Graduation date: 1992

Feedlot performance, carcass merit and chemical composition were compared using Waguli , Brangus, Hereford x Tuli and Wagyu x Crossbred Gene Combination (CGC) breeds. Steers were penned in the following manner: 6 Waguli steers, 6 Hereford x Tuli, 6 Wagyu x CGC and 8 Brangus. There was a significant difference (P<0.05) between Brangus and Waguli for ADGs. F:G was lower (P<0.05) for Hereford x Tuli compared to the other crossbreeds. A heavier final weight was observed (P<0.05) for the Wagyu x CGC than all other crossbreds. There was a significant difference (P<0.05) for REA between Wagyu x CGC and Hereford x Tuli and Waguli. Wagyu x CGC had higher shear force values (SFV) (P<0.05) than all other crossbreeds. Cost of gain was lower (P<0.05) for Hereford x Tuli compared the other breeds. Hereford x Tuli also had less protein (P<0.05) than to the other breeds.A second study was conducted comparing limit feeding (LF) vs. full feeding (FF) strategies. 23 steers and 27 heifers were penned by sex and were randomly assigned a treatment; 4 pens received the LF treatment and 4 were FF. ADG was lower (P<0.05) for LF and FF heifers compared to both LF and FF steers. Dressing percentage was lower (P<0.05) for LF steers compared to LF and FF Heifers. LF heifers YG was higher (P<0.05) compared to FF steers. Quality grades were higher (P<0.05) for LF and FF heifers compared to LF and FF steers. REA /cwt was significantly higher (P<0.05) for FF heifers compared to LF and FF steers. SFV were11lower (P<0.05) for FF heifers compared to LF and FF steers. A significant difference (P<0.05) in cost of gain was noted between LF steers and the rest, also between LF heifers and FF steers. Primal cut price/cwt was significantly lower (P<0.05) for LF heifers compared to FF steers. Lipid percentage was higher (P<0.05) LF heifers compared to FF steers. Moisture percentage was lower (P<0.05) for LF heifer compared to the other groups.

The purpose of this study was to investigate the economic feasibility of alternative crop rotations and to determine the economic implications of including forages and livestock during the transition to organic agriculture in Nova Scotia. The rotation systems were distinguished by: (i) frequency of forage in the rotation, (ii) source of nutrient supply, and (iii) type of farming operation. The economic analysis was divided in two parts. The first part analysed data from a four-year crop rotation experiment, using enterprise budgeting and statistical methods to compare differences among rotations under different treatments. The second part involved the development of a multi-period linear programming (LP) model to simulate a commercial operation. / The results from the statistical analysis suggest that crop enterprise net returns tended to be higher in forage-based rotations and in the livestock systems compared to cash crop rotations and the stockless system. Results from the LP model suggest that including forages and beef cattle during the transition to organic agriculture can provide considerable economic benefits, especially when crops were grown under ruminant compost.

Kikuyu pasture (Pennisetum clandestinum) is potentially the most important source of roughage used to feed dairy heifers in summer in KwaZulu-Natal. It is commonly believed that on kikuyu pasture beef breed females grow at a faster rate than those from dairy breeds when no supplementation is given. Little conclusive evidence is, however, available to support this. Explanations as to why such differences may exist are also limited. Eight Hereford and eight Holstein heifers of similar age and maturity stage were used in a trial. The trial was run over a twenty week period. For the first ten weeks all the animals in the trial grazed ad libitum kikuyu pasture with no supplementation except for a mineral lick. Over this (grass only) period the two breed groups formed the two treatments. During the second ten week period of the trial all of the Holsteins and four of the Herefords were fed a restricted but equivalent amount (1 .7 kg) of a maize meal based concentrate. The use of a computerized, mobile feeding system allowed concentrate intake of individual animals to be measured. Animal height, weight and condition score readings were taken weekly over the grass only and the concentrate (final seven weeks) periods of the trial. Herbage intake and digestibility were estimated using n-alkanes as indigestible markers in two experiments conducted during the grass only and concentrate periods. The Herefords had a significantly higher ADG than the Holsteins (0.82 vs. 0.04 kg/day; P < 0.01) over the grass only period. During the concentrate period the rate of mass gain of the Holstein treatment did not differ significantly (P >0.05) from the Hereford treatment receiving concentrate. The Herefords receiving concentrate were also not significantly different (P > 0.05) in rate of mass gain from the Herefords not receiving concentrate. Rate of height gain was not significantly different (P> 0.05) between treatments over either the concentrate or the grass only periods. During the grass only period the Holsteins lost condition (0.07 condition score units per week) whilst the Herefords gained condition at an equivalent rate. The voluntary intake of concentrates was not significantly different (P > 0.05) between the Herefords and Holsteins (19.19 vs. 16.40 g/kg/L.W(liveweight) (0.75)). Regression coefficients relating level of concentrate intake to rate of mass gain were also not significant (P > 0.05) for either of the treatments receiving concentrate. The use of n-alkanes as indigestible markers showed the intake of the Holstein treatment to have an intake 55% (P < 0.0 1) higher than the Herefords (185.4 vs. 120.5 g/kg L.W(0.75)) over the first experiment where both treatments were grazing ad lib. kikuyu alone (grass only period). During the concentrate period intake of the Herefords receiving concentrate exceeded that of the Holsteins (P < 0.01) by 23% (139.1 vs. 113.1 g/kg L.W(0.75)). Review of the literature, suggests that the double alkanes technique greatly over-estimated intake. Errors in herbage sampling (accentuated by pasture rotation in the first experiment), a low daily dose of the synthetic alkane (C(32)) and incorrect estimation of the C(32) content in the daily doses are identified as possible causes of the over-estimation of intake. Faecal recoveries of the herbage n-alkanes were demonstrated to increase with increasing chain length and hence C(35) was proposed as the most reliable herbage alkane for dry matter digestibility determination. Digestibility differences between treatments estimated using the C(35) alkane were not significantly different (P > 0.05) in either the first or second experiments. The mean digestibility estimates (using the C(35) alkane) for the first and second experiments were 64.9 and 56.61 %, respectively. In conclusion, higher growth rates of Herefords on kikuyu pasture would seem to be primarily due to differences in the dry matter intake of the grazed herbage. Further work using other breeds of dairy and beef animals is required. The underlying cause of differences in dry matter intake between breeds also requires investigation. / Thesis (M.Sc.Agric.)-University of Natal, Pietermaritzburg, 1995.

The release of the Illumina BovineSNP50 BeadChip in late 2007 has drawn attention from cattle breeders around the world to develop breeding programs that leverage association of these single nucleotide polymorphism (SNP) with economically important quantitative trait loci (QTL). In that context this project has come to study applications of the SNP panel in beef cattle. Analysis of linkage disequilibrium (LD) existing in Angus, Charolais, and crossbred animals revealed the pattern of LD within each breed group, as well as the persistence of LD phase between pairs of the breed groups. This is important for genomic selection where SNP are trained in one population and used to predict breeding value for animals in another population. Detection of chromosome regions potentially carrying QTL or causative mutations affecting the phenotypic variation in economically important traits was presented at individual SNP and haplotype levels. There were 269 SNP associated (P<0.001) with birth weight (BWT), weaning weight (WWT), average daily gain (ADG), dry matter intake (DMI), mid-test metabolic weight (MMWT), residual feed intake (RFI). They explained 1.64% - 8.06% of the phenotypic variation in these traits. There were 520 SNP associated (P<0.001) with carcass quality traits, namely hot carcass weight, back fat thickness, ribeye area, marbling scores, lean yield grade by Beef Improvement Federation, steak tenderness, and six rib dissection traits. These SNP explained 1.90 - 5.89% of the phenotypic variance of the traits. Many of the significant SNP were located on chromosome 6. Six haplotypes were found associated (P<0.05) with ADG, DMI, and RFI. In order for genomic selection to happen in beef cattle, higher density SNP panels should be made available at low genotyping cost. However, the cost of genotyping animals for high density SNP chip is still high, thus genotype imputation has come to practice. The last chapter of this thesis compared two approaches presently used in genotype imputation, investigated factors affecting imputation accuracy, as well as the impact of imputation accuracy on genomic estimated breeding value (GEBV). It proved that the highest possible accuracy of GEBV is attainable with sufficiently large groups of reference animals. / Ontario Ministry of Agriculture, Food and Rural Affairs. Ontario Cattlemen’s Association. Ontario Farm Innovation Program. Agriculture and Agri-Food Canada’s Growing Forward Program. Agriculture Adaptation Council. Ontario Research and Development Program. MITACS Accelerate. Beef Improvement Opportunities.

Made available in DSpace on 2014-06-11T19:32:57Z (GMT). No. of bitstreams: 0 Previous issue date: 2014-01-20Bitstream added on 2014-06-13T18:44:40Z : No. of bitstreams: 1 sarti_lmn_dr_botfmvz.pdf: 586571 bytes, checksum: 1ac7284e05a3eca975e4a50d8f0bcde2 (MD5) / O objetivo neste estudo foi avaliar os efeitos da adição de fontes de lipídeos naturais e protegidos da degradação ruminal na dieta de bovinos Nelore durante o período pré-condicionamento e confinamento no desempenho e características de carcaça. Foram utilizados cento e vinte bovinos, machos, não castrados, da raça Nelore (366,9 ± 28,7 kg) de aproximadamente 24 meses, provenientes de sistema de recria em pasto. O delineamento experimental foi inteiramente casualizado, composto por três dietas caracterizando os tratamentos: (CONTR) sem fonte adicional de lipídeo, (GDESP) com fonte de lipídeo natural a base de coprodutos do algodão (torta de algodão), e (GPROT) com fonte de lipídeo protegido rico em ácidos graxos poli-insaturados. O estudo foi dividido em duas fases: pré-condicionamento, 30 dias antes do transporte, com os animais mantidos em pasto recebendo suplementação a base de grãos com adição ou não de fonte de lipídeo conforme os tratamentos; e confinamento. Antes do embarque, os animais foram pesados e logo depois transportados por aproximadamente 16 horas. No confinamento, os animais foram mantidos em 24 baias com cinco animais por baia, sendo que cada tratamento foi composto por oito baias, consideradas as unidades experimentais, e pesados a cada 21 dias. O uso de torta de algodão (GDESP) proporcionou maiores ganhos de peso na fase de pré-condicionamento. Contudo, os animais suplementados com lipídios protegidos (GPROT) durante o período de confinamento apresentaram desempenho semelhante (peso vivo final, ganho de peso diário, conversão e eficiência alimentar)... / The aim of this study was to evaluate the effects of adding sources of natural lipids and rumen-protected PUFA to the diet of Nellore cattle in the preconditioning and feedlot periods on performance and carcass characteristics. One hundred and twenty 24-mo-old Nellore yearling bulls were used (366.9 ± 28.7 kg), coming from rearing on pasture system. The experimental design was completely randomized, consisting of three diets according to the treatments: (CONTR) without additional source of lipid, (GDESP) with source of natural lipid based on co-products from cotton (cottonseed cake), and (GPROT) with rumen-protected lipid source rich in polyunsaturated fatty acids. The study was divided into two phases: pre-conditioning, 30 days before shipping, the animals were kept on pasture receiving supplement just described with or without lipid source according to the treatments; and feedlot. Prior to shipment, the animals were weighed and transported approximately for 16 hours. In feedlot, animals were kept in 24 pens with five animals per pen, 8 pens per treatment, which were considered the experimental units, and weighed every 21 days. The use of cottonseed cake (GDESP) led to greater weight gains during preconditioning. However, animals supplemented with GPROT during the feedlot period presented similar performance (final body weight, average daily gain, feed conversion and efficiency) to animals that consumed GDESP treatment, but lower intake of dry matter was observed in the GPROT treatment compared GDESP. The fat sources did not influence carcass characteristics... (Complete abstract click electronic access below)

Resumo: Características de carcaça preditas por ultrassonografia foram incluídas nos programas de avaliação genética, uma vez que estas estão associadas à qualidade e rendimento de carcaça. Neste trabalho, os objetivos foram estimar os parâmetros genéticos e as tendências genéticas para área de olho de lombo (AOL), espessura de gordura subcutânea (EG) e espessura de gordura subcutânea de garupa (EGP8), peso corporal aos 210 (P210) e aos 365 (P365) dias de idade em bovinos da raça Nelore. Foram analisados dados de animais nascidos entre 1998 e 2008, oriundos de fazendas participantes do Programa de Melhoramento Genético da Raça Nelore (Nelore Brasil). As estimativas dos componentes de (co) variância, dos parâmetros genéticos e valores genéticos para as características estudadas foram obtidas pelo método da máxima verossimilhança restrita, sob modelo animal multi-característica. Para as características de peso as estimativas de herdabilidade genética direta e materna foram: 0,26 ± 0,003 e 0,18 ± 0,01, para P210 e 0,39 ± 0,02 e 0,05 ± 0,01, para P365. As estimativas de herdabilidade para AOL, EG e EGP8 foram iguais a 0,28 ± 0,03; 0,21 ± 0,02; 0,25 ± 0,03, respectivamente. Mudanças significativas nos valores genéticos médios anuais das características de carcaça indicaram que estas estão sendo indiretamente influenciadas pelo índice de seleção aplicado para estes rebanhos / Abstract: Carcass traits by ultrasound measurements were included in genetic evaluation programs because they are associated with carcass yield and quality. This study aimed to estimate genetic parameters and genetic trends for back fat thickness (BF), rump fat thickness (RF), rib-eye area (REA) and body weight at 210 (BW210) and 365 (BW365) days of age. It data from animals whose herds participating in the Nelore breeding program (Nelore Brasil) born between 1998 and 2008, were used. Genetic parameters, (co)variance components and breeding values were estimated for each trait, in multi traits analysis, using maximum restricted likelihood method. Heritability estimates were equal to 0.28 ± 0.03 (REA); 0.21 ± 0.02 (BF) and 0.05 ± 0.01 (RF). In the growth traits the direct and maternal heritability estimates were respectively 0.26 ± 0.003; 0.18 ± 0.01 for BW210 and 0.39 ± 0.021; 0.05 ± 0.010 for BW365. Significant changes in the annual breeding values indicated that the carcass traits are being indirectly influenced by the selection index / Orientador: Danísio Prado Munari / Coorientador: Claudia Cristina Paro de Paz / Banca: Joslaine Noely dos Santos Gonçalves Cyrillo / Banca: Fernando Sebastián Baldi Rey / Mestre

Orientador: Henrique Nunes de Oliveira / Banca: Marcilio Dias Silveira da Mota / Banca: Maria Eugênia Zerlotti Mercadante / Resumo: O Objetivo deste trabalho foi avaliar o valor adaptativo anual para possível utilização como critério de seleção para a eficiência reprodutiva de fêmeas da raça Nelore. Foram estudadas medidas de valor adaptativo do 4º ao 13º ano de permanência no rebanho de 21.610 fêmeas. Os valores adaptativos anuais foram calculados com base na capacidade de sobrevivência e no número de crias deixado ano após ano. O modelo de melhor ajuste aos dados, segundo os critérios adotados, foi o de 5ª ordem para a tendência média da população, 5ª ordem para o efeito genético aditivo direto e 3ª ordem para efeito de ambiente permanente de animal. O modelo heterogêneo com 10 classes foi o mais adequado na modelagem da das variâncias residuais. As herdabilidades para valor adaptativo anual aumentaram com a idade dos animais (0,05 a 0,55). As correlações entre os valores adaptativos em diferentes idades foram baixas nas idades menores e altas entre as idades adultas. A tendência genética para valor adaptativo anual foi realizada com base nos valores genéticos preditos referentes às medidas adaptativas do 4º (Pti4), 8º(Pti8) e 13º(Pti13) ano de idade. Como critério de comparação foram utilizadas as características idade ao primeiro parto (Ipp) e stayability (Stay). As associações entre os valores genéticos preditos das características foram feitas utilizando a correlação de Pearson e porcentagem de touros coincidentes. Estimativas de herdabilidade para Ipp, Stay1 e Stay2 foram respectivamente 0,12, 0,33 e 0,40. As tendências genéticas indicaram que houve ganhos para Pti4 e Pti13 e, para Pti8 as médias dos valores genéticos se mantiveram quase que constantes com o passar dos anos. As associações entre os valores genéticos indicaram maior associação entre valores genéticos preditos para valor adaptativo medido no 4º ano e valores genéticos preditos para as características Ipp e Stay / Abstract: The objective of this study was to evaluate the annual Fitness as selection criteria for reproductive performance of Nelore cows. We studied measures of fitness of the 4th to the 13th year of stayability of 21,610 females. The annual fitness was calculated based on survivability and the number of offspring left year after year. The most appropriate model, according to criteria adopted, was a 5th order for the average trend of the population, 5th order for the direct genetic effect and 3th order for the permanent environmental effect of animal. The heterogeneous model with 10 classes was the most appropriated in modeling of residual variances. Heritability estimates for annual fitness increased with age of animals (0.05 to 0.55). The correlations between fitness at ages different were lower in younger ages, and high among the adult ages. The genetic trend for annual fitness was based on predicted breeding values to adaptive measures relating to the 4th (Pti4), 8th (Pti8) and 13th (Pti13) years of age. As criterion for comparison were used the traits age at first calving (IPP) and stayability (Stay). The associations between predicted breeding values of traits were made using Pearson correlation and percentage of bulls coincide. Heritability estimates for Ipp, and Stay1 Stay2 were respectively 0.12, 0.33 and 0.40. The genetic trends indicated that there were gains for Pti4 and Pti13, however for Pti8, the average genetic values remained almost constant over the years. The associations between breeding values indicate greater association between breeding values for annual fitness measured in year 4th year and the breeding values for the traits Ipp and Stay / Mestre

Este trabalho propõe uma metodologia para auxiliar o empresário rural no momento de decidir qual a tecnologia menos arriscada para aumentar a taxa de prenhez em seu sistema de produção de bezerros. Para tanto, foram avaliadas as percepções de especialistas quanto a sete fatores a partir dos quais foi desenvolvida uma equação para calcular este risco. Tais parâmetros e suas definições foram apresentados em questionários aos 18 especialistas, selecionados por amostragem não probabilística. Neste documento foram listadas 32 tecnologias, avaliadas de acordo com os parâmetros conforme a escala Likert de cinco níveis. Foram utilizados os parâmetros relacionados diretamente ao risco das tecnologias, atribuindo-se um valor conforme a nota dos especialistas, de forma a ajusta-las conforme sua influência no risco, se positiva ou negativa. Não houve diferença significativa entre o risco calculado e o estimado pelos especialistas, além de ambos apresentarem alta correlação, validando esta metodologia. As tecnologias de insumo se apresentaram mais arriscadas, indicando custo, complexidade operacional e conhecimento técnico mais elevados do que as de processo. Da mesma forma, as tecnologias de manejo demonstraram menor risco em relação às nutricionais e reprodutivas, que não apresentaram diferença entre si. As tecnologias consideradas inovadoras foram mais arriscadas do que as consolidadas, apresentando todos os parâmetros mais elevados, com exceção da flexibilidade. Dessa forma, a metodologia desenvolvida foi capaz de determinar o risco das tecnologias, obtendo resultados semelhantes às percepções dos especialistas. / This study proposes a methodology to assist the farmers in deciding which technology is less risky to reduce the inefficiencies of their cow-calf production. Thus, were evaluated the perceptions of experts about seven factors predetermined from which were developed a formula to calculate this risk. These parameters and their definitions were reported in questionnaires to 18 experts, selected by nonprobability sampling. This document listed 32 technologies evaluated according to the parameters in the Likert scale of five levels. Were used the parameters directly related to the risk, assigning a value to the experts notes, in order to adjust these as their influence on the risk, whether positive or negative. There was no significant difference between the calculated and the estimated risks; they also had a high correlation, validating this methodology. The innovative technologies were more risky, indicating cost, operational complexity and technical knowledge higher than the process technologies. Likewise, the management technologies showed less risk than the nutritional and reproductive ones, which appear to have no difference among them. The innovative technologies were riskier than the consolidated ones, with all the standards higher, with the exception of flexibility. The methodology was able to determine the risk of technologies, obtaining similar results to the perceptions of the experts.

Made available in DSpace on 2015-03-26T12:54:25Z (GMT). No. of bitstreams: 1 texto completo.pdf: 514454 bytes, checksum: 1e25cf3070f5b6543d89aae898c67f64 (MD5) Previous issue date: 2008-09-02 / Conselho Nacional de Desenvolvimento Científico e Tecnológico / The current thesis was based on three trials. At the first trial, it was evaluated the effects of different supplementation levels on the performance, intake, digestibility, pH and ruminal ammonia concentration in growing bulls grazing Brachiaria decumbens Stapf. pasture, during the dry-rainy transition season. In the performance, intake and digestibility trial twenty five intact males with 11 months old and initial body weight of 270 kg, grouped in five lots of five animals, arranged in a completely randomized design were used. Each lot received one of the following treatments: mineral mixture (SAL) or supplements fed at 0.5, 1.0, 1.5 or 2.0 kg/animal/ day, which corresponded to supplementation levels of 0.18, 0.36, 0.54 and 0.72% of body weight. The experimental area was constituted of five paddocks of 2.0 ha each one. For the evaluation of the pH and ruminal ammonia concentration five crossbred bulls were used, with average body weight of 240 kg, fitted with esophageal, ruminal and abomasal cannula, disposed in a 5x5 Latin square design, with five treatments and five experimental periods. Animal performance increased linearly with the supplementation levels, being observed an increment of more than 80% in the animal performance of the highest supplementation level when compared to the animals that not receive the supplement. DM, OM and NDF intake were not influenced by the treatments. CP, NFC, EE and TDN intake as well as nutrient digestibility and ruminal ammonia concentration had a positive linear pattern in function of the supplementation levels. Increasing the amount of supplemental concentrate had a positive influence on the performance of growing bulls grazing Brachiaria decumbens pasture during the dry-rainy transition season. At the second trial it was evaluated the effects of supplementation levels on performance, intake, total apparent digestibility (TAD), pH and ruminal ammonia concentration (RAC) of finishing bulls grazing Brachiaria decumbens Stapf. pasture during the rainy season. For the performance, intake and TAD evaluation, sixteen intact males with 14 months old and initial body weight of 317 kg were used, arranged into four lots of four animals each, following a completely randomized design. Each lot received one of the following treatments: mineral mixture or supplements fed at 0.75; 1.50 and 2.25 kg/animal/day, which corresponded supplementation levels of 0.2; 0.4 and 0.6% of the average body weight. For pH and RAC evaluation, four animals fitted with rumen cannula were used, following a 4 x 4 Latin square design, with four treatments and four experimental periods. The average daily gain increased linearly as the supplementation levels increased, when the animals fed at the higher supplementation level presenting an additional daily gain of 261 g/day when compared to the animals not supplemented. DM, OM, CP, NFC, EE and TDN intake had a positive and linear response to the treatments. Although the treatments had no effect on DM TAD, there was a significant effect on nutrients TAD, in which the response was positive and linear for OM, CP, EE and NFC and linear but negative for NDF TAD. Ruminal pH values were affected quadratically while RAC increased linearly with the supplementation levels. Increasing supplementation levels can positively influence the performance, intake, nutrients digestibility and ruminal characteristics of bulls grazing Brachiaria decumbens during the rainy season. The objective in the third trial was to determine the energy, protein and macrominarals requirements of Zebu bulls grazing Brachiaria decumbens Stapf. pasture and supplemented with increasing amounts of concentrate during the rainy season. Twenty eight intact males, with seven months old and initial body weight of 180 kg were used. Eight baseline animals were slaughtered to determine the initial body composition, in different weight range. The right half carcass of eight animals, two per treatment, was dissected in muscle, fat and bones and all the body components were weighed to determine the empty body weight (EBW) and empty body composition. The net energy requirements for weight gain were obtained by regressing the log of the retained energy (RE) on the log of empty body weight gain (EBWG). The net energy requirements for maintenance (NEm) were obtained from regression of the log of the heat production (HP) on the metabolizable energy intake (MEI). The efficiency of ME utilization for maintenance (km) was calculated as the ratio of NEm to MEm and the slope of the linear regression of RE on ME intake was considered as an estimate of the efficiency of utilization of ME for weight gain (kg). The requirements of NEm of Zebu bulls, under pasture, was 82.4 kcal/EBW0.75/day or 76.12 kcal/BW0.75/day. Thus, grazing Zebu bulls have about 5% greater net energy requirements for maintencance than feedlot Zebu bulls. The daily requirements of MEm was 149.76 kcal/EBW0.75, and the efficiency of ME utilization for maintenance (km) of Zebu bulls under pasture was 55% and for gain (kg) 29%. To calculate the net requirements for gain in the different ranges of body weight the retained protein (RP, g/day) was regressed against empty body gain (EBG, kg/day) and retained energy (RE, Mcal/day). The total metabolizable protein requirements for an animal of 350 kg and average daily gain of 1.0 kg, were 593.59 g/day. That same animal, eating 7.40 kg of DM/day requires 12.97% of CP in DM. The net requirements of protein for gain of grazing bulls until 350 kg of bodyweight, decrease as the body weight or retained energy increase and can be estimated by the equation: RP (g/day) = -26.2946+247.4853×EBG-24.8436 ×RE. The net Ca, P, Mg, Na and K requirements were determined by the equation Y = b. 10a. Xb-1, where a and b represente the intercept and the regression coefficient, respectively, of the prediction equations of Ca, P, Mg, Na or K contents in the empty body weight. The net requirements of Ca and P for an animal of 400 kg of BW were, respectively, 11.13 g and 5.40 g. To determine the total dietary requirements, endogenous losses and bioavailability values found in the literature were used to calculate the dietary requirements for maintenance which were added to the dietary requirements for growth to obtain the total requirements. The total dietary requirements of Ca, P, Mg, Na and K for an animal of 400 kg of BW, with average daily gain of 1,0 kg were, respectively, 34.59; 17.36; 7.82; 5.19 and 41.11 g/day. The macrominerals requirements of supplemented grazing Zebu cattle were similar o those recommended by the BR-Corte for Zebu cattle on feedlot. / A presente tese foi elaborada com base em três experimentos. No primeiro experimento objetivou-se estudar os efeitos de diferentes níveis de suplementação sobre o desempenho, consumo, digestibilidade aparente total (DAT), pH e concentração de amônia ruminal (NAR), em bovinos recriados em pastagem de Brachiaria decumbens Stapf. durante o período de transição seca-águas. Para avaliação do desempenho, consumo e DAT, foram utilizados 25 novilhos, não castrados, com idade e peso médio iniciais de 11 meses e 270 kg, divididos em cinco lotes de cinco animais, seguindo um delineamento inteiramente casualizado. Cada lote recebeu um dos tratamentos: mistura mineral (SAL); e suplemento na base de 0,5; 1,0; 1,5 e 2,0 kg/animal/dia, o que representou 0,18; 0,36; 0,54 e 0,72% do peso corporal médio dos animais. A área destinada aos animais foi constituída de cinco piquetes de 2,0 ha cada. Para a avaliação do pH e concentração ruminal de amônia, foram utilizados cinco novilhos mestiços, não castrados, com peso médio de 240 kg, fistulados no esôfago, rúmen e abomaso, dispostos em quadrado latino 5x5, com cinco tratamentos e cinco períodos experimentais. O desempenho dos animais comportou-se de forma linear positiva em função dos níveis de suplementação, sendo observado um incremento de mais de 80% no ganho de peso dos animais do mais alto nível de suplementação em comparação aos animais não suplementados. Os consumos de MS total, MS do pasto, MO e FDN, não foram influenciados pelos tratamentos. Os consumos de PB, CNF, EE e NDT assim como a digestibilidade dos nutrientes e a concentração de amônia ruminal apresentaram comportamento linear positivo em função dos níveis de suplementação. Níveis crescentes de suplementação concentrada influenciam positivamente o desempenho de bovinos recriados sob pastejo no período de transição seca-águas. No segundo experimento avaliou-se os efeitos de níveis de suplementação sobre o desempenho, consumo, DAT, pH e NAR em bovinos de corte terminados em pastagem de Brachiaria decumbens Stapf., no período das águas. Para avaliação do desempenho, consumo e DAT foram utilizados 16 novilhos zebuínos, não castrados, com idade e peso médio iniciais de 14 meses e 317 kg, os quais foram divididos em quatro lotes de quatro animais, seguindo um delineamento inteiramente casualizado. Cada lote recebeu um dos tratamentos: mistura mineral e suplementos na base de 0,75; 1,50 e 2,25 kg/animal/dia, que corresponderam a 0,2; 0,4 e 0,6% do peso vivo médio dos animais. Para avaliação do pH e NAR, foram utilizados quatro animais fistulados no rúmen, organizados em quadrado latino 4x4, com quatro tratamentos e quatro períodos experimentais. O ganho de peso médio diário comportou-se de forma linear positiva, apresentando um ganho diário adicional de 261 g/dia para os animais do mais alto nível de suplementação em relação aos animais não suplementados. Os consumos de MST, MO, PB, CNF, EE e NDT apresentaram comportamento linear positivo em resposta aos tratamentos. Embora sem efeito de tratamentos sobre a DAT da matéria seca, houve efeito significativo dos tratamentos sobre a DAT dos nutrientes, sendo linear positivo para MO, PB, EE e CNF e linear negativo para FDN. Os valores de pH ruminal apresentaram comportamento quadrático e a NAR aumentou linearmente. Níveis crescentes de suplementação influenciam positivamente o desempenho, consumo, digestibilidade dos nutrientes e as características ruminais de bovinos de corte sob pastejo no período das águas. No terceiro objetivou-se estimar as exigências nutricionais de energia, proteína e macroelementos minerais de bovinos de corte suplementados em pastagem de Brachiaria decumbens durante o período das águas. Foram utilizados 28 novilhos zebuínos, não castrados, com idade e pesos médios iniciais de 07 meses e 180 kg. Oito animais foram abatidos como referência, em diferentes faixas de peso. A meia-carcaça direita de dez animais, dois por tratamento, foi dissecada em músculo, gordura e ossos e todos os constituintes do corpo pesados para determinação do peso de corpo vazio (PCVZ) e da composição corporal. Para determinação das exigências líquidas para ganho de peso foi construída uma equação de regressão entre o log da energia retida (ER) e o log do ganho de peso de corpo vazio (GPCVZ). As exigências de energia líquida para mantença (ELm) foram estimadas através do log da produção de calor (PC) em função do consumo de energia metabolizável (CEM). As eficiências de utilização da EM para mantença (km) foram estimadas pela relação entre os teores de ELm e a EM da dieta e a eficiência de utilização da energia para ganho de peso (kg) foi estimada como o coeficiente da regressão linear entre a ER e o CEM. As exigências de ELm de bovinos anelorados, sob pastejo, foram de 82,4 kcal/PCVZ0, 75/dia ou 76,12 kcal/PC0,75/dia. Com isso pode-se constatar que animais zebuínos, não castrados, sob pastejo, apresentam exigências líquidas de mantença cerca de 5% superiores aos zebuínos em confinamento. As exigências diárias de EMm foram de 149,76 kcal/PCVZ0,75 e a eficiência de utilização da EM para mantença (km) de animais anelorados sob pastejo foi de 55% e para ganho (kg) de 29%. Para determinação das exigências líquidas de proteína para ganho de peso nas diferentes faixas de peso corporal dos animais foi realizada uma análise de regressão dos conteúdos de proteína retidos no corpo dos animais (PR, g/dia) em função do ganho de peso de corpo vazio (GPCVZ, kg/dia) e da energia retida (ER, Mcal/dia). As exigências de proteína metabolizável total para um animal de 350 kg, com ganho diário de 1,0 kg, foram de 593,59 g/dia. Esse mesmo animal consumindo 7,40 kg de MS/dia necessita que a dieta total apresente 12,97% de PB na MS. O requerimento líquido de proteína para ganho de peso de animais zebuínos não- castrados sob pastejo, com até 350 kg de peso corporal, decresce à medida que o peso corporal ou a ER aumentam, podendo ser estimado a partir da equação: PR (g/dia) = -26,2946 + 247,4853 × GPCVZ -24,8436 × ER. As exigencias líquidas de Ca, P, Mg, Na e K foram determinadas pela equação Y = b. 10a. Xb-1, sendo a e b o intercepto e o coeficiente da equação de predição dos conteúdos corporais de macrominerais, respectivamente. As exigências líquidas de Ca e P para um animal de 400 kg de PC foram, respectivamente, 11,13 g e 5,40 g. Para estimar as exigências dietéticas de mantença e, posteriormente, somá-las às exigências dietéticas para ganho, no intuito de se obter as exigências dietéticas totais, foram adotas as perdas endógenas e a biodisponibilidade presentes na literatura, para cada macroelemento mineral. As exigências dietéticas totais de Ca, P, Mg, Na e K para um animal de 400 kg de PC, com ganho diário de 1,0 kg foram, respectivamente, 34,59; 17,36; 7,82; 5,19 e 41,11 g/dia. Pode-se concluir que as exigências em macrominerais de bovinos de corte suplementados a pasto foram semelhantes àquelas recomendadas pelo BR-Corte para bovinos de corte confinados.