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Context: Breech strike is a serious disease particularly in wool sheep. Skin wrinkle and dags are known predisposing factors for breech strike, although a large part of the variation between sheep is unexplained. Aims: We used sensor buttons to determine whether there were differences in humidity and temperature in the breech area of Merino sheep exposed to blowflies without traditional preventive measures being used in the flock. Methods: Sixty-two Merino rams and 62 Merino ewes that had high or low breeding values for breech strike were each fitted with a sensor button to record hourly temperature and humidity in the breech over 49 days. The sensors were fitted before the onset of the blowfly season. The sensor was tied to a wool staple close to the skin in the breech and was removed when a sheep was struck. All remaining buttons were removed prior to shearing. Breech wrinkle, neck wrinkle, breech cover and faecal soiling (dags) were recorded on all the sheep. A total of 98 213 hourly temperature and humidity records were analysed with cubic smoothing splines to assess how humidity and temperature differed between struck and unstruck sheep, and whether the breech indicator traits affect temperature and humidity in the breech. Results: Time of day and day-to-day variation prior to being struck explained most of the variation of temperature and humidity in the breech of the sheep. Humidity and temperature increased with an increase in breech cover. The humidity in the breech area was, on average, 2% higher in struck sheep prior to being struck. There was a sharp increase in humidity in struck sheep in the 8 days leading up to detection of breech strike relative to unstruck animals, most probably due to exudate from the wound. Conclusions: Sheep prone to be struck have higher humidity in the breech than sheep less prone to be struck. Implications: Temperature in the breech does not qualify as a potential indicator trait for breech strike in wool sheep, whereas humidity needs further research to determine its effectiveness as a potential indicator trait. Sheep were fitted with sensors to record hourly temperature and humidity in the breech over 49 days before the onset of the blowfly season. Sheep susceptible to breech strike had higher humidity in the breech than resistant sheep. Further studies needs to be undertaken to determine whether humidity may qualify as a potential indirect indicator trait to differentiate between sheep resistant and susceptible for breech strike. [ABSTRACT FROM AUTHOR]

The peri-parturient period is crucial for controlling worms as the acquired immunity of ewes is disrupted, resulting in an increase in faecal worm egg counts. Two hypotheses were tested in this experiment — that ewes bred for worm resistance would have lower faecal worm egg counts than unselected control ewes, during late pregnancy and lactation, under similar but separate grazing areas; and also that numbers of infective nematode larvae would be lower on pastures grazed by resistant ewes than pastures grazed by unselected control ewes. Faecal samples were collected from resistant and unselected ewes in late pregnancy and early lactation, during the winter rainfall season, and analysed for numbers of Trichostrongylus colubriformis and Teladorsagia circumcincta. Pasture samples were taken 1 week before and 7 weeks after lambing started and analysed for infective larvae. In all sheep, worm egg counts rose 2 weeks prior to lambing and continued into lactation. Worm egg counts were significantly lower in the resistant ewes from 1 week before lambing to 2 weeks after lambing. There were no differences in egg counts between single- and twin-bearing ewes in the resistant line. However, twin-bearing control ewes had significantly higher egg counts than single-bearing control ewes. Following lactation, plots grazed by resistant ewes had substantially less contamination with T. colubriformis larvae, but there were no differences in numbers of T. circumcincta larvae. Our results demonstrate that sheep bred for worm resistance has lower worm burdens during the peri-parturient phase and that lambs born to resistant ewes face a lower larval challenge during their introduction to grazing. In our environment, selection for low worm egg counts has produced sheep highly resistant to T. colubriformis, but has had less impact on resistance towards T. circumcincta. [ABSTRACT FROM AUTHOR]

Resistance of sheep worms against the available anthelmintic drenches is increasing. Breeding sheep for resistance against gastrointestinal parasites is the only long-term solution. Research has shown that breeding for worm resistance is a highly feasible option and that genetic gains of more than 2% per year can be achieved without loss of production. Replicated field trials in which resistant animals were managed separately from unselected control sheep showed that there was a 10-fold difference in worm egg counts between resistant and control ewes. Resistant ewes were 18% heavier than the controls at the time of peak worm-challenge in a Mediterranean environment. At weaning, there was a five-fold difference in worm egg counts between resistant and control lambs, which resulted in an improvement of weaning weight of up to 22%. It is therefore better to include selection for worm resistance in breeding programs than to omit it for fear of diminishing future genetic gains in other traits. [ABSTRACT FROM AUTHOR]

There is evidence of genetically determined host resistance mechanisms for most of the sheep parasites evaluated. The mechanisms vary; from no or reduced establishment, early expulsion, to suppression of parasites resulting in reduced size and fecundity. There is a need to integrate breeding for parasite resistance with the genetic improvement of production traits in farm animals, aiming for optimum solutions for potentially conflicting responses. Sustainable parasite control must be based on Integrated Parasite Management utilising an interdisciplinary approach., (Crown Copyright © 2012. Published by Elsevier B.V. All rights reserved.)

Immune-mediated scouring due to ingested parasite larvae is a major concern for sheep producers in Mediterranean climates. We investigated immune-mediated scouring in parasite-resistant Merino sheep in Australia. Forty-adult, parasite-resistant Merino rams were judged to be either susceptible or non-susceptible to immune-mediated scouring on the basis of dag scores taken under field conditions. We hypothesised that the susceptible rams would have lower faecal dry matter during larval challenge than non-susceptible rams and that, at post-mortem examination, inflammatory mediators and granulocytes would be negatively correlated with both faecal dry matter and worm numbers. In pens, the rams received a dose of 500 Teladorsagia circumcincta L(3) and 500 Trichostrongylus colubriformis L(3) each day for 6 weeks before euthanasia. Ten rams acted as unchallenged controls. Challenging sheep with larvae reduced faecal dry matter at 2, 3 and 4 weeks after challenge began and the greatest reductions were with the sheep susceptible to scouring. The sheep showed good resistance to the parasite challenge as evidenced by low faecal worm egg counts and low total worm counts at post-mortem, with the numbers of T. colubriformis particularly low. Sheep with low faecal dry matter had significantly higher numbers of eosinophils in small intestine tissue. Sheep with low total worm counts had significantly higher levels of bradykinin in abomasum mucus. Sheep with more granulocytes in tissue and inflammatory mediators in mucus tended to have fewer numbers of T. circumcincta but there was little relationship with numbers of T. colubriformis. Our results show that dag scores are correlated to a reduction in faecal dry matter, which can be attributed to the challenge with infective parasite larvae. Inflammation during worm infection is associated with rejection of the worm challenge and may result in more fluid faeces and consequently diarrhoea. Therefore, sheep breeders should focus on breeding for both low worm egg counts and also low dag scores., (Copyright 2010 Elsevier B.V. All rights reserved.)

We examined the changes to populations of Trichostrongylus colubriformis and Teledorsagia circumcincta in mature sheep selected for reduced faecal worm egg count (WEC). Worm resistant (n=19) and control (n=10) genotype sheep were penned and dosed with a total of 10,000 T. colubriformis and 10,000 T. circumcincta per week for 18-weeks. Sheep genotypes were from lines previously bred over 15 years for either low WEC (resistant) or non-selected (control). Weekly WEC and the proportion of larvae from each species in faecal culture were measured during weeks 3-17. Egg hatchability was assessed on a pooled faecal sample from worm resistant or control genotype sheep at weeks 7, 9, 10, 13, 14 and 17. At week 18 the number of adult and immature worms (early and late 4th, and 5th stage), and indicators of worm fecundity (female worm length and number of eggs in utero) were assessed at necropsy. Results show that resistant sheep had reduced mean WEC to only 18% of the control (P<0.05) and increased the proportion of T. circumcincta larvae in faecal culture during weeks 8-17 (P<0.10). Egg hatch assays indicated a slight reduction in the viability of eggs from worm resistant genotypes at weeks 14 (P<0.05) and 17 (P<0.10). At necropsy, resistant animals had 93% fewer adult T. colubriformis, 44% fewer adult T. circumcincta and had reduced indicators of fecundity in T. circumcincta by up to 40% (P<0.05). We observed no change in the number T. circumcincta worms but an 11% increase in the proportion of early 4th stage T. circumcincta larvae in resistant animals (P<0.05). There were different temporal patterns in WEC and different prediction equations for WEC from necropsy traits for the two sheep genotypes (P<0.05). Thus, our results suggest a changed host-parasite relationship in sheep selected for low WEC. We conclude that lower WEC is achieved through reduced number of adult worms for both species and reduced fecundity for T. circumcincta. These results support the hypotheses that worm resistant sheep with a strong immune function can regulate T. colubriformis by rejecting adult worms but that T. circumcincta is regulated through a combination of suppressed development and reduced female fecundity., (Copyright 2010 Elsevier B.V. All rights reserved.)

Sheep that are highly resistant to parasitic nematodes can suffer bad diarrhoea due to the inflammation associated with rejection of ingested larvae from pasture. We hypothesised that challenging parasite-resistant sheep indoors with nematode larvae would result in reduced faecal dry matter, and that faecal dry matter would be lowest in sheep challenged with a mixture of Trichostrongylus colubriformis and Teladorsagia circumcincta compared to those challenged with either species alone. We also hypothesised that inflammatory cells and serum antibodies and interleukin-5 would be highest in those sheep that received the mixed larval challenge. We found that faecal dry matter was reduced (P<0.05) in challenged sheep compared to unchallenged sheep, with the fastest reduction being in those sheep challenged with only Tric. colubriformis. At 14 and 23 days after challenge began, there were no differences in faecal dry matter between the three challenged groups. Within the abomasum, there were no differences in inflammatory cell numbers between unchallenged sheep and those challenged only with Tric. colubriformis. Cell numbers in sheep challenged with Tela. circumcincta were higher (P<0.05) than those in unchallenged sheep, but there were no differences between sheep challenged only with Tela. circumcincta or as a mixed challenge. In the small intestine, inflammatory cell numbers were higher (P<0.05) in sheep that received the mixed challenge compared to controls. Cell numbers in sheep challenged with either Tela. circumcincta or Tric. colubriformis were also slightly higher than those in controls. Larval challenge increased (P<0.05) levels of IgA and IgE in serum, but there were no differences between the three challenged groups. Larval challenge also increased (P<0.05) levels of IL-5, with the greatest increase being in those sheep challenged with both species. We concluded that both Tela. circumcincta and Tric. colubriformis can cause immune-mediated diarrhoea in sheep, and that a mixed challenge will not necessarily lead to worse diarrhoea or higher concentrations of antibodies in serum. We also concluded that challenge with Tric. colubriformis leads to no inflammation in the abomasum, but challenge with Tela. circumcincta may lead to some inflammation in the small intestine., ((c) 2010 Elsevier B.V. All rights reserved.)

Pruritic behaviour and deranged fleece are often used as indicators of sheep louse infestation but the exact relationship between infestation and the observation of signs of pruritus was unclear. Two studies were conducted to examine this association. In the first, 24 castrate Merino sheep were randomly assigned to six pens in groups of four and the sheep in three pens infested with 10 lice each on the right mid-side. Louse numbers were counted, fleece derangement scored and pruritic behaviour assessed periodically on each sheep until 38 weeks after infestation. In the second study a single moderately infested sheep was paddocked for 15 weeks with 32 uninfested sheep and louse numbers and fleece derangement monitored for 41 weeks. In the pen studies, differences between infested and non-infested sheep in fleece derangement and pruritic behaviour first became significant (p<0.05) at 8 and 14 weeks, respectively and at louse densities of 0.06 and 0.27 per 10 cm wool part. Some sheep showed definite signs of deranged fleece as early as 5 weeks after initial infestation. In the paddock studies, it took 37 weeks until lice were detected on all sheep in the flock. The correlation between louse numbers and fleece derangement score first became significant (r=0.44 and p<0.05) at 9 weeks after introduction of the lousy sheep, reached a maximum of r=0.79 (p<0.001) at 22 weeks when 84% of sheep had lice detected and the mean louse density was 0.29 per part, and then declined to r=0.12 (n.s.) at 41 weeks when all sheep were infested and the mean louse density was 3.04 per part. It is concluded that fleece derangement is a powerful early indicator of the presence of lice and that sheep may exhibit signs of pruritus well before lice can be readily found by direct inspection. Fleece derangement may be useful as a basis for establishing economic thresholds for the application of long wool treatments in developing louse infestations but appears to be a poor indicator of louse numbers once the infestation is advanced.