Breeding Objectives

SRS® Merino sheep are the result of selecting for low primary fibre diameter and high density and length of wool fibres. The breeding system was developed by Dr. Jim Watts, a research veterinarian who specialises in skin and fleece biology. It is based on Moore’s pre-papilla cell hypothesis of follicle formation and fibre growth (Moore, 1984; Moore et al, 1989, 1996, 1998; Wynn et al, 2010).

By selecting sheep this way, exceptional wool quantity and quality, processing performance and end product quality are realized.

Low primary fibre diameter ensures that more of the pre-papilla cells are channelled into producing more wool follicles on the animal's body.

High fibre density occurs when there are many wool follicles populating each follicle group in the sheep’s skin, and these follicle groups are packed closely together. When this happens, the wool fibres become highly aligned, evenly sized and are visible in the fleece as multitudes of “fibre bundles”, each growing from a follicle group in the skin.

High fibre length is expressed most clearly in fleeces that have high crimp amplitude (deep crimp) and low crimp frequency (bold crimp).

The sheep in SRS® Merino flocks are plain-bodied with wrinkle free skins. The animals are never mulesed. We are selecting for naturally short tails so that the sheep do not need to be tail docked.

Figure 1. SRS® Merino rams (recently shorn) in a commercial Merino flock at Brewarrina, New South Wales, Australia. photo: courtesy of The Land newspaper, Rural Press Group.

The SRS® breeding system has designated selection protocols and specific animal and fleece standards that are quantifiable at both genetic and phenotypic levels. The breeding system has been applied to Merino flocks, alpaca herds (www.srsalpacas.com), and Angora goat herds in Australia, New Zealand and Europe.

The Fleece and Skin

Figure 2. SRS® sheep are totally plain-bodied.

The wool on the underside of the neck drapes freely without any horizontal skin wrinkles or folds. There is also no skin wrinkling over the poll (no 'broken poll'), topside of the neck (no 'collars'), body trunk (no 'tiger stripes'), topline (no 'scribble'), tail (no 'fan tails') and no cross-folds down the back legs.

The fleece surface is distinctive (Figure 3). It is long and floppy, deeply crimped and lustrous. Staples are replaced by 'fibre bundles'. The ends of the fibre bundles are very thin, about 1.5 millimetres in diameter (equivalent to the width of the follicle group in the skin), and remarkably uniform in size over the entire fleece surface.

Figure 3. The fleece surface has a 'moppy' and lustrous appearance formed by the ends of very long fibre bundles.

On parting the fleece of an SRS® sheep, a densely packed arrangement of very long and thin fibre bundles is seen (Figure 4).

Figure 4. SRS® sheep have fleeces characterised by high density of fibre bundles and high numbers of fibres per bundle. This adult animal grew 150 millimetres of 19.5 microns wool for 10 months wool growth.

The fleece is: very soft with a resistance to compression of no more than 6.5 kilopascals; adequately nourished with a wax content between 15% to 20% of clean wool weight; white in colour with a suint content no greater than 3% of clean wool weight; lustrous; and has a high crimp amplitude with a fibre length to staple length ratio of greater than 1.3 to 1; and a low crimp frequency of no more than 3.0 crimps per centimetre.

At least 80% of the fibres are circular in cross-section with a mean scale height of no more than 0.3 microns and a mean scale length of no less than 12.0 microns. The orthocortex comprises 40% to 50% of the fibre volume.

The skin is able to be extended manually using gentle force by at least 5.0 centimetres (Figure 5).

Figure 5. The thin and loose skin of an SRS® sheep.

The skin of an adult SRS® sheep has at least 85.0 wool follicles per square millimetre and wool fibres that grow, on average, at the rate of at least 0.50 millimetres per day.

The mean diameter of the primary fibres is 2.0 to 6.0 microns finer than that of the secondary fibres. Secondary fibres do not exceed a mean diameter of 20.5 microns and have been observed to be as fine as 10.5 microns in individual animals. The standard deviation of fibre diameter does not exceed 3.0 microns for either fibre population.

The wool follicles in the skin of SRS® sheep are closely packed, highly aligned and evenly seated but never deeply seated (Figure 6).

Figure 6. Vertical skin section (magnified view) of the ordely and closely packed wool follicles and fibres of an SRS® Merino sheep.

Conventional Merinos have a mean primary fibre diameter that is similar to or up to 4.0 microns coarser that that of the secondary fibres. Wool follicle density is, on average, about 55 wool follicles per square millimetre and mean fibre length is about 0.30 millimetres per day. The wool follicles are usually deeply seated in the skin as a consequence of the skin being thick (see Figure 9).

Important Biological Considerations

For both density and length to increase in tandem, and reach the exceptionally high levels that are achievable, the sheep’s skin can not be thick. The skin must be thin and loose. When the skin is thin, the animal is plain bodied and free of wrinkle, thereby being naturally resistant to fly strike and not mulesed.

These biological relationships are critically important to understand and to observe when designing and implementing Merino breeding programs. Two key factors to recognise are:

1. that there is a strong and negative genetic correlation between fleece length and breech (and body) wrinkle. In other words, if Merino sheep are bred for long wools, the animals will be plain bodied (free of skin wrinkle) and will not need to be mulesed to protect them from fly strike. Conversely, if Merino sheep are bred for short wools, the animals will be wrinkly and susceptible to fly strike. This, in turn, has meant that sheep are being mulesed to prevent fly strike in countries like Australia where the blowfly pest is found.
   
   For many years, Merino producers worldwide, and especially those breeding fine wools and superfine wools, have bred high crimp frequency wools (Figure 7), usually in the belief that such wools are fine in diameter, have high spinning performance and produce end products of superior quality. However, the scientific evidence is to the contrary.
   
   
   
   Figure 7. High crimp frequency of low crimp amplitude wool at 16.0 microns.
   
   
   
   Figure 8. Low crimp frequency wool with high crimp amplitude at 16.0 microns.
   
   High crimp frequency is an unreliable indicator of fibre fineness (Bosman, 1934; Lang, 1944, 1947,1961). Bastawisy et al (1961) found that high crimp frequency wool did not spin as well as wool of the same diameter with lower crimp frequency. Lipson and Walls (1962) also showed that wool with fewer crimps per inch processed better and produced better cloth. In more recent work, Stevens (1994) and Stevens and Crowe (1994) showed that wools of low crimp frequency and high crimp amplitude make tops of 8 to 16 millimetres longer Hauteur, with approximately half the noil and card waste of wools of finer and less defined crimp – these beneficial effects of low crimp frequency and high crimp amplitude were found to be separative and additive.
   
   Yang (1993) and Lamb and Yang (1996) showed that longer Hauteur tops spin more efficiently and produce yarns that are more even and break less often. McGregor and Postle (2002, 2006) found that fabrics produced from low crimp frequency superfine wool were thinner, more compressible (softer), lighter and more permeable and had greater spirality, and less pilling compared with fabrics produced from high crimp frequency superfine wools. McGregor and Postle (2008) also showed that the physical properties of low crimp frequency superfine wool fabrics were closer to the properties of pure cashmere fabrics than were knitted fabrics made from high crimp frequency superfine wool.
   
   The indicators are that if Merino producers breed sheep with longer wool, that wool will process more efficiently and make better quality end-products whilst the animal will produce more wool, will be plain-bodied, free of breech wrinkle and likely to be naturally resistant to fly strike.
   
   
2. that the genetic regulation of fibre diameter differs between primary wool follicles and secondary wool follicles in the sheep’s skin.
   
   Selection experiments have shown that when sheep are bred for increased follicle depth (mimicking thick skins), the primary fibres increased markedly in diameter (by about 3 to 4 microns), wool follicle density decreases and secondary fibre diameter remains largely unchanged. As a result, the sheep are born with “hairy birthcoats”, and grow fleeces that are harsh handling, yellow from high suint content and susceptible to fleece rot and fly strike.
   
   

Figure 9. Vertical skin section (magnified view) of the disorderly and entangled arrangement of wool follicles and fibres in the skin of a thick skinned (wrinkly) Merino sheep.

A detailed explanation of the biological and genetic relationships that need to be considered is given in the Subscribers Section. Ignoring these relationships can lead to unacceptable breeding outcomes that can adversely affect the health, reproduction and welfare of Merino sheep.

The Animal

SRS® Merino sheep are long and deep bodied with a 'triple-wedge' shape (Figure 10).

The sheep have open faces with the wool margins ending at or behind the poll and behind the jaw. The muzzle is long, wide and deep often with a 'Roman nose' and has a smooth, silky and ripple free appearance. The nostrils are wide. The teeth are correctly aligned, long and chunky. In Merino rams, the horns are wide-set and deep, being well clear of the horns, and set wide of the face and curve below the jaw line.

The ears and neck are long. The shoulders are correctly positioned and not set forward. We strive for a loin length of about 60% of the body length (when measured from the shoulders to the point of the hips). Wide hindquarters with full muscling on the inside and outside of the thighs are important. The hindlegs are naturally curved and not straight. Wool ends at the hocks and knees and does not carry down to the points. Feet structure must be correct with no uneven wearing on the undersoles of the hooves. We look for no pigment on the face, ears, legs, perineum, and hooves. Belly wools need to be white and remain so on wet, long pastures.

Figure 10. SRS® Merino ram in 3 months wool.

Increasingly, we are breeding SRS® sheep with long ears and long necks (Figure 11). This is deliberate. Long ears, open faces and bare points appear to be adaptations to hot and humid environments which allow the sheep to cope better with low water intake than conventional Merinos do. The long necks and tall frame of the sheep also appear to assist the animal forage more efficiently, especially when feeding on tall plants under drought conditions.

Figure 11. Eight months old mixed sex Merino lambs in drought, note the long necks and long ears.

SRS® sheep all have wrinkle free breeches. This means that the animals are naturally resistant to breech strike and are never mulesed.

In addition, there are a high proportion of SRS® sheep with no wool growing on the crutch, scrotum, pizzle, and udder (Figure 12). This is an important genetic development for enhanced protection against fly strike which may eliminate the need for crutching.

Figure 12. Wool free zones have been bred on the crutch, scrotum, pizzle and udder of SRS® Merino sheep.

We have been breeding for naturally short tails. This has been done so tails do not need to be docked. Already we are seeing encouraging results (Figure 13).

Figure 13. SRS® Merino lambs (third and fourth from left) with naturally short tails and better muscular control alongside Merino lambs with long tails.

Maximising lamb numbers and minimising lamb losses

Our Merino flocks are now averaging weaning rates of 120% lambs. Some are as high as 160%. At the same time, we are reducing lamb losses to low levels (Figure 14).

Figure 14. SRS® Merino ewes with 8 week old lambs of high growth rate, high fat cover and good body muscling.

How have we set about achieving this in SRS® breeding flocks?

Briefly, it has involved:

* identifying the sires with minimal lamb losses in their progeny.

* identifying the ewes which rear multiple lambs repeatedly throughout life.

* breeding ewes which produce more milk and are able to nurture more lambs by having four (rather than two) milking teats (Figure 15).

* preferentially retaining and breeding from sheep with long, fine and soft birthcoats as lambs in order to ensure good protection of lamb progeny from rain, wind and cold (Figure 16),

* selecting sires and dams with high breeding values for: body weight at weaning; scrotal circumference; fat cover and eye muscle depth.

Figure 15. Breeding SRS® Merino ewes with 4 milking teats has lifted weaning percentage and weaning body weight by 10% to 15%.

Figure 16. These 5 month old SRS® Merino ram lambs were born with long, soft and fine outer coats, which provide excellent weather protection for the newborn lamb and are also an early indicator of high fibre density and length. This excellent trait is unfortunately mistaked by many Merino breeders as being undesirable.

High lifetime wool production

In 10 trials conducted across Australia, SRS® Merino sheep grossed $67 per fleece compared to $29 per fleece for non-SRS® Merino sheep, producing 10% more wool that was 2.5 microns finer. These results are shown in Figure 17.

Figure 17. Comparisons of fleece value, fibre diameter and fleece weight differences between plain-bodied SRS® Merino sheep and thick-skinned and wrinkly Merino sheep.

Figure 18 shows the exceptionally productive fleece that is produced on the plain-bodied SRS® Merino from an early age.

Figure 18. A nine month old SRS® Merino ewe (unshorn). Because SRS® Merino sheep are genetically equipped with high fibre density and length, the animals produce high fleece weights of fine diameter, high quality wool from early in life onwards Note that the fleece is already about 140 millimetres long.

Easy to shear

Figure 19. The plain bodies and no skin wrinkling of SRS® Merino sheep make them easy to shear.

No fly strike and minimal chemicals

The sheep are difficult to wet and dry rapidly, even during periods of prolonged and heavy rain. Consequently, fleece rot and body strike are rarely seen.

No body strike means no insecticides are needed as a preventative.

Our 40 studs can provide over 10,000 rams annually to breed millions of sheep that do not need to be mulesed.

Bounce back quickly after tough times

Being plain-bodied with good muscle patterning, high fat cover and reared with minimal supplementary feeding, SRS® Merino sheep bounce back quickly after drought and other stressful times, saving a fortune in handfeeding costs.

References

• Bastawisy, A.D., Onions, W.J. and Townend, P.P. (1961). Some relationships between the properties of fibres and their behaviour. Journal of the Textile Institute, 50, T1-20
  
  
• Bosman , V. (1934). Fibre fineness of S.a. Merino wool. Onderstepoort J. Vet. Sci. 3, 1, 223-231.
  
  
• Lamb, P.R. and Yang, S. (1996). Choosing the right top for spinning. In TOPTECH 96. Papers presented at Geelong, Australia, 11-14 November 1996. CSIRO Division of Wool Technology and International Wool Secretariat. Pp. 258-276.
  
  
• Lang, W.R. (1944). A survey of the fineness of Australian Merino wool. Publs Gordon Inst. Technol. No. 5
  
  
• Lang, W.R. (1947). Crimp-fineness relationship in Australian wool. J.Text. Inst. 38, T241-270.
  
  
• Lang, W.R. (1961). Fibre thickness, crimp frequency and quality number of Australian wool. Wool Technol. Sheep Breed. 8, 11-20.
  
  
• Lipson, M. and Walls, G.W. (1962). Processing of wool from a flock selected for high fleece weight. J. Text. Inst. 53, P416-422.
  
  
• McGregor, B.A., and Postle, R. (2002). Single yarn knitted fabrics produced from low and high curvature superfine Merino wool. Wool Tech. Sheep Breed., 50 (4), 691-697.
  
  
• McGregor, Bruce A. (2006). A comparison of the ICI Pillbox and the random tumble methods in assessing pilling and appearance change of worsted spun cashmere and cashmere-wool blend knitwear. International Journal of sheep and Wool Science, 54 (3)
  
  
• McGregor, B.A. and Postle, R. (2008). Mechanical properties of cashmere single jersey knitted fabrics blended with high and low crimp superfine Merino wool. Textile Research Journal 78, 399-411.
  
  
• Morley, F.H.W. (1955a). Selection for economic characters in Australian Merino sheep. V. Further estimates of phenotypic and genetic parameters. Aust. J. Agric. Res. 6, 77-90.
  
  
• Morley (1955b). Selection for economic characters in Australian Merino sheep. VI. Inheritance and interrelationships of some subjectively graded characteristics. Aust. J. Agric. Res. 6, 873-881.
  
  
• Moore, G.P.M. (1984). Growth and development of follicle populations and critical stages of growth. Proceedings of a seminar on wool production in Western Australia. (ed. S.K. Baker, D.G. Masters and I.H. Williams). Australian Society of Animal Production (WA Branch).
  
  
• Moore, G.P.M., Jackson, N. and Lax, J. (1989). Evidence of a unique developmental mechanism specifying both wool follicle density and fibre size in sheep selected for single skin and fleece characteristics. Genet. Res. Camb. 53, 57-62.
  
  
• Moore, G.P.M., Jackson, N., Issacs, K., and Brown, G. (1996). Development and density of wool follicles in Merino sheep selected for single fibre characteristics. Aust. J. Agric. Res. 47, 1195-1201.
  
  
• Stevens, D. (1994). Handle: Specification and Effects. In WOOLSPEC 94. Specification of Australian wool and its implications for marketing and processing. Papers presented at the seminar held by CSIRO Division of Wool Technology and International Wool Secretariat. Sydney, 23-24 November 1994. Pp. H1-H10.
  
  
• Stevens, D. and Crowe, D.W. (1994). Style and processing effects. In WOOLSPEC 94. Specification of Australian wool and its implications for marketing and processing. Papers presented at the seminar held by CSIRO Division of Wool Technology and International Wool Secretariat. Sydney, 23-24 November 1994. Pp. E1-E12.
  
  
• Turner, H. N. (1958). Relationships among clean wool weight and its components. Aust. J. Agric. Res. 9 (4), 521-552.
  
  
• Wynn, P.C., Watts, J.E., Thomson, P.,and Moore, G.P.M .(2010). Analysis of fleece and wool follicle traits of sheep selection based on visual markers (in preparation).
  
  
• Yang, S. (1993). The effect of fibre length distribution on yarn evenness and tensile properties. Restricted Investigation Report, CSIRO Division of Wool Technology, Ryde”

Further reading:

• Ferguson, Ken. (1995). The evidence for selecting sheep the Watts way. Australian Farm Journal WOOL. November issue. pp. 28-31.
  
  
• Ferguson, Ken and Watts, Jim. (1999). Biology of the SRS Merino package. Australian Farm Journal WOOL, May issue. pp. 22-23.
  
  
• Ferguson, K.A., and Watts, J.E. (2000). Index measures productivity of wool growing enterprise. Australian Farm Journal. September issue. pp. 67-69.
  
  
• Francis, Pat (1994). Get skin right and wool cut follows. Australian Farm Journal. December issue. pp. 12-15.
  
  
• Jackson, N., Lax, J., and Maddocks, I.G. (1988). Selection criteria for wool growth: significance of primary fibre types and their diameter distributions. In AWC review of CSIRO Division of Animal Production Project: Genetic and phsiological determinants of wool growth and quality. CSIRO Division of Animal Production.
  
  
• Watts, J.E., Nay, T., Merritt, G.C., Coy, J.R., Griffiths, D.A., and Dennis, J.A. (1980). The significance of certain skin characteristics in resistance and susceptibility to fleece-rot and body strike. Aust. Vet. J. 56, 57-63.
  
  
• Watts, J.E., Merritt, G.C., Lunney, H.W.M., Bennett, N.W., and Dennis, J.A. (1981). Observations on fibre diameter variation of sheep in relation to fleece-rot and body-strike susceptibility. Aust. Vet. J. 57, 372-376.
  
  
• Watts, Jim. (1990). Staple structure reflects wool quality. FARM. March issue. pp. 36-37.
  
  
• Watts, J.E. (2002). The Practical Guide to SRS® Breeding of Merino Sheep. (published by Esther Price Promotions and iikon). 23. pp.
  
  
• Watts, Jim. (2003). Celebrating SRS®. Australian Farm Journal / SRS® Company special publication. April issue. 37 pp.
  
  
• Watts, J.E. (1995a). Elite wool - from fibre to fabric. (WRIST and DPIE: Melbourne).
  
  
• Watts, Jim (1995b). The secret of wool cut quality. Australian Farm Journal WOOL. April issue. pp. 32-35.