High follicle density does not decrease sweat gland density in Huacaya alpacas

When exposed to high ambient temperatures, mammals lose heat evaporatively by either sweating from glands in the skin or by respiratory panting. Like other camelids, alpacas are thought to evaporate more water by sweating than panting, despite a thick fleece, unlike sheep which mostly pant in response to heat stress. Alpacas were brought to Australia to develop an alternative fibre industry to sheep wool. In Australia, alpacas can be exposed to ambient temperatures higher than in their native South America. As a young industry there is a great deal of variation in the quality and quantity of the fleece produced in the national flock. There is selection pressure towards animals with finer and denser fleeces. Because the fibre from secondary follicles is finer than that from primary follicles, selecting for finer fibres might alter the ratio of primary and secondary follicles. In turn the selection might alter sweat gland density because the sweat glands are associated with the primary follicle. Skin biopsy and fibre samples were obtained from the mid-section of 33 Huacaya alpacas and the skin sections were processed into horizontal sections at the sebaceous gland level. Total, primary, and secondary follicles and the number of sweat gland ducts were quantified. Fibre samples from each alpaca were further analysed for mean fibre diameter. The finer-fibred animals had a higher total follicle density (P<0.001) and more sweat glands (P<0.001) than the thicker-fibred animals. The fibre diameter and total follicle density were negatively correlated (R²=0.56, P<0.001). Given that the finer-fibred animals had higher follicle density and more sweat glands than animals with thicker fibres, we conclude that alpacas with high follicle density should not be limited for potential sweating ability.     

Polymorphism of the ovine β3-adrenergic receptor gene (ADRB3) and its association with wool mean staple strength and yield

We investigated the possibility that variation in ovine ADRB3 is associated with various wool traits, in particular mean staple strength (MSS). Polymerase chain reaction-single strand conformational polymorphism analysis of part of the ADRB3 intron was used to genotype 695 Merino lambs born on three farms in the South Island of New Zealand and which were shorn as 2-tooths. For each fleece, MSS, mean fibre diameter, mean staple length and yield were measured. The results from mixed-effects models and half-sib analyses suggest that ADRB3 alleles A and D have a negative impact on some wool traits, whereas ADRB3 alleles C and E appear to have a positive impact, with allele C potentially having a greater impact than allele E on MSS. This variation in the ADRB3 may assist in the genetic selection for increased MSS and yield in Merino sheep.     

The effects of short-term manipulation of thyroid hormone status coinciding with primary wool follicle development on fleece characteristics in Merino sheep

Thyroidectomy surgery performed late in gestation results in perturbations in wool follicle development in foetal sheep, showing the importance of thyroid hormones for wool follicle development. The aim of this study was to determine the influence of transient manipulation of thyroid hormone status at a time corresponding with foetal primary wool follicle initiation. Pregnant Merino ewes (n = 12 per treatment) were treated daily between gestational days 55 and 64 with control (vehicle), exogenous thyroxine (T4) or propylthiouracil (PTU), an inhibitor of T4 synthesis, and conversion to the active form of the thyroid hormone (triiodothyronine). There were no significant differences in birth weight, gestational lengths and birth coat scores of the resultant lambs. The total primary and secondary follicle densities were significantly lower in lambs exposed to exogenous T4 compared with other treatments (P < 0.05). However, the T4 group displayed a higher proportion of mature secondary follicles (reflected by increased mature secondary follicle densities and mature secondary/primary follicle ratios) than the other treatment groups (P < 0.05). The skin morphology of the lambs differed 12 months later, with the T4 group having significantly higher total follicle densities compared with the PTU group, largely attributed to increased mature and total secondary follicle densities. However, this increase in wool follicle densities did not translate to differences in the fleece yields and weight, fibre diameter, staple lengths or any other fibre parameters. This study showed that transient manipulation of thyroid hormone status during foetal primary follicle initiation does have long-term consequences on the morphology of wool follicles, in particular the maturity of secondary wool follicles.     

Merino sheep: a further look at quantitative trait loci for wool production

A quantitative trait loci (QTL) analysis of wool traits from experimental half-sib data of Merino sheep is presented. A total of 617 animals distributed in 10 families were genotyped for 36 microsatellite markers on four ovine chromosomes OAR1, OAR3, OAR4 and OAR11. The markers covering OAR3 and OAR11 were densely spaced, at an average distance of 2.8 and 1.2 cM, respectively. Body weight and wool traits were measured at first and second shearing. Analyses were conducted under three hypotheses: (i) a single QTL controlling a single trait (for multimarker regression models); (ii) two linked QTLs controlling a single trait (using maximum likelihood techniques) and (iii) a single QTL controlling more than one trait (also using maximum likelihood techniques). One QTL was identified for several wool traits on OAR1 (average curvature of fibre at first and second shearing, and clean wool yield measured at second shearing) and on OAR11 (weight and staple strength at first shearing, and coefficient of variation of fibre diameter at second shearing). In addition, one QTL was detected on OAR4 affecting weight measured at second shearing. The results of the single trait method and the two-QTL hypotheses showed an additional QTL segregating on OAR11 (for greasy fleece weight at first shearing and clean wool yield trait at second shearing). Pleiotropic QTLs (controlling more than one trait) were found on OAR1 (clean wool yield, average curvature of fibre, clean and greasy fleece weightand staple length, all measured at second shearing).     

Effects of intravenous infusion of mimosine on wool growth of Merino sheep.

Merino sheep were given continuous intravenous infusions of L-mimosine for periods of 1 1/2, 2 or 21 days; efficacy as a defleecing procedure and effects on subsequent wool growth were measured. In addition, the amino acids tyrosine, phenylalanine and cystine were investigates as antagonists to the effects of mimosine. Infusions for 1 1/2 or 2 days at the daily rate of 80-120 mg/kg caused a cessation of wool growth by 1 1/2-2 days from the start of infusion, and all sheep were subsequently defleeced. It was estimated that, on average, fibre growth stopped for 10 1/2-13 days in four sheep after a 2-day infusion, and for 5 1/2 and 9 1/2 days in two sheep after an infusion for 1 1/2 days. There was considerable variation in the time taken for new fibres to recommence growth. During the period 3-5 weeks after infusion of mimosine, length growth rate was consistently greater than the pretreatment rate. Likewise, fibre diameter was greater in three out of the four sheep. As a result, the volume growth rate of fibres was greater post-treatment than it was pretreatment. Infusion for 3 weeks at the daily rate of 21-24 mg/kg did not stop wool growth. However, both length growth rate and fibre diameter were considerably depressed, and after 12 days' infusion, fibre diameter and volume growth rate were reduced to less than half the pretreatment values, and wool fibres were very weak. After the mimosine infusion stopped, fibre diameter increased to above pretreatment values and remained ther for the period of 2-3 weeks studied. The concurrent infusion of tyrosine, phenylalanine or cystine with mimosine failed to prevent any of the effects of mimosine on wool growth.     

The effect of host nutrition on itch mite, Psorergates ovis, populations and fleece derangement in sheep

Abstract. A group of thirty-two Merino sheep infested with itch mites (Psorergates ovis) and fed a maintenance diet which imposed moderate nutritional stress had a significantly higher mite population, significantly more skin scurf, and significantly more fleece damage or derangement (P < 0.05) than a second group of thirty-two infested sheep fed a diet designed for unrestricted body weight gain and wool growth. Histologically there were no significant differences between the groups in the numbers of mast cells, neutrophils or eosinophils observed in skin sections, but sheep that had high mite counts (>10 per 200 cm² of skin area) in both groups, had more dermal mast cells than sheep with fewer mites irrespective of the plane of nutrition. Skin thickness and greasy fleece weight in die group maintained on the low plane of nutrition were significantly less (P < 0.05) than in die well-nourished group, reflecting the difference in protein and energy content of the two diets. Within the nutritionally stressed group, the sheep with low mite counts had a significantly lower (P < 0.05) greasy fleece weight and a shorter mean staple length than the sheep with high mite counts. There was no significant difference in greasy fleece weight between sheep with low or high mite counts in the group fed on the high plane of nutrition.     

Investigation of some amino acid analogues and metabolites as inhibitors of wool and hair growth

Sheep were given intravenous infusions of ethionine together with cycloleucine or reduced glutathione, in attempts to prevent the inhibition of wool growth by ethionine. Other sheep were given cycloleucine alone to measure effects on wool growth. Twenty-two compounds related to cystine, methionine, ethionine, lysine, phenylalanine and tyrosine were given as intravenous infusions to sheep to investigate their potential as depilatory agents. Nineteen of these compounds were also tested in mice during their first cycle of hair growth. The concurrent administration of cycloleucine with ethionine prevented the weakening of wool fibres caused by ethionine, but reduced glutathione was ineffective. Cycloleucine weakened wool fibres, as judged subjectively, and caused a small reduction in fibre diameter. Selenocystine and selenomethionine caused some hair loss in mice but selenocystine was also toxic. Both seleno-amino acids were toxic for sheep; selenocystine was lethal at 0.025 mmol kg-0.75 and selenomethionine at 0.09 mmol kg-0.75. Doses that permitted survival of sheep did not have depilatory effects. However, the presence of autophagic vacuoles in the cytoplasm of follicle bulb cells of sheep indicated that a toxic dose of selenocystine had potential depilatory activity. Other compounds investigated did not induce loss of wool or hair. Some compounds, notably 3-methylthiopropionic acid and S-(2-aminoethyl)-L-cysteine, were toxic to mice but not sheep. The methionine analogue, methoxinine (O-methyl-DL-homoserine), caused a substantial reduction in the strength of wool fibres and a prolonged alteration of the crimp pattern. It is suggested tentatively that cycloleucine inhibits methionine adenosyltransferase and thereby reduces or prevents the formation of S-adenosylethionine. The failure of various compounds related to methionine and ethionine to have any depilatory activity in sheep supports the view that ethionine influences wool growth via the formation of S-adenosylethionine.     

Hair follicle characteristics and fibre production in South American camelids

Hair follicle and fibre characteristics of Peruvian alpaca and llama and Bolivian llama were analysed in three experimental studies. The first experiment was designed to determine the age at which all the secondary follicles reach maturity, as well as to compare the skin follicular structure and activity among these different types of Peruvian camelids. It is concluded that the South American camelids investigated in this study gained a complete and mature skin follicle apparatus at an early age, and hence producers should practise an early first shearing. A second Peruvian experiment investigated comparative fibre cuticular structure on twenty Peruvian domestic camelids comprising huacaya, suri and llama (woolly) 'chacos' genotypes. The results showed that the number of cuticular scales per 100 μm fibre length proved to be strongly affected by both the fleece type and the fibre diameter. The suri fleece was clearly differentiated from those of both huacaya and llama by possessing the highest percentage of fibres with a number of scales less than eight, the lowest percentage of fibres with more than nine scales, along with the lowest percentage of fibres with a diameter of more than 35 μm. It is concluded that, with the exception of the scale height, the cuticular parameters investigated in this study can be utilised in textile fibre analyses for distinguishing among these three types of fleece, as well as in selection projects designed to produce homogeneous fibres from Peruvian domestic camelids. A further study was conducted to determine the age at which the hair follicles in Bolivian llamas reach maturity as well as for comparing the skin follicular structure and activity between the two distinct genotypes. Thirty-one llama kids were chosen. They were born between January and April 1998 and were of different sex and of 'Q'aras' (or Carguera) or 'T'amphullis' type. Skin biopsies were taken from the right mid-costal region at 2, 4, 6, 8,10,12 and 14 months of age in order to monitor four follicular parameters. In this experiment, secondary to primary (S/P) data show that the Bolivian llama population analysed possessed a complete and mature skin follicle apparatus at birth that remained essentially constant throughout the investigation period. Due to the variation of these traits inside the same genetic population, the present results showed that T and Q types could only be subjective on the basis of S/P ratio.     

Influence of nutrition on the crimping rate of wool and the type and proportion of constituent proteins.

When the nutritional level of sheep is restricted, the staple crimp frequency of the resultant fleece increases substantially whereas the cystine and high-sulphur protein contents decrease. This is in marked contrast to the direct relationship between crimp frequency and cystine content among sheep. These observations can be reconciled by assuming that variations in crimp frequency are attributable solely to a combination of follicle shape and fibre length growth rate without recourse to the more generally accepted theories relating to the proportion and distribution of ortho- and paracortical cells in the firbre cortex. The major portion of the decrease in the cystine content of high-crimp wools is due to the decreased synthesis of a specific protein fraction (ultra-high-sulphur protein) as would be expected from the results of dietary supplementation experiments. Low-crimp wools do not appear to contain this protein fraction and in this respect they may differ from high-crimp wools.     

IGFBP-3基因多态性及其与中国美利奴羊部分羊毛性状的关联性分析

采用PCR-SSCP方法对中国美利奴羊和哈萨克羊中IGFBP-3基因的多态性进行了检测, 并对不同基因型与中国美利奴羊部分羊毛性状间的关联性进行了分析。结果在位于内含子1区的一段178 bp的扩增产物经SSCP分析后出现了3种基因型, 基因型AA、AB和BB及等位基因A、B在中国美利奴羊中的频率分别为0.70、0.24、0.06和0.82、0.18; 在哈萨克羊中的频率分别为0.87、0.13、0.00和0.93、0.07。序列分析发现: 在该序列的122位碱基表现多态性 (g.122 G>T)。所研究的两个群体在该位点上均处于Hardy-Weinberg不平衡状态(P<0.01)。不同基因型对部分羊毛性状有一定的影响: 不同基因型个体在剪毛后体重和净毛率上没有明显差异。AA、AB及BB基因型个体的羊毛伸直长度逐渐变短, 其中AA与AB基因型之间差异极显著(P<0.01)。AA型个体的剪毛量和羊毛密度要明显低于AB型(P<0.01)和BB型个体(P<0.05); 羊毛纤维直径则明显高于AB型(P<0.01)和BB型(P<0.05)个体。     

Genetic analysis of fibre characteristics in adult Targhee ewes and their relationship to breeding value estimates derived from yearling fleeces

Fleeces from 847 adult (2–7-year-old) Targhee ewes enrolled in the U.S. National Sheep Improvement Program were evaluated using an optical fibre diameter assessment system (OFDA2000; BCS Electronics Pty Ltd., Ardross, WA, Australia). Measurements recorded included the average, S.D. and CV for fibre diameter, comfort factor (percentage of fibre below 30 μm), spinning fineness, staple length, average curvature, and uniformity (S.D.) along the staple. Significant ewe age effects were observed for all measurements except the CV of fibre diameter and uniformity along the staple. Fleeces became coarser as ewes aged, but staple length and curvature were maximized at 2 and 3 years of age, respectively. Heritability estimates (h²) for OFDA measurements exceeded 0.50 for average fibre diameter, spinning fineness, and average curvature and were below 0.30 only for uniformity along the staple (h² = 0.19). Associations between OFDA measurements of fleece fineness in adult ewes and estimated breeding values (EBV) for average fibre diameter derived from yearling fleeces were very strong. The regression coefficient relating the OFDA average fibre diameter measurement in adult ewes to fibre diameter EBV in yearling fleeces of 1.08 ± 0.07 μm/μm was consistent with its expected value of 1.00 and suggests that selection on yearling fibre diameter EBV would nearly maximize selection response in adult fleeces. The EBV for staple length in yearling fleeces was closely associated with the OFDA measurement of staple length in 2-year-old ewes (regression coefficient of 1.21 mm/mm), but this relationship weakened as ewes aged, perhaps as a result of negative associations between adult staple length and the number of lambs produced, and the regression coefficient averaged 0.65 ± 0.10 mm/mm across all ewe ages. In general, relationships between EBV for growth, maternal, and reproductive traits and OFDA measurements in adult ewes were consistent with those observed in yearling fleeces.     

Effects of mimosine, a potential chemical defleecing agent, on wool growth and the skin of sheep.

Twenty-two Merino sheep were dosed with various amounts of L-mimosine, given either as an intravenous or an intraperitoneal injection, or as a continuous intravenous infusion for periods of 1-4 days. Single injections of mimosine (1-16 g) had no effect on the strength of wool, and wool growth rates were not appreciably altered by injections of small amounts (4 g or less). Injections of larger amounts slightly reduced both length growth rate and diameter of tibres during the 4 days after dosing. The effects of intravenous infusions of mimosine depended on the rate and the duration of administration. Small amounts (0.5 or 1 g/day given for 4 days) has no effects on the strength of wool or on wool growth rates. Infusions of a total of 8 g, either at the rate of 2 or 8 g/day, weakened the wool but not sufficiently to allow the sheep to be defleeced. Both these treatments caused a temporary reduction in length growth rate and in diameter of fibres, and transient degenerative changes were observed in wool follicles. A region of the fibres representing 1-2 days' growth was constricted to about half the pre-infusion diameter when 8 g was given for 1 day. Infusions of at least 8 g mimosine over a period of 1 1/2-2 days were effective for defleecing all sheep dosed. This corresponded to a daily rate of infusion of about 80 mg/kg. No toxic effects were observed with infusions given for periods of 2 days. Defleecing was judged to be possible by 6-7 days after the start of infusion, and was readily carried out by about 14 days. Defleecing was associated with follicle retrogression and an abrupt cessation of wool growth within 2 days of the start of the infusions. It was estimated that fibre growth stopped for about 10 dyas; regrowth was first observed 17-18 days from the beginning of dosing. Low rates of infusion of mimosine (up to 2 g/day) resulted in plasma levels below 0.1 mmol/l. Infusion at the rate of 4 g/day or above, which produced defleecing, quickly resulted in levels of mimosine in plasma above 0.1 mmol/l; after 2 days the concentration was steady at aboug 0.2 mmol/l. Injections of 8 or 16 g mimosine resulted in very large, but transient, rises of the level in plasma.     

Wool fibre crimp is determined by mitotic asymmetry and position of final keratinisation and not ortho- and para-cortical cell segmentation

Crimp, a distinguishing feature of sheep fibres, significantly affects wool value, processing and final fabric attributes. Several explanations for fibre bending have been proposed. Most concentrate on relative differences in the physicochemical properties of the cortical cells, which comprise the bulk of the fibre. However, the associations between cortical properties and fibre crimp are not consistent and may not reflect the underlying causation of fibre curvature (FC). We have formulated a mechanistic model in which fibre shape is dictated primarily by the degree of asymmetry in cell supply from the follicle bulb, and the point at which keratinisation is completed within the follicle. If this hypothesis is correct, one would anticipate that most variations in fibre crimp would be accounted for by quantitative differences in both the degree of mitotic asymmetry in follicle bulbs and the distance from the bulb to the point at which keratinisation is completed. To test this hypothesis, we took skin biopsies from Merino sheep from sites producing wool differing widely in fibre crimp frequency and FC. Mitotic asymmetry in follicle bulbs was measured using a DNA-labelling technique and the site of final keratinisation was defined by picric acid staining of the fibre. The proportion of para- to ortho-cortical cell area was determined in the cross-sections of fibres within biopsy samples. Mitotic asymmetry in the follicle bulb accounted for 0.64 (P < 0.0001) of the total variance in objectively measured FC, while the point of final keratinisation of the fibre accounted for an additional 0.05 (P < 0.05) of the variance. There was no association between ortho- to para-cortical cell ratio and FC. FC was positively associated with a subjective follicle curvature score (P < 0.01). We conclude that fibre crimp is caused predominantly by asymmetric cell division in follicles that are highly curved. Differential pressures exerted by the subsequent asymmetric cell supply and cell hardening in the lower follicle cause fibre bending. The extent of bending is then modulated by the point at which keratinisation is completed; later hardening means the fibre remains pliable for longer, thereby reducing the pressure differential and reducing fibre bending. This means that even highly asymmetric follicles may produce a straight fibre if keratinisation is sufficiently delayed, as is the case in deficiencies of zinc and copper, or when keratinisation is perturbed by transgenesis. The model presented here can account for the many variations in fibre shape found in mammals.     

母体遗传效应对青海细毛羊生产性能遗传参数估计的影响

为了研究母体遗传效应对青海细毛羊生长性状、产毛性状的影响,文章采用平均信息最大约束似然法应用不同混合动物模型估计青海细毛羊生产性状的遗传参数,并采用似然比检验对不同模型进行比较分析。各模型中均包括固定效应、个体直接加性遗传效应、残差效应;随机效应为:个体永久环境效应、母体遗传效应、母体永久环境效应。不同模型对随机效应作了不同考虑:模型1不考虑个体永久环境效应、母体遗传效应、母体永久环境效应;模型2考虑母体永久环境效应;模型3考虑母体遗传效应;模型4考虑母体遗传效应和母体永久环境效应;模型5考虑个体永久环境效应和母体遗传效应;模型6考虑个体永久环境效应、母体遗传效应、母体永久环境效应。各模型估计的初生重遗传力为:0.1896~0.3781;断奶重遗传力为:0.2537~0.2890;周岁重遗传力范围:0.2244~0.3225;成年羊体重遗传力范围:0.2205~0.3983;产毛量遗传力为:0.1218~0.1490;羊毛细度遗传力为:0.0983~0.4802;羊毛长度遗传力为:0.1170~0.1311。与模型1相比,模型3对于初生重、断奶重差异显著(P<0.01),对于周岁重、成年羊体重各模型与模型1的似然比检验差异不显著(P>0.05);与模型6相比,模型4、5对于羊毛细度差异显著(P<0.01),模型4对羊毛长度差异显著(P<0.05),对于产毛量各模型与模型6似然比检验差异不显著(P>0.05)。生长性状中初生重、断奶重受母体遗传效应影响显著,周岁重、成年羊体重受母体遗传效应影响不显著;产毛性状中羊毛细度、长度受母体遗传效应影响显著,产毛量受母体遗传效应影响较弱。     

母体遗传效应对青海细毛羊生产性能遗传参数估计的影响

为了研究母体遗传效应对青海细毛羊生长性状、产毛性状的影响, 文章采用平均信息最大约束似然法应用不同混合动物模型估计青海细毛羊生产性状的遗传参数, 并采用似然比检验对不同模型进行比较分析。各模型中均包括固定效应、个体直接加性遗传效应、残差效应; 随机效应为：个体永久环境效应、母体遗传效应、母体永久环境效应。不同模型对随机效应作了不同考虑：模型1不考虑个体永久环境效应、母体遗传效应、母体永久环境效应; 模型2考虑母体永久环境效应; 模型3考虑母体遗传效应; 模型4考虑母体遗传效应和母体永久环境效应; 模型5考虑个体永久环境效应和母体遗传效应; 模型6考虑个体永久环境效应、母体遗传效应、母体永久环境效应。各模型估计的初生重遗传力为：0.1896~0.3781; 断奶重遗传力为：0.2537~0.2890; 周岁重遗传力范围：0.2244~0.3225; 成年羊体重遗传力范围：0.2205~0.3983; 产毛量遗传力为：0.1218~0.1490; 羊毛细度遗传力为：0.0983~0.4802; 羊毛长度遗传力为：0.1170~0.1311。与模型1相比, 模型3对于初生重、断奶重差异显著(P<0.01), 对于周岁重、成年羊体重各模型与模型1的似然比检验差异不显著(P>0.05); 与模型6相比, 模型4、5对于羊毛细度差异显著(P<0.01), 模型4对羊毛长度差异显著(P<0.05), 对于产毛量各模型与模型6似然比检验差异不显著(P>0.05)。生长性状中初生重、断奶重受母体遗传效应影响显著, 周岁重、成年羊体重受母体遗传效应影响不显著; 产毛性状中羊毛细度、长度受母体遗传效应影响显著, 产毛量受母体遗传效应影响较弱。     

Morphological changes in the skin and wool fibres of Merino sheep infused with mouse epidermal growth factor

Intravenous infusion of 4.5-4.7 mg of mouse epidermal growth factor (mEGF) into nine castrated male Merino sheep for 26 h resulted in complete casting of the fleeces 6-8 days later. The morphological changes which occurred in the skin were studied in skin samples taken before infusion and at intervals between 1 h and 42 days after the infusion had begun. Wool fibres from the shed fleeces were examined with the scanning electron microscope. Increased cell proliferation occurred in the epidermis and sebaceous glands, whereas the wool follicles regressed. Transient dermal haemorrhages occurred during the first 3 h of infusion. The fibre and inner root sheath in the keratogenous zone of 30-40% of the follicles were partially disrupted within the first 6 h of mEGF infusion; catagen began in all follicle bulbs within 24 h. Fibre and inner root sheath production, although markedly reduced, continued in about 60% of follicles which had partially regressed, but production ceased in the remainder in which tapered ends formed on the fibres prior to shedding. Follicles began to regenerate asynchronously 4-8 days after the beginning of infusion and completed their development during the next 3 weeks. The follicle regression and fleece casting induced by mEGF infusion, and subsequent follicle regeneration were completed more rapidly than observed previously with other depilatory agents, and, except for prolonged epidermal thickening, there was no lasting cutaneous abnormality.     

Migration and keratinization of cells in wool follicles

Migration of cells in wool follicles of an adult Merino sheep was studied autoradiographically in skin samples taken at intervals after an intravenous injection of [3H]thymidine. Fibre and inner root sheath cells incorporated [3H]thymidine in a cone-shape region of the follicle bulb. Labelled inner sheath cells migrated out of the bulb ahead of contemporaneous cells in the fibre and remained in advance, although to a progressively lesser extent, until the inner sheath cells sloughed into the follicle lumen. Outer root sheath cells incorporated [3H]thymidine along the length of the follicle. Cells in the proximal half of the outer sheath migrated inwards and distally and sloughed into the follicle lumen before contemporaneous inner sheath cells. Other cells in the distal half of the outer sheath migrated past the level where cells from the proximal population were shed and also sloughed into the lumen. In the most distal part of the outer sheath, which formed the epidermis-like lining of the follicle canal, little migration of cells was observed during 8 days of observation. The specific activity of tritium in fibres plucked from the same sheep at intervals after the intravenous injection of [3H]thymidine was determined by scintillation counting and assessed in terms of cell migration and hardening of the fibres. The time which the specific activity of solvent-degreased fibres reached a maximum was found to give an estimate of the time for cells in the fibre to migrate to the upper limit of the keratogenous zone. When the plucked fibres were extracted with 8 M urea the times of the maximum specific activities of the urea-dispersible and urea-insoluble material provided respectively estimates of the times at which hardening of the fibres began and ended. The effects of different planes of nutrition were examined in two other Merino sheep by radioassay of fibres plucked after intravenous injections of [3H]thymidine given after equilibration period of at least 2 months on each level of feeding. A high plane of nutrition the rate of cell migration and hastened the onset of hardening of the fibres, but prolonged the hardening process. The prolongation of the hardening process was confirmed by the specific activities of fibres plucked after intravenous injections of [35S]cystine.     

Genetic parameters for physical and quality traits of mohair in South African Angora goats

The continuous evaluation and genetic improvement of fleece traits in Angora goats are of major importance to the Angora goat industry. The objective of this study was to estimate variance components and genetic parameters for both physical and quality traits of mohair in South African Angora goats. The data used for this study were collected on between 898 and 6211 kids (depending on the trait measured) born between 2000 and 2006 in 11 different Angora goat studs. Variance components and genetic parameters were estimated with the ASREML programme for fleece weight, fibre diameter, coefficient of variation of fibre diameter, standard deviation of fibre diameter, comfort factor, spinning/effective fineness and standard deviation of fibre diameter along the length of the staple. Most of these traits (excluding fleece weight) are measured using OFDA technology exclusively, and this study was the first attempt to calculate genetic parameters for these traits in South Africa. A model including the direct additive genetic effects only, were the most appropriate for estimation of all parameters. Heritability estimates were 0.24 ± 0.03 for fleece weight, 0.45 ± 0.03 for fibre diameter, 0.37 ± 0.10 for coefficient of variation of fibre diameter, 0.32 ± 0.11 for standard deviation of fibre diameter, 0.63 ± 0.10 for comfort factor, 0.61 ± 0.10 for spinning/effective fineness and 0.14 ± 0.08 for standard deviation of fibre diameter along the length of the staple. Results from this study can now be applied for the estimation of breeding values for fleece production of South African Angora goats and in incorporation into selection programs.     

Cell proliferation and cortical cell production in relation to wool growth

The relationship of wool growth to cell proliferation in the follicle bulb and to the subsequent migration and growth of the fibre cortical cells was investigated in 10 Peppin Merino sheep. These sheep had been maintained on a low, medium or high level of nutrient intake to ensure a wide range in wool growth. The number and mitotic activity of the germinal cells in the follicle bulb were determined after administration of colchicine. Cortical cell size was measured following isolation of the fibre cells by acid-treatment of wool. The average fibre production of the follicle varied from 4.1 x 10(4) to 13.2 x 10(4) micron3/day in these sheep. There were also substantial differences between sheep in the mitotic activity of the germinal cells in the bulb, the rate of cell proliferation being highly correlated with the average daily fibre production of the follicle (r = + 0.88, n = 10). However, the size of the germinal cell population differed from sheep to sheep and was not closely related to the level of fibre production (r = + 0.48, n = 10). The average turnover time of these cells was inversely related to fibre production and varied from 41.6 to 19.4 h (r = -0.82, n = 10). Multiple regression analysis of the data showed that the average daily fibre production of the follicle was largely determined by the number of germinal cells present in the bulb and their rate of proliferation (R = +0.95, n = 10). Variations in cell turnover time and in cortical cell size were not significant in influencing the rate of fibre production. In these sheep, the average cortical cell varied in size from 658 to 1279 micron 3 and the positive correlation (r = + 0.83, n = 10) found between cell size and fibre production is considered to merely reflect an allometric relationship. The proportion of germinal cells contributing to the fibre cortex was found to be small and variable, ranging from 9.4 to 17.8%. Furthermore, this proportion was not related to the nutritional level of these sheep, and it is thought that the variability in the distribution of cells to the fibre may be attributed to genetic differences between sheep.     

Kinetic disposition of an emulsifiable concentrate formulation of deltamethrin applied to sheep in a plunge-dip and its effect on lice

An emulsifiable concentrate formulation of the synthetic pyrethroid insecticide deltamethrin was applied in a plunge dip, 3 weeks after shearing, to a group of 5 Merino sheep infested with sheep body lice, Bovicola ovis. Deltamethrin concentrations on the wool were measured at regular intervals between 1 and 98 days after treatment and were not significantly different (P > 0.05) between sites on the dorsal mid-line, upper or lower flank. Levels in the tip of the fleece were significantly greater than those in the base, indicating that there was little movement of deltamethrin down the staple as the wool grew. Most lice were killed after 20 h of exposure in vitro to wool samples collected between 1 and 28 days after treatment. However, many lice survived in samples containing a similar concentration of deltamethrin, but collected between 35 and 98 days after treatment. Numbers of lice surviving increased with the sampling time after treatment, suggesting that the bioavailability of the deltamethrin changed as the insecticide aged in the fleece. Some transfer of deltamethrin occurred from treated to untreated sheep. The levels of deltamethrin were higher in sheep placed in contact with the treated group at 14 days after treatment than in those which were in contact from 43 days after treatment.