Sheep suffer from a range of chondrodysplasias, reviewed by Piripi (2007). These include the presumed genetic diseases 'spider lamb syndrome,' a disease primarily affecting Suffolks and Hampshires, Ancon mutant, 'lethal dwarfism,' Texel chondrodysplasia and South Down dwarfism. Piripi also mentions ectrodactyly, a chondrodysplasia of unknown aetiology affecting Cheviot sheep. Toxic plants are also known causes of chondrodysplasia in sheep (Piripi 2007). Most notable are plants of the Trachymene genus, associated with outbreaks of bent leg in western NSW and Queensland. For many years, graziers have associated the condition with a proliferation of wild parsnip (Trachymene ochracea, glaucifolia and cyanatha), (Edgar and Ropert 1942, Clark et al 1975 and Philbey 1990). However, it appears to have been reproduced experimentally only once (Laws, cited by Everist 1974). Similar conditions of unknown aetiology have been reported in South Africa, New Zealand and elsewhere (Radostits et al 2007).
This paper describes a sporadic chondrodysplasia in lambs. In the experience of the author, this disorder (or disorders) occurs at low prevalence across a wide area central NSW and it not associated with the presence of plants of the Trachymene genus.
CASE 1. Limekilns, north of Bathurst, NSW.
In December 2008, the owner a flock of self-replacing merinos reported four lambs from a mob of 494, 4-5 year old merino ewes with deformed legs. The ewes were joined for six weeks from 10 May 2008 and during and after joining, ran on native pastures paddocks. None of the lambs from a mob of 220 maiden ewes was affected.
The four lambs were examined. As can be seen from figure 1, all lambs were bright, alert, and well grown. In all cases, the carpal joints had reduced flexion and had either varus or valgus deformities. The metacarpo-phalangeal joints were also abnormal and were either hyper flexed or contracted with reduced flexion.
The pastures were inspected subsequently. No Trachymene plants were discovered.
CASE 2. Blayney NSW
The owner of a fine wool merino flock was visited on 23 January 2009 because two of 998 late September-October 2008 drop lambs had deformed legs. The owner has run merino ewes for about 50 years. She has observed that in most years two or three are affected although this varies. She runs a performance recorded flock and commented that she has not seen the problem repeated in the subsequent lambs from ewes bearing affected lambs. Pastures are based on cocksfoot, tall fescue and phalaris. A single lamb was examined (figure1). It has a varus deformity of the carpii.
The author occasionally saw cases resembling the lambs in Figure 1 in his flock of Merinos run over two decades northwest of Condobolin. Trachymene species were not known to occur. A photograph of a single case was recently found in the author's transparency collection dated 1981. The affected lamb was one of several thousand from a fine wool merino property near Lismore in western Victoria. Several other sheep breeders running large flocks over many years have commented that they see 1-2 cases every year or two. It seems most common in Merinos but crossbred and British breed producers also report the condition.
This widespread but low prevalence condition unlikely to be associated with Trachymene intoxication. Trachymene species do occur in central NSW. However the three species recorded on the central tablelands (T composita, T. incisa and T. scapigera) are uncommon to endangered and occur in swampy or forest country, not on the improved or modified pastures that predominate on the tablelands (PlantNet, 2008).
While this condition is widespread, its low prevalence means that it is a trivial problem, rarely reported by southern graziers except as an oddity. This disorder may be genetic although this seems unlikely. It is presumably caused by an insult to the growing bones of the carpus at a critical time during gestation by one or more agents. Perhaps its low prevalence is because the window of opportunity for insult is short, requires several factors or the agent rarely reaches pathogenic levels in susceptible sheep.
The bovine disease, congenital chondrodystrophy of unknown origin ('acorn calf disease') shares some similarities with this form of chondrodysplasia in lambs. While the aetiology remains unknown, it appears most likely to be due to maternal under nutrition. The protocol recommended by White and Windsor (2012) seems appropriate should this form of ovine chondrodysplasia emerge as a more significant problem.