The objective of these studies was to design an optimal nutritional supplement suitable for grazing horses using fat and fiber to replace the grain and molasses in the traditional sweet feed. Thoroughbred mares and foals grazing bluegrass/clover pastures were used in these studies, twenty mares and their foals in 1994 to 1995, and twenty mares and foals in 1995 to 1996. Seasonal variation in pasture was examined, and the need for supplementation of nutrients and fibers was assessed. The nutritional status of grazing mares, foals, weanlings and yearlings, fed either a starch and sugar supplement (SS) or a fat and fiber supplement (FF), was examined using growth measurements, radiographic bone evaluations, milk composition and glucose tolerance tests. These studies suggest that fiber may be an important component of an ideal supplement for improved grass/legume pastures. Seasonal variation in pasture indicated an increase in hydrolyzable and rapidly fermed carbohydrates during periods of rapid growth. The FF supplement may have buffered seasonal changes and the increased hydrolyzable carbohydrate content in rapidly growing pasture, as evidenced by smoother growth curves in the yearlings. Young horses, after weaning until the following May, had lower estimated bone mineral content when fed the FF supplement. The lower bone mineral content in the FF supplemented horses may have been due to decreased absorption of calcium or metabolic and hormonal changes associated with adaptation to the different energy sources in the supplements. Milk composition of FF supplemented mares was influenced in ways likely to improve foal health. The FF supplemented mares had enhanced linoleic acid content, which may reduce the risk of gastric ulcers in foals, and increased immunoglobulin G concentration, which may enhance passive immunity. The carbohydrate status of mares, as assessed by glucose tolerance tests, indicated a slower glucose clearance that could be a metabolic adaptation of the mares to the SS and FF supplements. / Ph. D.

The objective of this study was to evaluate the nutritional profile of mono- or multi-species pastures of native warm season grasses. One of four treatments were randomly assigned to Twelve pastures: 1) BG; 2) IG; 3) Mix G; 4) Mix NG. Growing steers (n = 225) were randomly assigned to one of nine pastures. Grass samples were taken from all pastures every 28 days during a four-month period and were analyzed for nutrient composition. Bermudagrass pastures had greater crude protein and ADF, but less NDF concentrations compared with the native warm-season grasses. Crude protein, IVDMD, and NDF IVDMD concentration decreased while NDF, ADF, and Hemicellulose concentration increased as grasses matured. Steers grazing IG and Mix G pastures gained more weight and consumed more forage than those on BG pastures. It appears that native warm-season grasses may offer a viable alternative to BG for grazing cattle during the summer.

Individual and multiple stress factor effects of temperature on cotton growth and development were studied in four cotton cultivars. In Experiment I, seedling emergence rate and shoot and root morphological growth traits were measured on plants grown at five day/night temperatures from 20/12 to 40/32 °C. In Experiment II, multiple stress factors (CO2, temperature, UV-B radiation) and their interactions were evaluated during the seedling growth stage. Seed emergence and above- and below-ground growth and developmental traits were recorded in both experiments. Linear (TM-1 and PHY496W3R) and quadratic (DP1522B2XF and ST47447) functions best described seed emergence rate with an increase in temperature. Similar responses were also observed for many root traits among the cultivars. Based on vigor and principal component analysis, DP1522B2XF was identified as the most tolerant, PHY496W3R and ST4747GLB2 as moderately tolerant, and TM-1 as the least tolerant cultivar to multiple environmental stresses.

Southeastern wildrye (Elymus glabriflorus (Vasey ex L.H. Dewey) Scrib & C.R. Ball) is a relatively new perennial cool-season grass that has shown potential as a forage crop in the Southeastern United States. However, there is a lack of research on this species assessing its agronomic performance. To assess the agronomic performance and it’s tolerance to imazapic field trials were established in Newton and Starkville, MS. A forage production trial included five nitrogen (N) 0, 56, 112, 168, and 224 kg N ha -1 (high input) and five annual clover (low input) treatments. Tolerance to imazapic was assessed with applications of four pre- and early post-emergent applications applied at 0.0, 0.35, 0.7, 0.105, and 0.14 kg ai ha -1. Results from both field trials combine to validate southeastern wildrye as a potential forage crop and continued research and development of agronomic traits in this species.

The hippocampus is a brain region that can undergo tremendous plasticity in adulthood. The hippocampus is related to the formation of spatial memories in birds and mammals. In birds, plasticity in the hippocampus occurs when formation of such memories is directly relevant to survival or reproduction, such as for breeding or food caching. In reptiles, the homologues to the hippocampus are the dorsal and medial cortices (DC and MC). In several lizard, snake and turtle species, these structures have been related to spatial memory. Experimental investigations indicate that differences in DC volume are related to space use associated with differing foraging ecologies. Differences in MC volume have been associated with territory size-based mate acquisition strategies. Furthermore, territory size has previously been correlated with plasma testosterone (T) levels. Therefore, I hypothesized that neuroplasticity within the MC/DC is controlled by demands on spatial navigation and seasonal differences and that these changes may involve the action of T. During two experimental trials, male Western Fence Lizards (Sceloporus occidentalis) were placed into either large or small semi-natural enclosures and allowed to interact with a female and intruder males over the span of seven weeks. One trial was performed during the spring breeding season and the other during the summer non breeding season, to examine seasonal differences in plasticity. Blood samples were collected at initial time of capture and before sacrifice to measure plasma T. Immunostaining for doublecortin was used to determine the density of immature neurons in each region, and cresyl violet staining allowed for volume measurements of specific regions. MC cell layer neurogenesis was higher in lizards placed in large enclosures than those in small enclosures and higher in the summer than in the spring. DC volume was smaller in lizards held in large enclosures than those in small enclosures. The decreased DC volume seen lizards held in large enclosures may indicate a cost to the increased neurogenesis in the MC of lizards in the same enclosures. These results indicate a possible trade-off between DC volume and MC neurogenesis that allows for switching between the ability to solve novel spatial tasks using the DC while storing a cognitive map in the MC. During the spring, T had no relationship with MC volume, while during the summer this was negative, so effects of T on the MC may be seasonal.

No description available.

No description available.

A more thorough knowledge of rooting behavior of transplanted trees is needed to better understand plant establishment. The objectives of this research were to: 1) determine if transplant timing affected root system regeneration of northern red oak (Quercus rubra L.) and willow oak (Q. phellos L.), 2) determine the effect of transplant timing and nursery production system on root, shoot, and trunk growth periodicity of balled-and-burlapped (B&B) and pot-in-pot (PIP) sugar maple (Acer saccharum Marsh.), and 3) characterize seasonal patterns of root production and mortality of transplanted sugar maple. No new root growth occurred outside or within the root balls of red or willow oak between November transplanting and January excavation. However, new root growth was observed when November- and March-transplanted oaks were excavated in April, indicating that new root growth occurs primarily in late winter and/or early. Transplanted and non-transplanted sugar maples exhibited a pattern of maximum rates of shoot extension in early May, root length accumulation in late May, and trunk expansion in mid June. Rate of root length accumulation was less in summer and fall. Transplanting did not appear to disrupt the normal growth periodicity of sugar maple, except when transplanted in July. Abundant root length accumulation occurred in the July transplants at a time when root length accumulation had slowed in all other treatments, resulting in the July transplants having similar standing root lengths as the other transplants by fall. Standing root length of non-transplanted PIP sugar maple declined dramatically in spring. While root production in sugar maple was limited to the growing season, root mortality occurred at a steadier rate throughout the year. Most root mortality occurred in winter in transplanted trees and spring and summer in non-transplanted trees. Non-transplanted PIP trees had greater standing root length, production, and mortality than the other treatments. Indices of root activity (analogous to turnover rates) and production:mortality ratios illustrated the dominant role that root production plays relative to mortality in recently transplanted trees. These data indicate that transplanting and the PIP production system disrupt typical patterns of root production and mortality in sugar maple. / Ph. D.

The objective was to evaluate the insulin-leptin interactions in grazing mares and their impact on aspects of reproductive function using a series of four studies. Fourteen mares were first examined, 10 grazing and 4 confined to stalls in four 22-h studies in April, August, October (2005) and January (2006). There was a positive relationship between insulin and leptin concentrations (r = 0.50; P < 0.001). The second study used 24 mares maintained at pasture and fed supplements rich in either FF, or SS, or pasture forage. Nonstructural carbohydrate (NSC) content of forage was correlated to insulin concentration (r = 0.55; P < 0.01). Insulin was associated with leptin (r = 0.55; P < 0.001) and progesterone (r = 0.48; P < 0.001). In the third study nine mares adapted to FF, SS or forage only underwent two FSIGT tests; once during the luteal phase and again during the follicular phase of the estrous cycle. Minimal model analysis was used to describe insulin sensitivity (SI), glucose effectiveness (Sg), acute insulin response to glucose (AIRg) and the disposition index (DI). SI was lower (P < 0.001) in the luteal phase (3.1 ± 0.6) compared to the follicular phase (5.0 ± 0.6). In the fourth study 15 mares had their follicular fluid collected during the luteal and follicular phase of the estrous cycle. Insulin concentration (ln (x+1)) was 52% higher (P < 0.01) in large (> 25 mm) follicles (1.4 ± 0.1 mIU/L) than either medium (16 to 25 mm) or small (le; 15 mm) follicles (0.9 ± 0.1; 0.9 ± 0.1 mIU/L, respectively) irrespective of estrous cycle phase. A correlation was observed between follicular fluid (FFL) leptin and plasma leptin (r = 0.30; P < 0.001). A similar relationship was observed between FFL insulin and plasma insulin (r = 0.25; P < 0.001). Plasma insulin and leptin were positively associated (r = 0.45, P < 0.0001), along with FFL insulin and FFL leptin (r = 0.46, P < 0.0001). Both leptin and insulin were affected by season and this observation contradicts the use of single sample analysis for determining detrimental concentrations of these hormones. / Ph. D.

Monitoring and understanding plant phenology is becoming an increasingly important way to identify and model global changes in vegetation life cycle events. Although numerous studies have used synoptically sensed data to study phenological patterns at the continental and global scale, relatively few have focused on characterizing the land surface phenology of specific ecosystems. Mountain environments provide excellent examples of how variations in topography, elevation, solar radiation, temperature, and spatial location affect vegetation phenology. High elevation biomes cover twenty percent of the Earth's land surface and provide essential resources to both the human and non-human population. These areas experience limited resource availability for plant growth, development, and reproduction, and are one of the first ecosystems to reflect the harmful impact of climate change. Despite this, the phenology of mountain ecosystems has historically been understudied due to the rough and variable terrain and inaccessibility of the area. Here, we use two MODIS/Terra satellite 16-day products, Vegetation Index and Nadir BRDF Adjusted Reflectance, to assess start of season (SOS) for the 2007 calendar year. Independent data for elevation, slope, aspect, solar radiation, and temperature as well as longitude and latitude were then related to the SOS output. Based on the results of these analyses, we found that SOS can be predicted with a significant R² (0.55-0.64) for each individual zone as well as the entire western mountain range. While both elevation and latitude have significant influences on the timing of SOS for all six study areas. When examined at the regional scale and accounting for aspect, SOS follows closely with Hopkins' findings in regard to both elevation and latitude. / Master of Science