The UK goat population is estimated to be around 111 000 in total (APHA, 2022), thereby placing them in the category often referred to as a minor species. Although most of our day-to-day veterinary involvement with a goat may be by application of dairy cow and sheep knowledge, experience and technical approaches, there are a few important yet subtle differences for the reader to be aware of:
- They have evolved as browsing not grazing ruminants — and this has had an evolutionary impact on their ability to develop age dependent resistance to nematode parasites. It should also be a consideration when investigating nutritional problems
- There are very few pharmaceutical products with a marketing authorisation for use in goats in the UK, with many products used under current ‘cascade’ principles
- Some laboratory tests commonly used in other ruminants may not have validation data for use in goats
- Some laboratory tests may lack ‘goat’ reference ranges, and these may well differ to commonly used sheep and cattle ranges
- A disease common to all ruminant species may have a differing clinical profile and lesion presentation in goats
- The expectation of the owner (particularly of pet goats) may extend to laboratory and other expensive diagnostic procedures not generally requested in other farmed ruminants (personal experience).
Nematodes
A knowledge of the apparent lack of age dependent resistance to nematode parasites in goats is key to investigating weight loss and diarrhoea in goats of all ages in which clinical parasitic gastroenteritis (PGE) can occur. It is for this reason that most of the large commercial dairy goat units are permanently housed. Conventional faecal worm egg counts (Figure 1) form the basis of any investigation, and the laboratory should give goat reference ranges, but there are many variables to consider when attempting to give guidelines on the significance of worm egg count results, and each case must be assessed with reference to the age of the goat and the clinical signs present. As a general guide however, egg counts in excess of 2000 eggs per gram (epg) are usually indicative of clinical disease. Counts of 500–2000 epg are suggestive of sub-clinical parasitism and subsequent reduced production, or reduced milk yield. Haemonchosis (Figure 2) is clinically similar to the condition in sheep, in which severe anaemia and sub-mandibular oedema are common features, significantly, however, diarrhoea is not a feature of this parasite unlike other nematode species. Haemonchus contortus has increased egg producing fecundity, and often results in very high faecal egg counts, which, with the clinical signs outlined above, should raise a suspicion.
Coccidiosis
Coccidiosis can be confirmed by faecal examination and oocyst counts. As with sheep, numerical counting needs to be undertaken alongside speciation to assess population significance. Although around 20 species of Eimeria have been reported in goats, the most pathogenic (and hence significant) species are Eimeria ninakohlyakimovae, Eimeria caprina, Eimeria christenseni, Eimeria arloingi and Eimeria hirci in descending order of significance (Taylor, 2017). Lesions at post-mortem examination (PME), are fairly non-specific, although in acute coccidiosis, the mucosa may be thickened, haemorrhagic and necrotic. Histological examination is only of benefit in very fresh carcases.
Enterotoxaemia
Although caused by Clostridium perfringens Type D (the causative organism of pulpy kidney in sheep), the clinical presentation of enterotoxaemia in goats is quite different — although in per-acute infections goats can be found dead. Disease can develop in goats of any age, but is more common in mature goats, in which diarrhoea of varying severity can develop, which may contain blood and shredded mucous membrane. The pathology is essentially a severe entero-colitis, often resulting in haemorrhagic content (Figure 3). Laboratory confirmation is based on the clinical signs, gross pathology and demonstration of epsilon toxin in gut content at postmortem examination (and less reliably in faeces from clinical cases). Histological examination of brain can also be useful.
Caprine arthritis encephalitis
Caprine arthritis encephalitis (CAE) is a ‘goat specific’ condition caused by a persistent lentivirus infection (Dawson and Wilesmith, 1985) — maedi visna of sheep is a further example of this group of diseases. The two conditions are often grouped together as small ruminant lentiviruses (SRLVs). The main clinical presentation is of progressive limb joint arthritis, and/or an indurative mastitis in which the affected half of the udder can become firm and swollen or will shrink and stop milk production (Figure 4). Encephalomyelitis is a rarer manifestation of disease seen in young kids.
Diagnosis is based on these clinical signs, further supported by a positive CAE enzyme-linked immunosorbent assay (ELISA) test result. A negative test result can effectively ‘rule out’ CAE as a cause of the clinical syndrome under investigation. This same serological test is used for CAE herd monitoring. There are few gross pathology lesions evident, but histological examination of joints shows thickening of the joint capsule and marked proliferation of synovial villi.
Johne's disease
Johne's disease is a common condition in cattle, sheep, and goats, and the clinical presentation in goats is more similar to that of sheep than cattle. Characterised by a long period of latency following infection in early life, most conventional laboratory tests are of minimal value as until clinical disease develops, there will be little if any humoral response detectable, and the sporadic shedding of organisms in faeces may be below detectable limits (Stevenson, 2009).
Once triggered to develop, clinical signs may go unnoticed initially, but include a progressive weight loss and reduction in milk yield if lactating, although appetite may be unaffected. As the condition develops, anaemia and a lack-lustre coat may become apparent together with sub-mandibular oedema (a feature of the progressive hypoalbuminaemia). The diarrhoea associated with disease in cattle is not a feature of the condition in goats (although it may develop in the terminal stages). It is not known why but may simply be linked to the drier faeces naturally produced by goats compared with cattle.
The blood ELISA test becomes more reliable with increasing sensitivity as clinical disease progresses beyond the latent phase. A blood actiphage test is showing promising results. Faeces samples from suspect clinical cases can be subjected to the polymerase chain reaction (PCR) test, or microscopic examination of Ziehl-Neelsen (ZN) stained smears. Lesions at post-mortem examination can be very subtle and difficult to identify. Any pathology will be found predominantly in the ileum, caecum and colon, and often no more than a slight thickening of the mucosal surface (Figure 5). In a series of confirmed Johne's disease cases examined by the author, similar lesions were also seen in the lower jejunum.
The corrugated mucosal thickening seen in cattle tuberculosis (TB) cases is not a feature in goats. On opening, the affected mucosa has a ‘velvet’ appearance with mucosal fissures. Mesenteric lymph nodes may be enlarged and oedematous, and if disease is well established focal areas of caseation and calcification may be evident within the lymph node tissue. Very fresh gut can be placed in fixative for histological examination, although post-mortem blood can be subjected to the ELISA test, and faeces and intestinal smears examined as above.
Caseous lymphadenitis
Caseous lymphadenitis (CLA) is caused by the bacterium Corynebacterium pseudotuberculosis, and is common to both goats and sheep — an important factor when running together. In goats lesions tend to be mainly superficial, and associated with anatomically located lymph nodes (Smith and Sherman, 2009a), although the author has seen heavy visceral involvement in goats housed together in large numbers. Laboratory confirmation is based on confirming the bacteria by culture. Aspirated pus (if this is attempted) can often be sterile, with the bacteria more likely to be present around the capsular wall which should be ‘rubbed vigorously’ with a swab end (Figure 6). Serological tests developed for sheep have been used in goats, but the author has been aware of the occasional ‘false positive’ result.
Skin problems
Goats can be affected by a number of ectoparasites including lice and mange mites. The clinical signs are similar to those seen in other affected species and include pruritus, hair loss and skin scurf, with the sucking louse Linognathus spp. additionally causing anaemia, particularly in young kids (Smith and Sherman, 2009b). The lesion distribution pattern associated with Chorioptes spp. however is unusual, in that it tends to be limited to the distal limb and is often referred to as ‘foot mange’ (Figure 7).
Laboratory examination of skin scrapes and hair plucks is a first step in investigating skin problems, and in valuable or pet goats, skin biopsy may also be of value.
Two goat specific lesions the reader needs to be familiar with are: pygmy goat syndrome (PGS) and zinc responsive dermatoses.
Pygmy goat syndrome
PGS is a condition specific to this type of goat, presenting as an alopecic, exfoliative dermatitis (Figure 8). The typical early age of onset is <5 months, and the distribution of scaling lesions (with some alopecia and occasionally crusting) typically affects the head, limbs, and ventral body (groin to axilla), with some extension to the tail (Foster, 2022). Diagnosis is based predominantly on the breed of goat, the signs described and exclusion of other causes — skin biopsy may be of benefit.
Zinc responsive dermatoses
Zinc responsive dermatoses is an ill-defined syndrome showing many similarities in its clinical presentation to PGS — and it may be that the two conditions co-exist in certain individuals. It has also been identified in other breeds, often diagnosed by response to zinc supplementation. Zinc assay can be undertaken on clotted blood samples taken into tubes with plastic (not rubber) tops; the Animal and Plant Health Agency (APHA) quoted reference range is >12 µmol/litre adequate, <6 µmol/litre deficient (Harwood and Mueller, 2018).
Udder conditions
Suspect mastitis cases can be investigated by undertaking bacteriological examination of aseptically collected milk samples. Clinical mastitis however is comparatively rare in milking goats, with Staphylococcus aureus the most commonly isolated pathogen (APHA, n.d.). If investigating such an incident, the reader is advised to check the udder skin surface for ‘acne’ like lesions (so called udder impetigo), a common prelude to mastitis incidents (Harwood, unpublished observations).
Beware relying on cell count data or individual California Mastitis Test (CMT) results if contemplating any mastitis culling and control programme. Individual goat cell counts of >1 000 000 are not uncommon in goats in which the udder and milk secretion are unremarkable. This is in part because goat milk is produced by apocrine milk secretion as opposed to merocrine milk secretion in cows.
Metabolic conditions and profiling
Hypocalcaemia
Unlike dairy cows in which clinical hypocalcaemia is a relatively common occurrence, true clinical disease is more unusual in periparturient goats, although sub-clinical manifestation may be more common and can be easily overlooked. Blood calcium assay should be considered 10 days either side of kidding.
Pregnancy toxaemia
Pregnancy toxaemia tends to be a problem in over conditioned high yielding goats in commercial dairy herds (Figure 9), but can also be a problem in any overfat pregnant goat in late pregnancy. Monitoring beta-hydroxybutyrate (BHB) levels in susceptible goats may be of benefit (Chamberlain, 2015).
Unlike sheep, the majority of fat is laid down in the abdomen creating a particular problem during late pregnancy with multiple kids (Figure 10) (personal experience).
Metabolic profiles
The minimal profile (Figure 11) should include:
- BHB/non-esterified fatty acids (NEFA) — assessing energy status and possible pregnancy toxaemia or ‘ketosis’ post kidding
- Urea N — assessing daily effective rumen degradable protein (ERDP) intake and short-term protein status. Low or very variable levels might indicate issues with ration particle size or mixing, feed space allowance or ‘sorting’ by the animals
- Albumin assessing long-term protein intake and possible protein losing disease or parasitism
- Globulin assessing chronic inflammation and possible disease
- Copper in any suspicion or history of related disorder on farm such as copper deficiency or toxicity.
Tuberculosis
Goats are susceptible to bovine TB and will always be at risk as ‘spillover hosts’ if located in areas of known high TB incidence in cattle and the local wildlife population. Disease can develop more rapidly in goats (Crawshaw, 2013) (particularly if it develops in large groups of housed goats). As a result, at PME, any lesion may not resemble the more typical caseous lesion recognised in cattle — Figure 12 shows such a lesion from a Golden Guernsey goat. This abscess was more typical of a pyogenic organism such as Arcanobacterium pyogenes — although bovine TB was confirmed.
Abortion
The infectious causes of goat abortion virtually mirror those recognised in sheep, such that any laboratory investigation will follow a similar approach. One specific ‘goat problem’, is that because they have evolved as a ‘prey species’ they will rapidly consume any placenta that is passed (Figure 13). This is a problem, because in goats it is the placenta that is by far the most useful material for a laboratory to examine — owners should be encouraged to supervise any goat that is aborting and to collect the placenta before it disappears! Without the placenta (including cotyledons), it can be difficult to confirm toxoplasma abortion as the widely used fetal fluid toxoplasma indirect fluorescent antibody test (IFAT) uses a sheep specific monoclonal antigen. The cotyledon allows the direct toxoplasma FAT to be undertaken.
Neoplasia
Unlike other ruminants, goats kept as pets will often ‘live out’ their lives, and as a result, elderly teenage goats can develop a range of neoplasia that may be identified at PME. These include, e.g. thymic and multi-centric lymphosarcoma, mandibular fibrosarcoma, neoplasia of the female genital tract and mammary tumours (personal observation) — with metastases always a possibility (Figure 14).
Poisoning
As browsing animals, goats may consume a wide range of plants and shrubs available to them. Rhododendron is attractive to goats, yet is highly toxic, with ‘vomiting’ a recognised clinical sign. If poisoning is suspected at PME, the reader (or by proxy the owner) is urged where possible to ‘search’ the environment in which the goat was prior to its death. This can be invaluable in identifying potential sources — rather than hoping to identify plant fragments in rumen or regurgitated rumen content (Figure 15).
Conclusions
This article has attempted to provide some guidance when presented with a goat displaying clinical signs that may necessitate further laboratory testing or post-mortem examination. Although there are many similarities with these approaches to other ruminants in the UK, there are also subtle and important differences.
KEY POINTS
- Goats are ruminants — most of the common disease presentations and laboratory approaches are common to goats, sheep, and cattle, but not all.
- Goats may be kept for profit (commercial dairy sector) or for pleasure (pet and hobby keeping). Owner aspirations may be quite different particularly with respect to ‘a test and cull policy’, and more costly testing regimens.
- Goats remain susceptible to parasitic gastroenteritis (PGE) throughout their lives even after annual exposure.
- Enterotoxaemia is the most common cause of acute illness and diarrhoea.
- Goat skin problems can be problematic — be aware of goat specific problems.