P. J. James

Genetic alternatives to mulesing and tail docking in sheep: a review

A genetic solution to breech strike control is attractive, as it is potentially permanent, cumulative, would not involve increased use of chemicals and may ultimately reduce labour inputs. There appears to be significant opportunity to reduce the susceptibility of Merinos to breech strike by genetic means although it is unlikely that in the short term breeding alone will be able to confer the degree of protection provided by mulesing and tail docking. Breeding programmes that aim to replace surgical techniques of flystrike prevention could potentially: reduce breech wrinkle; increase the area of bare skin in the perineal area; reduce tail length and wool cover on and near the tail; increase shedding of breech wool; reduce susceptibility to internal parasites and diarrhoea; and increase immunological resistance to flystrike. The likely effectiveness of these approaches is reviewed and assessed here. Any breeding programme that seeks to replace surgical mulesing and tail docking will need to make sheep sufficiently resistant that the increased requirement for other strike management procedures remains within practically acceptable bounds and that levels of strike can be contained to ethically acceptable levels.

Genetic parameters for wool production and quality traits in South Australian Merinos of the Collinsville family group

Heritabilities and phenotypic and genetic correlations for fleece traits were estimated from a data set comprising 805 male and female progeny of 44 sires of the Collinsville family group. Characteristics included in the study were greasy and clean fleece weight, yield, mean, standard deviation and coefficient of variation of fibre diameter, resistance to compression, scoured and greasy wool colour (expressed as yellowness, lightness and yellowness index), wax content, suint content, and subjectively assessed scores for greasy colour, character, handle, quality number, condition, staple formation, tip formation and density. Heritabilities of greasy and clean fleece weight, yield, mean fibre diameter and subjectively assessed fleece scores were in broad agreement with estimates from other Merino strains, but the genetic correlations of mean fibre diameter and associated characters (handle, quality number) with clean fleece weight were lower than previous estimates. Heritabilities for scoured yellowness of wool, resistance to compression and coefficient of variation of fibre diameter, which are potential additional measurements for the specification of wool in sale lots, were 0.42 (¦. 0.14), 0.57 (¦ 0.15) and 0.47 ( ¦ 0.15) respectively. Estimated heritabilities of wax and suint content were 0.24 (¦0.11) and 0.44 ( ¦ 0.14). Although the phenotypic correlations between measures of greasy wool colour and the corresponding measures of scoured wool colour were low (less than 0.3), the genetic correlations were moderate to high (0.4-0.9). Thus selection on the basis of greasy wool colour should lead to genetic improvements in scoured colour. The genetic correlations of resistance to compression with clean fleece weight and fibre diameter were: 0.46 (¦0.21) and 0.44 (¦ 0.20) respectively, but there were no other strong, unfavourable correlations.

Insecticidal and repellent effects of tea tree (Melaleuca alternifolia) oil against Lucilia cuprina.

Laboratory studies were conducted to assess the effect of tea tree oil (TTO) from Melaleuca alternifolia (terpinen-4-ol chemotype) against different stages of the Australian sheep blowfly Lucilia cuprina. When applied to wool, 3% TTO formulation repelled gravid female L. cuprina and prevented oviposition for six weeks. Formulations containing 1% TTO caused 100% mortality of L. cuprina eggs and 1st instar larvae and 2.5% TTO caused mortality of most second and third instar larvae in agar feeding assays. In experiments where third instar larvae were dipped in TTO formulations for 60s, concentrations of up to 50% TTO gave less than 50% kill. TTO at concentrations of 0.5%, 2% and 5% was strongly repellent to third instar larvae and caused them to evacuate treated areas. Inclusion of TTO in formulations with diazinon, ivermectin and boric acid reduced mortality in comparison with the larvicides used alone, at least partially because of avoidance behaviour stimulated by the TTO. Addition of TTO to wound treatments may aid in wound protection and myiasis resolution by preventing oviposition by L. cuprina adults, insecticidal action against L. cuprina eggs and larvae, stimulating larvae to leave the wound and through antimicrobial and anti-inflammatory properties that aid in wound healing.

Seasonal dynamics and variation among sheep in densities of the sheep biting louse, Bovicola ovis

Cyclic patterns and variations among sheep in numbers of Bovicola ovis are described in Polypay and Columbia ewes that were initially infested with equal numbers of lice and penned indoors continuously for 2 years. Bovicola ovis populations were censused at 3-4-week intervals at 69 body sites on each animal. In the second year of the study, the ewes were reinfested and half were mated. Louse populations were monitored on the resulting lambs from birth until 25 weeks of age. Strong seasonal cycles in louse numbers were observed on the ewes, with peaks in spring and troughs in summer. These cycles occurred in the absence of shearing, direct solar radiation or rainfall. Populations began to decline when daily mean and maximum temperatures were 11.5 degrees C and 15 degrees C, respectively, well below temperatures thought to cause warm season decline. Louse densities on Polypay ewes were approximately 10 times higher than on Columbias at most inspections. There were also large differences among sheep within breeds and sheep counts were highly correlated among dates, both within and between years. One third of the ewes failed to become infested despite having lice applied on five separate occasions and being penned together with other infested sheep. Pregnancy and lactation did not significantly affect louse numbers on the ewes. There was a significant negative correlation between louse counts and weight gains in the lambs, and lamb counts were significantly correlated with those of their dams up until, but not after, weaning. It is suggested that sheep may exert regulatory influences on lice which contribute to cycles in B. ovis populations.

Lucilia cuprina genome unlocks parasitic fly biology to underpin future interventions

Lucilia cuprina is a parasitic fly of major economic importance worldwide. Larvae of this fly invade their animal host, feed on tissues and excretions and progressively cause severe skin disease (myiasis). Here we report the sequence and annotation of the 458-megabase draft genome of Lucilia cuprina. Analyses of this genome and the 14,544 predicted protein-encoding genes provide unique insights into the flys molecular biology, interactions with the host animal and insecticide resistance. These insights have broad implications for designing new methods for the prevention and control of myiasis.

Reduced efficacy of macrocyclic lactone treatments in controlling gastrointestinal nematode infections of weaner dairy calves in subtropical eastern Australia

Faecal Egg Count Reduction Tests (FECRTs) for macrocyclic lactone (ML) and levamisole (LEV) drenches were conducted on two dairy farms in the subtropical, summer rainfall region of eastern Australia to determine if anthelmintic failure contributed to severe gastrointestinal nematode infections observed in weaner calves. Subtropical Cooperia spp. were the dominant nematodes on both farms although significant numbers of Haemonchus placei were also present on Farm 2. On Farm 1, moxidectin pour-on (MXD) drenched at 0.5mg kg(-1) liveweight (LW) reduced the overall Cooperia burden by 82% (95% confidence limits, 37-95%) at day 7 post-drench. As worm burdens increased rapidly in younger animals in the control group (n=4), levamisole was used as a salvage drench and these calves withdrawn from the trial on animal welfare grounds after sample collection at day 7. Levamisole (LEV) dosed at 6.8mg kg(-1)LW reduced the worm burden in these calves by 100%, 7 days after drenching. On Farm 2, MXD given at 0.5mg kg(-1)LW reduced the faecal worm egg count of cooperioids at day 8 by 96% (71-99%), ivermectin oral (IVM) at 0.2mg kg(-1)LW by 1.6% (-224 to 70%) and LEV oral at 7.1mg kg(-1)LW by 100%. For H. placei the reductions were 98% (85-99.7%) for MXD, 0.7% (-226 to 70%) for IVM and 100% for LEV. This is the first report in Australia of the failure of macrocyclic lactone treatments to control subtropical Cooperia spp. and suspected failure to control H. placei in cattle.

Do sheep regulate the size of their mallophagan louse populations

Alternatives to chemicals for controlling parasites are required to minimise problems from resistance, residues in animal products and occupational exposure. Utilisation of host response to parasites through selection of resistant types or vaccination is an appealing option. To date most studies have been with haematophagous or invasive parasites which directly contact elements of the host immune system. Sheep lice (Bovicola ovis) feed superficially on the skin of sheep ingesting lipid, scurf, bacteria and loose stratum corneum squames. Evidence is presented that despite their surface feeding habit Bovicola ovis stimulate an immune response in sheep and that this response may play a part in regulating the size of louse populations.

Resistance to insect growth regulator insecticides in populations of sheep lice as assessed by a moulting disruption assay.

Abstract Low‐volume, backline applications with the benzoylphenyl urea insecticides triflumuron and diflubenzuron represent in excess of 70% of treatments for the control of sheep lice, Bovicola ovis (Schrank) (Phthiraptera: Trichodectidae), in Australia. Reports of reduced effectiveness from 2003 and subsequent controlled treatment trials suggested the emergence of resistance to these compounds in B. ovis populations. A laboratory assay based on the measurement of moulting success in nymphs was developed and used to assess susceptibility to diflubenzuron and triflumuron in louse populations collected from sheep where a control failure had occurred. These tests confirmed the development of resistance to triflumuron and diflubenzuron in at least two instances, with estimated resistance ratios of 67–94X at LC50.

Pruritis and dermal response to insect antigens in sheep infested with Bovicola ovis

This study examined the relationships among louse density, pruritus and dermal response to insect antigens in sheep infested with Bovicola ovis. Polypay and Columbia ewes were allocated to two groups, infested and naive, and louse densities and pruritus were monitored for 15 months. Ten months after the initial infestation, all sheep were tested for hypersensitivity on the midside and ears by intradermal injection of soluble extracts of B. ovis, Stomoxys calcitrans and Musca autumnalis. The areas of skin reactions were measured at 20 min, 1, 3 and 24 h after injection and skin thickness was measured at 24 h. Louse densities on Polypays were approximately 10 times greater than on Columbias, and pruritus was correlated with louse numbers at most inspections. Most pruritic behaviour was directed to the sides of infested sheep. Wheal and flare reactions developed rapidly to all extracts in both infested and naive ewes. Reactions to louse extract were larger in infested than naive sheep at all four times after injection. In the infested Polypays, reactions to louse extract were greater than to the fly extracts, but in naive sheep there was little difference among extracts. Reactions in naive Columbias were larger than in naive Polypays at 20 min, 1 and 3 h, but had almost completely abated in both groups at 24 h. Reactions in infested Columbias were greater than in infested Polypays at 20 min, but at 24 h reactions in the Polypays were larger. Louse numbers and pruritus were correlated with wheal areas and skin thickness at 24 h, but there was little relationship with the size of reactions at earlier times. These findings are consistent with the development of a hypersensitive response to B. ovis and suggest that dermal reactions to lice may influence sheep susceptibility.

Spatial distribution and spread of sheep biting lice, Bovicola ovis, from point infestations.

The spatial distribution of chewing lice (Bovicola ovis) on their hosts was examined in Polypay and Columbia ewes initially artificially infested on the midside or the neck. Densities of lice were determined at 69 body sites in eight body regions at approximately monthly intervals for 2 years. In the second year, half of the ewes were mated and lice were counted at 26 body sites on the resulting lambs. Polypay ewes had higher densities of lice than Columbias at most inspections but there was little effect of infestation point or mating on either numbers or the distribution of lice. During periods of high louse numbers densities were generally greatest on the sides or the back. Densities on the head were also high at times and peaked later than overall louse densities. Shearing markedly reduced density but increased the proportion of lice found on the neck, belly and lowleg sites. The distribution of lice on the lambs was similar to that on the ewes except that fewer lice were found on the head. Comparisons of lice per part with the numbers of lice extracted from clipped patches indicated that a sheep with wool bearing area of 1 m2 and a mean count of one louse per 10 cm fleece parting carried approximately 2000 lice. At most times of the year inspections for sheep lice should be concentrated on the sides and back, but in recently shorn sheep greater attention should be paid to the lower neck and ventral regions. Implications of the observed distributions of lice for the efficacy of chemical treatments are discussed.