH %), wind speed (WS, m/s), solar radiation (SR), black globe temperature (BGT °C), and physiological parameters, such as respiratory rate (RR) and rectal temperature (RT)) at 6 a.m., 12 p.m., 6 p.m., and 12 a.m. to determine the thermal comfort situation of the animals. Thermographic images of the environment and animals were captured in order to obtain the body surface temperature (BST) through infrared thermography. The Benezra Thermal Comfort Index (BTCI), Environmental Stress Index (ESI), Equivalent Temperature Index (ETI), and Iberian Heat Tolerance Index (Iberian HTI) were used. The results showed that the silvopastoral system, with shading by chestnut trees and an ample vegetative area, presented better thermal conditions, with an average of 28.98 °C, in comparison with the traditional system (35.93 °C) and the integrated one (34.11 °C). It was observed that the body surface temperature of cattle did not differ significantly between the anatomical regions of the body and the studied systems (p > 0.05). As for the respiratory rate, the traditional system registered higher values, with an average of 41 movements per minute, indicating possible thermal stress (p < 0.05). The thermal comfort indices revealed that all systems presented moderate stress conditions during times of higher solar intensity. It is concluded that the silvopastoral system proved to be more favorable for cattle, providing shade and reducing thermal stress, which may have a positive impact on animal welfare and productivity in this region. [ABSTRACT FROM AUTHOR]

The goal of this study was to verify the effect of heterogeneity of variance (HV) on milk production in up to 305 days of lactation (L305) of daughters of Girolando, Gir and Holstein sires, as well as in the genetic evaluation of these sires and their progenies. in Brazil. The model included contemporary groups (consisting of herd, year and calving season) as a fixed effect, cow age at calving (linear and quadratic effects) and heterozygosity (linear effect) as covariates, in addition to the random effects of direct additive genetic and environmental, permanent and residual. The first analysis consisted of the single-trait animal model, with L305 records (disregarding HV). The second considered classes of standard deviations (SD): two-trait model including low and high classes (considering HV), according to the standardized means of L305 for herd-year of calving. The low SD class was composed of herds with SD equal to or less than zero and the high class with positive SD values. Estimates of (co)variance components and breeding values were obtained separately for each scenario using Bayesian inference via Gibbs sampling. Different heritability was estimated. Higher for the high DP class in the Gir (0.20) and Holstein (0.15) breeds, not occurring the same in the Girolando breed, with a lower value among the classes for the high DP (0.10). High values of genetic correlations were also found between low and high SD classes (0.88; 0.85 and 0.79) for the Girolando, Gir and Holstein breeds, respectively. Like the order correlations (Spearman) which were also high for the three breeds analyzed (equal to or above 0.92). Thus, the presence of HV had a smaller impact for L305 and did not affect the genetic evaluation of sires. [ABSTRACT FROM AUTHOR]

Our aim was to evaluate the use and application of different nonlinear mixed models, as well as to compare them with approach in nonlinear fixed models, for describing the growth curve of meat-type quails according to gender. A total of 15,002 and 15,408 records of males and females were used, respectively. The body weights were regressed on age of the animals using nonlinear models (Brody; Gompertz; Logistic, Morgan-Mercer-Flodin, Richards and Von Bertalanffy). All model parameters were considered fixed, whereas parameters related to asymptotic weight and maturity rate were fitted as random effects. The Bayesian Information Criterion was used to find the model of best fit. For both genders, the model that used the Morgan-Mercer-Flodin function with the inclusion of asymptotic weight as a random effect was considered the best-fitting model because it reduced the residual variance and increased the accuracy. Based on the lower absolute growth rate and growth velocity of male quails compared to that of females, it can be inferred that males should be slaughtered later. Given the results of this study, it can contribute to the current knowledge about animal yield, specifically at the best moment to slaughter and, this sense, improv the quality genetic of the populations in time. [ABSTRACT FROM AUTHOR]

The work aims to study the economical losses of the condemnation of bovine and buffalo carcasses, in order to estimate the losses in animals slaughtered in Santarém-Pará, Brazil, between 2016 and 2018, with data obtained from the Municipal Department of Agriculture and Fisheries. Sex, age, origin, total number of animals slaughtered and causes of condemnation of carcasses were considered. All analyzes were performed in RStudio version 1.1.463. In this study, 71,277 bovine carcasses and 2,016 buffalo carcasses were inspected, of which 300 bovine and 71 buffalo were condemned. The highest prevalence of causes of condemnation in cattle was recorded for brucellosis (0.0020%) and tuberculosis (0.0019%). In buffaloes, tuberculosis (0.0307%) peritonitis (0,0019%) were the main causes of condemnations. Economical losses were more evident in females, for both species. The projection of economical losses related to the condemnation of carcasses showed a sharp growth for the next three years, if the average growth remains constant. The biggest projected loss was for bovine females, with an accumulated projection of $ 5,451.44. The smallest estimated loss was for buffalo males, projected at more than thirty-two thousand reais. The most important causes of condemnation report the diseases brucellosis and tuberculosis, as the ones with the greatest impact. In the buffalo species this was even more accentuated, even though the number of buffaloes slaughtered is more than 35 times smaller than the number of cattle. [ABSTRACT FROM AUTHOR]

Simple Summary: Mixed nonlinear models are an extension of mixed models combined with nonlinear models, allowing one or more parameters of the nonlinear regression function to be considered both as fixed and random effects. This work was carried out with the objective of comparing the use of several nonlinear functions of the fixed and mixed linear models to determine the body growth of both sexes in Nelore cattle. For this, body weight records were used to describe the growth curve of the animals. The Brody function obtained the best adjustments according to the evaluators, finding a reduction in the residual variance of 79 and 83%, for males and females, respectively. The absolute growth rate for males ranged from 0.921 to 0.261 kg/day and for females from 0.922 to 0.198 kg/day, while the relative growth rate ranged from 2.55 to 0.06% for females and from 2.39 to 0.08% for males. Males showed greater growth acceleration at the beginning of the growth trajectory, equaling the females at 397 days of age, and thereafter presented lower estimates. Nonlinear regression in the context of mixed models allows for a reduction in residual variance and an increase in model precision. Body weight records were used to characterize the growth curve of Nelore cattle. Body weight was regressed as a function of age, for both sexes, by using nonlinear models through the functions of Brody, Gompertz, Logistic, Richards, Meloun 1, Von Bertalanffy, and Von Bertalanffy. The quality of the model arrangements was evaluated by employing Akaike and Bayesian Schwarz information criteria. The Brody function provided the best adaptations by the evaluators and, considering the asymptotic weight and the maturation rate as random, a reduction in residual variance of 79% for males and 83% for females was obtained in relation to the models under fixed contexts. In males, the absolute and relative growth rates ranged from 0.921 to 0.261 kg/day and 2.39 to 0.08%, respectively. For the same rates, under another approach, females ranged from 0.922 to 0.198 kg/day and 2.55 to 0.06%, respectively. Males showed greater growth acceleration at the beginning of the growth trajectory, being equal to females at 397 days of age and from that age onward they presented lower estimates. The nonlinear regression model approach under the mixed-models context allows reduction of residual variance, increasing model accuracy. [ABSTRACT FROM AUTHOR]