Influence of chosen effects on efficiency of beef breeds Aberdeen Angus, Charolais, Limousine and meat-type Siemental, which were breeded in South Bohemia, was observed in this study. Impact of breed on average weight of calves in different ages, calving month and the serial number of the birth, influence of father´s relative breeding value, dependence of average age of pure bred female on reason of elimination and effect of stocking rate of a pasture on daily weight gain were evaluated.

No Brasil, os sistemas de produção em ruminantes são principalmente a base do fornecimento de forragens cultivadas em grandes, medianas ou pequenas extensões do território nacional. A maior parte destas pastagens estão em um avançado estado de degradação por causa de um mal aproveitamento das vantagens que oferecem as gramíneas utilizadas nestes sistemas de produção. Um dos motivos pelos quais muitos estes sistemas ainda não são sustentáveis, é o mal uso ou não uso de suplementos no solo, levando o esgotamento de recursos em el solo muy importantes para o bom desenvolvimento de uma gramínea como o é o nitrogênio e o potássio. Como consequência disto, o desempenho animal, fator crítico nos sistemas de produção pecuário são baixos e o rendimento econômico faz que a empresa produtora de carne e leite bovino não seja rentável. Objetiva-se com este estudo avaliar o efeito a eficiência biológica de doses crescentes de adubação em pastagens de capim-marandu e capimmombaça durante os períodos de verão e outono com 3 tratamentos, e duas repetições. Foram 3 as doses de adubação avaliadas: 1) 50 kg N/ha + 50 kg K2O/ha; 2) 300 kg N/ha + 300 kg K2O/ha e 3) 600 kg N/ha + 600 kg K2O/ha, sobre os seguintes parâmetros: 1) massa de forragem produzida em cada um dos tratamentos no pré-pastejo; 2) Composição morfológica; 3) taxa de lotação; 4) frequência de pastejo; 5) composição químico-bromatológica. Foram utilizados 6 piquetes, cada um de 2 ha (3 de variedade Marandu e 3 de variedade Mombaça), nos quais foram coletadas as informações do trabalho de campo. Adicionalmente, dois piquetes com as mesmas dimensões, cada um, com uma das variedades de capim estudadas foram usados como área de reserva. Todos os piquetes foram divididos em 6 partes iguais e contaram com uma área de lazer de 15x30 metros. 181 novilhas foram utilizadas como agentes desfoliadores em ciclos de pastejo de 5 dias de ocupação e 25 de descanso para o campi-marandu e 7 dias de ocupação e 35 de descanso para o campi-mombaça. No período da seca foi testado o desempenho de 103 novilhas entre prenhes e vazias suplementadas com dietas a base de cana-de açúcar e 4 fontes de proteína (farelo de soja, farelo de soja + uréia, uréia e uréia de liberação lenta). A taxa de lotação tive um efeito linear positivo às doses de N e KCl avaliadas. A qualidade do capim foi pouco influenciada pelos tratamentos. Todos os suplementos usados na época da seca permitiram manter o peso médio e obter um ganho de peso adicional. O uso de adubos nitrogendos e potássicos permite aumentar a eficiência do uso da terra permitindo disponibilizar áreas dedicadas à pecuária para outro tipo de atividades no agronegócio. / In Brazil the ruminant production systems are mainly based on the offer of pastures cultivated in large, medium or small areas of the country. Most of the prairies in these production systems are in an advanced state of degradation due to misuse of the gramineae advantages making them unsustainable. The misuse or non-use of soil supplements leads to the depletion of resources such as nitrogen and potassium highly important for the proper development of grass. As a consequence the animal performance, a critical factor in livestock production systems is low, causing a negative impact on economic efficiency of the meat and milk production enterprise making it not profitable. The aim of this study was to evaluate the effect and biological efficiency of increasing doses of fertilizers on Marandu and Mombaça pasture prairies during summer and autumn periods with three treatments in two repetitions. With three fertilizer doses evaluated: 1) 50 Kg of N/ha + 50 Kg of K2O/ha; 2) 300 Kg of N/ha + 300 Kg of K2O/ha and 3) 600 Kg of N/ha + 600 Kg of K2O/ha; on the following parameters: 1) mass of forage produced in each of the treatments on the pre-grazing, 2) morphological composition, 3) livestock rate, 4) frequency of grazing, 5) chemical and bromatological composition. 6 paddocks were used, each one of 2 ha (3 with Marandu variety and 3 Mombaça variety) were field work information was collected. Additionally, two fields with the same dimensions mentioned above, each one with the grass varieties tested were used as a reserve area. All paddocks were divided into 6 equal parts and counted with a rest area of 15 x 30 meters. 181 heifers were used to consume the accumulated pasture in grazing cycles, 5 days of occupation and 25 days off in Marandu pasture prairies and 7 days of occupation and 35 days off for Mombaça pasture prairies. In the drought period the performance of 103 pregnant heifers both pregnant and non-pregnant was evaluated, they were fed with diets supplemented with sugar cane and 4 protein sources (soybean meal; soybean meal+ urea; urea; and slow release urea).Lifestock rate had a positive linear effect on increasing doses of the N and KCl evaluated.. Pasture quality was poorly influenced by the treatments. All supplements used in the dry season allowed maintaining weight and additional weight gain. The use of nitrogen and potassium fertilizers allowed the increase of efficiency of soil and to use areas dedicated to livestock to other activities in the agribusiness.

Esse estudo foi composto por dois experimentos, o primeiro referente ao pastejo durante o período de verão e outono cujo objetivo foi avaliar a resposta de duas espécies forrageiras (capim-marandu e capim-mombaça) com doses crescentes de adubação. O segundo correspondeu ao período seco, quando os animais foram confinados com objetivo de avaliar a suplementação da silagem de cana-de-açúcar com duas fontes proteicas (farelo de soja e farelo de algodão) no desempenho animal de três categorias (vaca, novilha e bezerro). O estudo foi conduzido no Laboratório de Pesquisas em Gado de Corte (LPGC), da Faculdade de Medicina Veterinária e Zootecnia, Universidade de São Paulo, campus Pirassununga. Para o experimento 1, a área experimental foi composta por 12 ha, divididos em oito módulos de pastejo (4 para o capim-marandu e 4 para o capim-mombaça), sendo utilizados 2 módulos como reserva, e cada módulo foi composto por 6 piquetes. O delineamento utilizado foi de blocos casualizados em arranjo fatorial 2x3 sendo duas espécies forrageiras (Brachiaria brizantha cv. Marandu e Panicum maximum cv. Mombaça) e três doses de adubação por ciclo de pastejo, totalizando 42, 333 e 667 kg de N e K2O ha-1 para o capim-marandu e 50, 400 e 800 kg de N e K2O ha-1 para o capim-mombaça, avaliados durante o verão e outono. Foram avaliadas as seguintes características: altura de entrada e saída das forrageiras, período de descanso, taxa de lotação, composição bromatológica de folha e colmo, relação folha/colmo/material morto e desempenho dos animais em pastejo. Para avaliação do desempenho animal, foram utilizadas 60 novilhas da raça Nelore, divididas nas seis unidades experimentais. Para ajuste da taxa de lotação, foram utilizadas vacas e novilhas do rebanho LPGC. No experimento 2 os animais foram alocados nas áreas de lazer, dos módulos de pastejo. A alimentação foi composta por silagem de cana-de-açúcar e duas fontes proteicas (farelo de soja ou farelo de algodão), sendo a relação volumoso:concentrado de 80:20. Os animais receberam alimentação ad libitum uma vez ao dia e os animais foram pesados a cada 21 dias a fim de avaliar o desempenho individual. De maneira geral, o incremento na dose de adubação aumentou linearmente (P<0,05) a altura de entrada, altura de saída, período de descanso, taxa de lotação (6,0 até 10,5 UA ha-1), PB, Lig/FDN, DIVMS, DIVFDN, proporção de colmo, e reduziu o teor de MS e folhas. O capim-mombaça apresentou menor período de descanso e teor de Lig/FDN, e maior teor de MM, FDN e Lig/FDN (P<0,05) em relação ao capim-marandu. Na estação de verão houve um aumento na altura de entrada, no teor de FDN, Lig/FDN e redução no teor de PB, DIVMS e DIFDN. Para o desempenho animal, não houve diferença entre doses de adubação (P=0,55) e espécie forrageira (P=0,07), sendo média de 0,850 kg dia-1. A suplementação com fontes proteicas apresentou efeito para a interação categoria*tratamento no CMS (P=0,03), sendo que vacas alimentadas com farelo de soja tiveram maior CMS em comparação às alimentadas com farelo de algodão. O desempenho animal não foi influenciado pelas fontes proteicas (P=0,10), no entanto houve efeito para categoria animal (P<0,05), sendo 0,677, 0,416 e 0,244 kg dia-1 para vacas novilhas e bezerros. Portanto, o uso de doses crescentes de adubação e o confinamento das categorias de cria permitiu o aumento na eficiência do uso da terra. / This study consisted of two experiments, the first referring to rotational grazing system during the summer and fall that aimed to evaluate the response of two forage species (marandugrass and mombaça) with increasing doses of fertilizer. The second corresponded to dry season, when animals were confined to evaluate the supplementation with sugarcane silage with two protein sources (soybean meal and cottonseed meal) on animal performance of animal three categories (cow, heifer and calf). The study was conducted at the Laboratory of Research in Beef Cattle (LPGC), Faculty of Veterinary Medicine and Animal Science, University of São Paulo, campus Pirassununga. For the experiment 1, the experimental area was composed of 12 ha, divided into eight grazing modules (4 for marandugrass and 4 for mombaça), 2 of these modules were used as reservation. The design was a randomized complete block in factorial arrangement of treatments 2 x 3 with 2 forage species (Brachiaria brizantha cv. Marandu and Panicum maximum cv. Mombaça) and 3 fertilizer levels by grazing cycle, totalying 42, 333 and 667 kg N and K2O ha-1 for Marandu grass and 50, 400 and 800 kg N and K2O ha-1 for Mombaça grass evaluated during the summer and fall. The following characteristics were evaluated: pre and post-grazing sward height of forage, grazing interval, stocking rate, chemical composition of leaf and stem, leaf/stem/dead material ratio and performance of grazing animals. For evaluation of animal performance, we used 60 Nellore heifers, divided into six experimental units. To adjust the stocking rate, cows and heifers, from LPGC herd, were used. In experiment 2 the animals were kept at the resting areas of grazing modules. The feed consisted of sugarcane silage and two protein sources (soybean meal or cottonseed meal), at a forage-to-concentrate ratio 80:20. The animals were fed ad libitum once daily and weighed every 21 days to assess individual performance. Overall, the increase in the dose of fertilizer increased linearly (P < 0.05) the pre and post-grazing sward height, grazing interval, stocking rate (6.0 to 10.5 AU ha-1), PB, Lig/NDF, IVDMD, IVNDFD, stem content, and reduced DM content and leaves. The mombaça showed lower grazing interval and Lig/NDF content and higher MM content, NDF and Lig/NDF (P < 0.05) compared to brachiaria grass. In the summer season there was an increase in the pre-grazing sward height, NDF, Lig/NDF and reduced CP content and IVDMD and IVNDFD. For the animal performance, there was not differences between fertilization doses (P = 0.55) and forage specie (P = 0.07), the ADG was 0.850 kg dia-1. Supplementation with protein sources presented effect of category*treatment interaction for DMI of cows (P = 0.03), while cows fed soybean meal had higher DMI than those fed cottonseed meal. The ADG was not affected by protein sources (P = 0.10), however, there was a category effect (P < 0.05), the means was 0.677, 0.416 and 0.244 kg dia-1 for cows, heifers and calves, respectively. Therefore, the use of increasing doses of fertilizers and the feedlot of calf rearing categories increased the land use efficiency.

A 2-yr grazing study quantified pasture and animal responses of four forage systems (FS) grazed at two stocking rates (SR; 3 or 6 animals ha-1). Using „Marshall? annual ryegrass (Lolium multiflorum Lam.) and „Durana? white clover (Trifolium repens L.), FS treatments included spatially separated grass and legumes within the same paddock (SS), monoculture grass (MG), monoculture legume (ML), and a binary grass and legume mixture (MIX). Annual herbage mass (HM) was similar among FS at high SR (1900 kg ha-1), but at low SR, grass plots had greater HM (2900 vs. 2000 kg ha-1) than plots of legume monocultures. Animals on SS (1.12 kg) had greater average daily gain (ADG) than ML (0.97 kg), but neither was different from MG (1.08 kg) or MIX (1.00 kg). Low SR animals had greater ADG than high SR (1.09 vs. 0.99 kg). These results indicate that SS grazing system can improve pasture productivity.

As pesquisas com métodos de pastejo têm culminado em divergência de resultados no desempenho de plantas e animais. As diferenças quantitativas e qualitativas entre métodos de pastejo poderiam ser elucidadas se estes fossem comparados, considerando o manejo ideal proposto para cada método. O objetivo do presente trabalho foi comparar métodos de pastejo, manejados com diferentes estratégias. O delineamento experimental utilizado foi em blocos completos e casualizados com 3 tratamentos e 3 repetições. Os tratamentos consistiram em três métodos de pastejo: lotação rotativa, utilizando altura do dossel como critério de manejo (AL); lotação rotativa, utilizando oferta de forragem como critério de manejo (OF); lotação contínua, mantida a 18 cm de altura (CO). O experimento foi realizado em área total de 25,2 hectares, formada com Brachiaria brizantha cv. Marandu localizada na Faculdade de Zootecnia e Engenharia de Alimentos da Universidade de São Paulo, em Pirassununga-SP. O período experimental de 93 dias, compreendido entre 15 de dezembro de 2011 e 15 de março de 2012 foi dividido em 3 períodos de avaliações. As variáveis foram comparadas pelo teste de Tukey a 10% de significância. Foram observadas interações entre tratamentos e períodos de avaliação para a maioria das respostas relacionadas à planta forrageira bem como para desempenho e taxa de lotação. O teor de proteína bruta não foi afetado pelos métodos de pastejo, porém, o teor de fibra em detergente neutro foi maior para o tratamento AL. A produtividade não foi afetada pelos métodos de pastejo. Assim, o método de lotação contínua é o mais atrativo com produtividade semelhante aos demais. / Research comparing grazing methods have resulted in conflicting findings on forage and animal performance. Quantitative and qualitative differences between grazing methods could be elucidated whether the methods are compared considering the ideal management proposed for each method. The objective of this study was to compare grazing methods, managed with different strategies. The experimental design was randomized complete blocks, with three treatments and three replications. Treatments consisted in three grazing methods: rotational stocking using canopy height as a management criteria (AL), rotational stocking using forage allowance as a management criteria (OF), continuous stocking held at 18 cm height (CO).The experiment was conducted in a total area of 25.2 hectares, planted with Brachiaria brizantha cv. Marandu, located at the Faculty of Animal Science and Food Engineering, University of São Paulo, in Pirassununga - SP. The 93 days experimental period, from December 15th of 2011 to March 15th of 2012, was divided into three assessment periods. The variables were compared by the Tukey test at 10% significance. Interaction between treatments and assessment periods were observed in the most of the variables related to forage plant as well as animal performance and stocking rate. Crude protein concentration was not affected by grazing methods, although the neuter detergent fiber was greater to AL treatment. Productivity was not affected by grazing methods. Thus, continuous stocking method is the most attractive, with similar productivity to the others.

O objetivo deste estudo foi avaliar as consequências bioeconômicas do aumento da taxa de lotação de vacas de cria em campo nativo com o uso de feno de palha de arroz. O experimento foi realizado em uma propriedade rural de Cachoeira do Sul 30º14’29” S 52º58’47” O, sul do Brasil, utilizando 110 vacas prenhas cruza Angus, com idade entre três e seis anos e alocadas nos tratamentos experimentais: SPF10 2.000 kg de peso vivo (PV/ha) e oferta de 10 kg feno/animal/dia; SPF5 1.000 kg PV/ha e oferta de 5 kg feno/animal/dia; SPF0 1.000 kg PV/ha sem oferta de feno. No início do experimento as vacas foram pesadas e avaliadas quanto ao escore de condição corporal (ECC) e distribuídas nos tratamentos: SPF10 (464 kg; 2,74); SPF5 (457 kg; 2,69); SPF0 (459 kg; 2,75) para PV e ECC, respectivamente. Todos os animais receberam um suplemento diário de 0,200kg/animal/dia de sal proteinado com 40% de PB. O período de suplementação com feno foi realizado no pré-parto das vacas, de 08 de maio a 01 de agosto. A partir do parto, os três grupos de vacas foram reunidos em um único lote e alocadas em pastagem anual de inverno (Lolium multiflorum e Avena strigosa). O acasalamento subsequente foi por meio de IATF e posterior repasse com touros na relação de 1:30 por um período de 60 dias. Foram avaliados o peso ao parto (PP; Kg), escore de condição corporal (ECC; 1-5), peso ao nascer (PN; kg), intervalo parto cio (IPC; dias), taxa de prenhez (TP; %) e produtividade (kg PV/ha) e resultado econômico (R$). Os sistemas não afetaram (P>0,05) o PP (492,0; 491,1; 479,7 kg), ECC (2,867; 2,692; 2,778) e PN (36,5; 35,9; 35,8 kg) para SPF10, SPF5 e SPF0, respectivamente. O IPC (52,2; 54,0; 56,1 dias) e a TP (65; 65; 72%) também não diferiram (P>0,05) entre os grupos experimentais. Contudo, no SPF10 a produtividade foi maior do que SPF5 E SPF0 (557,1 kg vs 288,9 e 320,0 kg) e o resultado econômico foi 181 e 190% superior aos sistemas SPF0 e SPF5, respectivamente. Esses resultados revelam o potencial nutricional do feno de palha de arroz como alternativa para viabilizar o aumento da taxa de lotação no pré-parto de vacas em sistemas de cria, mantidas em campo nativo, e assim produzir um maior número de bezerros por área associados ao benefício econômico. / The objective of this research was evaluate the effect of the baled rice straw in the beef cows pre-partum supplementation on the performance productive of the cow-calf systems. The 110 Angus cows between three and six years old allocated at experimental treatments on the farm at southern Brazil: SPF10 2.000 kg LW/ha and 10 kg of rice straw/cow/day; SPF5 1.000 kg LW/ha and 5 kg rice straw/animal/day; SPF0 1.000 kg LW/ha without rice straw offer. At the start of the experimental period the cows were weighed and evaluated in BCC. Thereby, the cows were allotted in the treatments according: SPF10 464 kg LW and 2,74 BCC; SPF5 457 kg LW and 2,69 BCC; SPF0 459 kg LW and 2,75 BCC. All the experimental groups received 0.200 kg/cow/day the protein salt with 40% CP. The supplementation period was the pre-partum phase, between May 8 and August 1 (85 days). The cows was kept in one lot in the start de parturition and transferred to a winter pasture (Lolium multiflorum e Avena strigosa). The breeding season period was by IATF and natural mount with bulls during 60 days. Was evaluated the cows weight at calving (PP;kg), body condition score (1-5), calf birth weight (BW: kg), resumption cyclicity postpartum interval (IPC;days), pregnant rate (PR;%) and productivity. The systems supplementation has no effect (P>0.05) on the cows PP (492.0; 491.1; 479.7kg), BCS (2.86; 2.69; 2.77) and calf BW (36.5; 35.9; 35.8 kg) to SPF10, SPF5 and SPF0, respectively. The IPC were 52.2; 54.0; 56.1 days and PR 65; 65; and 72%, to SPF10, SPF5 and SPF0, respectively (P>0.05). However, in SPF10 the productivity was higher (557.1 kg vs 288.9 e 320.0 kg) than SPF5 and SPF0, respectively, and your economics results evidenced the superiority of the 180% in ratio the other systems. Therefore, this results showed the potential of baled rice straw as an alternative to enable the increase of the stocking rate pre-partum cows, maintained in the natural pastures, and thus increase the productivity in cow-calf operations.

O experimento foi conduzido na Estação Experimental Agronômica da Universidade Federal do Rio Grande do Sul durante a estação de outonoinverno, com o objetivo de avaliar os parâmetros produtivos de uma pastagem natural fertilizada com diferentes níveis de N e submetida a diferimento e a sua influência sobre a produção animal. A fertilidade do solo foi corrigida 7 anos antes deste experimento (1996) com calcário e adubação de P e K. A área experimental foi roçada e diferida em 15/01/2003, quando foram aplicados os três níveis de nitrogênio (zero, 50 e 100 kg N/ha/ano). O período experimental ocorreu de 15 de abril (entrada dos animais) a 1º de setembro (final do inverno). Foram utilizados novilhos de sobre-ano (18 meses) em lotação contínua com carga variável de forma a manter uma oferta média de forragem de 10 kg de MS/100 kg PV/dia. O delineamento utilizado foi o de blocos completos casualizados com parcelas subdivididas no tempo sendo o tempo considerado na parcela principal e o N na subparcela. A pastagem nativa fertilizada quando diferida no verão por um período de 90 dias permite manter altas cargas animais durante o outono e inverno e em níveis crescentes conforme a adubação nitrogenada (958, 1072 e 1443 kg PV/ha, para zero, 50 e 100 kg N/ha respectivamente). Este efeito é devido fundamentalmente às taxas de crescimento observadas durante o período de diferimento. A performance animal somente é adequada durante o primeiro mês de utilização do pasto, ocorrendo perdas de peso a partir de meados de maio. Os níveis de nitrogênio utilizados não contribuem para atenuar estas perdas. Ainda assim é possível chegar ao final do inverno com o mesmo peso individual inicial dos animais. O diferimento de áreas de pastagem natural adubada revela-se uma estratégia interessante dentro de sistemas de produção animal a pasto, desde que integrado num planejamento forrageiro global da propriedade. / The experiment was conducted at the Agronomic Experimental Station of Federal University of Rio Grande do Sul, at Eldorado do Sul district, during the autumn-winter seasons of 2003, aiming the evaluation of the parameters of natural pasture and animal production at different levels of nitrogen fertilization and submitted to deferment. Soil fertility was amended seven years before this trial (1996) with limestone and P and K fertilizers. Experimental area was mowed and deferred in 15/01/2003, when three levels of nitrogen fertilization (zero, 50, 100 kg N/ha) were applied. Evaluation period extended from April 15th (beginning of grazing period) to September 1st (final of winter), using eighteen months steers in continuous grazing an variable stocking in order to maintain average dry matter (DM) allowance of 10 kg DM/100 kg LW/day. A randomized complete block design with two replications was utilized, with time considered as main plot and N as sub-plot. Deferring fertilized native pasture at mid summer by 90 days make possible to maintain high stocking rates during the critical autumn-winter period dependent on nitrogen level (958, 1072 e 1443 kg LW/ha, for zero, 50 e 100 kg N/ha respectively). This differential effect is due to the forage growth rate verified during rest period. Animal performance was adequate only during the first month of pasture utilization and losses occur after mid may. The utilized N levels do not contribute to avoid these losses. Instead the observed weight losses, it is possible to keep the animals with the same initial weight of the beginning of autumn by the final of the winter. Deferring areas of natural pasture is a useful strategy inside animal production systems, if integrated on a global feed budget.

Data collected between 1992/93 and 1996/97 from two long-term grazing trials were used to investigate the interaction between grazing animals and veld grass. In the first trial, the impacts of stocking rate and time of stocking in spring on both livestock performance and veld vigour (defined as the ability of a grass plant to regrow after defoliation) and condition were investigated. In the second trial comparisons were made, firstly between the impacts of sheep and cattle grazing, and secondly between various types and frequencies of rest, on veld vigour and condition. Treatments applied in the first trial comprised four stocking rates, namely 7, 10, 13 and 16 sheep ha¯¹ for the duration of the grazing season, and two times of stocking, namely as early as possible after spring burning and three weeks later. Sheep grazed each treatment continuously throughout the growing season. Treatments were applied to alternate blocks in a two-year cycle with each block resting for a year within a grazing cycle. Animal performance (mass gains over the season) was measured to quantify livestock performance. Herbage availability was measured on a species basis at intervals throughout each season using a dry-weight-rank procedure to determine grazing patterns. Residual effects of the grazing treatments on vigour were determined by measuring herbage regrowth on a species basis during the rest season which followed a season of grazing and comparing these measures to a previously ungrazed control treatment. Effects of the grazing treatment on proportional species composition were determined using a nearest plant point technique. Stocking rate had a non-linear effect on livestock performance, with livestock performance on the lightest stocking rate being less than on the two intermediate stocking rates. The mass gains on the heaviest stocking rate were generally the smallest. Delaying the time of stocking in spring resulted in smaller mass gains during the resultant shorter season. The sheep from both the early and late time of stocking groups had similar mean masses at the end of the season. The advantage of stocking early can thus be attributed more to saving the cost of alternative feed for the interim period than to additional mass gains due to stocking early. Quantification of livestock performance in terms of selected and available feed quality, quantity and species availability throughout each season was extremely complex due to multiple thresholds in the measured variables and no simple cause and effect relations could be established that would hold for spatial or temporal extrapolation. The negative impact of grazing on veld vigour was severe. Stocking rate and time of stocking had a secondary impact with the vigour loss positively related to increasing grazing pressure. The main factor influencing vigour loss was grazing, irrespective of time of stocking or stocking rate, as opposed to no grazing. The impact of grazing on vigour was severely negative in the palatable species, variable in the species of intermediate palatability and positive in the unpalatable species that were rarely, if ever, grazed. The stocking rate and time of stocking rate had an impact on the proportional species composition, with the more palatable species declining in proportion. There was an observable relation between impact of grazing on vigour and on species composition. Treatments applied in the second trial involved applying a full growing season rest in alternate years, half a growing season rest (late season) in alternate years and no rest to veld grazed by sheep or cattle at similar stocking rates. Residual effects of the treatments on veld vigour were determined by measuring species regrowth using a dry-weight-rank technique during the season following treatment application, and comparing it to controls ungrazed for one and two seasons respectively. Changes in proportional species composition were determined using a nearest plant point technique. The vigour of veld grazed by sheep declined rapidly relative to veld grazed by cattle. The vigour of palatable species was severely impacted, vigour of intermediate species was variably impacted and vigour of unpalatable species increased dramatically on veld grazed by sheep compared to the control treatments. Similar trends occurred in veld grazed by cattle, but to a lesser degree. Resting was beneficial for vigour recovery in both sheep and cattle treatments but it seems that the grazing treatment between rests has a greater influence on the veld vigour and condition than the rest itself. The veld grazed by sheep remained at a substantially lower productivity level than veld grazed by cattle. This was particularly evident in the change in productivity balance between palatable and unpalatable species in the sheep treatments, where palatable species vigour declined and unpalatable species vigour increased relative to veld grazing by cattle. Species composition of veld grazed by sheep deteriorated over the trial period in contrast to the veld grazed by cattle, which improved in species composition. Grazing management recommendations for sourveld should include a bias towards cattle, optimising stocking rate for improved performance and resting for enhancing vigour of the palatable grasses. / Thesis (Ph.D.)-University of Natal, Pietermaritzburg, 1999.

Considerable understanding of the functioning of semi-arid systems is still needed to enable range managers to formulate management policies, with a degree of confidence. Long term data sets that encompass a wide range of interactions between the various major components of a semi-arid system (vegetation, herbivory, animal performance, landscape and rainfall), are unfortunately rare but essential to provide sufficient depth of data to adequately test various hypotheses about rangeland dynamics. This study comprises an analysis of a ten year data set derived from two cattle stocking rate trials in the semi-arid savanna of KwaZulu/Natal. Statistical analysis revealed that the most pronounced and rapid compositional change was due to rainfall, but that stocking rates between 0.156 and 0.313 AU ha ¯¹ had an important effect as well. Sites on steeper slopes with heavy stocking rates, exhibited the greatest amount of compositional change between 1986 and 1996 (40 Euclidean points in heavy stocking rate treatments on slopes vs 21-24 Euclidean points in heavy stocking rate treatments on flatter land, or 11-24 Euclidean points in low stocking rate treatments). Heavy stocking rates in conjunction with low rainfall tended to cause decreases in densely tufted perennial grasses and increases in annuals and weakly tufted perennials. Multiple regression analysis revealed that seasonal peak grass production (measured as disc height) declined between 1986 and 1996 only at those sites on steeper slopes with heavy stocking rates. The camps that declined in productivity also underwent the greatest degree of compositional change. The decline in grass productivity in certain high stocking rate camps did not translate into a decline in cattle performance. Depending on rainfall, cattle gained on a seasonal basis between 112 and 241 kg at low stocking rates, 82 and 225 kg at medium stocking rates and 84 and 217 kg at high stocking rates Rainfall, compared with stocking rate, accounted for the greatest amount of variance in seasonal peak grass production and cattle performance. Cattle performance had a strong curvilinear response to rainfall, which also proved to be a better predictor of cattle performance than grass biomass. There were no clear trends in soil physical and chemical characteristics between low and high stocking rates that could provide convincing evidence that loss of soil nutrients was an important mechanism of range degradation. The total standing crop of plant nitrogen but not of phosphorus tended to decline at high stocking rates. Plant nutrient and van Soest analyses suggested that forage quality was higher at heavy stocking rates. The results of this study generally supported traditional concepts of rangeland dynamics with regard to rainfall and grazing effects on compositional change and seasonal grass production. The results were important in being able to show quantitatively that heavy stocking rates result in a decline in grass production and that this effect is dependent on an interaction between stocking rate and landscape position or slope, and that there is a link between a decline in seasonal grass production and compositional change. The results also highlighted areas for future research that would be useful for furthering our understanding of various aspects of rangeland dynamics and mechanisms of degradation. / Thesis (M.Sc.)-University of Natal, Pietermaritzburg, 1998.

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior / The work was carried out to evaluate the defoliation patterns and quantify the leaf tissue flows in Alexandergrass, grazed by beef heifers in different feeding systems, in rotational grazing method. The experimental design was completely randomized with repeated measures, three levels of supplementation with whole rice bran (0; 0.5 and 1% of body weight) and two area replications. The supply of whole rice bran for heifers grazing in Alexandergrass allows can increase 13% the stocking rate. The leaf tissue flows, consumption of leaf blades and the grazing intensity are not changed by supplement. Regardless of the system feeding the heifers graze the leaf blades growing in a smaller period of time compared to other types of leaf, which allows the leaf crop top extract canopy. / Objetivou-se avaliar os padrões de desfolhação e quantificar os fluxos de tecidos foliares em papuã, pastejado por novilhas de corte, em diferentes sistemas alimentares, em método rotativo de pastejo. O delineamento experimental foi o inteiramente casualizado, com medidas repetidas no tempo, três níveis de suplementação com farelo de arroz integral (0; 0,5 e 1 % do peso corporal) e duas repetições de área. O fornecimento de farelo de arroz integral para novilhas em pastejo em papuã permite aumentar 13% a taxa de lotação. Os fluxos de tecidos foliares, o consumo de lâminas foliares e a intensidade de pastejo não são alterados pelo fornecimento de suplemento. Independente do sistema alimentar as novilhas pastejaram as lâminas foliares em expansão num menor intervalo de tempo em relação aos demais tipos de folha, o que permite a colheita de folhas do extrato superior do dossel.