Com o objetivo de avaliar a substituição de uma fonte de proteína verdadeira (farelo de soja; dieta deficiente em PDR), por uréia ou amiréia (A-150S - fonte de nitrogênio não protéico de suposta liberação gradativa de nitrogênio; dietas adequadas em PDR), foram realizados três experimentos. Experimento I: Seis machos da raça Nelore, não castrados, com peso médio inicial de 420 kg, foram utilizados em quadrado latino 3x3 duplicado, avaliando-se: a digestibilidade, o balanço de nitrogênio, parâmetros ruminais e sanguíneos (capítulo 3); a estimativa da digestibilidade no trato gastrintestinal utilizando indicadores externo e internos comparados com colheita total de fezes (capítulo 6). O volumoso utilizado foi o BIN (20% da MS). A digestibilidade da MS, MO, CNF, EE, PB e o NDT não diferiram (P>0,05) entre os tratamentos. A digestibilidade da FDA e FDN foram superiores (P<0,05) nos tratamentos uréia e amiréia. Não houve efeito de tratamento e da interação tratamento x horários (P>0,05) nos valores de pH, AGV total, acetato, propionato, butirato e relação acetato:propionato do fluido ruminal. A concentração de nitrogênio amoniacal no fluido ruminal foi superior (P<0,05) no tratamento com uréia, comparado ao tratamento com farelo de soja, sendo similar aos dois, o tratamento com amiréia. O tratamento com amiréia apresentou maior (P<0,05) perda de N na urina. A retenção de N e o valor biológico da proteína foram superiores (P<0,05) para o tratamento com uréia, comparado aos demais. A concentração de nitrogênio uréico no plasma e a concentração de glicose plasmática foram similares (P>0,05) entre os tratamentos. A estimativa da digestibilidade utilizando o óxido de cromo apresentou resultados similares (P>0,05) à colheita total de fezes. O mesmo foi observado com a lignina no tratamento deficiente em PDR (FS), mas nos de uréia e amiréia, os coeficientes de digestibilidade foram subestimados (P<0,05). A FDNi subestimou (P<0,05) a estimativa da digestibilidade em todas as frações independente do tratamento. A fluorescência de raios-X demonstrou ser uma técnica promissora de análise do cromo (capítulo 6). Experimento II: oitenta e um machos não castrados em crescimento foram utilizados em um delineamento experimental de blocos ao acaso com três tratamentos, tendo três animais por baia e nove baias por tratamento, com a mesma dieta anterior, para avaliar o desempenho dos animais (capítulo 4). O tratamento FS apresentou menor consumo e ganho de peso (P<0,01) e pior (P<0,01) conversão alimentar. Os tratamentos uréia e A-150S não diferiram (P>0,05) entre si. Experimento III: realizou-se outro experimento de desempenho similar ao anterior, utilizando-se apenas outro volumoso (45% de BTPV e 5% de BIN) e os animais estavam na fase de terminação (capitulo 5). O tratamento FS apresentou maior (P<0,01) consumo e ganho de peso e melhor conversão alimentar do que os tratamentos uréia e A-150S. Os tratamentos uréia e A-150S não diferiram (P>0,05) entre si. A amiréia promoveu resultados similares a uréia convencional no consumo dos nutrientes, digestibilidade, parâmetros ruminais e sanguíneos e no desempenho de bovinos de corte confinados. / Experiment I: Six Nellore bulls, with 420 kg of body weight, were used to evaluate the replacement of a true protein source (soybean meal-SBM), in an inadequate RDP diet, by urea or starea (non protein nitrogen source supposedly of slow N release), being the last two N sources in an adequate RDP diet. Sugar cane bagasse in natura (BIN) was the only source of diet forage (20% of DM). This trial evaluated: digestibility, ruminal parameters, ruminal ammonia, blood parameters and N balance (chapter 3); total tract digestibility estimated by using internal and external markers compared to total feces collection (chapter 6). DM, OM, NFC, EE, CP and TDN digestibilities (%) did not differ (P>0.05) among treatments. ADF and NDF digestibilities (%) were higher (P<0.05) for urea and starea treatments. There was no treatment or treatment X time effect (P>0.05) on pH, total VFA, acetate, propionate, butirate and acetate:propionate ratio. Ruminal ammonia N concentration was greater (P<0.05) for urea compared to soybean meal and starea was similar to both. Starea treatment had the higher (P>0.05) urinary N loss. N retention (g/d and % of ingested) and protein biological value (N retention, % of N digestible) were higher (P<0.05) for urea treatment. Plasma urea nitrogen and glucose concentrations were similar (P>0.05) among treatment (chapter 3). The digestibility estimated by using cromium oxide was similar (P>0.05) to that of using total feces collection. Lignin used as an internal marker resulted in similar pattern as feces collection when the diet contained soybean meal (RDP deficient diet), however, when the diet N was urea or starea, the digestibility coefficients were underestimated (P<0.05). The NDFi underestimated (P<0.05) the digestibility of all portion independent of treatment. X-ray fluorescence showed be a promising technique for cromium determination (chapter 6). Experiment II: Eighty-one growing intact males were used in a totally random block design, with three treatments (three animals/pen and nine pens/treatment) to evaluate beef cattle performance in feedlot (chapter 4). Diets were the same used in Exp. I. DM intake, ADG and feed conversion were 6.56, 7.18 and 6.97 kg/day; 0.889, 1.114 and 1.088 kg/day and 7.3, 6.5 and 6.7 kg DM/kg gain, for SBM, urea and starea, respectively. SBM treatment had the smaller (P<0.01) DM intake, ADG and feed conversion. Urea and starea treatment were similar (P>0.05). Experiment III: Another performance trial was done (chapter 5), similar to Exp. II, differing only by the forage portion of the diet (45% hidrolized sugar cane bagasse-BTPV and 5% bagasse in natura–BIN) for finishing cattle. DM intake, ADG and feed conversion were 8.99, 7.43 and 7.69 kg/day; 0.983, 0.368 and 0.404 kg/day and 9.56, 20.14 and 19.54 kg DM/kg gain for SBM, urea and starea treatments, respectively. SBM had the higher (P<0.01) DM intake and ADG and better feed conversion compared to urea and starea. Urea and starea treatments were similar (P>0.05). Starea showed similar results to urea.

Os objetivos deste estudo foram avaliar estratégias de suplementação energética para bovinos em recria, mantidos em pastagens tropicais bem manejadas durante as águas, quanto ao desempenho animal, capacidade de suporte das pastagens, ganho de peso por área e desempenho dos animais durante a terminação em confinamento. Os tratamentos testados foram: T1) Controle: somente mistura mineral; T2) Constante: fornecimento contínuo do concentrado na dose de 0,6% do PC; T3) Crescente: fornecimento de 0,3% do PC em concentrado no primeiro terço, 0,6% do PC no segundo terço e de 0,9% do PC no terceiro terço do período de recria dos animais. Foram utilizados 76 garrotes de corte, com peso inicial de 208 kg e 8 meses de idade. Os animais foram alocados em 8,5 ha de pastagem de capim Brachiaria brizantha cv. Marandu, manejados em sistema rotacionado com intervalo de desfolha variável. Foram avaliadas a massa de forragem (MF) pré e pós pastejo (kg MS ha-1), a composição morfológica (% de folhas, colmos e material morto) e valor nutritivo da forragem, o ganho de peso individual (kg cab-1 dia-1), a taxa de lotação (cab ha-1) e o ganho de peso por área (kg ha-1) durante a fase de recria dos animais. Na fase de confinamento dos animais foram avaliados o ganho de peso diário individual (GPD em kg cab-1), o consumo de matéria seca (kg dia-1) e a eficiência alimentar dos animais (kg de ganho diário kg de alimento consumido-1).Os animais suplementados apresentaram GPD superiores aos animais não suplementados (0,535, 0,787 e 0,867 kg cab-1 dia-1, respectivamente para os tratamentos controle, constante e crescente). Além disso, os animais do tratamento crescente apresentaram desempenho superior àquele dos animais do tratamento constante, mesmo consumindo quantidades semelhantes de suplemento. A suplementação foi, ainda, eficiente em aumentar a taxa de lotação dos pastos que foi, em média, de 5,94, 7,13 e 6,90 UA ha-1, respectivamente para os tratamentos controle, constante e crescente. Durante a fase de confinamento, não houve diferença entre os tratamentos para GPD, que apresentou média de 1,06 kg dia-1. A suplementação energética de bovinos durante a fase de recria em pasto é uma estratégia eficaz para aumentar o GPD dos animais, a taxa de lotação das pastagens e a produção de carne por área de pasto. / The objective of this study was to evaluate the effect of strategies of feeding an energetic supplement to growing cattle, grazing well managed tropical pastures during the rainy season, on the grazing animal performance, pasture stocking rate, total body weight gain per area, and on feedlot finishing phase. The treatments tested were: T1) Control: animals fed only a mineral mixture; T2) Constant level: constant daily feeding of energetic supplement at 0.6% of BW; T3) Increased level: daily feeding of energetic supplement at increasing levels of 0.3, 0.6, and 0.9% BW, according to the experimental period. Seventy six beef steers, averaging 208 kg BW and 8 months of age, were used. Animals were allocated in a 8.5 ha area of Brachiaria brizantha cv. Marandu pasture under a rotational grazing system with a variable defoliation interval. Pre- and post-grazing forage mass (FM, kg MS ha-1), morphological composition (leaves, stem, and dead material percentages), nutritive value of the forage, average daily gain (kg animal-1 day-1), stocking rate (animal ha-1), and weight gain per area (kg ha-1) were evaluated during the growing phase. At the feedlot phase were evaluated the average daily gain (kg animal-1 day-1), dry matter intake (kg day-1), and the gain to feed ratio. Supplemented animals had greater ADG than animals not supplemented (0.535, 0.787, and 0.867 kg animal-1 day-1), respectively for the control, constant, and increasing treatment levels. Furthermore, animals in the increasing supplementation group presented a highest performance when compared to the constant supplementation, although animals from both treatments have consumed similar amount of supplement. Supplementation also was efficient in improving the pasture stocking rate, which averaged 5.94, 7.13, and 6.90 AU ha-1, respectively for the control, constant, and increasing treatment levels.During the feedlot phase, there were no ADG differences among any treatment, which averaged 1.06 kg day-1. DMI and feed efficiency were also not affected by supplementation strategies during the grazing phase.

Made available in DSpace on 2016-04-28T20:13:47Z (GMT). No. of bitstreams: 1 2007- Rafael Leite Pinto de Andrade.pdf: 2052684 bytes, checksum: 572c21efa815c459377bf79668a2251e (MD5) Previous issue date: 2007-12-14 / The proposal of the thesis was to identify and analyze the most important positive consequences, stemming from the efforts of brazilian export companies of products related to agribusiness, to overcome the non-tariff barriers imposed by the companies and / or importing countries. These consequences are little explored in discussions and can be considered as external to the process of implementation of non-tariff barriers. In order to make the proposed work would be feasible, the chain's beef was elected as a target of further studies, the fact that an item be expressive of the Tariff Brazilian export, and because the wide variety of norms, standards and regulations of these products, widespread in all the links of its production chain. The results point to the need to create instruments of Brazil institutional and technical competence in order to administer and live in the best way possible with the inexorable increase in the presence of technical barriers to trade in agricultural products. Finally, although not always be possible to establish a direct relationship of cause and effect, the study developed to say that there is a close correlation between the movements in the interests of overcoming the technical barriers in world trade in products of agribusiness, and the benefits to Brazilian society as a whole. Benefits have been identified related to: technological development, the environment, improvement of legislation, aggregation of trade blocs, managerial innovation, reduce competition, maintain competitive advantage and labor relations. In this context, the chain of meat proved a good example for the hypothesis raised, because all segments studied showed, albeit in different degrees, the conversion of the requirements of international buyers in benefits for the internal market and for the Brazilians in general. / A proposta da tese consiste em identificar e analisar as conseq??ncias positivas mais relevantes, advindas do esfor?o das empresas brasileiras, e exportadoras de produtos relacionados ao agroneg?cio, para superarem as barreiras n?o-tarif?rias impostas pelas empresas e/ou pa?ses importadores. Estas conseq??ncias s?o pouco exploradas nos debates e podem ser consideradas como sendo externalidades ao processo de implementa??o das barreiras n?o-tarif?rias. De modo a fazer com que o trabalho proposto fosse exeq??vel, a cadeia da carne bovina foi eleita como alvo mais aprofundado dos estudos, pelo fato desta ser um item expressivo da pauta de exporta??o brasileira, e devido a grande variedade de normas, padr?es e regulamentos, disseminados por todos os elos de sua cadeia produtiva. Os resultados apontam para a necessidade do Brasil criar instrumentos institucionais e compet?ncia t?cnica de forma a administrar e conviver da melhor forma poss?vel com o inexor?vel aumento da presen?a das barreiras t?cnicas ao com?rcio de produtos agropecu?rios. Finalmente, embora nem sempre seja poss?vel estabelecer uma rela??o direta de causa e efeito, o estudo desenvolvido permite afirmar que h? uma correla??o estreita entre os movimentos em prol da supera??o das barreiras t?cnicas do com?rcio mundial de produtos do agroneg?cio, e benef?cios para a sociedade brasileira como um todo. Foram identificados benef?cios relacionados: ao desenvolvimento tecnol?gico, meio-ambiente, legisla??o nacional, agrega??o de blocos comercias, inova??es gerenciais, redu??o de concorr?ncia, manuten??o de vantagem competitiva e rela??es trabalhistas. Neste contexto, a cadeia da carne mostrou ser um bom exemplo para a hip?tese levantada, pois todos os segmentos estudados apresentaram, ainda que em graus distintos, a convers?o das exig?ncias dos compradores internacionais em benef?cios para o mercado interno e para os brasileiros de modo geral.

O estudo teve como objetivo avaliar os efeitos de diferentes níveis de suplementação energética sobre os parâmetros metabólicos (ruminais e sanguíneos), consumo de forragem, comportamento animal e cinética de fermentação ruminal de novilhos Nelore recriados em pastagem tropical na época das águas. Os tratamentos foram: T1) controle (somente suplementação mineral); T2) 0,3% PC; T3) 0,6% PC; e T4) 0,9% PC em milho moído fino e monensina sódica. Foram utilizados 8 novilhos Nelore, fistulados no rúmen, com aproximadamente 410 kg e 48 meses de idade. O delineamento estatístico utilizado foi o de quadrado latino, com 2 quadrados latinos 4x4. Os animais foram alocados em 1 ha de pastagem de capim Brachiaria brizantha cv. Marandu. Os parâmetros avaliados foram o consumo de forragem, comportamento animal, pH e amônia ruminais, concentrações de ácidos graxos de cadeia curta (AGCC), teores plasmáticos de glicose e uréia, cinética de degradação ruminal, síntese de proteína microbiana e excreção de nitrogênio. Dois marcadores foram testados para estimar o consumo, LIPE e óxido crômico, e o escolhido para estimar o consumo foi o óxido crômico. A suplementação energética reduziu linearmente (P<0,05) o consumo de forragem, mas aumentou o consumo total de MS e de NDT (P<0,05). As taxas de substituição foram mais altas no nível 0,3%, intermediária no nível 0,6% e mais baixa no nível 0,9% do PC (P<0,05). Entre as variáveis do comportamento animal houve efeito apenas para o tempo de pastejo (P<0,05), que foi reduzido, e para o tempo de ócio (P<0,10) que foi aumentado com a suplementação. Houve efeito da suplementação apenas na produção de propionato, entre os AGCC, sendo aumentada linearmente (P<0,05) em função da suplementação. O pH não foi alterado em função dos níveis de suplementação, estando entre valores recomendados para manutenção dos microrganismos celulolíticos. A concentração ruminal de N-NH3 e a excreção de nitrogênio foram reduzidas com a suplementação (P<0,05). A síntese de proteína microbiana foi aumentada (P<0,05) em função dos níveis crescentes de suplementação, o que demonstra o efeito da sincronia de energia e proteína no rúmen. Não houve efeito significativo para os parâmetros sanguíneos (glicose e uréia). A suplementação melhorou a degradação da fração fibrosa, aumentando a fração potencialmente degradável da FDN (P<0,05), e reduzindo a fração indigestível da FDN. Não houve efeito (P<0,05) no lag time para a degradação da fibra. A redução no consumo de forragem em função da suplementação energética não está associada a prejuízos no pH ruminal e na degradação da fração fibrosa. A suplementação energética de bovinos de corte mantidos em pastagens de bom valor nutritivo e manejadas intensivamente no período das águas promove aumentos na síntese de proteína microbiana e melhorias na degradação da fibra. / The objective of this trial was to evaluate the effects of different levels of energy supplementation on metabolic parameters (blood and ruminal), forage intake, animal behavior and ruminal kinetics of Nelore steers raised in tropical pasture during the rainy season. Each level of supplementation was considered a treatment and consisted of: T1) control (only mineral supplementation); T2) supply of 0.3% BW of energetic concentrate; T3) supply of 0.6% of BW of energetic concentrate; T4) supply of 0.9% of BW of energetic concentrate. Eight Nelore rumen-cannulated steers, averaging 410 kg BW and 48 months of age were assigned to two 4x4 Latin square and allotted in 1 ha of Brachiaria brizantha cv. Marandu pasture. The parameters evaluated were forage intake, ruminal pH and concentration of NH3 and short chain fatty acids (SCFA), blood nitrogen urea and blood glucose, ruminal kinetics, microbial synthesis, nitrogen excretion and animal behavior. The marker that better estimated the intake was chromium oxide. Forage intake (% BW) decreased (P<0.05) and total DM intake increased (P<0.05) as levels of supplementation increased. Substitution rates decreased (P<0.05) as the supplementation level increased, explaining the higher total DM intake. Among the ingestive behavior variables, only grazing time, that decreased (P<0.05), and rest time, that increased (P<0.10), as the supplement level increased, were affected by supplementation. Among the SCFA, only the propionate concentration was affected (P<0.05) by the treatments, increasing as the levels increased. The ruminal pH was not affected by supplementation and was among the recommended values for maintenance of cellulolytic microorganisms. The concentration of NH3 and nitrogen excretion decreased (P<0.05), and the microbial synthesis increased (P<0.05) as levels of supplement increased, as a result of the better synchronization between energy and protein in the rumen. Blood variables (glucose and urea nitrogen content) were not affected by treatments. Supplementation improved fiber degradation, by increasing the potential degradable fraction of NDF (P<0.05). There was no effect on the lag time of fiber degradation, confirming that the supplementation had no negative effects on the ruminal environment. The decreasing on forage intake as the supplement level increased was not associated neither to inadequate ruminal pH nor to impairment of fiber degradation. Energetic supplementation for beef cattle grazing tropical pastures intensively managed during rainy season improves microbial synthesis and fiber degradation.

Neste trabalho, foram utilizadas duas ferramentas computacionais para fins de auxiliar tomadas de decisões na produção de bovinos de corte, criados de maneira extensivas, em condições de manejo encontrados no Brasil. A primeira parte do trabalho visou à construção de um software utilizando a técnica de Simulação Monte Carlo para analisar características de produção (ganho de peso) e manejo (fertilidade, anestro pós-parto, taxa de natalidade e puberdade). Na segunda parte do trabalho foi aplicada a técnica de Redes Neurais Artificiais para classificar animais, segundo ganho de peso nas fases de crescimento (nascimento ao desmame, do desmame ao sobreano) relacionado com o valor genético do ganho de peso do desmame ao sobreano (GP345) obtidos pelo BLUP. Ambos modelos mostraram potencial para auxiliar a produção de gado de corte / Herein we applied two different computational techniques with the specific objective to help the decision-making at Brazilian extensive beef cattle production systems. The first part of the work was dedicated to the construction of software based on Monte Carlo Simulation. Two different models were designed for further fusion and willing the analysis of productions (weight gain) and reproduction traits (fertility, post partum anestrus, born rate and puberty). The second part of the work applied Artificial Neural Network techniques to classify animals related to the weight gain during growing period (Weight at Calving, Weaning Weight, Weight at 550 days) comparing data with genetic value of the daily gain from weaning to 550 days adjusted to 345 days BLUP output. The results obtained in both models showed potential to help beef cattle production

O fornecimento de alimentos é o input de maior custo nos empreendimentos pecuários. A seleção para eficiência alimentar em bovinos de corte foi ignorada principalmente pela dificuldade e custo de mensurar o consumo individual. Além disto assumiu-se por décadas que a eficiência estaria altamente correlacionada com a taxa de ganho. Um índice alternativo para medir a eficiência alimentar, não associado ao aumento do tamanho adulto, é o Consumo Alimentar Residual (CAR). Além de avaliar a variabilidade genética dentro da raça Nelore para CAR, o objetivo deste trabalho foi investigar as conseqüências da seleção para este parâmetro de eficiência sobre as características de carcaça e a qualidade da carne em novilhos Nelore terminados em confinamento. Novilhos (n=75), filhos de 8 touros, de genealogia conhecida, com aproximadamente 18 meses de idade e peso vivo médio inicial de 394,4 ± 29 kg foram confinados em baias individuais por 85 dias, após 15 dias de adaptação, recebendo dieta 25% silagem de sorgo e 75% concentrado na matéria seca. Ao final dos 85 dias os animais foram abatidos. Seguindo o critério CAR 0,5 desvio-padrão abaixo ou acima da média, 33% dos animais foram classificados como alto CAR, 28% como baixo CAR e 39% se enquadraram no grupo de médio CAR. A amplitude foi de CAR foi de -1,26 a 1,64 kg/dia e o desvio-padrão 0,71 kg/dia. Os grupos de CAR não diferiram entre si quanto ao peso inicial, final e altura de garupa (P>0,05). Os animais do grupo baixo CAR apresentaram menor consumo de matéria seca e NDT (P<0,01) e foram mais eficientes (P<0,05) em relação aos de médio e alto CAR. O ganho de peso diário não diferiu entre os grupos com valores de 1,153 e 1,215 kg/dia, para alto e baixo CAR, respectivamente. Não foram observadas diferenças entre os grupos de CAR quanto ao rendimento e peso da carcaça (P>0,01). Não houve diferença entres os grupos para características de qualidade de carne (P>0,10). Não foram detectadas diferenças (P>0,05) entre as médias das progênies de cada touro quanto a altura, peso inicial, peso final, ganho de peso, consumo de matéria seca e eficiência alimentar. As progênies de diferentes touros apresentaram diferentes rendimentos de carcaça (P<0,05) e espessura de gordura (P<0,05). Houve tendência (P<0,10) de diferença para área de olho de lombo e peso de carcaça. Progênies de diferentes touros apresentaram diferenças (P<0,05) quanto a força de cisalhamento. Quanto ao índice de fragmentação miofibrilar foi verificada tendência (P=0,06) de diferença. O teor de extrato etéreo e escore de marmoreio foram semelhantes para as progênies (P>0,05). Há variação entre animais Nelore para eficiência alimentar medida como CAR. Não houve relação entre CAR e o desempenho, peso adulto, características de carcaça e qualidade de carne de novilhos Nelore. / The supply of food is the highest cost input in livestock enterprises. Selection for feed efficiency in beef cattle was mostly ignored by the difficulty and cost of measuring individual consumption, besides the fact that efficiency is correlated with gain rate. An alternative index for measuring feed efficiency, not associated with increased adult size, would be the residual feed intake (RFI). In addition to assessing the genetic variability in Nellore to RFI, the objective of this work was to investigate the consequences of selection for this parameter of efficiency on carcass characteristics and meat quality of beef steers finished in feedlot. Nellore (n=75), progeny of 8 bulls of known pedigree, with approximately 18 months and weighting 394.4 ± 29 kg were kept in individual stalls after 15 days of adaptation receiving a 25% sorghum silage and 75 % concentrated diet. After the trial period of 85 days the animals were slaughtered to determine carcass characteristics and meat quality. According to the criterion RFI 0.5 standard deviation, 33% of the animals were classified as high-RFI, 28% as low RFI and 39% fit the group average RFI (-1.26 to 1.64 kg/day) and standard deviation (0.71 kg/day). RFI groups did not differ on hip initial and final weight (P>0.05). The animals of the low RFI had lower intake of dry matter and TDN (P<0.01) and were more efficient (P <0.05) when compared to animals of medium and high RFI. Differences in intake and feed efficiency between individuals most and least efficient was 1.74 kg DM/day, 1.49 kg TDN/day and 1.37 kg/kg. The daily weight gain did not differ between the groups with values of 1.153 and 1.215 kg/day for high and low RFI, respectively. There were no differences between groups of RFI on yield and hot carcass weight (P>0.01) and no effect of RFI on meat quality (P>0.10). There were no differences (P>0.05) among the progeny of bulls evaluated for height, initial weight, final body weight, daily weight gain, dry matter intake and feed efficiency. The progenies showed differences in carcass yield (P<0.05) and fat thickness (P<0.05). There was a tendency (P<0.10) to difference for ribeye area and hot carcass weight. The progenies showed differences on shear force (P<0.05). The myofibrillar fragmentation index was observed trend to difference (P=0.06). The lipid content and marbling scores were similar for the progeny (P>0.05). There was variation between animals for cattle feed efficiency measured as RFI. There was no relationship between RFI and performance, adult weight, carcass characteristics and meat quality of steers.

O presente estudo mensura o impacto no preço dos atributos de qualidade nos tourinhos da raça Nelore comercializados em leilões por meio de uma metodologia específica, baseada na Teoria dos Preços Hedônicos. Para tanto, utilizou-se como amostra três leilões - 368 observações - de uma fazenda padrão, o Nelore Jandaia. Assim, os atributos dos animais que mais contribuíram para a formação dos preços, em um primeiro plano, foram: a qualidade genética como um todo, expressa através do Mérito Genético Total - MGT, e a qualidade fenotípica global, demonstrada pelo índice EPMURAS. Em um segundo plano, mais específico, agregaram mais valor aos jovens reprodutores características relacionadas à precocidade e fertilidade do lado genético a Diferença Esperada na Progênie - DEP para perímetro escrotal aos 365 dias (dpe365) e no lado fenotípico a nota de precocidade. Por exemplo, os animais com MGT excelente tiveram um prêmio médio de 22% a mais em relação aos considerados como bons, paralelamente os com EPMURAS excelente tiveram um prêmio de 11% em relação aos classificados como muito bons, ceteris paribus. Para cada ponto a mais na precocidade e na DEP dpe365 o valor dos animais comercializados aumenta em, respectivamente, 5% e 5,8%, ceteris paribus. Do exposto, pode-se concluir que se os pecuaristas dedicados ao melhoramento dos seus rebanhos privilegiarem em seus objetivos de seleção animais com excelentes atributos de fertilidade e precocidade receberam prêmios superiores por isso. Em outras palavras, focar a seleção em precocidade e fertilidade agrega valor aos animais. / This study measures the impact on the price of quality attributes in Nelore steer sold at auction by a particular methodology, based on the theory of hedonic prices. To this end, we used as a sample three auctions - 368 observations of a standard farm, Nelore Jandaia. Thus, the attributes of animals that contributed most to the price formation were the genetic quality as a whole, expressed through the Total Genetic Merit - MGT, and the overall phenotypic quality, as demonstrated by the index EPMURAS. In a second model, more specific, added more value to young breeding characteristics related to precocity and fertility - the genetic side of the Expected Progeny Difference - EPD for scrotal circumference at 365 days (dpe365) and on the phenotypic note of precocity. For example, animals with excellent MGT had an average premium of 22% more than for those considered as good, along with the excellent EPMURAS had a premium of 11% over rated as very good. For each point on precocity and DEP dpe365 the value of animals traded increases, respectively, 5% and 5.8%, ceteris paribus. From the above, we conclude that if the farmers devoted to the improvement of their herds give priority in their selection goals animals with excellent attributes of fertility and precocity will receive premium for it. In other words, focus the cattle selection on fertility and precocity adds value to animals.

There has been increased interest in utilizing switchgrass (Panicum virgatum) as biomass. There are several challenges to developing this industry, and these have led to the potential use of switchgrass as hay for feeding beef cattle in Kentucky. The effect of increasing maturity on crude protein (CP), neutral detergent fiber (NDF), acid detergent fiber (ADF) and nutritive values of switchgrass hay has been well documented, but few in vivo intake and digestibility trials have been conducted to assess this effect on animal performance when feeding beef cattle. Two in vivo intake and digestibility trials were conducted in 2011 in which Angus x Hereford beef steers (200-265 kg) were fed Alamo and Cave-in-Rock switchgrass harvested as late vegetative, boot, and early flowering hay. The objectives of these trials was to evaluate the effect of increasing maturity on apparent dry matter intake (DMI), digestible dry matter intake (DDMI), and dry matter digestibility (DMD); and to discuss potential challenges that producers might face if incorporating switchgrass hay into their forage program for feeding beef cattle. Observed decreases in nutritive value, DMI, DDMI, and DMD indicate that producers should harvest Alamo and Cave-in-Rock switchgrass before it reaches the boot stage of maturity.

A long-term grazing trial was started in 1977 at Armoedsvlakte Research Station, about 10km west of Vryburg, in Tarchonanthus veld of the Ghaap’s Plateau, which is a variation of the Kalahari Thornveld veld type. The main aim of this study was to use the extensive veld condition and animal production data set to investigate the effects and interactions of stocking rate, grazing system applied and seasonal rainfall on veld condition and cattle production. The grazing trial has changed three times since its inception resulting in three different phases. The main changes in veld condition during phase one (1977-1991) was due to density independent effects (e.g. seasonal rainfall) and not density dependent effects (e.g. stocking rate). A major change occurred in 1985 following a multiple year drought. The drought resulted in adverse changes in species composition, basal cover and residual biomass of all treatments. The system did not recover from the drought during phase one, despite well above mean seasonal rainfall for a number of years after the drought. During phase two (1992-1999) and phase three (2000 to present) completely different vegetation dynamics occurred than what was experienced during phase one. Density dependent effects (e.g. stocking rate) were more important in explaining variation in veld condition during these two phases. High stocking rates resulted in adverse changes in species composition, poor basal cover and a low residual biomass production. It is however important to note that seasonal rainfall did explain a significant additional amount of variation in veld condition. This suggests that a continuum of non-equilibrium and equilibrium vegetation dynamics occurred in these two phases. The residual biomass and seasonal rainfall model for phase one indicate completely different results for the gain per animal data. In the seasonal rainfall model, stocking rate does not have a significant effect on gain per animal, but seasonal rainfall and the interaction of stocking rate with seasonal rainfall explains most of the variation in gain per animal. This suggest a continuum of non-equilibrium and equilibrium dynamics and that animal production is more sensitive to seasonal rainfall than to stocking rate, although the significant interaction of stocking rate with seasonal rainfall suggest that the seasonal rainfall effect on animal production is dependant on stocking rate. The residual biomass model however indicates that stocking rate is more important than rainfall in explaining variation in the mass gains per animal. The stocking rate effect on gain per animal was significant and indicated that as stocking rate increased, that gain per animal decreases. Seasonal rainfall and the interaction of stocking rate with seasonal rainfall had no significant effect on gain per animal. The amount of variation explained by the seasonal rainfall model was larger than the residual biomass model and this indicates that rainfall explains more variation in gain per animal, than residual biomass does. This possibly indicates that non-equilibrium effects are stronger than the equilibrium effects, but it is important to notice that stocking rate had a significant effect in some cases. The gain per hectare models (seasonal rainfall and residual biomass) for phase one indicates that stocking rate has a significant effect on gain per hectare. Increasing stocking rates resulted in higher gain per hectare, which suggests that the turning point of the typical “Jones and Sandland model” has not been reached and this might be due to light stocking rates applied during the duration of phase one. The seasonal rainfall model however has significant effects of seasonal rainfall and interactions of stocking rate with seasonal rainfall on gain per hectare. This suggests that the effect of stocking rate is dependent on seasonal rainfall and that seasonal rainfall explain an additional amount of variation in gain per hectare. In general, it appreared that the optimal stocking rate for animal production was higher than those applied during the duration of the trial, but this is due to lower than planned actual stocking rates applied during all three phases of the trial. It is very difficult to determine a generic optimal stocking rate for different rainfall volumes and it is recommended that the actual stocking rate for different ecological zones be determined based on rainfall, biomass, species compos[i]tion, basal cover and available browse and not just on the provisional recommendations. The type of grazing system applied did not show any statistically significant effects on both gain per animal and gain per hectare for the animal production data during phase one. This result is interesting and contradictive to most of the scientific literature where some authors concluded from their studies that rotational grazing systems produce higher animal production than continuous grazing systems, whereas others researchers state that continuous grazing systems produce higher animal production than rotational grazing systems. In phase two both the residual biomass and seasonal rainfall models for phase two did not show any significant effects and interactions of stocking rate, seasonal rainfall level and/or residual biomass on both gain per animal and gain per hectare. Both the residual biomass and seasonal rainfall models for phase three did not show any significant effects and interactions of stocking rate, seasonal rainfall level and/or residual biomass on animal gains per animal. The seasonal rainfall model did not show any any significant effects and interactions of stocking rate, seasonal rainfall level and/or residual biomass on animal gains per hectare. However, the residual biomass model indicated that stocking rate had a significant effect on gain per hectare and the production closely followed the Jones and Sandland (1974) model as at low stocking rates, gain per hectare increases at a rapid rate, but as stocking rates increases to high stocking rates, the rate of increase in gain per hectare declines, until it eventually reaches a turning point, where after gain per hectare declines with increasing stocking rates. Stocking rate only had a significant effect on the condition score of cows during phase two and phase three, as high stocking rates resulted in poor animal condition in both phases. No significant effects and interactions of stocking rate and seasonal rainfall were indicated on calving percentage, weaning percentage, conception rates and percentage of desirable meat produced during phase two. / Thesis (M.Sc.)-University of KwaZulu-Natal, Pietermaritzburg, [2011].

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