Acute-onset high-morbidity primary photosensitisation in sheep associated with consumption of the Casbah and Mauro cultivars of the pasture legume Biserrula

Abstract

BackgroundPrimary photosensitisation (PS) subsequent to ingestion of the pasture legume Biserrula pelecinus L. (biserrula) has recently been confirmed in grazing livestock. Given the potential utility of this pasture species in challenging climates, a grazing trial was undertaken to examine if both varieties ‘Casbah’ and ‘Mauro’ were able to cause photosensitisation in livestock, and if this could be mitigated by grazing in winter, or in combination with other common pasture species.ResultsA controlled grazing trial was undertaken in winter in Australia with plots containing a dominant pasture of Biserrula pelecinus L. cv. ‘Casbah’ or ‘Mauro’, or mixed biserrula/perennial ryegrass populations. A photosensitisation grading system was established. 167 prime meat ewe lambs were introduced to the plots and monitored twice daily. Mild clinical signs were observed at 72 h on pasture. All animals were removed from biserrula dominant stands at this point. Four animals grazing ‘Casbah’ dominant pasture rapidly proceeded to severe photosensitisation in the following 12 h. Animals remaining on mixed biserrula/ryegrass stands did not exhibit severe PS but showed an 89% incidence of mild to moderate photosensitisation over the following 14 days. Animals on mixed lucerne showed significantly lower PS score than animals grazing biserrula varieties of any composition. The trial was halted at 14 days as only plots with low biserrula proportion still contained unaffected animals.Necropsy revealed severe multifocal erythematous ulcerations and alopecia of the ear pinnae, severe bilateral periorbital and conjunctival oedema and variably severe subcutaneous facial oedema. No evidence of hepatopathy was present. A diagnosis of acute unseasonal primary photosensitisation caused by biserrula ingestion with no other underlying pathology was confirmed.ConclusionsWe report an unseasonal outbreak of acute photosensitisation in sheep grazing Biserrula pelecinus L cvs.’Casbah’ and ‘Mauro’ with exceedingly high morbidity. A grading system is also proposed as a tool for objective and consistent clinical appraisal of future PS outbreaks. This finding expands our definition of seasonal and temporal risk periods for biserrula photosensitisation, and is the first to identify that both commercial cultivars of biserrula can cause primary photosensitisation in sheep.

Relative perceptions of prevalence, impact and importance of photosensitisation in Australian livestock: A survey of veterinarians, livestock traders and livestock producers

“…Similar to previous findings, in this survey, more than half of the veterinary respondents rated secondary (hepatogeneous) photosensitisation as the most common type of photosensitisation, further supporting previous evidence that hepatogeneous photosensitising plants or agents are significantly more common than those containing primary photocytotoxic compounds 1,7 . Reasons for this commonality of presentation are that toxic plants know to contain hepatotoxic agents are found more frequently in nature than those containing primary sensitisers 8,9 . Equally, the least common type of photosensitisation, the congenital type (II) that requires specific genome mutations, is very uncommon in livestock 10,11 .…”

“…1,7 Reasons for this commonality of presentation are that toxic plants know to contain hepatotoxic agents are found more frequently in nature than those containing primary sensitisers. 8,9 Equally, the least common type of photosensitisation, the congenital type (II) that requires specific genome mutations, is very uncommon in livestock. 10,11 The relative commonality of secondary photosensitisation is increased compared to other presentations as hepatobiliary impairment resulting in secondary photosensitisation can also be caused by other agents such as hepatotoxic toxins in fungal contaminants in feed, infectious or inflammatory liver disease, liver parasites, metabolic disease, copper accumulation, or neoplasia, all of which could results in secondary symptoms of photosensitisation.…”

The aetiology, prevalence and morbidity of outbreaks of photosensitisation in livestock: A review

“…Australia has experienced outbreaks of primary photosensitisation that are specific and unique to this region. One examples is photosensitisation caused by the pasture legume Biserrula pelecinus , although a native of the southern Mediterranean, it is exclusively used as a livestock fodder only in Australia [102] where this pasture legume is now clearly identified as causing outbreaks of primary photosensitisation [37,38]. Outbreaks that have never been recorded in its native domains where it grows as a native only in mixed swards.…”

“…Previously, no objective photosensitisation scoring protocol had been defined in literature resulting in prevalence and severity of affected animals to be hard to compare between outbreaks. Recently, a semi-objective photosensitisation grading system has been developed for sheep to address this issue [37]. The use of such a grading system in future outbreaks will allow better correlation between access to potentially photosensitising pastures or feedstuffs with more accurate determination of the timing of onset of outbreaks, as well as a more definitive and consistent identification of the severity of the condition.…”

Photodermatitis and ocular changes in nine horses after ingestion of wild parsnip (pastinaca sativa)

“…However, many recent studies revealed that Streptococcus dysgalactiae subsp. equisimilis can cause various soft-tissue infections and occasionally more serious infections including neonatal sepsis, bacteremia, endocarditis, meningitis, peritonitis and arthritis [ 21 , 22 ]. In horses, Streptococcus dysgalactiae subsp.…”