Breech bareness

Crutching, dagging and mulesing are all ways of artificially producing a clean bare area in the breech, providing short and long term protection respectively. All of these practices are performed either for, or in part, to reduce the incidence of breech strike. Heath and Bishop (1995) found that 81.2% of flystrike in New Zealand occurred in the breech. Genetic selection for naturally increased bare area around the perineum is one possible alternative to the above practices.

Shedding breeds are naturally bare around the breech and belly, and are less susceptible to flystrike compared to full wool breeds. Reductions in breech strike incidence have been shown in Merinos crossed with Wiltshire Horn sheep in Australia as shown above in section 1.4.1 (Rathie et al., 1994). As the percentage of Merino increased so did flystrike incidence; lowest in 1/2 Merinos (mean 8.45%) compared to 5/8 (mean 17.18%) and 3/4 Merinos (mean 50.43%). This correlated to increasing fleece weight due to less shedding of the wool around the breech, belly and points in crosses with increasing Merino percentage (Rathie et al., 1994). In a comparable New Zealand study, the shedding feral Merino had lower incidence of flystruck lambs compared to the full wool Merinos (0 vs 33%) (Litherland et al., 1992). The shedding feral Merino and Wiltshire also accumulated significantly less dags than the Romney and Merino.

Breech bareness is the area of naturally bare skin around the perineum, and is scored on a 1 to 5 scale (Figure 1.5). Breech bareness is heritable, and current estimates range

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from 0.33 to 0.35 (Scobie et al., 2007, 2008). An easy-care sheep resource flock has been established with a breeding goal to produce a polled sheep with no wool on the head, legs, belly, and breech, and with a short tail (Scobie et al., 1999). Using this resource, the genetic parameters for breech bareness, dags, and flystrike incidence have been estimated (Scobie et al., 2007; Scobie et al., 2002). Heritabilities for breech bareness and dag score were estimated at 0.33±0.06 and 0.37±0.07 respectively. Breech bareness had a negative phenotypic and genetic correlation with dag score; -0.17 ±0.02 and -0.3 ±0.13 respectively (Scobie et al., 2007).

Figure 1.5: Breech bareness scoring system: 1: fleece cover extends to margins of anus, to 5: an extensive bare area either side of the anus. As proposed by Sheep Improvement Limited (www.sil.co.nz/getdoc/a9bb121b-2016-4b34-a163-399ae4b28471/Doc-ID-000010- GW-Bare-Points-Sheep.aspx).

These results have been reported in two New Zealand composite flocks (Scobie et al., 2008). In a Romney based composite, phenotypic and genetic correlations between breech bareness and dag score were -0.18 ± 0.02 and -0.44 ± 0.12, respectively. For a Perendale based composite, the correlations were -0.27 ± 0.03 and -0.72 ± 0.09 respectively. Heritabilities for breech bareness were 0.35 and 0.61, respectively for the Romney and Perendale based flocks. For dag score, heritabilities were 0.31 and 0.34, respectively (Scobie et al., 2008).

Scobie et al. (2002), in their resource flock, showed that as breech bareness increased, the proportion of flystruck lambs decreased. For a breech bareness of 1: 22% lambs were struck post-weaning. This was reduced to 16%, 11% and 0% as bareness increased from score 2 to 4. By breed, no Wiltshires were struck, 6% of Finn x Dorset Down, 21% of Finn x Romney and 12.5% of Feral Merino x Merino lambs were struck.

53 Mulesing, crutching and dagging are labour intensive practices, to artificially increase the bare patch around the anus. Crutching and dagging are also only temporary and needs to be repeated at least 3 times a year. Mulesing is permanent but ethically questionable. Natural breech bareness has been shown to be moderately heritable, and thus is an alternative tool that can lead to a permanent bare patch in the breech. This will result in reduced need for crutching, dagging, dipping, and drenching to control dags.

1.4.2.3 Wool type

Since domestication, a number of wool breeds have emerged. Wild type fleece was light, and consisted of coarse long fibres forming an outer coat and short fine fibres forming the inner coat (Henderson, 1968). They also tended to shed their coats in summer. From this base, animal selection was made for increased wool growth, around 5 to 10 times more (Henderson, 1968). Secondly, via selection for a uniform fleece, the separation of the inner coat and the outer coat is now no longer identifiable (Henderson, 1968). Thirdly, via selection for the diameter and number of fibres (Henderson, 1968), some breeds have been selected for their fineness (Merinos), others for medium and strong wool for use in carpets and other apparel (Romney, Drysdales). There are still breeds that more closely resemble their ancestors in fleece type, including the Wiltshire and Dorset Horn. However, the selection away from the wild-type fleece has introduced a number of problems including, wool staining, dermatophilosis, fleece rot, and flystrike.

The fleece has its own microclimate, with its own relative humidity and temperature (Henderson, 1968). The architecture and structure of the fleece affect wetting and drying processes of the fleece, and the nature of the microclimate. Wetting of the fleece and presence of water droplets contained within the spaces between staples increases the relative humidity of the microclimate (Henderson, 1968). In a fleece with compact distinct staples, the fleece can dry quickly. However, a fleece that has irregular fibre size and crimp and no defined staples may resemble a confused mass of fibres or become cotted (Henderson, 1968). This type of fleece takes longer to dry out; thus causing wool stains. Another feature of the fleece that is important is termed wool ‘yolk’ (Henderson, 1968). This substance is made up of the wool wax, that when purified is known as lanoline, and suint which consists of mainly dried sweat. The wax helps provide a waterproofing effect on the fleece (Hayman, 1953), while the suint proportion contains nitrogenous material and potassium salts, that influence the growth

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of bacteria (Henderson, 1968). It is the combined effect of all these fleece features: microclimate, architecture and structure that influence the growth of microorganisms that lead to conditions such as fleece rot, dermatophilosis and flystrike.

1.4.2.3.1 Fleece rot

Fleece rot is a consequence of prolonged wetting of the fleece, leading to the breakdown of the wax layer on the skin (McGuirk et al., 1978). The skin, sensitive to moisture, exudes serous material which forms horizontal bands within the fleece, yellow in colour and containing hard brittle material (Henderson, 1968; McGuirk et al., 1978). Bacterial growth within the serous material contributes to the colourful staining associated with fleece rot. The bacterium Pseudomonas aeruginosa is the most common

organism associated with fleece rot (Norris et al., 2008). Other pseudomonads have also been implicated (Australian Wool Innovation and Meat Livestock Australia, 2007; Norris et al., 2008). It is unusual for fibres to become rotten (Henderson, 1968), but if there is a failure of keratinisation in the wool follicle, breaks can occur (McGuirk et al., 1978).

Between family differences in susceptibility to fleece rot have been observed in Merino strains (Dunlop and Hayman, 1958; Hayman, 1953). Heritability estimates for fleece rot range between 0.14 and 0.33 (Atkins, 1979; Li et al., 1999; McGuirk and Atkins, 1984; Mortimer et al., 2009). Correlated responses with production traits include; negative phenotypic and genetic correlation with mean fibre diameter (Li et al., 1999; Mortimer et al., 2009), low phenotypic and a low to moderate genetic correlations with greasy fleece weight and clean fleece weight (Li et al., 1999; Mortimer et al., 2009). Wool colour has high genetic (0.47) and moderate phenotypic (0.18) correlations with fleece rot incidence (Li et al., 1999). All these results imply reduced fleece rot is associated with decreased fleece weight, increased fibre diameter, and brighter whiter wool.

The Trangie research flock was the largest resource focusing on fleece rot and body strike as outlined previously (McGuirk et al., 1978). After a decade, a subset of the animals were used to estimate susceptibility to body strike between 1984 and 1986 (Raadsma, 1991b). Prevalence rates of fleece rot and body strike in each line were 75.8% and 11.3%, respectively, for resistant and 83.3% and 20%, respectively, for susceptible lines. Body strike was only observed in animals with fleece rot (Raadsma,

55 1991b). After 17 years of selection, the lines had diverged at a rate of 2.8% and 0.4% per annum for fleece rot and body strike respectively (Mortimer et al., 1998).

Fleece rot is correlated to body strike, especially in Australian Merinos, and significant gains can be made in both traits when fleece rot is incorporated into a selection program. In New Zealand, fleece rot is not as prevalent, thus selection for fleece rot will not produce the same effect on body strike. However, the processes that lead to fleece rot, humidity and bacterial growth, are implicated in the attraction of flies to the fleece.

1.4.2.3.2 Dermatophilosis

Mycotic dermatitis or dermatophilosis as it is now known is also caused by prolonged wetting. It involves the zoospores of a fungi Dermatophilus dermatonomous

(Henderson, 1968; Norris et al., 2008). The disease starts after transmission of the zoospores, free-moving fragments of the mycelium, to the skin (Henderson, 1968). At the skin surface the zoospores develop into the mycelia form. At this stage the skin is tender, red and has a slight swelling. A dome like scab forms as the skin hardens and dries. Beneath the scab the mycelia thrive in the low oxygen environment and exudate is secreted from beneath the scab (Henderson, 1968). The exudate binds the fibres together in pencil like clumps perpendicular to the skin.

The wax content of the fleece with its waterproofing ability is the main barrier to this disease (Roberts, 1963). Removal of the wax layer with petroleum allowed the initiation of dermatophilosis by the zoospores. Outbreaks of the disease also occurred in Merinos soon after birth or shearing, when wax levels are low (Roberts, 1963).

There has been little research done into the genetic component of this disease. Raadsma et al. (1992) investigated induced dermatophilosis in Merinos. Preliminary analysis estimated heritability for scab severity at high dose of 0.25 and heritability at a low dose of 0.42. This study also noted the results of previous work, heritability of liability to induced dermatophilosis of 0.14 (Raadsma et al., 1992). Surveys in Western and Southern Australia observed an association between body strike and dermatophilosis (Gherardi et al., 1983). Laboratory results found L. cuprina were

attracted to, and deposited eggs on, dermatophilosis lesions. These results were repeated in a field experiment where more strikes occurred on animals affected by dermatophilosis than by fleece rot or on unaffected controls (Gherardi et al., 1983).

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1.4.2.3.3 Summary

As outlined above, fleece rot and dermatophilosis, diseases of the fleece, are associated with flystrike. The odours produced by the leaking exudates, and the organisms involved in the two diseases attract the flies to deposit their eggs. However, flystrike can develop in the absence of these two diseases.

The main factor influencing flystrike is humidity. A period of high relative humidity is required for the successful hatching and survival of first stage larvae (Davies, 1948; Wall et al., 2001). Humidity builds up as a combination of the presence of moisture at the skin level and warm temperatures. This can be by rain, water, urine stain, faecal adhesion, or through sweat accumulation. Moisture entering the fleece can become trapped if body conformation prevents drainage down the sides of the animal, for example ‘devils grip’ the dip present behind the shoulder, and a flat broad back (Henderson, 1968). The resulting odour produced by the high humidity, be it due to bacterial growth, sweat, fleece rot, or dermatophilosis, provides an indication of the moisture and humidity levels of the fleece, optimal for egg viability and hatching. It is the ability of the fleece to reduce moisture accumulation, by body conformation and fleece structure that will be targeted for reduced flystrike susceptibility.