The Skin Story
The Skin Story: the elephant in the room
Most of the Merino sheep in Australia have thick and wrinkly skins and have been that way since at least 1880.
There has been no concerted effort to remove this genetic fault, which brings with it the animal welfare concerns of mulesing, stressful shearing and too many lambs dying. It has made the Merino sheep susceptible to fly strike and unsuitable for thriving in the environment in which it lives.
Merino sheep types
There are two types of Merino sheep in Australia: the classic wrinkly Merino sheep and the plain bodied Merino sheep, Skin Figure 1.
Skin Figure 1: The classic wrinkly (left) and plain bodied (right) Merino types, recently shorn. Both sheep produce similar fleece weights (6.0 and 6.2 kilograms respectively at the same fibre diameter (18 microns).
The classic wrinkly Merino sheep has been selected for large skin surface area as the means of increasing fleece weight. It represents about 90 % of the Merino sheep population in Australia. It presents major animal welfare concerns. The sheep are mulesed to prevent breech strike but remain highly susceptible to body strike in wet summers. The sheep are difficult to shear, are inefficient feed converters, and appear to suffer from heat stress and dehydration in hot environments. The ewes have at least 20 % fewer lambs and lose more lambs than plain bodied Merino sheep do. It is the elephant in the room.
And there is the plain bodied Merino sheep. Among this type, the one bred specifically for high fibre density and length ( to deliver high wool per unit area of skin whilst slightly increasing skin surface area) is known as the SRS Merino. It represents about 10 % of the Merino sheep population of Australia. This sheep type has been bred using new technology and breeding methods introduced and established as industry practice by Dr. Jim Watts in the 1990s.
The SRS Merino is a highly profitable animal. Typically, it generates a gross margin of $72 per dry sheep equivalent, compared with $28 per dry sheep equivalent for the classic wrinkly Merino, Skin Figure 2.
Skin Figure 2: Gross margin comparison for current Glenwood ewes (centre) and future (right) with performance of traditionally bred Merino flocks (left)
The SRS Merino is naturally resistant to all forms of fly strike. It does not need to be mulesed. It is easy to shear. It has more lambs and rears more lambs, and survives and thrives well in climate extremes. From each fleece approximately 30 % more yarn of 25 % lighter weight, and therefore of far greater textile worth, can be produced, Skin Figure 3.
Skin Figure 3: Predicted spinning performance of SRS wool and other wool types. Source: P. Swan, 1996.
Breaking the fleece weight myth
It is important to realise that wrinkly Merino sheep are not needed to produce high fleece weights.
Plain bodied Merino sheep produce as much wool as wrinkly sheep. This was reported a long time ago (Belschner et al 1937). The researchers commented that, “contrary to opinions frequently expressed, there was very little difference between the wool production of the two types”. They re- ported that the wool quality was better on the plain bodied sheep.
Dr. Jim Watts first developed and implemented the SRS breeding system, the breeding of plain bodied sheep, in Australian Merino flocks, commencing in 1988. The Merino studs, Gowandale and Wallaloo Park in the Wimmera district of Victoria, Australia, were among the first to engage. At Gowandale in 1987, the ewe flock averaged 7.8 kilograms for greasy fleece weight and 23.5 microns for fibre diameter. By 1994 the corresponding values were 9.5kg and 21.3 microns. At Wallaloo Park the five-year averages for ewes from 1983-87 were 7.5kg and 22.2 microns, for 1990-94 were 8.6kg and 21.1 microns and for 1994 alone 9.1kg and 20.7 microns.
In 1995, a more detailed comparison of the fleece and skin traits of the two Merino sheep types, the SRS Merino and semi SRS Merino, was made on the ewe hoggets at Wallaloo Park (see Table 1).
In this comparison, the SRS Merinos produced an average of 0.9 kg more clean wool, and were 1.3 microns finer. The SRS Merino sheep were measurably denser, longer and had finer primary fibres (mean 19.2 microns) than the wool semi SRS Merino sheep (mean 22.5 microns).
Table 1: Differences in wool follicle and fibre properties of Merino ewes, 20 months old, visually selected as SRS Merinos and semi SRS Merinos (35 sheep per group; source: Brown, 1995).
|Trait||SRS Merino||Semi SRS|
|Clean fleece weight (kgs)||6.6 a||5.7 b|
|Fibre diameter (microns)||20.4 a||21.7 b|
|Fibre length ( 8 months wool growth mm)||90.6 a||79.3 b|
|Follicle density (per mm2)||83.5 a||73.2 b|
Footnote: means with different superscripts in the same row differ significantly (P < 0.05).
In the period, 1995 to 2000, Dr. Watts conducted “blind test” demonstrations at 10 workshops across Australia comparing the fleece weights, fibre diameter and fleece values of SRS Merinos and classic wrinkly Merinos in the same flocks. SRS Merinos grossed $67 per fleece compared with $29 per fleece for traditionally selected sheep, producing 10% more wool that was 2.5 microns finer. Examples of these demonstrations are shown in Table 2.
Table 2: Impact of SRS selection on greasy fleece weight, wool yield and fibre diameter in demonstrations across Australia.
|Sheep type||Fleece weight (kgs)||Wool yield (%)||Fibre diameter (microns)||Fleece length (mm)|
|Bullaring, Western Australia, 1998 (40 wethers per type):|
|Dubbo, New South Wales, 1999 (6 ewes per type):|
|Cooma, New South Wales, 2000 (9 ewes per type):|
|Cooma, New South Wales, 2001 (5 ewes per type):|
|Badgingarra, Western Australia, 2000 (6 ewes per type)|
The subjective indicators of loss of wool quality are well known, viz : “hairy birth- coat” lambs, harsh handling wools, loss of crimp definition etc.Table 2: Impact of SRS selection on greasy fleece weight, wool yield and fibre diameter in demonstrations across Australia.
There is also a very sensitive measurement called Dp/Ds ratio. It is the ratio of primary fibre diameter (Dp) to secondary fibre diameter (Ds) of the sheep. Wools of low quality have high Dp/Ds ratios eg. 1.2 to 1 or higher. It signifies that the sheep are regressing genetically toward the primitive, two-coated animals (Jackson et al, 1988). Conversely, wools of high quality have low Dp/Ds ratios eg. 0.8 to 1 or less.
Selection of Merino sheep for deep seated wool follicles (aka thick skin; Jackson et al, 1988) showed that within 3 generations, the lambs developed “hairy” birthcoats and grew yellowish, harsh handling wools that predis- posed the sheep to fleece rot and fly strike.
The primary wool fibres were much coarser in diameter (Dp of 25.7 microns) than the secondary wool fibres (Ds of 20.5 microns). The Dp/Ds ratio averaged 1.25 to 1.
Dr. Harold Carter’s survey of unclassed ewe hoggets from leading Merino studs in Australia from 1947 to 1953 showed that Dp/Ds ratios averaged 1.31 to 1, 1.29 to 1 and 1.13 to 1 for strong wool, medium wool and fine wool studs respectively.
Watts and Ferguson’s survey from 1988 to 1994, of Merino sires used in 120 studs across Australia revealed Dp/Ds ratios of traditional stud flocks averaged 0.95 to 1, 0.94 to 1 and 0.98 to 1 for strong wool, medium wool and fine wool flocks. The SRS Merino studs being developed at the time, had lower Dp/Ds ratios, averaging 0.86 to 1, 0.92 to 1 and 0.74 to 1 for strong wool, medium wool and fine wool flocks
Crooks et al (1997) reported an average Dp/Ds ratio of 1.21 to 1 for 563 unclassed ewe hoggets from 28 Peppin Merino studs in New South Wales. The average standard deviations of fibre diameter was high for both the primary fibres (6.15 microns) and the secondary fibres (5.62 microns). It is clear that medium wool Merino studs had not reduced the Dp/Ds ratios of their stud ewes to any appreciable extent to that reported by Carter (Dp/Ds ratio averaging 1.29 to 1) 50 years earlier.
Sutton et al (1995) reported that in wrinkly Merino sheep the wool grown on wrinkles was 0.7 microns greater, more variable in diameter, shorter and less dense than the wool grown between the wrinkles, that is, wrinkly Merinos produce poor quality wool.
At the present time, Dp/Ds ratios of SRS Merino rams and ewes have fallen further than the average 0.84 to 1 reported in 1994, now averaging 0.70 to 1.
Fertility and lamb survival
Numerous research trials, dating back as far as the 1950s, have shown that wrinkly Merino sheep have fewer lambs and lose more lambs than plain bodied Merino sheep.
Dun (1964) compared the net reproductive rate of Merino sheep for nine joinings (1951 to 1960) of “ single character” selection flocks – Folds Plus (selection for high skin wrinkle score) and Folds Minus (selection for low skin wrinkle score) – at Trangie in central western New South Wales. The net reproductive rate (the number of 19 month old replacement ewes produced by a ewe in her lifetime) was 1.25 for Fold Plus ewes and 2.3 for Folds Minus ewes.
The big difference in fecundity resulted from “the Folds Minus flock having a higher percentage of ewes wet and twins mothered, from it having lower mortality rates of young sheep between birth and mothering, between mothering and weaning, and between weaning and 19 months of age, as well as from it having lower death and casting rates of mature ewes”.
Reciprocal matings were carried out in 1961 and 1962 (Dun and Hamilton, 1965). “Folds Minus rams were more fertile than Folds Plus rams as shown by the ewes lambing per insemination (72 % versus 48 %) and by the incidence of twinning per ewe lambing (57 % versus 34 %).
Approximately 80 % of the difference in net reproductive rate between the Folds Minus and Folds Plus flocks were explained on the basis of the infertility of Folds Plus rams and excessively heavy birth weights of Folds Plus lambs.”
In 14 Merino flocks throughout New South Wales, plain bodied Merino sheep were shown to have at least 15 % more lambs than wrinkly Merino sheep (Drinan and Dun, 1965).
Fleece weight selection has been based traditionally on skin surface area (the breeding of wrinkly sheep) when it should have been, and now needs to be, based on fleece weight per unit area of skin (breed- ing for high fibre density and length on plain bodied sheep).
Choosing the second breeding option provides us with the opportunity to breed Merino sheep that produce more kilome- tres of lightweight yarn per fleece, as indi- cated in Dr. Swan’s mini-processing trial (Chapter 1).
It allows us to increase fleece weight in a sensible and considered way, without placing burdens on the animal’s comfort and well-being, and to stop mulesing. It also al- lows us to produce wool of exceptional quality and textile worth.
We simply do not have the right to “over- wool” sheep, compromise its fertility and survival and general well-being.
- Belschner, H.G. Carter, H.B. and Helen Newton Turner (1937a). “Fleece characteristics of stud Merino sheep in relation to the degree of wrinkliness of the skin of the breech”. Aust. Vet. J. pp. 16 -28.
- Brown, C. (1995) Why select sheep for soft rolling skin ? BSc (Hons) thesis, The University of New South Wales, November 1995.
- Crooks, B.J. and Purvis, I.W.(1997). Wool follicle traits in the NSW Peppin Merino Stud industry: preliminary estimates from a sample survey. Proc. Assoc. Advmt. Anim. Breed. Genet. 12, 158-162.
- Drinan, J.P. and Dun, R.B. (1965). Skin folds and Merino breeding. 3. The association between skin fold and the productivity of Merino ewes in fourteen New South Wales flocks. Aust. J. exp. Agric. Anim. Husb. 5 (19), 345-352.
- Dun, R.B. (1964). Skin folds and Merino breeding. 1. The net reproductive rates of flocks selected for and against skin fold. Aust. J. Agric. exp. Agric. Anim. Husb. 4:376-385.
- Dun, R.B. and Hamilton, B.A. (1965). Skin folds and Merino breeding. 2. The relative influence of the ram and the ewe on fertility and perinatal lamb mortality in flocks selected for and against skin fold. Aust. J. exp. Agric. Anim. Husb. 5 (18), 236 – 242.
- Jackson, N., Lax, J. and Maddocks, I.G. (1988). Selection criteria for wool growth: significance of primary and secondary fibre types and their diameter distributions. In Australian Wool Corporation Review of CSIRO Division of Animal Production project: Genetic and physiological determinants of wool growth and quality, September 8-9, 1988.
- Swan, P.G. (1996). The processing significance of various fleece types, unpublished notes.