Clinical Signs of Liver Disease

A large proportion of liver diseases are subclinical. This is due to the liver’s substantial capacity for cellular regeneration. Liver failure occurs only when the loss of hepatocyte function exceeds their regenerative capacity, which generally requires damage to around 80% of the organ. This highlights the importance of recognising and interpreting non-specific clinical signs at an early stage, such as lethargy, inappetence, icteric sclerae and mucous membranes, weight loss, reduced performance, or episodes of colic. Early identification of a mild hepatopathy is associated with a positive prognosis.

More severe signs include hepatic encephalopathy, hepatocutaneous syndrome, bleeding tendency, photosensitivity, and diarrhoea.

 

Diagnostics

The laboratory diagnostic evaluation of liver diseases in horses is primarily based on the interpretation of liver-specific enzyme activities and functional parameters in serum. Additional laboratory results provide valuable information on the extent of liver damage as well as on possible underlying systemic diseases. Often, further investigations such as sonography and liver biopsy are required to clarify the aetiology (Fig. 1).

 

Blood Tests – Enzymes

Blood tests often provide the first indications of liver disease through the detection of elevated liver enzyme activities. The parameters are distinguished according to their localisation within the liver (hepatocellular, biliary). They can also be classified based on whether they are liver-specific or ubiquitous.

1. Hepatocellular Enzymes

a. Glutamate dehydrogenase (GLDH)
GLDH is an enzyme specifically found in hepatocytes. It is rapidly released into the serum during acute, cellular liver damage.
Due to its short half-life (approximately 14 hours, with complete decline after 3–5 days), it is particularly useful for detecting acute hepatocellular damage and is considered the most sensitive marker.

b. Aspartate aminotransferase (AST)
AST is not liver-specific, as it is present not only in hepatocytes but also in muscle cells and erythrocytes. Isolated elevations should always be interpreted in the context of GLDH, creatine kinase (CK), and LDH.

c. Lactate dehydrogenase (LDH)
LDH is present in numerous tissues, including cardiac and skeletal muscle as well as erythrocytes. Because of this widespread distribution, its diagnostic value for the liver is meaningful only when interpreted alongside other enzymes.

 

2. Biliary Enzymes

a. γ-Glutamyltransferase (γ-GT)
γ-GT is a liver-specific enzyme with a half-life of 3–4 days, although in some cases it may remain elevated for several weeks. This enzyme is mainly produced in the bile duct epithelium. Increased serum activity occurs primarily in cholestasis and biliary diseases. While also present in the kidney and pancreas, it is mainly liver-specific. In sport horses, isolated γ-GT elevations (>50–150 U/l) can occur during intensive exercise.

b. Alkaline phosphatase (AP)
AP also shows increased activity in cholestatic processes but is less organ-specific, as it is present in bone, placenta, and intestine. In young animals, elevated AP due to bone growth should be considered physiological.

 

Proper interpretation of values is essential to guide further diagnostics or determine the optimal timing for re-testing. For γ-GT, in cases of mild elevation (Table 1), re-evaluation after 2–4 weeks, possibly including additional herd mates, is recommended to clarify a toxic or infectious aetiology and to assess disease progression.

 

Table 1: Classification of liver enzyme elevation by degree

Degree of Elevation
Mild	2–3 × upper cut-off
Moderate	4–5 × upper cut-off
High	10 × upper cut-off

 

 

Blood Tests – Liver Function

Changes in liver enzyme levels provide only limited information on disease severity, prognosis, or aetiology. Additional liver function parameters can help to better assess the extent of damage and prognosis. Bile acids constitute the primary parameter for assessment.

1. Bile Acids
   Bile acids are produced in hepatocytes, continuously secreted into the duodenum, and 90–95% are reabsorbed. When cell function is impaired, reabsorption is reduced or absent, leading to accumulation and increased serum concentrations. Values above 25 μmol/l are regarded as pathological and indicate a poor prognosis in chronic cases. In acute cases, high values are of less prognostic concern, but require close surveillance. Bile acids are a highly sensitive marker for functional liver insufficiency, particularly in chronic diseases.
2. Bilirubin
   Bilirubin is derived from degradation of haemoglobin, conjugated in the liver, and excreted via bile. Values above 75 μmol/l are associated with the characteristic yellow discoloration of the sclera and mucous membranes (icterus, jaundice). Differentiating between conjugated and unconjugated bilirubin in the blood allows the cause to be classified as pre-hepatic, intra-hepatic, or post-hepatic.
   A conjugated fraction of more than 25% indicates a hepatocellular or hepatobiliar origin. In chronic conditions, however, serum bilirubin concentrations may remain within the normal range.
3. Ammonia
   Elevated blood ammonia levels indicate advanced liver insufficiency and can lead to hepatic encephalopathy. Measurement is challenging due to its low stability (maximum 30 minutes).

 

Imaging / Biopsy

Ultrasonography of the liver is a useful supplementary diagnostic tool, even if only a portion of the organ is accessible for imaging due to anatomical reasons. Although many changes are diffuse, ultrasonography can still provide valuable information. The absence of pathological findings does not rule out liver disease. Liver biopsies are indicated when clinical signs and laboratory values do not allow a definitive diagnosis. Samples can be submitted for histology, bacteriology, and pathogen detection via PCR.

 

Aetiology

Intoxication

Intoxications are among the most common causes of hepatopathies. They can arise from, for example, mycotoxins or moulds in roughage, microcystins from algae-contaminated water, or excessive iron intake.

Particular attention should be paid to poisonous plants in pastures and hay. Although horses usually avoid them, ingestion can occur under certain conditions (e.g. in young animals, during feed shortages, in the presence of exotic plants, or when plant parts are fragmented).

Species of Senecio, such as ragwort, can lead to altered liver enzyme activities even in the early stages of intoxication, often without clinical symptoms. The toxic agents are pyrrolizidine alkaloids (PAs), which can cause irreversible liver fibrosis with chronic exposure.

LC-MS analysis of urine allows detection of senecionine/senecionine-N-oxide and indicates toxin exposure in the preceding hours to days. Additionally, roughage analysis (e.g., through agricultural testing facilities) is recommended.

 

Infections

Viruses

Viral hepatitis in horses is increasingly well studied. Of particular relevance are equine hepacivirus (EqHV) and equine parvovirus-hepatitis virus (EqPV-H).

EqPV-H is associated with Theiler’s disease – an acute hepatitis with fulminant liver necrosis and usually fatal outcome. Transmission is likely via blood products (e.g., tetanus antitoxin, stem cell products, equine plasma), and possibly via vectors. The virus is widespread worldwide, with seroprevalences in healthy horse populations (e.g., Germany, Austria) ranging between 15% and 34.7%, though only about 2% develop clinical disease. EqPV-H should be considered in the differential diagnosis when relevant symptoms are present.

EqHV, first described in 2012, can cause acute or chronic persistent infections. Symptoms range from weight loss, anorexia and jaundice to neurological abnormalities.

Both viruses are detectable by PCR in blood or liver tissue during the acute stage. Histopathological examination of liver biopsies can additionally help to assess the severity and prognosis of liver damage.

 

Bacteria

Bacterial liver disease is rare and usually secondary. When it occurs, it is often severe. It typically involves ascending bacterial infections, e.g., with Streptococcus equi or Staphylococcus aureus. In foals, liver abscesses can be caused by Rhodococcus equi and young animals may develop Tyzzer’s disease due to Clostridium piliforme. Clinically, bacterial hepatitis usually presents with jaundice, fever and colic. Pathogen detection can be performed on liver biopsy samples, which can be evaluated microbiologically and histologically. PCR-based detection is also an option.

 

Parasites

Parasitic liver damage occurs due to migrating stages of, for example, Strongylus spp. and Parascaris equorum. Liver fluke (Fasciola hepatica) is rare in horses but may occur in mixed pastures with ruminants or in wetland areas where water snails are present. Lesions can affect both liver parenchyma and bile ducts. In suspected cases, faecal samples can provide proof of infection; for some parasites (Fasciola hepatica, small strongyles/ small redworm), serology is more sensitive.

 

Conclusion

Hepatopathies are often detected late due to non-specific symptoms and subclinical cases. Diagnosis is based on the determination of liver enzyme activities and functional parameters, supported by diagnostic imaging techniques and, if necessary, liver biopsy. Toxic and infectious causes are most common, while environmental and dietary factors should also be considered when investigating the aetiology. Treatment efficacy is monitored through regular assessment of liver enzyme activities.
Recovery, however, can take weeks to months. As a preventive measure, depending on the aetiology, feed and pasture hygiene as well as evidence-based parasite control management can be helpful.

 

Dominika Wrobel-Stratmann, Dr. Svenja Möller,
Dr. Michaela Gentil

 

 

Our Services in Equine Liver Diagnostics

Profile	Parameters	Sample Material
Liver 1	AST, GLDH, γ-GT, bile acids	Serum
Liver 2	GLDH, AST, AP, γ-GT, total bilirubin, cholesterol, urea, bile acids, protein, albumin, globulins, albumin/globulin ratio, glucose, Na, K, Cl	Serum and NaFB
Hepatotropic Viruses	PCR: equine parvovirus, equine hepacivirus	Serum, EDTA blood, liver tissue
Parasite Profile	Flotation, SAFC, modified McMaster method	Faeces
Coagulation	PT, PTT, thrombin time, fibrinogen	Citrate plasma
Bilirubin	Total and direct	Serum, EDTA plasma, heparin plasma
Single Analyses
Bile Acids		Serum
Serum Protein Electrophoresis	Albumin, α-globulins, β-globulins, γ-globulins, total protein	Serum
Liver Fluke (Antibody Detection)		Serum
Small Redworm Test (Antibody Detection)	Detects infection levels of all small redworm stages	Serum
Meadow Saffron	Colchicine	Urine
Ragwort	Senecionine, senecionine-N-oxide	Urine
Bacteriology	Aerobes, anaerobes	Swab with medium, tissue (native)
Histopathology		Tissue (fixed)

Further Reading

Tallon R, McGovern K. Equine liver disease in the field. Part 1: approach. UK-Vet Equine. 2020;4(1):14-18. doi:10.12968/ukve.2020.4.1.14

Tallon R, McGovern K. Equine liver disease in the field. Part 2: causes and management. UK-Vet Equine. 2020;4(1):71-76. doi.org/10.12968/ ukve.2020.4.3.71

Ramsauer AS, Badenhorst M, Cavalleri JV. Equine parvovirus hepatitis. Equine Vet J. 2021 Sep;53(5):886-894. doi: 10.1111/evj.13477

Pathogenesis and Clinical Symptoms

Haemonchus contortus feeds on blood from the gastric mucosa in its adult stage. A single worm can cause an estimated daily blood loss of approximately 0.05 ml. Infections involving more than 5,000 worms may therefore lead to a loss of around 250 ml of blood per day. This results in anaemia, hypoalbuminaemia, and associated deficiencies in nutrients and minerals. Clinical signs can range from chronic to acute, and in some cases even to peracute progression.

Chronic infections are typically characterised by reduced performance and weight loss (emaciation). Gastrointestinal symptoms are not typical for this parasitosis, although diarrhoea may occur. Dark-coloured faeces may be observed as a result of occult blood leaking from lesions in the gastric mucosa. Oedema in the head and chest region – particularly the characteristic submandibular oedema, also known as “bottle jaw” – is a consequence of hypoalbuminaemia.

In cases of severe to massive Haemonchus contortus infestation, where the parasite can rapidly complete its reproductive cycles, acute massive anaemia may develop. This condition is characterised by porcelain-coloured mucous membranes (Fig. 1), tachycardia, tachypnoea, general weakness, and apathy – sometimes progressing to recumbency. Young animals are particularly vulnerable, as are pregnant females and nursing dams. Lambs, for example, can only mount an effective immune response against the parasite from around six months of age, leaving them susceptible to uncontrolled colonisation of the abomasum. Due to their lower body mass, the heavy blood loss affects young animals especially severely, often resulting in death within a few days.

 

Diagnostics

Clinical Examination
A clinical examination combined with anamnesis provides an initial indication of infection. The most important differential diagnosis for anaemia in small ruminants and New World camels is haemonchosis. Other potential causes to consider include haemotropic mycoplasma infection, ulcers of the abomasum or C3, other sources of bleeding, and chronic nutritional deficiencies.

Clinical diagnosis can be supported by blood tests or haematocrit measurements. Additionally, Body Condition Score (BCS) and FAMACHA© scoring are useful tools for monitoring infection severity and guiding treatment (see Treatment and Prophylaxis).

Coproscopy
For parasitological examination, faecal samples collected over three consecutive days are most suitable. The samples should be fresh and collected without prolonged contact with the ground to avoid contamination. Ideally, several faecal samples from successive defecations should be gathered.

In parasitological examination using flotation, eggs of Haemonchus contortus can be detected microscopically but cannot be morphologically distinguished from those of other gastrointestinal strongyles (MDS) (Fig. 2). A high concentration of MDS eggs may indicate a significant Haemonchus infection. Differentiation of species is possible through larval culture or fluorescent staining with peanut agglutinin. Although larval culture allows identification of MDS species, it is time-consuming and requires careful analysis.

Fluorescence staining takes advantage of the differing lectin-binding abilities of MDS eggs. Peanut agglutinin, coupled with a dye, binds to the egg surface of Haemonchus contortus and can then be visualised in colour under a fluorescence microscope (Fig. 3). This allows for clear differentiation from other MDS eggs, as the agglutinin does not bind to their surface.

Molecular Biological Methods
The polymerase chain reaction (PCR) detects specific DNA sequences of the parasite and allows for highly sensitive and specific identification of Haemonchus contortus. PCR does not detect intact structures, but rather DNA fragments.
As a result, a sample may still test positive even when no infectivity remains – for instance, following deworming. For this reason, PCR is not suitable for assessing the success of anthelmintic treatment. However, it can be used to analyse older samples that would no longer be fresh enough for reliable coproscopy.

Treatment and Prophylaxis
Worldwide, resistance to anthelmintics in gastro- intestinal nematodes is increasing at an alarming rate. Due to the high reproductive rate of Haemonchus contortus, large populations develop in which more spontaneous mutations occur, potentially leading to resistant worms. Because of the significant animal health and economic damage caused by Haemonchus contortus, the parasite is also under strong selection pressure from frequent treatments. Treatment failure due to resistance occurs across all active ingredient groups, and resistance to newer active substances has already been reported. Careful use of anthelmintics, combined with a well-planned deworming strategy and good pasture management, is essential.

For each herd, it is important to identify the anthelmintics that are most effective. This is achieved through egg count reduction tests (FECRT). Faecal samples are collected before deworming and 10–14 days afterwards, and worm burden is quantified using the McMaster method (eggs per gram of faeces = EpG). A treatment is considered successful if the egg count is reduced by at least 95%.

If deworming is unsuccessful, not only should the active ingredient be changed, but the entire active ingredient group should be switched. A follow-up success check using the McMaster count should then be performed.

To limit the further development of resistance, selective deworming should be practised. This means that only specifically identified animals receive treatment. This is important because, in treated animals, only resistant worms survive. If all animals were dewormed and then possibly moved to a new pasture, the fresh grazing area would become contaminated solely with eggs from resistant worms. This so-called ‘dose and move’ approach must therefore be abandoned. If some animals remain untreated within a herd, they continue to shed eggs from non-resistant worms. This helps dilute the population of resistant worms, allowing sensitive worms to keep passing on their sensitive genes to the overall population.

Which animals should be dewormed?
The selection of animals to be dewormed is based on faecal sample analysis. If there is a high-level infestation, treatment should be carried out.
A precise quantification is also possible here using the McMaster method. Different threshold values for eggs per gram (EpG) are defined for the various nematode species.

For infestation with Haemonchus contortus, deworming is recommended in sheep at counts greater than 200 EpG. For goats, llamas, and alpacas, the recommendation is above 100 EpG. Furthermore, deworming should be performed according to age groups. All young animals should be dewormed, as they are very susceptible and vulnerable. Adult females become increasingly resistant to gastrointestinal nematodes with age and can be assessed, for example, using clinical scores. Their need for treatment can be estimated based on weight development or body condition score (BCS). The mucous membranes of the eyes are also assessed, for example by using a FAMACHA© card. The so-called dag score (named after the English term for the dirty wool around the perianal area and hind legs in sheep) also provides indications of endoparasitosis. However, when looking specifically for Haemonchus contortus, the dag score should only be used in combination with the afore-mentioned assessment criteria, since diarrhoea is not a characteristic symptom of haemonchosis.
Correct dosing of anthelmintics is also crucial to avoid resistance development. Similar to antibiotic resistance, underdosing promotes the survival of partially resistant worms. Long-acting anthelmintics also encourage the selection of resistant worms, since among newly ingested L3 larvae only the resistant ones survive.

Good pasture management can help reduce infection pressure. Ideally, grazing and mowing of the pasture should alternate to reduce the larval burden. If possible, animals should not graze the pasture until it is completely short, as the larvae mainly reside close to the ground. Mixed or rotational grazing with other animal species can have a beneficial effect. These animals can ingest infectious larvae without becoming ill, thereby interrupting the reproduction cycle since they are not susceptible to species-specific parasites. Collecting faeces from the pasture can significantly reduce infection pressure. This is particularly feasible with New World camelids, as they tend to have designated dunging areas, enabling daily and thorough removal of Furthermore, it is advisable to observe a quarantine period for new arrivals in the herd. These animals should undergo quarantine treatment, including faecal examination with quantification and deworming if infested, followed by a success check using a Faecal Egg Count Reduction Test (FECRT)

Our services related to parasitoses

• Parasitological examination (flotation, SAFC) including differentiation of Haemonchus contortus
• Parasite profile(flotation, SAFC, modified McMaster method)
• Modified McMaster method(eggs per gram of faeces)
• Haemonchus contortus PCR

Dr. Britta Beck, Dr. Anna-Linda Golob,
Swanhild Wagenfeld

Furter literature

Kultscher L, Joachim A, Wittek T. Auftreten und Management von Endoparasiten bei Alpakas in Deutschland und Österreich. Tierarztl Prax Ausg G Grosstiere Nutztiere 2018; 46: 241–248. dx.doi.org/10.15653/ TPG-170766

Voigt K, Geiger M, Jäger M. Fünf nach zwölf – zur Resistenzlage gastrointestinaler Nematoden bei kleinen Wiederkäuern in Deutschland.
Tierarztl Prax Ausg G Grosstiere Nutztiere 2023; 51: 153–159. dx.doi. org/10.1055/a-2097-9361

Werne S, Heckendorn F et al. Weideparasiten bei Schafen und Ziegen nachhaltig kontrollieren. Merkblatt Ausgabe Schweiz Nr. 2515. FiBL, BioSuisse. LWZ Visp.2019; www.fibl.org

Diagnosis of Fungal Infections

Cytological samples (biopsies of the uterine mucosa are more reliable) provide indications of the cycle status and mucosal formation, as well as signs of inflammation. Bacteria can be detected directly under the microscope without further identification of the species. If the inflammatory cell profile suggests an infection with fungi, special stains can be used to determine whether it is a yeast or a fungi.
For the culture examinations, the sample should be taken from the cervix or uterus using a sterile speculum, if possible. Both bacteriological and mycological cultures can be obtained from this sample.
For the mycological culture, Sabouraud dextrose agar with chloramphenicol and gentamicin is used to inhibit the bacterial flora. Incubation takes place at 36 °C for 48 hours, followed by the first reading. Negative cultures are checked again for fungal growth after a further 5 days of incubation. The yeasts and filamentous fungi are differentiated using MALDI-TOF mass spectrometry and microscopically after staining with cotton blue lactophenol solution.

 

Results of Our Own Investigations

Out of 1,365 mycologically examined cervical and uterine swabs, 7.4% (n = 101) showed positive growth on the fungal culture medium. Of these, yeasts of the species Candida spp. were isolated in 61% of cases.
In the differentiation, Candida parapsilosis (Fig. 1) dominated the Candida complex with 46%, while 16% and 17% exhibited moderate or high levels of this yeast (Fig. 2 and 3). Other Candida species were isolated only sporadically. Filamentous fungi, including Aspergillus and Penicillium species, as well as black fungi such as Alternaria alternata, were only cultivated in isolated cases, usually at low levels.

 

Evaluation

In addition to the detection of yeasts and fungi, the clinical findings must also be considered.
Yeast or fungal endometritis is suspected if chronic endometritis does not improve or only improves temporarily after antibiotic treatment. A highly distended uterus with cloudy secretion is often present. The cervical mucosa and the endometrium appear distinctly inflamed, with a dirty red discolouration. Low levels of yeasts without clinical changes are generally negligible. The detection of a low level of fungi is more likely to be interpreted as contamination during sample collection.

In many cases, endometritis caused by yeasts or fungi is preceded by intrauterine treatment with antibiotics to treat an inflammation caused by bacteria. The applied antibiotics can damage the mucous membrane, while yeasts and fungi can be introduced from outside during intrauterine treatment. There is also discussion about whether the use of semen thinners containing antibiotics can lead to a fungal manifestation.

 

Therapy

Lavage is used to clean the uterine lumen and flush out cellular debris, such as dead neutrophils, along with microorganisms and other inflammatory products. The fluid induces uterine contractions and cleansing due to temporary mucosal irritation. For irrigation, warmed balanced electrolyte solutions such as Ringer’s or saline solutions are used.
Mild antiseptics, such as povidone-iodine or chlorhexidine, can be added to these solutions. Care must be taken to ensure that they are used in a diluted form; otherwise, severe inflammation or even mucosal necrosis may occur. Povidone-iodine solution should be used at a maximum concentration of 0.05% (5 ml of a 10% povidone-iodine solution in 1 litre of saline solution), and chlorhexidine digluconate at a maximum concentration of 0.25%. The use of dimethyl sulfoxide (DMSO) as an irritating chemical agent to remove inflamed endometrial tissue is rather questionable from an animal welfare perspective. After irrigation, the use of antimycotics can be considered. Currently, no active agent is approved for horses for systemic or intrauterine application. Various substances, such as nystatin, amphotericin B, or clotrimazole, are used intrauterinely for the treatment of fungal or yeast infections (off-label use). Nystatin, 0.5 to 2.5 million units dissolved in 100–250 ml of sterile water, is suitable for yeasts. Since it is poorly soluble in water, it must be prepared immediately before application and brought into suspension by vigorous shaking. Miconazole, 200–700 mg in 40–60 ml sterile saline solution daily for up to 10 days, is reported to be most effective against Candida.Therapy with antimycotics should be continued for at least 7–10 days. If necessary, an antimycogram can be performed to determine susceptibility to the antifungal agents.

 

Conclusion

Stallions that have been kept alone for long periods should also undergo a mycological examination as part of the breeding hygiene assessment. The likelihood of successfully eliminating the pathogen remains uncertain despite treatment.

Dr. Anton Heusinger

 

 

Services related to breeding hygiene

• Breeding hygiene
• Breeding hygiene + mycology
• Breeding hygiene + CEM (Taylorella equigenitalis)
• CEM culture or PCR
• CEM profiles for mares and stallions