Is there a specific weakness in staple strength around the break of season?

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.

The wool growth response to nutrition by Merino weaners (liveweight 33· 2±0·58 kg) bred for high or low staple strength (SS) and fed to produce changes in liveweight was examined. The hypothesis tested was that genetic differences in SS are associated with differences in along-fibre variation in diameter. Sheep fed to maintain liveweight produced wool at a more constant rate with smaller and less rapid changes in fibre diameter than that produced by sheep which lost and then gained liveweight ( P < 0·001). There were significant ( P < 0·05) but relatively small differences in wool growth rate and fibre diameter between the SS selection flocks, and wool from sheep selected for high SS had less ( P < 0 ·001) variation in diameter between individual fibres than wool from sheep selected for low SS Minimum fibre diameter was most closely associated with SS, accounting for 66% ( P < 0·001) of the total variance in SS generated by selective breeding and nutrition. An increase in minimum fibre diameter of 1µm was associated with an increase in SS of about 5 N/ktex. Minimum fibre diameter and the rate of change in fibre diameter to the point of break along the staple collectively accounted for 72% ( P < 0·001) of the total variance in SS. Addition of a term for between-fibre variation in diameter measured at the point of break removed an additional 8% ( P < 0·001) of the variance in SS. We conclude that the mechanisms responsible for nutritionally induced and genetic differences in SS are not the same. Nutrition influences SS by affecting along-fibre diameter changes, whereas genetic differences in SS, at least as far as they are represented by the flocks used here, are largely attributable to between-fibre variations in diameter. The independence of nutritional and genetic effects on SS means that they should be exploited concurrently to reduce the incidence of tender wool production.

The effects of different supplementary feeding practices in summer-autumn and management strategies on green pasture on liveweight change, wool growth rate, annual wool production and wool characteristics of young Merino wethers were examined at 2 farms. The grain feeding treatments were lupins (L) or lupins and oats (LO) fed in amounts that were adjusted to try and maintain liveweight, or lupins and oats (LOG) fed at a higher rate. The objectives of liveweight maintenance or gain were not always achieved, but liveweight patterns differed between LOG compared with L or LO during summer-autumn. The sheep used at farm 1 were aged 4.5 months and liveweight 32 kg at the start of the experiment, while those at farm 2 were 6.5 months and liveweight 39 kg. The stocking rate in summer-autumn was 8 wethers/ha at both farms. During supplementation, sheep on LOG had a higher (P<0.05) liveweight change compared with those on L or LO (farm 1, 15 v. -8 g/sheep. day; farm 2, -35 v. -51 g/sheep. day) and clean wool growth rates (farm 1, 7.1 v. 6.4 g/sheep. day; farm 2, 5.1 v. 4.8 g/sheep.day). The sheep on LOG grew broader (P<0.05) wool than those on L or LO (farm 1, 19.0 v. 18.5 �m; farm 2, 21.7 v. 20.8 �m), and at farm 1 length was also greater (P<0.05) (114 v. 111 mm), while at farm 2 staple strength was greater (P<0.01) (22.9 v. 16.4 N/ktex). There were no significant differences in annual clean wool production. There were positive (P<0.01) relationships between staple strength and liveweight change to the time of minimum liveweight in summer-autumn. After green pasture on offer reached 500 kg DM/ha in autumn, different liveweight change patterns were achieved in 2 groups (LS, lower stocking rates; HS, higher stocking rates) of sheep at each farm by adjusting stocking rates. Within a farm, the LS and HS groups were comprised of equal numbers of sheep from each replicate of the supplementary feeding treatments. There were differences (P<0.05 to 0.01) in liveweight change between LS and HS (farm 1, 93 v. 72 g/day; farm 2, 127 v. 60 g/day), the differences being more pronounced at farm 2. The differential stocking rates at farm 2 resulted in differences in clean wool growth rates (P<0.01), in clean wool production (4.22 v. 4.53 kg, P<0.05), and fibre diameter (20.8 v. 21.4 �m, P<0.01), but there were no significant effects on staple length or strength. There were no significant effects of the supplementary feeding treatments imposed in summer-autumn on the responses to the stocking rate treatments on green pasture.

The biological mechanisms underlying differences in wool staple strength were examined in 2 groups of Merino sheep that have been genetically selected for high or low staple strength, while holding fibre diameter constant. The sheep were fed below maintenance for 87 days, and then re-fed ad libitum for 63 days with a diet containing either 9% or 23% crude protein, in a cross-over design, after which they returned to the paddock until shearing. The fleeces of the 2 groups differed in staple strength (25·2 v .17·5 N/ktex, P < 0·001) but were similar in mean fibre diameter and clean fleece weight. However, the pattern of wool growth was different. When fed below maintenance, sheep from the sound group grew more wool than sheep from the tender group ( P < 0·05), but lost more liveweight ( P < 0·01). During re-feeding, the sound sheep grew less wool than the tender sheep ( P < 0·05), but gained more liveweight. The mean fibre diameter at the point of break was similar in both groups. Immediately after re-feeding, the fibre diameter increased more rapidly in the tender group than in the sound ( P < 0·001), but a similar difference was observed between the high and low protein diets, with no effect on staple strength. The sound sheep had a lower standard deviation of fibre diameter than the tender sheep ( P < 0·001), both in the whole fleece and in 3-weekly midside patches. The data indicated that the variability of fibre diameter between fibres made a larger contribution than the variability along fibres to the difference between the groups in overall variability of fibre diameter. The sheep were then grazed together at pasture for a second year and again differed in staple strength. In addition, the sound sheep grew less wool on green spring pastures and had a lower clean fleece weight ( P < 0·05). The differences in wool growth rates between sheep from the sound and tender lines depended more on whether pasture was green than on the amount of pasture available. We conclude that the difference in staple strength between the sound and tender groups was most closely associated with the variability between fibres in diameter, and was also affected by a difference in variation in diameter along the fibres. Staple strength was not affected by the amount of wool at the point of break, or by the rate of change in fibre diameter after feeding. The sheep in the sound group grew less wool than those in the tender group when on good nutrition.

This paper investigates the contribution of single fibre stress-strain properties to variations in staple strength induced by both selective breeding for staple strength and nutritional manipulation. Merino weaners (n = 40), selected from ‘sound’ and ‘tender’ lines of staple strength selection flocks, were allocated to feeding regimes designed to induce liveweight changes simulating typical Mediterranean seasonal changes. Average staple strength differed by 5 N/ktex between ‘sound’ and ‘tender’ selection flocks and 18 N/ktex between extreme nutritional treatments. The force-extension properties of individual wool fibres (n = 100 per sheep) were measured using a single fibre strength meter. After normalising for differences in fibre cross-sectional area at the point of break, the key parameters used to describe the stress-strain curve for each fibre were: Young’s modulus (GPa), yield stress (MPa), stress at 15% strain (MPa), stress at break (MPa), strain at break (%) and work to break (MPa). The average stress-strain properties of single fibres differed widely between individual sheep. Stress at break ranged from 163 to 235 MPa (44% range), strain at break ranged from 21 to 44% (103% range) and work to break from 43 to 71 MPa (65% range). There were no significant differences in any of the single fibre properties between the staple strength selection flocks, nor was there any significant interaction (P > 0.05) between staple strength selection flock and nutritional regimes. Nutritional regime had a significant effect on stress at break, strain at break and work to break, but none of the single fibre stress-strain properties removed any appreciable variance in staple strength over and above that accounted for by differences in along- and between-fibre diameter variation. There appears to be little scope for improvement of single fibre stress-strain properties as a means of increasing staple strength in normal production environments. Selection directly for staple strength or indirectly using the fibre diameter variability traits is an effective method to improve staple strength.

This study examined differences in fibre diameter profiles (FDPs) and midside characteristics of Merino sheep in 2 environments, 4 bloodlines, 3 years, and 44 sire groups. Environment significantly ( P < 0.05) influenced all characteristics except one measure of fibre diameter change and staple length. Bloodline also significantly ( P < 0.05) influenced all characteristics except staple strength. The maximum fibre diameter, one measure of fibre diameter change, and staple length were significantly different ( P < 0.05) between sires. Variation in fibre diameter profile characteristics between bloodlines and sires changed across the environment in which the sheep are maintained. Despite these differences between bloodlines and sires in the FDP, midside mean fibre diameter, fibre diameter variation, and staple length, there were no significant differences between bloodlines in staple strength. The relationships between the FDP and midside characteristics with staple strength were also examined over these bloodlines and environments. Along-staple variation in fibre diameter ( r = –0.32 to –0.50), between-fibre fibre diameter variation ( r = –0.25 to –0.48), rate of fibre diameter change ( r = –0.16 to –0.38), and midside variation in fibre diameter ( r = –0.25 to –0.51) were all negatively correlated with staple strength. Maximum fibre diameter ( r = 0.08 to 0.18), minimum fibre diameter ( r = 0.25 to 0.49), and midside mean fibre diameter ( r = 0.09 to 0.35) were positively associated with staple strength. FDP characteristics explained 5–30% more variation in staple strength than could be explained using the standard midside characteristics of mean fibre diameter, fibre diameter variation, and staple length alone. These relationships were also different between environments and bloodlines. The inclusion of the FDP characteristics as explanatory variables provided an alternative interpretation for how absolute fibre diameter and fibre diameter variation combine to explain staple strength. These results suggested that animals and sires might be able to be selected on FDP characteristics to improve staple strength. More detailed genetic studies are required before these selection strategies can be recommended.

Cortisol-induced follicle shutdown is related to staple strength in Merino sheep

Three strains of Merino wethers (strong, medium and fine wool; n = 30 each; 3 years old) were grazed under 3 different management regimes (10 from each strain) in a semi-arid environment to test the hypothesis that attempting to keep liveweight stable at upper and lower levels would improve staple strength relative to sheep in which no attempt was made to limit liveweight fluctuations, and that strength and wool colour would not differ between strains. Sheep in the low grazing regime were managed in an attempt to keep liveweight stable at a level below that of sheep in the high grazing regime, which were managed in an attempt to keep liveweight stable at a level higher than sheep in the low grazing regime. For the control group, no attempt was made to limit liveweight fluctuations through grazing management. Sheep in the high grazing regime had greater liveweights throughout the experiment than sheep in the low grazing regime, while the liveweight of sheep in the control group was usually intermediate. Staple strength did not differ significantly between the strains, but was greater (P<0.05) for sheep in the high grazing regime (58.3 ± 2.2 N/ktex) than for sheep in the control (39.0 ± 2.3 N/ktex) and low (33.8 ± 2.3 N/ktex) grazing regimes, which did not differ significantly from each other. Wool yellowness was not affected by grazing regime, but was lower (P<0.05) in fine wool sheep (1.0 ± 0.1%) than medium wool sheep (1.4 ± 0.1%), which, in turn, was less (P<0.05) than in strong wool sheep (1.7 ± 0.1%). Staple strength was significantly (P<0.05) correlated with mean liveweight (0.27), mean fibre diameter (0.25), minimum fibre diameter (0.36), coefficient of variation of fibre diameter (–0.50), coefficient of variation of diameter along fibres (–0.48) and between fibres (–0.41). The results indicate staple strength was not adversely affected by the choice of strain in a semi-arid environment, and that nutritional management to limit fibre diameter variability can be an effective strategy to improve staple strength, regardless of strain.

A grazing study was conducted on irrigated pastures to assess the influence of manipulating the availability of green pasture at different stages of pregnancy and lactation on the staple strength of broad-wool Merino ewes lambing in July. Sheep subjected to different treatments produced wool ranging between 14 and 48 N/ktex for single-rearing and 22 and 53 N/ktex for non-lambing ewes. Single-bearing/rearing ewes produced wool of strength +4.7 (P>0.05) to –23 N/ktex (P<0.001) in comparison with non-lambing ewes. Reproduction was associated with a reduction in staple strength of 51, 24 and 9% for ewes grazed throughout the experiment at low, medium and high pasture levels, respectively. A staple strength greater than 40 N/ktex was achieved in single-rearing ewes which grazed high pasture mass throughout pregnancy and lactation, during late pregnancy and early lactation, or during mid-pregnancy. Single-rearing ewes, which grazed low pasture biomass throughout either mid, late or all of pregnancy, or during lactation, produced wool with staple strength less than 30 N/ktex. In comparison to grazing the medium pasture allowance throughout the experiment, manipulation of pasture availability had relatively small effects on lamb growth and average fleece measurements, compared with the effects on staple strength. The exception was ewes grazing only the low pasture allowance. The interaction between reproduction and nutritional management influenced staple strength by altering the minimum fibre diameter and the uniformity of along-staple fibre diameter and rate of wool growth. It was concluded that managing pasture availability to promote a uniform along-staple fibre diameter or rate of wool growth can prevent reductions in staple strength associated with reproduction.

A study was conducted to examine the relationship between fibre shedding and staple strength in Merino weaners genetically different in staple strength and fed different levels of nutrition. Fibre shedding at the point of break along the staple was estimated using 3 different techniques: ( i ) a subjective scoring system of wool follicle activity, based on their morphology in transverse skin sections; ( ii ) the number of fibres with club-ends after differential staining to identify remnants of the shed-follicle bulb; and ( iii ) changes in the number of fibres in the cross-section along individual staples. Irrespective of the technique used, the estimated proportion of shed fibres did not differ significantly between the sheep bred for sound and tender wool, but increased significantly ( P < 0·05) in response to adverse nutritional conditions. Across all treatments, there was a significant ( r 2 = 0·63; P < 0·001) correlation between the proportion of shutdown follicles and the percentage decrease in the number of fibres in the staple cross-section, although the average difference between the techniques was 11·5%. Both techniques indicated that, on average, about 30% of the total follicle population became inactive and shed their fibre under the most adverse nutritional conditions, and that this was as high as 50–60% for some individual sheep. Neither of these techniques was closely correlated to the proportion of fibres with club-ends ( r 2 = 0·15 and 0·20, respectively; P < 0·01). The proportion of shutdown follicles and the percentage decrease in the number of fibres in the staple cross-section explained 54% and 52% of the variance in staple strength, respectively, compared with only 19% explained by the percentage of fibres with club-ends at the point of break. However, as fibre shedding failed to remove any variance in staple strength additional to that already attributed to along- and between-fibre changes in diameter, it is concluded that fibre shedding per se does not contribute significantly to nutritional-induced differences in staple strength.

This study was conducted to evaluate the intensive and rural (non-intensive) rearing conditions effect on growing lambs’ performance and wool characteristics of Rahmany sheep. A total of 40 lambs at the age of one year were used from intensive and rural rearing systems (20 lamb each, of equal male and female number). The folk of intensive system was housed at a governmental station located in El-Serw, Damietta city, Egypt. The rural folk was owned by householder located in the same area of the city. The wool sample represents the first shearing harvested from the northern shoulder area of the lambs and used to investigate some wool measurements. The studied rearing systems showed no significant differences found for lambs’ birth weights, while, the intensive rearing system enhanced significantly lambs’ daily weight gain. Lambs weights at one year aged and the total weight gain in the intensive system were significantly higher than rural system lambs. The rearing system insignificantly affected the lambs’ fibre length growth, but affected significantly the clean wool yield, fibre diameter and crimp/cm of lambs. The rearing system affected significantly the lambs’ staple strength, point of break and elongation rate, while no effect on staple length was detected.

SUMMARY The present study aimed to define those wool traits of significant processing performance to be included in the sheep breeding program. About 1.64 tons of wool was harvested from the flock of Barki sheep at Maryout Research Station belonging to the Desert Research Center. The harvested wool was subjected to a clip preparation technique and subjectively graded for harshness and bulkiness into four lines; L1: coarse wool with high bulk, L2: coarse wool with low bulk, L3: fine wool with high bulk and L4: fine wool with low bulk in addition to another one (L5) as a wool line left without grading for comparison. Representative wool samples were taken from each line to measure fibre diameter (FD), standard deviation of FD (SDfd), medullated fibre percentage (M%), prickle factor (PF%), loose wool bulk (BUL), resilience (RES), staple strength (SS), point of break (POB) and staple elongation (EL) in order to determine the characteristics of each line of the raw wool. The formed wool lines were sent to the manufacture to be processed according to the normal procedures practiced in such mill. Representative wool samples were also taken from each line after carding, after spinning and from the processed blankets. These samples were tested according to the Egyptian Standards for blankets. The same wool traits measured in the raw wool were tested again from those samples taken from each line after carding. Samples collected to represent each processed line after spinning were used to measure yarn count, yarn strength and elongation, coefficient of variability of irregularity of yarn mass and yarn hairiness. Some blanket properties such as weight of blanket/ m 2 , heat loss, air permeability, strength and elongation as well as covering factor were also recorded from samples taken from each line of processed blanket. Results indicated that L1 and L2 had significantly higher FD, SDfd, M% and PF% as well as less SS and EL compared with L3 and L4. L1 and L3 had significantly higher BUL and RES compared with L2 and L4. Blanket weight/ cm 2 was significantly lighter for blankets processed from those lines of more harshness (L1 and L2) and more bulkiness (L1 and L3). Moreover, blankets made from higher BUL wool lines tended to maintain more heat and being less permeable with significantly better covering, while blankets made from finer wool lines tend to be stronger and more extensible. The present study recommend that blanket made from L1 line to be the best since it provides better processing efficiency in terms of yarn count as well as producing blanket with the least blanket weight/ cm 2 and maintaining more heat. Moreover, the manufacturer could save about 20% of the

Comparative productivity and grazing behaviour of Huacaya alpacas and Peppin Merino sheep grazed on annual pastures

This review outlines the factors that may influence the strength of wool fibres and the associated changes in structure and protein composition that have been observed in weakened fibres. The strength of a wool staple is dependent on the intrinsic strength of the fibres that it contains and the total cross-sectional area of fibre being tested. The minimum fibre diameter and the rate of change of diameter along a staple are important determinants of strength. Different sheep kept under similar conditions show a large range of staple strengths. Estimates of heritability for staple strength are sufficiently high (0.17 to 0.49 in Merinos; 0.20 to 0.58 in Romneys) to prompt the establishment of selection programmes in both breeds. A variety of physiological and environmental factors influence the strength of wool fibres. Nutrient supply exerts a major influence via effects on fibre diameter. In addition, there are specific effects of some amino acids (methionine and lysine), trace elements (copper and zinc) and vitamins (folic acid). Seasonal effects are important in breeds which exhibit a large annual rhythm of wool growth, e.g. Romneys, but not in Merinos. Pregnancy and lactation influence fibre strength through competition for essential nutrients but hormonal factors may also be involved. Fibre strength may also be influenced by stress involving excessive secretion of glucocorticoids and by various parasites and diseases which can influence nutrient supply and cause stress. No clear association has been established between the strength of wool fibres and the proportions of the constituent proteins. The content of high-tyrosine proteins in the matrix of weak fibres is frequently, but not invariably, reduced. Likewise, fibre strength has been associated with the proportions of components of the high-sulfur proteins in some studies, but not in others. Thus in Romneys, but not Merinos, tender (weak) wool contained a higher proportion of orthocortex than sound wool, and hence contained less ultra-high-sulfur proteins. Weak fibres produced by specific nutritional treatments in adult sheep and lambs show a loss of cuticle scale pattern and malformed or degraded fibres.

Young Merino sheep (7-8 months of age, weighing about 40.5 kg) were given weekly supplements of 1050 gfsheep of lupins, lupins coated with potassium sulfate (25 g/kg lupins), lupins and access to a mineral lick (offered at 175 g/sheep.week), or lupins coated with potassium sulfate and access to the lick. The sheep grazed an annual pasture at a stocking rate of 15 sheepha and were given the supplements between 14 December and 5 April. The amount of pasture on offer in mid December exceeded 3000 kg DMha but declined to 1500 kg DMha in late March.There were significant amounts of green feed present in December and March (>20% of pasture DM), a small amount in January, and no green feed in February. Despite this the percentage of sheep licking the minerals was over 70% in January , February; and March, with average intake being about 10 g/sheep.day. No significant differences occurred between treatments for liveweights of sheep during the feeding period or at shearing. Over the feeding period sheep lost weight at about 30 g/day. Neither the additional sulfur nor the mineral lick had any significant effects on fleece weight, mean fibre diameter of the fleece, staple length, or staple strength. Wool growth rates were not different between treatments during the feeding period. These results indicate that under good pasture conditions with some green feed available, and when lupins are supplied, responses to mineral supplements are unlikely.