Most managed turfgrass species require frequent inputs to maintain an acceptable level of quality. Among these inputs, nitrogen (N) fertilization is usually the most limiting in terms of growth and development. However, N fertilization is also linked to non-point source (NPS) pollution. White clover (WC) is known for its ability to provide N when mixed into stands of turfgrass, and does not pose a threat for NPS pollution. Two field studies were designed to investigate the effects of WC inclusion in stands of cool-season turfgrasses. In the first field study, three cultivation techniques were examined for establishment of WC into preexisting turfgrass stands at three different seasonal timings. Scalping during the summer was seen as providing the highest WC populations, although scalping treatments also caused the most initial damage to the turfgrass. In the second field study, mixed stands of turfgrass and WC were examined for response to several weeks of traffic simulations, with WC withstanding the traffic events. Additionally, a greenhouse study was implemented to examine the effects of several commercial broadleaf herbicides on two WC varieties. Only 2,4-D was shown to be safe for application to both WC varieties, although Microclover did show tolerance to quinclorac applications.

Phosphate (P) supply is one of the major determining factors to plant productivity, since the element affects the growth and the development of plants. In response to Pdeficiency treatment, plants display alterations in root system architecture caused by changes in primary root (PR) and lateral root (LR) length and LR density. In this thesis, the root growth of the agronomically important legume, white clover (Trifolium repens L.) was found to be slightly stimulated in terms of PR length, LR number and total LR length when plants were grown in a P-deficient media (0.01 mM orthophosphate; Pi) when compared with plants grown in a P-sufficient media (1.00 mM Pi) when using a hydroponic growth system. When plants are grown in a P-sufficient media, treatment with 100 nM exogenous 1- aminocyclopropane-1-carboxylic acid (ACC) and exogenous auxin (5 nM 1- naphthylacetic acid, NAA) resulted in significant increases in white clover PR length, LR number and LR length. However, when ethylene action or auxin transport were inhibited using 300 ppm 1-methylcyclopropene (1-MCP) and 100 nM 1-Nnaphthylphthalamic acid (NPA), respectively, root growth was significantly reduced which suggests roles for ethylene and auxin in mediating white clover root growth. To examine the effects of these hormones on plants grown in P-deficient media, 100 nM ACC treatment significantly enhanced the stimulatory effects of growth on Pdeficient media only, while exposure of plants to P-deficiency alone was sufficient to significantly neutralise the inhibitory effects of 1-MCP on root growth. Hence, exposure to P-deficiency is proposed to increase either ethylene biosynthesis or ethylene sensitivity in white clover roots. In contrast, for plants grown in P-deficient media, treatment with 5 nM NAA significantly abolished the stimulation of white clover root growth observed with P-deficiency so it is proposed that exposure to Pdeficiency increases either auxin biosynthesis or auxin sensitivity, but the 5nM NAA concentration used was too high to stimulate root growth. Using DR5p::GUS transgenic white clover, auxin activity was found in the root tips and root primordia. Using these plants, it is suggested that P-deficient treatment and ACC treatment influenced white clover root growth through an increase in auxin sensitivity. Overall, ethylene and auxin are found to be essential in mediating white clover root growth in P-sufficiency, and also in mediating root responses to P-deficiency through changes in terms of the biosynthesis and the sensitivity of these two hormones.

Phosphate (P) supply is one of the major determining factors to plant productivity, since the element affects the growth and the development of plants. In response to Pdeficiency treatment, plants display alterations in root system architecture caused by changes in primary root (PR) and lateral root (LR) length and LR density. In this thesis, the root growth of the agronomically important legume, white clover (Trifolium repens L.) was found to be slightly stimulated in terms of PR length, LR number and total LR length when plants were grown in a P-deficient media (0.01 mM orthophosphate; Pi) when compared with plants grown in a P-sufficient media (1.00 mM Pi) when using a hydroponic growth system. When plants are grown in a P-sufficient media, treatment with 100 nM exogenous 1- aminocyclopropane-1-carboxylic acid (ACC) and exogenous auxin (5 nM 1- naphthylacetic acid, NAA) resulted in significant increases in white clover PR length, LR number and LR length. However, when ethylene action or auxin transport were inhibited using 300 ppm 1-methylcyclopropene (1-MCP) and 100 nM 1-Nnaphthylphthalamic acid (NPA), respectively, root growth was significantly reduced which suggests roles for ethylene and auxin in mediating white clover root growth. To examine the effects of these hormones on plants grown in P-deficient media, 100 nM ACC treatment significantly enhanced the stimulatory effects of growth on Pdeficient media only, while exposure of plants to P-deficiency alone was sufficient to significantly neutralise the inhibitory effects of 1-MCP on root growth. Hence, exposure to P-deficiency is proposed to increase either ethylene biosynthesis or ethylene sensitivity in white clover roots. In contrast, for plants grown in P-deficient media, treatment with 5 nM NAA significantly abolished the stimulation of white clover root growth observed with P-deficiency so it is proposed that exposure to Pdeficiency increases either auxin biosynthesis or auxin sensitivity, but the 5nM NAA concentration used was too high to stimulate root growth. Using DR5p::GUS transgenic white clover, auxin activity was found in the root tips and root primordia. Using these plants, it is suggested that P-deficient treatment and ACC treatment influenced white clover root growth through an increase in auxin sensitivity. Overall, ethylene and auxin are found to be essential in mediating white clover root growth in P-sufficiency, and also in mediating root responses to P-deficiency through changes in terms of the biosynthesis and the sensitivity of these two hormones.

The investigation in this thesis is divided into two parts. In the first part, the expression and accumulation of 1-aminocyclopropane-1-carboxylic acid (ACC) oxidase (ACO), the enzyme which catalyses the final step of ethylene biosynthesis in higher plants, is examined during exposure of white clover (Trifolium repens L.) to a water deficit. The second part of this thesis is focused on the identification and characterisation of a water-deficit-associated ACC synthase (ACS), the enzyme which catalyses the production of ACC. In the first part, two white clover varieties with differing sensitivity to water deficit, a drought-tolerant Tienshan ecotype and a drought-sensitive Grasslands Challenge cv. Kopu II cultivar were exposed to two water deficit treatments: one cycle of water deficit (designated non-prestressed; NPS) and a water deficit, a rehydration period and then a second water deficit treatment (designated pre-stressed; PS) in the New Zealand Climate Environment Laboratory (NZCEL). Treatments were terminated when the petiole elongation rate (PER) in the first fully-expanded leaf reached zero. Water relations, growth responses, the expression of the white clover ACO genes, TR-ACO1 TR-ACO2 and TR-ACO3 and the accumulation of two of the corresponding proteins, TR-ACO1 and TR-ACO2, were then examined. The soil water content (SWC) and leaf water potential (LWP) measured in both varieties and in both water deficit treatments declined progressively. The rate of decline in SWC and LWP was slower in the Tienshan ecotype with no difference between the NPS and PS treatments. However, the LWP in the Tienshan ecotype at the point at which the PER ceased was less negative (ca. -1.4 MPa) compared to Kopu (ca. -1.7 MPa). In addition, the decline in the PER differed between NPS- and PS-treated Kopu. In the NPS-treated Kopu, the PER was maintained at a high rate when plants were exposed to SWC above 18%, but declined sharply as the SWC declined further. However, in the PS-treated Kopu, the PER declined more progressively in a similar pattern to that determined for NPS- and PS-treated Tienshan. Expression of TR-ACO1 and accumulation of TR-ACO1 was observed in the apical structure of the stolon. As the water deficit progressed, no significant alteration in TR-ACO1 expression and TR-ACO1 protein accumulation was observed in the apical structures of both the NPS- and PS-treated Tienshan ecotype suggesting some degree of protection of the meristem tissues in this more drought-tolerant variety. However, a discernable decline in expression of TR-ACO1 and accumulation of TR-ACO1 protein was observed in the NPS-treated Kopu suggesting some degree of tissue injury in this more drought-susceptible variety. However, after the pre-stress (PS) treatment, no real changes in TR-ACO1 expression and TR-ACO1 protein accumulation were observed, in common with the observations for the NPS- and PS-treated Tienshan ecotype suggesting that meristem protection may now be occurring. The results suggest further that the pre-stress treatment of the more drought-susceptible Kopu may result in a degree of acclimation to the water deficit. For the first-fully expanded leaves, expression of two transcripts, TR-ACO2 and TR-ACO3 and accumulation of TR-ACO2 protein was monitored as the SWC decreased. The expression of TR-ACO2 and accumulation of TR-ACO2 decreased as the water deficit progressed in both the NPS- and PS-treated Tienshan ecotype and correlated with the decrease in PER. By contrast, in the NPS-treated Kopu, TR-ACO2 expression and TR-ACO2 protein accumulation increased, but again, after a period of pre-stress, TR-ACO2 expression and TR-ACO2 accumulation decreased, in common with the Tienshan ecotype. Again, the pre-stress treatment of the drought-susceptible Kopu may result in a degree of acclimation to the water deficit such that the responses become similar to those observed in the more drought-tolerant Tienshan ecotype. However, in both NPS- and PS-treated Tienshan and Kopu there was no significant alteration in the expression of TR-ACO3 in the first fully-expanded leaf. The expression of TR-ACO2 and TR-ACO3 and accumulation of TR-ACO2 protein were also observed in the second fully-expanded leaves (an older tissue). Again similar patterns in the expression of TR-ACO2 and TR-ACO3 and accumulation of TR-ACO2 protein were observed in both NPS- and PS-treated Tienshan and Kopu. In these leaves, expression of TR-ACO2 and accumulation of TR-ACO2 protein decreased as the water deficit progressed, but expression of TR-ACO3 increased as the water deficit decreased to less than 10%. These results suggest that responses of younger tissues (apical structure; first-fully expanded leaf) maybe the critical determinant for the tolerant (or otherwise) of white clover plants to water deficit. In the second part of this thesis, four ACS genes were identified from the Tienshan ecotype exposed to water deficit and designated TR-ACS-T. Three of these were similar to previously identified TR-ACS genes from Grasslands Challenge genotype 10F while the fourth was a novel gene designated TR-ACS4-T. TR-ACS4-T is 64%, 64% and 63% homologous to TR-ACS1-T, TR-ACS2-T and TR-ACS3-T, respectively in terms of nucleotide sequence. In the GeneBank database, TR-ACS4-T shares highly homology to ACC synthase sequences from a wide range of tissues including seedlings and fruit tissues, in addition to a high homology to ACS genes induced in auxin-, wounding- and ethylene-treated tissues. The pattern of TR-ACS4-T expression observed during leaf development suggests that the gene is expressed initially in the apical structures and in the newly initiated leaves, and then again in the later mature leaves and those at the onset of senescence. Expression decreases again during senescence. TR-ACS4-T expression is not altered by water deficit, but is induced by both ethylene and NAA treatment, but the auxin-induced TR-ACS4-T is mediated by ethylene treatment.

Phosphate (P) supply is one of the major determining factors to plant productivity, since the element affects the growth and the development of plants. In response to Pdeficiency treatment, plants display alterations in root system architecture caused by changes in primary root (PR) and lateral root (LR) length and LR density. In this thesis, the root growth of the agronomically important legume, white clover (Trifolium repens L.) was found to be slightly stimulated in terms of PR length, LR number and total LR length when plants were grown in a P-deficient media (0.01 mM orthophosphate; Pi) when compared with plants grown in a P-sufficient media (1.00 mM Pi) when using a hydroponic growth system. When plants are grown in a P-sufficient media, treatment with 100 nM exogenous 1- aminocyclopropane-1-carboxylic acid (ACC) and exogenous auxin (5 nM 1- naphthylacetic acid, NAA) resulted in significant increases in white clover PR length, LR number and LR length. However, when ethylene action or auxin transport were inhibited using 300 ppm 1-methylcyclopropene (1-MCP) and 100 nM 1-Nnaphthylphthalamic acid (NPA), respectively, root growth was significantly reduced which suggests roles for ethylene and auxin in mediating white clover root growth. To examine the effects of these hormones on plants grown in P-deficient media, 100 nM ACC treatment significantly enhanced the stimulatory effects of growth on Pdeficient media only, while exposure of plants to P-deficiency alone was sufficient to significantly neutralise the inhibitory effects of 1-MCP on root growth. Hence, exposure to P-deficiency is proposed to increase either ethylene biosynthesis or ethylene sensitivity in white clover roots. In contrast, for plants grown in P-deficient media, treatment with 5 nM NAA significantly abolished the stimulation of white clover root growth observed with P-deficiency so it is proposed that exposure to Pdeficiency increases either auxin biosynthesis or auxin sensitivity, but the 5nM NAA concentration used was too high to stimulate root growth. Using DR5p::GUS transgenic white clover, auxin activity was found in the root tips and root primordia. Using these plants, it is suggested that P-deficient treatment and ACC treatment influenced white clover root growth through an increase in auxin sensitivity. Overall, ethylene and auxin are found to be essential in mediating white clover root growth in P-sufficiency, and also in mediating root responses to P-deficiency through changes in terms of the biosynthesis and the sensitivity of these two hormones.

Phosphate (P) supply is one of the major determining factors to plant productivity, since the element affects the growth and the development of plants. In response to Pdeficiency treatment, plants display alterations in root system architecture caused by changes in primary root (PR) and lateral root (LR) length and LR density. In this thesis, the root growth of the agronomically important legume, white clover (Trifolium repens L.) was found to be slightly stimulated in terms of PR length, LR number and total LR length when plants were grown in a P-deficient media (0.01 mM orthophosphate; Pi) when compared with plants grown in a P-sufficient media (1.00 mM Pi) when using a hydroponic growth system. When plants are grown in a P-sufficient media, treatment with 100 nM exogenous 1- aminocyclopropane-1-carboxylic acid (ACC) and exogenous auxin (5 nM 1- naphthylacetic acid, NAA) resulted in significant increases in white clover PR length, LR number and LR length. However, when ethylene action or auxin transport were inhibited using 300 ppm 1-methylcyclopropene (1-MCP) and 100 nM 1-Nnaphthylphthalamic acid (NPA), respectively, root growth was significantly reduced which suggests roles for ethylene and auxin in mediating white clover root growth. To examine the effects of these hormones on plants grown in P-deficient media, 100 nM ACC treatment significantly enhanced the stimulatory effects of growth on Pdeficient media only, while exposure of plants to P-deficiency alone was sufficient to significantly neutralise the inhibitory effects of 1-MCP on root growth. Hence, exposure to P-deficiency is proposed to increase either ethylene biosynthesis or ethylene sensitivity in white clover roots. In contrast, for plants grown in P-deficient media, treatment with 5 nM NAA significantly abolished the stimulation of white clover root growth observed with P-deficiency so it is proposed that exposure to Pdeficiency increases either auxin biosynthesis or auxin sensitivity, but the 5nM NAA concentration used was too high to stimulate root growth. Using DR5p::GUS transgenic white clover, auxin activity was found in the root tips and root primordia. Using these plants, it is suggested that P-deficient treatment and ACC treatment influenced white clover root growth through an increase in auxin sensitivity. Overall, ethylene and auxin are found to be essential in mediating white clover root growth in P-sufficiency, and also in mediating root responses to P-deficiency through changes in terms of the biosynthesis and the sensitivity of these two hormones.

White clover mosaic virus (WClMV) virions were purified using a modified method of Wetter (1960). Antisera were produced by rabbit immunisation and virus-specific polyclonal antibodies were obtained. Suitable conditions were optimised for serological detection of virus by DAS-ELISA and compared with a commercial kit.

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior / The objective of this research was to evaluate the effect of private supplementation with concentrated or legume, on the pasture characteristics, performance, carcass traits, body components, physico-chemical and sensory characteristics of the meat from suckling lambs kept on ryegrass pasture. Twenty seven suckling lambs were used with about 17 days of age and weighing 9,91 ± 0,594kg, which are distributed in the treatments that corresponded to feeding systems: suckling lambs kept on ryegrass pasture, suckling lambs kept on ryegrass pasture and supplemented with concentrated in private feeder (creep feeding) and suckling lambs kept on ryegrass pasture and supplemented with legume in the private pasture (creep grazing). The concentrate supplement was composed by corn, soybean meal and limestone, and was supplied ad libitum. The supplementary pasture was composed by legume white clover. It was evaluated the characteristics of ryegrass pasture and performance of lambs, which were slaughtered when reached 32 kg of body weight. Subsequently, evaluated the carcass characteristics, body components and characteristics of meat. The experimental design was completely randomized, where the results were submitted to analysis of variance and means compared by Tukey test at 5% of significance level. Supplementation, through concentrated or legumes, did not increase the performance of suckling lambs grazing ryegrass, despite differences in neutral detergent fiber and acid detergent fiber by consumed pasture from animals that were smaller for the supplemented with legume. Suckling lambs kept in ryegrass produce similar carcasses of animals receiving supplement, despite gastrointestinal tract content with bile and urine and the proportion of the esophagus be higher (P<0,05) in lambs maintained in ryegrass and not supplemented and proportions of liver and intestine are higher (P<0,05) in lambs supplemented with concentrate. The color of the meat of was affected (P<0,05) by feeding system, being less opaque and red but more yellow the meat from not supplemented lambs. The tocopherol and cholesterol levels were higher (P<0,05) in meat of lambs not supplemented as well as lower contents of ash (P<0,05) were found in the meat of these animals. The water hold capacity was lower (P<0,05) in meat from animals supplemented with concentrate. Most intense characteristic flavor (P<0,05) was observed in meat from lambs who consumed concentrated; and more tender (P<0,05) was the meat of suckling lambs supplemented with legume. The use of white clover legume as supplementary private pasture provides rapid finishing of lambs with carcass and meat with quality, which makes this feeding system an option to finishing lambs. / Esta pesquisa foi realizada com o objetivo de avaliar o efeito da suplementação privativa, com concentrado ou leguminosa, sobre as características da pastagem, desempenho, características de carcaça, componentes corporais, características físico-químicas e sensoriais da carne de cordeiros lactentes mantidos em pastejo de azevém. Foram utilizados 27 cordeiros lactentes com aproximadamente 17 dias de idade e pesando 9,91±0,594kg, sendo estes distribuídos nos tratamentos que corresponderam aos sistemas de alimentação: cordeiros lactentes mantidos em pasto de azevém, cordeiros lactentes mantidos em pasto de azevém e suplementados com concentrado em comedouro privativo (creep feeding) e cordeiros lactentes mantidos em pasto de azevém e suplementados com leguminosa no pasto privativo (creep grazing). O suplemento concentrado era composto por milho, farelo de soja e calcário calcítico e foi fornecido ad libitum. O pasto suplementar foi composto pela leguminosa trevo branco. Avaliou-se as características do pasto de azevém e o desempenho dos cordeiros, que foram abatidos ao atingirem o peso corporal de 32 kg. Posteriormente avaliaram-se as características de carcaça, componentes corporais e características da carne dos animais. O delineamento experimental foi o inteiramente casualizado, onde os resultados foram submetidos à análise de variância e as médias comparadas pelo teste Tukey a 5% de significância. A suplementação privativa, concentrada ou através de leguminosa, não elevou o desempenho de cordeiros lactentes mantidos em pastejo de azevém, apesar das diferenças nos teores de fibra detergente neutro e fibra detergente ácido da pastagem consumida pelos animais que foram menores para os suplementados com leguminosa. Cordeiros lactentes mantidos em azevém produzem carcaças similares a dos animais que recebem suplemento, apesar do conteúdo do trato gastrintestinal juntamente com bile e urina e da proporção de esôfago ser maiores (P<0,05) nos cordeiros mantidos em azevém e não suplementados e as proporções de fígado e intestino grosso serem maiores (P<0,05) nos cordeiros suplementados com concentrado. A coloração da carne dos cordeiros foi influenciada (P<0,05) pelo sistema de alimentação, sendo a carne dos cordeiros lactentes que não receberam suplementação considerada a carne menos opaca, menos vermelha e mais amarela. Os teores de colesterol e tocoferol foram maiores (P<0,05) na carne de cordeiros não suplementados, bem como menores teores de cinzas (P<0,05) foram encontrados na carne desses animais. A capacidade de retenção de água foi menor (P<0,05) na carne dos animais suplementados com concentrado. Sabor característico mais intenso (P<0,05) foi observado na carne dos cordeiros que consumiram concentrado e maior maciez (P<0,05) foi encontrada na carne dos cordeiros suplementados com leguminosa. O uso da leguminosa trevo branco como pasto privativo suplementar proporciona rápida terminação de cordeiros com carcaças e carne de qualidade, o que torna este sistema alimentar uma opção para terminação de cordeiros.

Tall fescue (Schedonorus arundinaceus), is a cool season perennial that provides grazing into the early summer months for southern livestock. Grazing the tall fescue variety, Kentucky-31, has negative effects on animal health, particularly after jointing. Two studies were arranged as randomized complete blocks in a split-plot design, with three replicates to compare: the effect of ten herbicides on seedhead suppression, or the effect of inter-seeding legumes [white clover (Trifolium repens) or alfafla (Medicago sativa)] coupled with nitrogen supplementation on fescue yield and forage nutritive value. The herbicides imazethapyr + 2,4-D and without, metsulfuron + chlorsulfuron, reduced seedheads emergence, but not yield compared to the control. Kentucky-31 inter-seeded with white clover and fertilized with 11 kg N ha-1 produced greater biomass than tall fescue fertilized with 11 kg N ha-1. The inter-seeding of white clover produced composite forage samples with greater in vitro dry matter disappearance than nitrogen supplemented alfalfa.

Experiments were conducted to investigate effects of endophyte (Acremonium coenophialum Morgan-Jones and Gams) infection of tall fescue (Festuca arundinacea Schreb.) on grazing cattle and subsequent feedlot performance, serum minerals and prolactin, intake, digestibility, bite size, and biting rate. Grazing animal performance was measured April to October, 1989 and 1990, at two locations in VA. Effects of grazing low (<5%) and high (>70%) endophyte infected tall fescue, with and without white clover (Trifolium repens L.), were studied with yearling steers. At each location, two replicates were used with a stocking rate of .3 ha/steer (116 steers/yr). At the end of grazing, all animals were finished on a high corn silage diet and slaughtered. Daily gains of steers grazing low endophyte-infected pastures were higher (P<.01) than for those grazing high endophyte-infected pastures. Cattle grazing high endophyte-infected tall fescue with clover at Glade Spring gained at the same rate as those grazing the low endophyte-infected tall fescue without clover during Summer, 1989. During 1990, cattle at Glade Spring had higher (P<.05) daily gains than did those at Blackstone. Rectal temperatures were .5 to 1 °C higher (P<.05) for steers grazing infected pastures by June of each year at both locations. Prolactin concentrations were lower (P<.01) in cattle grazing endophyte-infected fescue within 28 d of initiation of grazing at both locations. Visual evaluation indicated that steers grazing high-endophyte pastures had rough hair coats compared to those grazing low endophyte pastures (P<.01), showing evidence of tall fescue toxicosis. Serum mineral analyses indicated no consistent influence of the endophyte. During feedlot finishing, there were no detrimental effects from previously grazing endophyte-infected tall fescue on animal performance. Forage DM yield, and CP in 1990, and IVDMD in 1989 and 1990 from Glade Spring were higher (P<.05) compared to Blackstone. Forage from Blackstone was typically higher in NDF, ADF, and lignin compared to Glade Spring. Forage from Glade Spring was higher in Ca, Mg, P, and Cu, compared to Blackstone. Diet selection, digestibility, biting size, and biting rate were measured with esophageally-fistulated steers grazing low (<5%) and high (>70%) endophyte-infected tall fescue, with and without white clover. Bite size was smaller (P<.05) in July compared to May, corresponding to decreased quantity of forage available. Bite size and biting rate were not affected by endophyte infection or inclusion of clover. In vitro DM digestibility was higher (P<.05) for high endophyte-infected tall fescue in July. Animals consumed a higher percentage of clover than was available in the sward. Intake and digestibility were estimated using 48 experimental animals and four esophageally-fistulated steers. Chromic oxide sustained-release boluses and forage IVDMD were used to estimate intake. The chromic oxide boluses were determined to be reliable for predicting intake of steers during a 21 d trial involving total fecal collection. Intake was higher (P<.01) in cattle grazing low endophyte-infected tall fescue compared to animals grazing high endophyte-infected fescue. Twenty-one Angus steers (256 kg) were used to compare the effect of 0 and 40% endophyte-infected tall fescue and orchardgrass hay on DM intake, daily gain, body temperature, serum minerals, and prolactin concentrations during an 8 wk study. Quality of the diets was low, as indicated by low CP (8.1 to 10.3%), and IVDMD (41.3 to 47.1%). Daily DM intake and daily gain were higher (P<.05) for animals consuming the noninfected tall fescue compared to animals fed the other hays. Body temperature and serum prolactin were not affected by diet. These data suggest that other factors, besides endophyte infection, are important in the etiology of tall fescue toxicosis. Some of the decreased performance of steers grazing endophyte-infected tall fescue was related to lower intake. Additional research is needed to evaluate higher levels of clover to possibly ameliorate some of the problems of tall fescue toxicosis. / Ph. D.