Academic literature on the topic 'Finewool'

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.

Estimation of genetic parameters for growth traits of Gansu Alpine Finewool sheep that separately identify maternal effects has not been previously conducted. (Co)variance components and corresponding genetic parameters for lamb growth traits were estimated from Gansu Alpine Finewool sheep maintained at Gansu Sheep Breeding Technology Extension Station in north-western China. Records of 17 703 lambs at birth, born over 9 years (2000–2008) and sired by 315 rams, were used in the study. Birth type, sex, dam age, record age and birth year were fitted as fixed effects. Analyses were carried out using a restricted maximum likelihood procedure (ASReml). Six different animal models were fitted for all traits and the most appropriate model was selected through log-likelihood ratio testing. After identifying the appropriate model through single-trait analysis, bivariate analyses were used to obtain the phenotypic and genetic correlations among the growth traits. In addition to the direct genetic effect, and maternal genetic effects, significant negative correlations between direct genetic and maternal genetic effects were found for all the growth traits. The maternal permanent environmental effects were only significant for birthweight, weaning weight and pre-weaning growth rate. The estimates of direct heritability for birthweight, weaning weight, pre-weaning average daily gain, post-weaning average daily gain and yearling weight were 0.22, 0.16, 0.15, 0.27 and 0.19 respectively. The maternal heritability estimates were relatively high and ranged from 0.17 to 0.27. The study provides the breed and its associated finewool sheep industry with a more encompassing basis for designing more effective breeding programs for improvement of growth traits of Gansu Alpine Finewool sheep.

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.

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