Some physiological responses associated with reduced wool growth during blowfly strike in Merino sheep

Exploring genetic variation in potential indicators of resilience in sheep using fibre diameter measured along the wool staple

Production animals are increasingly exposed to a wide variety of disturbances that can compromise their productivity, health and well-being. As a result, there is a growing need to be able to select animals that are more resilient to environmental disturbances. Fibre diameter variation measured along a wool staple is expected to contain information about how resilient sheep are to the disturbances of their internal and external environment. This study aimed to develop potential resilience indicators from fibre diameter variation, estimate their genetic parameters and assess whether these traits are genetically correlated across three age stages. The study used 6 140 Merino sheep from the Sheep Cooperative Research Centre Information Nucleus Flocks recorded at yearling, 2 years old, and adult ages. Eight potential traits were defined based on theory, literature and exploratory analysis, which were suggested to capture the animal's ability to resist, respond and recover from potential disturbances. Genetic evaluation of the traits was conducted using pedigree-based animal models. The traits were shown to be low to moderately heritable (0.01-0.33) when examined at each of the three age stages. The potential indicators were generally well correlated with one another within age stages. Further, the genetic correlation between the same trait measured at different age stages was moderate to high between yearling and 2 years old (0.35-0.94) and between 2 years old and adults (0.18-0.70), while slightly lower between yearling and adult estimates (0.09-0.62). These results suggest that selection for resilience indicators from fibre diameter is possible; however, further studies are warranted to refine the trait definitions and validate these indicators against other measures of health, fitness and productive performance.

Australian surveys on incidence and control of blowfly strike in sheep between 2003 and 2019 reveal increased use of breeding for resistance, treatment with preventative chemicals and pain relief around mulesing

Blowfly strike or cutaneous myiasis, caused principally by the Australian sheep blowfly Lucilia cuprina is endemic to Australian sheep producing areas and is a major cause of suffering and economic loss. This article reports incidence and control practices as determined by three cross-sectional surveys of Australian sheep farmers covering the years 2003 (n = 1365), 2011 (n = 575) and 2018 (n = 354) with more questions relating to blowfly strike in the latter two surveys. Breech strike was reported at a higher rate than body strike in all survey years. Reported annual incidence of breech strike ranged from 2.2 to 4.7% of sheep nationally with minor differences between ewes and lambs. The incidence of body strike ranged from 1.0 to 7.1% with higher incidence in younger sheep in all years. The use of fixed time routine preventative chemical treatments increased during the survey period (43%, 46% and 66%, in 2003, 2011 and 2018 respectively) with dicyclanil (54%-58%) and cyromazine (23-36%) the main insecticides used for control since 2011. The use of the Mules operation (mulesing) to remove skin wrinkles from the breech area as a preventative modification did not change between 2011 and 2018 (47% in both), however, the use of pain relief at mulesing of replacement ewe lambs increased substantially between 2011 (59%) and 2018 (87%). The most commonly used methods to assist with flystrike control were timing of crutching (clipping of wool from susceptible areas) and shearing, with few respondents destroying maggots from treated sheep (21-26%) and very low use of fly traps (5-8%). Phenotypic selection of ewes for reduced susceptibility to flystrike based on visual traits was practiced by 61% of respondents in 2011 and 56% in 2018. Selection of rams for reduced susceptibility using estimated breeding values increased from 10% in 2011 to 17% in 2018. Breeding for resistance was the most commonly nominated (21%) most important change made to flystrike management in 2018. The results indicate that concern for sheep welfare has increased with almost universal use of pain relief at mulesing. Increased use of selection for blowfly resistance indicates farmer commitment to planning for a future without mulesing, although the practice remains prevalent. An increase in the reliance on preventative chemical treatments increases the risk of insecticide resistance.

Histological and Immunohistochemical Study of Wounds in Sheep Skin in Maggot Therapy by Using Protophormia terraenovae (Diptera: Calliphoridae) Larvae

A study was performed to evaluate the implication of Protophormia terraenovae larvae as a surgical therapy for wounded skin. Three groups of sheep (n = 25) were considered based on larval doses. Groups 1 and 2 were artificially infested with low and high concentrations of L1 stage P. terraenovae, respectively, and group 0 served as a control. Skin biopsies were taken at 4 and 14 d postinfestation (D.P.If). A histopathological study was carried out to evaluate the lesions with a score, numbers of eosinophils and mast cells, and an immunohistochemical analysis of CD3, CD79α, and CD68 as T lymphocytes, B lymphosytes, and macrophages, respectively. The results indicated that higher larval doses led to faster regeneration by 14 D.P.If. Furthermore, the higher larval doses showed a high number of the CD68 marker and eosinophils and a low number of CD3 and CD79α markers and mast cells. In addition, the number of mast cells, T lymphocytes, and macrophage markers increased when the lesion progressed; however, a low number of immunolabeled CD79α cells and eosinophils were observed. The results indicate a possible positive effect of larvae in the healing of certain wounds.

Patterns and variation in the mammal parasite-glucocorticoid relationship

Parasites are ubiquitous and can strongly affect their hosts through mechanisms such as behavioural changes, increased energetic costs and/or immunomodulation. When parasites are detrimental to their hosts, they should act as physiological stressors and elicit the release of glucocorticoids. Alternatively, previously elevated glucocorticoid levels could facilitate parasite infection due to neuroimmunomodulation. However, results are equivocal, with studies showing either positive, negative or no relationship between parasite infection and glucocorticoid levels. Since factors such as parasite type, infection severity or host age and sex can influence the parasite-glucocorticoid relationship, we review the main mechanisms driving this relationship. We then perform a phylogenetic meta-analysis of 110 records from 65 studies in mammalian hosts from experimental and observational studies to quantify the general direction of this relationship and to identify ecological and methodological drivers of the observed variability. Our review produced equivocal results concerning the direction of the relationship, but there was stronger support for a positive relationship, although causality remained unclear. Mechanisms such as host manipulation for parasite survival, host response to infection, cumulative effects of multiple stressors, and neuro-immunomodulatory effects of glucocorticoids could explain the positive relationship. Our meta-analysis results revealed an overall positive relationship between glucocorticoids and parasitism among both experimental and observational studies. Because all experimental studies included were parasite manipulations, we conclude that parasites caused in general an increase in glucocorticoid levels. To obtain a better understanding of the directionality of this link, experimental manipulation of glucocorticoid levels is now required to assess the causal effects of high glucocorticoid levels on parasite infection. Neither parasite type, the method used to assess parasite infection nor phylogeny influenced the relationship, and there was no evidence for publication bias. Future studies should attempt to be as comprehensive as possible, including moderators potentially influencing the parasite-glucocorticoid relationship. We particularly emphasise the importance of testing hosts of a broad age range, concomitantly measuring sex hormone levels or at least reproductive status, and for observational studies, also considering food availability, host body condition and social stressors to obtain a better understanding of the parasite-glucocorticoid relationship.

Acute phase biomarkers of diseases in small ruminants: an overview

Acute phase proteins (APPs) are a large group of proteins synthesised mainly by the liver. Their production is stimulated in response to disturbances in the systemic homeostasis. It is known that each species has a specific set of APPs. Serum amyloid A and haptoglobin are the main APPs in small ruminants and their plasma concentration is changed most significantly in comparison with minor APPs such as ceruloplasmin. In general, APPs could provide valuable information on the general condition of the organism but cannot point at the exact disease. Therefore, APPs should be included as an additional indicator in clinical diagnosis. Knowledge of APPs behaviour in disease states has a remarkable potential for detecting animals with subclinical infections, determining the prognosis of clinical infection, differentiation between viral and bacterial disease, treatment monitoring, vaccine effectiveness and stress conditions. The aim of this review is to present data on APPs behaviour during some parasitic and infectious diseases as well as pathological conditions leading to aseptic inflammation and stress in sheep and goats.

Sheep death and loss of production associated with flystrike in mature Merino and crossbred ewes

In eight well-managed Australian Merino and crossbred sheep flocks the adult ewes were monitored frequently for flystrike. Occurrences of flystrike and severity of strike scores were recorded, whereas bodyweights and condition scores were recorded regularly across two wool production and reproduction cycles. In these unmulesed flocks, 17% of Merino and 5% of crossbred ewes were struck, with 2% of those struck dead within 7 days of detection of the strike. For those adult ewes that survived the immediate period of the strike, the rate of loss over the following year was slightly greater than for ewes that were never struck, particularly for those with a high severity strike. Flystrike also contributed to losses of up to 2.7 (Merino ewes) and 5.2 (crossbred ewes) kg of bodyweight, and 0.3 condition score units at the time of the strike. Bodyweights were still 2 kg lower by 3 months after the strike occurred for Merinos, although condition scores returned to average levels. For ewes struck between mating and lambing, flystrike was associated with significant losses of lambs. Flystrike at severity level 1 (light) had only minor effects on wool production, but severity score 3 (heavy) reduced clean fleece weight.

Utility of Acute Phase Proteins as Biomarkers of Transport Stress in Ewes and Beef Cattle

The effect of transport on serum amyloid A (SAA), haptoglobin (Hp), Fibrinogen and white blood cells (WBC) was evaluated in 10 ewes and 10 beef cattle. All animals were transported by road for 6 h over a distance of about 490 km with an average speed of 80 km/h. Blood samples, collected via jugular venepuncture, were obtained before and after transport as well as after 12, 24 and 48 h rest time. One-way repeated measures analysis of variance showed a statistically significant effect of sampling time on SAA, Hp, and WBC in ewes and beef cattle. Based on these results, Hp and SAA levels, together with WBC, may be useful indicators of animal health and welfare and in predicting the risk assessment in meat inspection.

Utility of Acute Phase Proteins as Biomarkers of Transport Stress in Ewes and Beef Cattle

The effect of transport on serum amyloid A (SAA), haptoglobin (Hp), Fibrinogen and white blood cells (WBC) was evaluated in 10 ewes and 10 beef cattle. All animals were transported by road for 6 h over a distance of about 490 km with an average speed of 80 km/h. Blood samples, collected via jugular venepuncture, were obtained before and after transport as well as after 12, 24 and 48 h rest time. One-way repeated measures analysis of variance showed a statistically significant effect of sampling time on SAA, Hp, and WBC in ewes and beef cattle. Based on these results, Hp and SAA levels, together with WBC, may be useful indicators of animal health and welfare and in predicting the risk assessment in meat inspection.

Genetic aspects of sheep parasitic diseases

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.

Is ‘a life worth living’ a concept worth having?

A recent FAWC report introduced ‘a life worth living’ as a useful concept in farm animal welfare discussions and policy. But what does this concept mean? And is it a useful one? This paper extends FAWC's approach in several ways. It firstly provides an account of the concept of a life worth living in more detail, in relation to current animal welfare thinking, such as experiences and quality of life. It then describes how the concept might be applied in animal welfare management decisions and in setting standards for regulations and Farm Assurance schemes. The paper identifies several advantages to the concept: it is animal-based, intuitively understandable, and has direct prescriptive force in decision-making. But the concept also has certain limitations, especially that it is potentially complex and subjective and that it cannot include all ethically relevant concerns about farm animal welfare. Nevertheless, the paper concludes that the concept may become a useful addition to welfare dialogue, and finishes by identifying the core areas where further work is necessary.

A review of mulesing and other methods to control flystrike (cutaneous myiasis) in sheep

Flystrike (cutaneous myiasis) in sheep has the potential to have a major impact on the welfare of significant numbers of sheep worldwide, but particularly in Australia. The main control method used in Australia, the mulesing operation to remove folds of skin from the hindquarters of the sheep, is effective in controlling the disease, but will be terminated from 2010 as a result of concerns that the operation itself has too great a negative impact on sheep welfare. Alternative treatment methods are considered, and it is proposed that they need to be appraised for each farm separately, based on the conditions prevailing and the potential to apply the different treatments. Sheep are predisposed to flystrike if their fleece is wet or contaminated with faeces or urine. Monitoring and awareness of the weather conditions will enable farmers to strategically treat their sheep with insecticides, or to observe them and treat affected animals more regularly. Frequent removal of wool by crutching, dagging and shearing will aid wool desiccation after rainfall and decrease the likelihood of fleece contamination with excreta. Some control of diarrhoea can be achieved by good grazing management and treatment of diseases that predispose sheep to the disorder. Reducing fly populations can be achieved by the use of traps, and parasitoid wasps also offer some promise. Alternative methods of removing wool and wrinkles from the hindquarters of sheep, including the topical application of quarternary ammonium compounds, phenols, caustic soda or plastic clips, have yet to be proven to be effective, without severely impacting on the welfare of the animal as well as compromising operator safety. In the long term, the breeding of sheep without wrinkles or wool on their hindquarters offers the most likely method of control, although a small proportion of sheep are affected on other parts of their body.

Genetic resistance to growth of Lucilia cuprina larvae in Merino sheep

Cutaneous myiasis (fly strike), caused by Lucilia cuprina, is a major ectoparasitic infection of sheep. Previous research has identified contributions of body conformation, wool characteristics and resistance to bacterial dermatoses to resistance to fly strike. This paper investigates whether genetic variation occurs amongst sheep in growth of larvae on skin. Mixed sex Merino sheep in 27 half-sibling groups were challenged with freshly hatched Lucilia cuprina larvae, and survival and growth of larvae were measured after 50 h. Growth but not survival of larvae had moderate heritability (0.29 ± 0.22), comparable to that seen for resistance to nematode parasites in sheep. Phenotypic correlations between resistance to larval growth and wool traits, skin wheal response to intradermal injection of larval excretory secretory products and resistance to internal parasites were negligible; however, there was a significant negative phenotypic correlation with fleece rot score after exposure of sheep to simulated rain at a time independent to that of measurement of larval growth. Larval growth was negatively correlated with peripheral blood eosinophil numbers measured either before or after larval challenge. In addition, larval growth in vitro on serum collected from challenged sheep was moderately associated with larval growth in vivo. A search for quantitative trait loci (QTL) for larval survival and growth was conducted in data from 94 half-sibling progeny of a Merino × Romney sire backcrossed to Merino ewes. Potential QTL for larval growth were identified on chromosome 11 and for larval survival on chromosome 18, although phenotyping greater numbers of sheep and a higher marker density on these chromosomes is necessary to confirm the result. We conclude that this study has identified a novel level of resistance of Merino sheep to growth of L. cuprina larvae that may be mediated in part through actions of anti-larval factors in serum and eosinophils. Further studies are required to establish the impact of growth retardation on the severity of systemic responses of sheep to fly strike and on the biology of adult flies.

Welfare consequences of mulesing of sheep

Mulesing is traditionally performed on approximately 80% of Merino wool-producing sheep in Australia. Mulesing produces a stress response that persists for 24 to 48 hours. Behavioural changes indicative of pain and discomfort resolve within 24 and 48 hours, respectively. Reductions in weight gain may persist for 14 days. The acute stress response to mulesing has been shown to be similar to that produced by shearing, castration and mild flystrike, but mulesing has a longer duration of response (24 to 48 hours) than shearing (1 hour) or knife castration (8 to 24 hours), whereas flystrike response persists for the duration of infection. Theoretically, if mulesing were not used, with Merino sheep of existing genetics, increased chemical use and flock inspections could keep flystrike rates to approximately equivalent to present levels in some production systems. Increased handling events for chemical preventative application would represent a mild stressor for sheep, but cumulatively not more than that of mulesing. If producers were able and prepared to sufficiently increase resources into alternative anti-flystrike methods, then the welfare of Merino sheep would probably be equivalent or better to that of today. If constraints such as property size or finances dictate a sub-optimal level of flystrike prevention and treatment, then animal welfare will unquestionably be worse. The result of that equation would depend on individual flock managers, the physical characteristics of their production system, the profitability of their business, and seasonal variations in flystrike risk. It is likely that there would be some occasions when flystrike would increase. This highlights the need for alternative strategies, such as genetic selection, to reduce the susceptibility of Australian Merino sheep to flystrike.