The early life history dynamics of stocked, fingerling striped bass (Morone saxatilis) were evaluated in Smith Mountain Lake, Virginia, from 1994-96 and incorporated into an individual-based model to assess various stocking strategies in terms of their largest percent increases in first-year growth, overwinter survival, and recruitment to age 1. Age-0 striped bass exhibited dissimilar patterns of dispersion and size-dependent spatial distribution as a result of differences in habitat availability between stocking sites and water temperature preferences. Although size increased over the growing season, a bimodal length distribution developed by fall during both 1994 and 1995; this distribution consisted of large-mode juveniles (> 180 mm TL) that weighed several times more than small-mode fish (<140 mm TL). Differential growth was attributed primarily to size-dependent differences in food habits and diet quality: small-mode striped bass maintained a mixed, low quality diet of invertebrates and small, age-0 cyprinids, while large-mode juveniles consumed only larger, energetically more profitable age-0 alewives. This disparity in food habits, largely due to the inability of small-mode striped bass to consume distributionally- and morphologically-invulnerable age-0 alewives, resulted in size-dependent differences in physiological well-being as large-mode juveniles had amassed greater absolute energy stores than small-mode fish by the end of the growing season. Spring sampling revealed that the bimodal length distribution had become unimodal and was comprised almost entirely of large-mode juveniles. Because the few surviving small-mode striped bass collected during spring were extremely emaciated, it appears that this size group exhausted their energy stores and, consequently, starved over the winter. Individual-based model simulation results indicated that stocking juvenile striped bass at a median total length of 52 mm on 08 June, while maintaining the current stocking density at 300,000 fingerlings, would result in the largest percent increases in first-year growth, survival, and number of age-1 recruits. This strategy was also less sensitive to perturbations in alewife population parameters and water temperature regime, and was more robust to these variations than the existing stocking scheme (300,000 fingerling striped bass with a median total length = 42 mm introduced on 15 June). / Ph. D.

The largest agricultural enterprise in the Appalachia region of Virginia is livestock production, particularly beef cow calf operations. However; topography and land holding patterns have resulted in a majority of small farms operating part time on less than 150 acres. These farms, while abundant, are not necessarily profitable. Management intensive grazing has been suggested as an alternative to traditional production practices to increase profitability. A profitability analysis was conducted by comparing a traditional style of cow-calf management where hay was produced on farm with a full machinery complement to a management intensive grazing farm where forages are stockpiled and all hay was purchased on farm, requiring minimal machinery investment. Four farms were simulated using Finpack Farm Management software by utilizing production data from the Virginia Tech Shenandoah Valley Agriculture Research and Extension Center and secondary financial data. The first two farms were listed as having a traditional style of management with hay production and two different stocking rates, 1.75 acres per cow-calf unit and 2.25 acres per cow-calf unit, respectively. Farm 3 and Farm 4 were simulated utilizing management intensive grazing and the two socking rates. It was found that while none of the farms actually show a profit the management intensive farms did outperform the traditional style farms. Farm 3 with the 1.75 acre per cow-calf unit stocking rate was the best performing farm financially. With these findings, beef cow producers will be able to make better management decisions and explore more profitable alternatives. / Master of Science

Mob stocking is a variation of rotational stocking known for restricting a large number of animals to a small area before being moved to new grass after a few hours. This method allows a long (90-day) recovery period but was hypothesized to diminish the nutritional value of herbage relative to continuous and rotational stocking with lesser stocking density at similar stocking rates. This thesis summarizes two studies conducted in Blacksburg and Raphine, and in Steeles Tavern, VA, respectively, at a single beef cattle stocking rate of 12 animal unit months per hectare live body weight. The objectives were to: (1) compare the yield and nutritional value of herbage in pastures managed with three stocking methods, termed mob, rotational, and continuous stocking; (2) compare the abundance of seeded clover species among the stocking methods; and (3) estimate the nutritional value of herbage that is consumed by beef cattle during mob stocking using extrusa sampled from esophageally-cannulated animals. Analysis of standing herbage during two years produced several important findings. Although standing herbage mass was significantly greater in mob stocked pastures at Blacksburg and Raphine, aboveground net primary productivity in 2014 did not differ significantly among mob, rotational, and continuous stocking at any of the project locations. Herbage nutritive value did not differ significantly among stocking methods over two years at Blacksburg and Raphine; however, herbage from mob stocked pastures at Steeles Tavern contained significantly greater concentrations of crude protein in September and October relative to herbage from continuous- and rotationally-stocked pastures at those times. Differences in herbage mass likely contributed to significant differences in establishment of seeded clovers: red clover [Trifolium pratense L. Cinnamon Plus] establishment was similar among stocking methods but white clover [Trifolium repens L. Will] establishment was greater in continuously stocked pastures than mob and rotationally stocked pastures. Hand-clipped samples collected at Blacksburg in September 2014 significantly underestimated the crude protein content of the herbage selected by the steers, although the concentrations of fiber constituents in herbage did not differ significantly between clipped samples and esophageal samples. Although the nutritive value of the herbage on offer did not generally differ among stocking methods at this stocking rate, diet selected was at times less nutritious during mob stocking than continuous and rotational stocking methods. At this stocking rate, stocking method had less influence on pastures than seasonal variation in weather and plant maturity. / Master of Science

Tall fescue (Festuca arundinacea Schreb.) and alfalfa (Medicago sativa L.) have many desirable forage attributes, are grown extensively throughout the USA, and combined form a productive pasture mixture. The objective of this research was to develop recommended management practices for alfalfa-tall fescue mixtures and compare livestock performance, forage quality, and productivity of this mixture to N-fertilized endophyte-free tall fescue. Forty-eight Angus or Angus crossbred steers were rotationally stocked on a four-replicate alfalfa-tall fescue and N-fertilized tall fescue pasture system during 2002 and 2003. Livestock gain, forage quality, and forage production were monitored throughout the seasons. Management treatments conducted within wire exclosures included defoliation height, rest period, exclosure movement, and month and were evaluated using detailed botanical composition and persistence measurements. Defoliation height, rest period, and month all affected alfalfa-tall fescue competition. Alfalfa was generally more competitive with longer rest periods and shorter heights, although results were not consistent. Alfalfa composition and persistence declined dramatically over the 2003 season due to climate, grazing management, and cultivar. Cool, high moisture conditions stimulated tall fescue growth and reduced alfalfa vigor and survival. Livestock gains were higher for pure tall fescue at one date in 2002, but higher overall for alfalfa-tall fescue during 2003. Forage quality (CP, NDF and ADF) was consistently higher for alfalfa-tall fescue during both seasons. In conclusion, both alfalfa-tall fescue and N-fertilized endophyte-free tall fescue produce productive pastures and high ADG in beef steers in Virginia, but continued management research is required to maintain the alfalfa component of this mixture. / Master of Science

The influence of initial stocking and physiologically aged cuttings (taken from 1-year- old and 5-year-old parents) on corewood modulus of elasticity (MOE) in 6-year-old Pinus radiata D. Don was studied in a Nelder-design experiment in Rolleston, Canterbury. In the same experiment, the influence of initial stocking on MOE in 5-year- old Eucalyptus nitens was also investigated. The study incorporated 19 different stocking levels ranging from 207 to 40,446 stems/ha. Green dynamic modulus of elasticity was assessed in standing trees using the TreeTap stress-wave method over the lower part of the stem (0.3 – 1.9m) for 151 P. radiata trees and 115 E. nitens trees. The interaction between species and stocking significantly influenced MOE (P<0.001). MOE of P. radiata increased by 55% (or 3.9 GPa) between 271 and 40,466 stems/ha, and by 41% (or 2.2 GPa) between 271 and 4370 stems/ha. MOE of E. nitens was also influenced by stocking but the slope was significantly lower indicating that the effect of stocking was less pronounced than for P. radiata. Over the usual range of stockings for E. nitens there was an insignificant relationship between stocking and stiffness (P=0.335). Trees were also assessed for DBH, height, and stem slenderness (height/ DBH). None of these latter variables had a significant influence on MOE after the effects of stocking and species were accounted for. No effects of physiological age of cuttings were detected in this study. The findings of this study highlight the importance of stocking as a tool that forest managers can utilize to regulate corewood stiffness in P. radiata trees. These results also suggest that for E. nitens, where wood stiffness is a priority, forest managers could reduce establishment costs by planting at much lower initial stockings. This study also highlights the superior stiffness of E. nitens in direct comparison with P. radiata, with many trees in the experiment already exceeding stiffness thresholds for structural timber in New Zealand.

Two consecutive experiments were conducted to test a hypothesis that mixed grazing outcome is influenced by the type of stocking system applied. The objective of both experiments was to investigate the influence of co-grazing with sheep on cattle liveweight gain (LWG) under continuous (C) and rotational (R) stocking, where sheep weekly liveweight change under the two stocking systems was kept similar. In experiment I nine yearling heifers (266 ± 4.5 kg liveweight) and 27 ewe hoggets (54±0.9 kg liveweight) were continuously stocked for 19 weeks on an irrigated perennial ryegrass-white clover pasture (2.95 ha) maintained at a sward surface height (SSH) of 5cm by adding or removing additional animals in a fixed ratio (1: 1 W⁰.⁷⁵ cattle:sheep). An equal area of pasture was rotationally stocked by a similar group of animals where they received a new area of pasture daily and also had access to the grazed area over the previous 2 days. The size of the new area provided daily was such that the weekly liveweight change of rotationally co-grazed sheep was equal to that of those continuously co-grazed with cattle. Similar groups of animals were used in the second experiment with additional group of 9 heifers grazed alone on C and R pastures. Liveweight of animals was recorded weekly and final fasted weight was determined after 24-hour total feed restriction. SSH on both treatment swards was recorded daily. There were three intake measurement periods spread over the trial period. Organic matter intake (OMI) was predicted from the ratio of N-alkanes in faeces and herbage. Diet composition was determined by dissecting oesophageal extrusa samples. Grazing behaviour (bite rates and grazing time) were also recorded. The mean SSH for C pasture was 5.1±0.09 cm. Overall pre- and post-grazing SSH for R pasture was 15.9 ±0.12 and 5.6 ±0.07 cm, respectively. As determined by the protocol average daily LWG of sheep was similar between C and R (147 (±5.8) vs 138 (±6.7) g day⁻¹; (P>0.05). In contrast, cattle continuously stocked with sheep grew 200 g day⁻¹ slower than those rotationally stocked with sheep (800 (±41.6) vs 1040 (±47.7) g day⁻¹, P<0.0l). R heifers achieved 30 kg higher final fasted liveweight than C heifers (350 vs 381 kg; P<0.01). Overall LWG per ha was also 6 % higher under R than C stocking (674 vs 634 kg ha⁻¹). The OMD of both sheep (73.5 vs 75.8 %) and cattle (75.8 vs 78.0 %) diets was similar under continuous and rotational stocking. There was no significant difference OMI data also concurred with the L WG data (Cattle: 7.94 vs 6.31 (±0.32) kg day⁻¹ (P<0.05); sheep: 1.40 vs 1.44 (±0.04) kg day⁻¹ for Rand C treatments, respectively). There was no difference in clover content of cattle diet under C and R treatments. C heifers had higher number of bites per minute than R heifers (62 vs 56; P<0.05). Proportion of heifers seen grazing (every 15-minute) during four 24-hour observations was greater on C than R pasture (0.44 vs 0.31 (±0.03); P<0.05). The similarity coefficient between sheep and cattle diet was 0.61 and 0.76 under C and R stocking, respectively. The lower daily LWG of C heifers was attributed to (a) the lower SSH under C than R stocking and/or (b) the inability of cattle to compete well with sheep where there is small, continual renewal of resources (C) in contrast to a large periodic renewal under R stocking. This experiment showed that the outcome of mixed gruing can be influenced by the stocking system chosen. But it was not possible to apportion the difference in LWG of cattle between mixed grazing per se and the difference in mean grazed sward height (5.1 for C vs 10.8 cm for R). A second experiment was conducted to determine the relative performance of cattle co-grazed with sheep (CS) and grazed alone (CA) under each stocking system. Hence, there were four treatments. CA- continuous stocking (CA-C), CS- continuous stocking (CS-C), CA- rotational stocking (CAR) and CS- rotational stocking (CS-R). A total area of 4.42 ha was allocated to each stocking system. Under C stocking, 2.95 ha (2/3) was assigned to CS-C and 1.47 ha (1/3) to CA-C, and SSH on both treatments was kept at 4 cm by adding or removing extra animals. Under R stocking, CA-R and CS-R grazed side by side separated by an electric fence. They were given a fresh area daily, the size of which was varied such that the weekly LW change of R sheep was equal to that of the C sheep. CA-R received one-third of the new area though the size was adjusted regularly to achieve the same post-grazing SSH with CS-R. Measurements included: weekly liveweight change, OMI (two periods) and diet composition (using N-alkanes). The mean SSH of CA-C and CS-C swards was 4.27 and 4.26 (±0.02) cm, respectively. CA-R and CS-R swards had mean pre-grazing SSH of 14.9 and 15.2 (±0.08) cm and post-grazing heights of 4.87 and 4.82 cm (±0.03), respectively. The proportion of areas infrequently grazed was higher for CA-C than CS-C swards (0.22 vs 0.17, respectively). C and R sheep daily LWG: 155 (±0.6) and 147 (±0.7) g, and OMI: 1.96 and 2.04 (±0.ll) kg, respectively, were not significantly different. They also had similar diet composition. In comparison, CS-C heifers grew only at 69 % of the daily LWG achieved by CS-R heifers (706 vs 1028 (±72) g; P<0.05). LWG of CA-C and CA-R was 916 and 1022 (±72) g day⁻¹, respectively. The difference in LWG between CS-R and CS-C (D₁) heifers was due to difference in mean sward height, stocking system and mixed grazing, while D₂ (difference in LWG between CA-R and CAC) was due to difference in mean sward height and stocking system. D₁-D₂ (the effect of stocking system on mixed grazing) was 216 g and made up 67 % of the total difference between CS-R and CS-C. There was a significant stocking system-species mixture interaction in the final fasted LW achieved by heifers. Final fasted LW was significantly lower for CS-C than CA-C heifers (283 vs 323 (±9.7) kg), but did not differ between CS-R and CA-R (332 vs 330 (±9.7) kg, respectively). The digestibility of diet OM was similar for both continuously and rotationally stocked sheep (84.4 vs 83.2 %, respectively). Cattle diet OMO was 76.5, 74.7, 79.4 and 77.8 for CA-C, CS-C, CA-R and CS-R respectively (P>0.05). Differences in OMI followed a similar pattern to daily LWG. Mean daily OMI was 8.98, 6.24, 8.80 and 9.45 (±0.40) kg for CA-C, CS-C, CA-R and CS-R, respectively. Clover content of the diet of CA-C heifers was three times higher than that of CS-C heifers (30.7 vs 10.4 % OM; P<0.05); there was no difference in clover content of diets of CS-R and CA-R heifers (21.5 vs 23.9 % OM, respectively). In both stocking systems LWG per ha was higher on CA than CS treatments. These results suggested that the disadvantage of selective clover grazing by sheep outweighed the advantages of sheep grazing around cattle dung patches under continuous stocking. Under rotational stocking, rapid diurnal changes in sward conditions probably limited selective grazing by both sheep and cattle such that there was no disadvantage to CS cattle. The results do not provide a basis for recommending grazing cattle with sheep rather than cattle alone, but do provide some basis for recommending co-grazing of sheep and cattle using rotational rather than continuous stocking.

O conhecimento dos aspectos relacionados à interface planta:animal em sistemas de produção em pastagens ganha enorme relevância quando se tem como objetivo principal trabalhar dentro de princípios baseados no equilíbrio e racionalidade do uso dos recursos inerentes ao processo produtivo. Dessa forma, caracterizar os componentes da estrutura do dossel forrageiro e o efeito que os mesmos exercem sobre o comportamento ingestivo de animais em pastejo assume grande importância, uma vez que podem influenciar de forma relevante o consumo de forragem. Dentro desse contexto, o presente trabalho teve como objetivo procurar elucidar aspectos pertinentes à interface planta:animal através da quantificação do tamanho e da taxa de bocado, tempo gasto nas atividades de pastejo, ruminação e ócio pelos animais, e o consumo diário de forragem em pastos de Brachiaria brizantha cv. Marandu pastejados por bovinos em regime de lotação contínua e taxa de lotação variável. O experimento foi realizado em área do Departamento de Zootecnia da USP/ESALQ, em Piracicaba, SP, entre 01 de novembro de 2001 e 14 de fevereiro de 2003. Os tratamentos corresponderam a quatro alturas de dossel forrageiro (10, 20, 30 e 40 cm) mantidas em steady state, e foram alocados às unidades experimentais segundo um delineamento de blocos completos c casualizados, com quatro repetições. Os resultados revelaram uma redução em consumo de forragem com a diminuição da altura do dossel forrageiro (1,3; 1,8, 1,8 e 2,0 kg MS.kg PV -1 para 10, 20, 30 e 40 cm, respectivamente), conseqüência da redução em tamanho de bocado (0,5; 0,8; 1,2 e 1,5 g MS.bocado -1 para 10, 20, 30 e 40 cm, respectivamente). Os animais, na tentativa de tentar compensar a redução em consumo, aumentaram a taxa de bocado (46,3; 30,3; 23,8 e 17,5 bocados.minuto -1 para 10, 20, 30 e 40 cm, respectivamente) e, na condição de 10 cm de dossel forrageiro, aumentaram, também, o tempo de pastejo (11,4; 10,7; 10,6 e 10,5 horas.dia -1 para 10, 20, 30 e 40 cm, respectivamente). Concluiu-se que a ingestão de forragem pode ser controlada através de variações em condição e estrutura do dossel forrageiro, situação essa que demonstra o potencial de planejamento e monitoramento de estratégias de pastejo baseadas em metas de condição de dossel para níveis variáveis de exigências nutricionais, épocas do ano e espécie animal. / Knowledge of aspects related to plant:animal interface in pastoral systems acquire greater importance when the main objective is to rationalize and optimize the use of any resource available. In that scenario, characterization of structural sward components and their effect on ingestive behaviour of grazing animals is a key element, since they can have a relevant influence on herbage intake. Against this background, the objective of this experiment was to study aspects of the plant:animal interface quantifying bite size, bite rate, time spent on grazing, rumination and rest as well as herbage intake of cattle grazing Brachiaria brizantha cv Marandu pastures submitted to continuous stocking managements. The experiment was carried out at Departamento de Zootecnia, USP/ESALQ, Piracicaba, SP, from 01 November 2001 until 14 February 2003. Treatments corresponded to four steady state conditions characterized by sward surface heights (SSH) of 10, 20, 30 and 40 cm, assigned to experimental units according to a complete randomized block design, with four replications. The results revealed a reduction in herbage intake with decreasing SSH (1.3, 1.8, 1.8 and 2.0 kg DM.kg LW -1 for 10, 20, 30 and 40 cm, respectively), consequence of a reduction in bite size (0.5, 0.8, 1,2 and 1.5 g DM.bite -1 for 10, 20, 30 and 40 cm, respectively). Animals, in an attempt to compensate the decrease in herbage intake, increased their bite rate (46.3, 30.3, 23.8 and 17.5 bites.minute -1 for 10, 20, 30 and 40 cm, respectively) and, for the 10 cm SSH, increased, also, their grazing time (11.4, 10.7, 10.6 and 10.5 hours.day -1 for 10, 20, 30 and 40 cm, respectively). It was concluded that herbage intake can be controlled by variations in sward structure and condition, which points to the potential for planning and monitoring grazing strategies based on sward targets for variable levels of animal requirements, time of the year and animal species.

The objective of this research was to evaluate the forage yield and nutritive value of elephantgrass on conventional and organic systems. In the organic system, species with complementary growth periods were combined; elephantgrass was planted in lines 3m apart from each other; between the rows of elephantgrass, during the winter period, ryegrass was sown and in the summer period the development of species of spontaneous growth was allowed. In the conventional production, two pastures were studied, one with the same strategy of organic production, but with chemical fertilization and another with elephantgrass cultivated alone. 100 kg of N ha-1 were applied with mineral and organic fertilization (bovine manure and pig slurry) in conventional and organic systems, respectively. Holstein cows receiving 0.9% of body weight complementary concentrate feed were used in the evaluation. The experimental design was completely randomized, with three treatments (forage systems), three repetitions (paddocks) and with repeated measures in time (seasons). Forage mass parameters of pre and post grazing, botanical composition, forage production and nutritive value were evaluated. Forage samples were collected by hand-plucking technique for the determination of organic matter, crude protein and in situ digestibility of organic matter. During the experimental period (337 days) seven grazing cycles were performed. Forage production and stocking rate were 12548; 10270; 19168 kg ha-1 and 3.3; 2.1; 4.5 AU ha-1 dia-1, respectively, for the forage systems. Pastures mixed, on conventional and organic production, present best forage distribution throughout the seasons. Higher value of forage production was observed in elephantgrass cultivated alone, on conventional system. Better value of nutritional value parameters were observed in organic pasture. / O objetivo desta pesquisa foi avaliar a produção de forragem e o valor nutritivo do capim-elefante nos sistemas convencional e orgânico. No sistema orgânico, combinaram-se espécies com períodos de crescimento complementares; o capim-elefante foi plantado em linhas com 3m de distância uma da outra; entre as fileiras de capim-elefante, durante o período de inverno, foi semeado azevém e no período de verão permitiu-se o desenvolvimento de espécies de crescimento espontâneo. Na produção convencional, foram estudadas duas pastagens, uma com a mesma estratégia de produção orgânica, porém com adubação química e outra de capim-elefante sob cultivo singular. Foram aplicados 100 kg de N ha-1 com adubação mineral e orgânica (esterco de bovinos e dejetos de suínos) nos sistemas convencional e orgânico, respectivamente. Como animais experimentais foram utilizados vacas da raça Holandesa, recebendo alimentação complementar na forma de concentrado à razão de 0,9% do peso corporal. O delineamento experimental foi o inteiramente casualizado, com três tratamentos (sistemas forrageiros), três repetições (piquetes) e medidas repetidas no tempo (estações). Foram avaliados os parâmetros de massa de forragem pré e pós-pastejo, composição botânica, produção de forragem e valor nutritivo. Para a determinação de matéria orgânica, proteína bruta e digestibilidade in situ da matéria orgânica, foram coletadas manualmente amostras de forragem mediante técnica de simulação de pastejo. Durante o período experimental (337 dias) foram realizados sete ciclos de pastejo. A produção de forragem e a taxa de lotação foram de 12548; 10270; 19168 kg ha-1 e 3,3; 2,1; 4,5 UA ha-1 dia-1, para os sistemas forrageiros. Pastos com misturas forrageiras, sob produção convencional e orgânica, apresentam a melhor distribuição de forragem ao longo das estações. O maior valor de produção de forragem foi observado em pastagens cultivadas singularmente, no sistema convencional. Melhores parâmetros de valor nutricional foram observados em pastagens orgânicas.

O conhecimento dos aspectos relacionados à interface planta:animal em sistemas de produção em pastagens ganha enorme relevância quando se tem como objetivo principal trabalhar dentro de princípios baseados no equilíbrio e racionalidade do uso dos recursos inerentes ao processo produtivo. Dessa forma, caracterizar os componentes da estrutura do dossel forrageiro e o efeito que os mesmos exercem sobre o comportamento ingestivo de animais em pastejo assume grande importância, uma vez que podem influenciar de forma relevante o consumo de forragem. Dentro desse contexto, o presente trabalho teve como objetivo procurar elucidar aspectos pertinentes à interface planta:animal através da quantificação do tamanho e da taxa de bocado, tempo gasto nas atividades de pastejo, ruminação e ócio pelos animais, e o consumo diário de forragem em pastos de Brachiaria brizantha cv. Marandu pastejados por bovinos em regime de lotação contínua e taxa de lotação variável. O experimento foi realizado em área do Departamento de Zootecnia da USP/ESALQ, em Piracicaba, SP, entre 01 de novembro de 2001 e 14 de fevereiro de 2003. Os tratamentos corresponderam a quatro alturas de dossel forrageiro (10, 20, 30 e 40 cm) mantidas em steady state, e foram alocados às unidades experimentais segundo um delineamento de blocos completos c casualizados, com quatro repetições. Os resultados revelaram uma redução em consumo de forragem com a diminuição da altura do dossel forrageiro (1,3; 1,8, 1,8 e 2,0 kg MS.kg PV -1 para 10, 20, 30 e 40 cm, respectivamente), conseqüência da redução em tamanho de bocado (0,5; 0,8; 1,2 e 1,5 g MS.bocado -1 para 10, 20, 30 e 40 cm, respectivamente). Os animais, na tentativa de tentar compensar a redução em consumo, aumentaram a taxa de bocado (46,3; 30,3; 23,8 e 17,5 bocados.minuto -1 para 10, 20, 30 e 40 cm, respectivamente) e, na condição de 10 cm de dossel forrageiro, aumentaram, também, o tempo de pastejo (11,4; 10,7; 10,6 e 10,5 horas.dia -1 para 10, 20, 30 e 40 cm, respectivamente). Concluiu-se que a ingestão de forragem pode ser controlada através de variações em condição e estrutura do dossel forrageiro, situação essa que demonstra o potencial de planejamento e monitoramento de estratégias de pastejo baseadas em metas de condição de dossel para níveis variáveis de exigências nutricionais, épocas do ano e espécie animal. / Knowledge of aspects related to plant:animal interface in pastoral systems acquire greater importance when the main objective is to rationalize and optimize the use of any resource available. In that scenario, characterization of structural sward components and their effect on ingestive behaviour of grazing animals is a key element, since they can have a relevant influence on herbage intake. Against this background, the objective of this experiment was to study aspects of the plant:animal interface quantifying bite size, bite rate, time spent on grazing, rumination and rest as well as herbage intake of cattle grazing Brachiaria brizantha cv Marandu pastures submitted to continuous stocking managements. The experiment was carried out at Departamento de Zootecnia, USP/ESALQ, Piracicaba, SP, from 01 November 2001 until 14 February 2003. Treatments corresponded to four steady state conditions characterized by sward surface heights (SSH) of 10, 20, 30 and 40 cm, assigned to experimental units according to a complete randomized block design, with four replications. The results revealed a reduction in herbage intake with decreasing SSH (1.3, 1.8, 1.8 and 2.0 kg DM.kg LW -1 for 10, 20, 30 and 40 cm, respectively), consequence of a reduction in bite size (0.5, 0.8, 1,2 and 1.5 g DM.bite -1 for 10, 20, 30 and 40 cm, respectively). Animals, in an attempt to compensate the decrease in herbage intake, increased their bite rate (46.3, 30.3, 23.8 and 17.5 bites.minute -1 for 10, 20, 30 and 40 cm, respectively) and, for the 10 cm SSH, increased, also, their grazing time (11.4, 10.7, 10.6 and 10.5 hours.day -1 for 10, 20, 30 and 40 cm, respectively). It was concluded that herbage intake can be controlled by variations in sward structure and condition, which points to the potential for planning and monitoring grazing strategies based on sward targets for variable levels of animal requirements, time of the year and animal species.

Master of Science / Department of Agricultural Economics / Kevin C. Dhuyvetter / The 2008 National Stocker Survey defines the backgrounding/stocking of cattle as ―operations where calves are grown after weaning and/or preconditioning but before the feedlot. This includes calves purchased for this purpose as well as those retained by cow-calf producers post-weaning, but before marketing or retention through the feedlot. Backgrounding offers many benefits to farmers including, but not limited to, adding value to their feedstuffs—hay, grain, etc.—by feeding it to their cattle and potentially spreading risk by increasing marketing time or engaging in contracts with feedlots. However, producers also take on increased costs as it takes more time to wean, bunk-train, vaccinate, etc. compared to other operations in the cattle industry. This thesis attempts to analyze two studies using the 2008 National Stocker Survey. The first is how producer and operation characteristics—producer age, type of operation, income derived from backgrounding—relate to why producers find variables such as cattle prices, animal health management, marketing practices, and nutrition important. The second is how producer and operation characteristics relate to producers that use futures market contracts and options on futures. Binary and ordered logit models were used to find the statistical significance of the aforementioned studies.Since this survey was specifically designed to profile the stocking/backgrounding industry, some of the estimated models did not add a lot of value beyond the summary statistics for the various dependent variables. That is, the ordered logit models did not identify any strong relationships given that almost all of the producers that responded to these questions found feeder cattle prices, animal health management, marketing practices, and nutrition very important, which can be seen by analyzing the summary statistics. In addition, the binary logit models that were used for the futures market contract and options on futures models, found that the best way to pinpoint producers using either futures contracts or options was if producers were already using risk management strategies. Therefore, the survey’s purpose of profiling the stocker industry may be its best use.