Добірка наукової літератури з теми "Strongwool"

The genetic differences in the structure and function of wool follicles and their association with wool and fibre production were examined in 6 finewool Merinos (Camden Park) and 6 strongwool Merinos (East Bungaree). The strongwool Merinos produced 2.4 times more wool per unit area of skin and 3.5 times the volume of fibre per follicle than the finewool Merinos, when both groups were maintained under similar environmental conditions. The finewool Merinos had a higher follicle density, but a lower average volume of germinative tissue in the follicle bulb and the skin, than the strongwool Merinos. The number and volume of cells in the bulb, bulb cell production rate, cortical cell size and the proportion of bulb cells entering the fibre tended to be greater in the strongwool Merinos than the finewool Merinos, but were not statistically different between strains due to a high between-sheep, within-strain variation. In a stepwise linear regression, wool production per unit area was best predicted by the volume of germinative tissue in the bulb, together with follicle density. It is concluded that genotype determines the volume of potential mitotically-active tissue in the skin, however the dynamic mechanism of fibre production is not controlled by a single character, but rather a combination of a number of characteristics.

Laser Doppler velocimetry was used to investigate the cutaneous circulation and its relationship to wool growth in Finewool and Strongwool Merinos. Skin blood flow measured with the laser Doppler velocimeter (LDV) was highly correlated with estimates of blood flow obtained using 57Co-labelled microspheres (R2 = 0.85; P < 0.01), although the absolute values estimated by the microsphere technique were significantly higher (P < 0.001). Strongwool Merinos had a greater rate of blood flowing through the skin than Finewool Merinos, and this was associated with both wool production per unit area of skin (R2 = 0.27, P < 0.01) and with the total volume of germinative tissue in the skin (R2 = 0.54; P < 0.04). The relationship between the microvascular anatomy of the skin and blood flow was also examined in four Finewool Merinos and four Strongwool Merinos. Silicone rubber was infused into the deep circumflex iliac artery within the abdominal flank, from which an index of the area of vascular tissue per unit volume of skin was estimated. This index was not related to blood flow, wool growth or follicle density within nor between strains of Merinos. Both the usefulness and limitations of the LDV are discussed, and it was concluded that (a) blood flow has an important role in the level of wool produced both within and between strains of Merinos, and (b) laser Doppler velocimetry is a useful tool for the study of blood flow in the skin of sheep.

An experiment was conducted to determine the impact of stocking rate and Merino strain on follicle morphology before and after the break of the season in the highly seasonal Mediterranean environment of southern Australia. Groups of Finewool and Strongwool Merino sheep were allocated to 9 stocking rates on mixed legume-grass pastures, and skin biopsy samples were taken at monthly intervals from February to June. A scoring system, based on the morphology of follicles in transverse section, was used to characterise these samples. The proportion of follicles classified as ‘normal’ dropped markedly, and the proportion of follicles which contained no fibre correspondingly increased, after the break of the season in April. On average about 10% of the follicles became inactive but there was considerable variability (range 2-63%) between animals. The proportion of inactive follicles was significantly affected by stocking rate but there was little difference between Merino strains. Maximum follicle inactivity coincided with the period of minimum fibre diameter and minimum liveweight in May, approximately 1 month after the break of the season. The proportion of inactive follicles accounted for 27% and 28% of the variance in staple strength of the Finewool and Strongwool strains, respectively. Minimum fibre diameter accounted for 63% and 61% of the variance in staple strength, and coecient of variation in fibre diameter accounted for 49% and 58% of the staple strength variance, respectively, in the 2 strains. Together, minimum fibre diameter and coecient of variation in fibre diameter accounted for almost 75% of the variance in staple strength in both strains. Addition of a term for the proportion of inactive follicles did not remove any additional variance in staple strength. These results suggest that the follicles of Merino sheep in Mediterranean environments undergo significant morphological changes throughout the year. These changes differ from the normal sequence of events associated with the hair cycle and appear to be associated with the break of the season in autumn. The morphological changes which occur in the follicles are similar to those induced by epidermal growth factor or cortisol, and may reflect a stress response. Our results suggest that nutritional stress is at least partially responsible for the follicular pathology described. Management strategies aimed at reducing the decrease in fibre diameter which occurs in autumn, shearing sheep in autumn to coincide with the minimum fibre diameter, and selection of sheep which have a low coecient of variation of fibre diameter, are likely to be the most effective means of preventing low staple strength in sheep grazing in Mediterranean environments. Nevertheless, the impact of follicle shutdown and changes in follicle morphology on wool characteristics other than staple strength needs to be determined.

Wide phenotypic variation in fibre output per follicle was generated by selecting sheep (five South Australian strongwool Merinos, one finewool Merino and one Corriedale) on this basis, and by offering these sheep a low-protein diet for 9 weeks, followed by a high-protein diet for a further 8 weeks. Clean wool production was measured over the final 3 weeks of each period, while fibre diameter, the rate of length growth of fibres and a number of follicle characters were measured over the last 7 days of each period. The rate of division of follicle bulb cells and the total volume of the germinative region of the follicle was estimated by image-analysis of bulb sections in skin biopsy samples.With the change from the low-protein diet to the high-protein diet, the rate of clean fleece production was increased by 33% (P<0.002), reflecting an increase in fibre diameter (8%) and rate of length growth of fibres (26%); the volume of the germinative region of the average bulb increased 30% (P<0.012) and the rate of bulb cell division by 35% (P<0.004); cortical cell volume also did not change (923 8m3 v. 965 8m3; the average proportion of fibre cross-sectional area occupied by paracortical cells increased from 0.2 1 to 0.35 ( P < 0.01 0); the proportion of dividing cells entering the fibre cortex ranged from 0.25 to 0.42 (mean, 0.31) between sheep on the low-protein diet, and from 0.22 to 0.39 (mean, 0.32) when the animals were fed the high-protein ration; the effect of diet on cell distribution to fibre and inner root sheath was not significant (P<0.601).Phenotypic differences in fibre output were primarily related to differences in the rate of bulb cell division (r= 0.896, P < 0.001), but inclusion of a term for the proportion of bulb cells entering the fibre cortex, removed an additional, significant proportion of the variance. Cortical cell volume, on the other hand, was poorly related to fibre output.

The Route 601 Bridge spans 39 ft over Dickey Creek in Sugar Grove, VA and represents the first use of Strongwell's 36 in. double web beam (DWB) as the main load carrying members for a traffic bridge. The bridge was designed for AASHTO HS20-44 and AASHTO alternate military loading with a targeted deflection limit of L/800. For the preliminary design, conservative properties for the 36 in. DWB were assumed based on experience at Virginia Tech with Strongwell's 8 in. DWB used in the Tom's Creek Bridge. An elastic modulus (E) of 6,000 ksi and a shear stiffness (kGA) of 20,000 ksi-in2 were assumed and used with Timoshenko shear deformable beam theory to characterize the beams and determine the deflections. This thesis details the experimental work conducted in conjunction with the design of the Route 601 Bridge, which had two goals. First, a deck-to-girder connection was tested to determine if a bolted connection could develop composite action between the girder and the deck. This connection was shown to provide a significant amount of composite action when used with the 8 in. DWB and a composite deck, but little or no composite action when used with the 36 in. DWB and a glue-laminated timber deck. Second, eleven 36 in. DWB's were tested to determine their stiffness properties (EI and kGA) to insure that these properties were above the values assumed in the preliminary design, and all the beams had stiffness properties that were close to or above the assumed values. The eleven beams were also proof tested to a moment equivalent to five times the service load moment to insure the safety of the Route 601 Bridge, and one beam was tested to failure to determine the failure mode and residual stiffness of the 36 in. DWB. Finally, based on these results eight beams were chosen for the Route 601 Bridge.
Master of Science

The Route 601 Bridge in Sugar Grove, Virginia spans 39 ft over Dickey Creek. The Bridge is the first to use the Strongwell 36 in. fiber reinforced polymer (FRP) double web beam (DWB) in its superstructure. Replacement of the old bridge began in June 2001, and construction of the new bridge was completed in October 2001. The bridge was field tested in October 2001 and June 2002. This thesis details the field evaluation of the Rt. 601 Bridge. Using mid span deflection and strain data from the October 2001 and June 2002 field tests, the primary goal of this research was to determine the following AASHTO bridge design parameters: wheel load distribution factor g, dynamic load allowance IM, and maximum deflection. The wheel load distribution factor was determined to be S/5, a dynamic load allowance was determined to be 0.30, and the maximum deflection of the bridge was L/1500. Deflection results were lower than the AASHTO L/800 limit. This discrepancy is attributed to partial composite action of the deck-to-girder connections, bearing restraint at the supports, and contribution of guardrail stiffness. Secondary goals of this research were to quantify the effect of diaphragm removal on girder distribution factor, determine torsion and axial effects of the FRP girders, compare responses to multiple lane symmetrical loading to superimposed single lane response, and compare the field test results to a finite element and a finite difference model. It was found that diaphragm removal had a small effect on the wheel load distribution factor. Torsional and axial effects were small. The bridge response to multilane loading coincided with superimposed single lane truck passes, and curb-stiffening effects in a finite difference model improved the accuracy of modeling the Rt. 601 Bridge behavior.
Master of Science

Wool production differences between sheep maintained under similar environmental conditions appear to reside in the functioning of individual follicles. The investigations presented in this thesis utilise the differing wool producing abilities of two strains of Merino, finewool and strongwool Merinos. The relationships between wool production (on both a unit area and individual follicle basis) and skin and follicle characteristics, blood flow and microvasculature of the skin and incorporation of ³H-glucose and ³⁵S-cystine by the skin were examined. The differences in the structure and function of wool follicles and their association with fibre production were examined in 6 finewool Merinos (Camden Park) and 6 strongwool Merinos (East Bungaree). The strongwool Merinos produced 2.4 times more wool per unit area of skin and 3.5 times the volume of fibre per follicle than the finewool Merinos, when both groups were maintained under similar environmental conditions. The finewool Merinos had a higher follicle density, but a lower average volume of germinative tissue in the follicle bulb and the skin than the strongwool Merinos. The rate of cell production in the follicle bulb was greater in the strongwool Merinos than the finewool Merinos, but the proportion of bulb cells entering the fibre was not significantly different between strains. The number and volume of cells in the bulb and the cell length and volume of the cortical cells, and tended to be greater in the strongwool Merinos than the finewool Merinos, but also were not statistically different between strains due to a high 'between-sheep, within-strain' variation. Wool production per unit area of skin was highly correlated with the total volume of germinative tissue in the skin (r = 0.91; P < 0.01). This relationship was true for the strongwool and finewool Merinos and also in two groups of sheep from the same genetic base with one group selected using a WOOLPLAN index and the other a randomly-bred flock. It was concluded a) that genotype may determine the volume of potential mitotically-active follicle tissue in the skin, and b) that wool production on both a follicle and unit area of skin basis is not controlled by a single character, but rather is the result of a cumulative effect of a number of characteristics. The physiology of the skin associated with high levels of wool production was further examined. In particular, blood flow through the skin of the strongwool and finewool Merinos was investigated using a laser Doppler velocimeter. This method was highly correlated with estimates obtained using ⁵⁷Co-microspheres (r = 0.92;P < 0.01) although the absolute values estimated by the microsphere technique were significantly greater (P < 0.001). Strongwool Merinos had a significantly greater rate of blood flowing through the skin than finewool Merinos (P < 0.011) and this was associated both with wool production per unit area of skin (r = 0.58; P < 0.02) and with follicle density (r = -0.M; P < 0.1). It was concluded that a) blood flow has an important role in the level of wool produced both within and between strains of Merino, and b) the laser Doppler velocimeter is a useful tool for the study of blood flow in the skin of sheep. The microvasculature of the skin was examined using an infusion of silicone rubber into the deep circumflex iliac artery within the abdominal flank region of eight Merinos. The area of cascular tissue per unit volume of skin was independent of blood flow, wool growth and follicle density, both within and between strains of Merinos. The limitations of the technique used to examine the microvasculature, and its effect on the results are discussed. The uptake of ³H-glucose and ³⁵S-cystine by the skin and follicles was examined both in vitro and in vivo to determine if the follicles of the strongwool Merinos were capable of utilising the large nutrient pool supplied by the high rates of blood flowing through the skin. The skin and follicles of strongwool Merinos incorporate similar amounts of ³H-glucose and ³⁵S-cystine per unit weight of skin than finewool Merinos. It was also found that the amount of radioactivity retained by the skin generally was not dependant on the amount of radioactivity supplied to the skin and follicles. In summary, this study determined that strongwool Merinos have higher levels of wool production than finewool Merinos due to the presence of a large amount of tissue capable of producing fibre. This characteristic is maintained by a high rate of blood flowing through the skin. Wool production and blood flow through the skin are not influenced by the underlying anatomy of the microvasculature, nor is wool production restricted by the ability of the follicles to utilise nutrients from an extracellular pool for fibre production. Finally, the implications of this study and the usefulness in, and effect on, programs for selection of superior wool-producing genotypes are discussed.
Thesis (Ph.D.) -- University of Adelaide, Dept. of Animal Sciences, 1994

Bibliography: leaves 325-341. Skin and fleece measurements were recorded at different ages for both male and female sheep from the Turretfield Merino Resource Flock and used to estimate the heritability of each trait and the phenotypic and genetic correlations among and between the skin and fleece traits. Generally, the heritability of each trait was high, which indicates that both the fleece and skin traits should respond well to selection.

Includes bibliographical references (leaves 325-341).
xxvii, 341 leaves : ill. ; 30 cm.
Skin and fleece measurements were recorded at different ages for both male and female sheep from the Turretfield Merino Resource Flock and used to estimate the heritability of each trait and the phenotypic and genetic correlations among and between the skin and fleece traits. Generally, the heritability of each trait was high, which indicates that both the fleece and skin traits should respond well to selection.
Thesis (Ph.D.)--University of Adelaide, Dept. of Animal Science, 2001