Fatty Liver Syndrome (Hepatic Lipidosis)

Fatty liver syndrome (hepatic lipidosis) is a metabolic disorder of transition dairy cows, characterized by excessive accumulation of triglycerides in hepatocytes, leading to hepatic dysfunction, decreased gluconeogenesis, and increased susceptibility to other periparturient diseases. It typically occurs in the periparturient period, especially in high-producing dairy cows, and is associated with negative energy balance (NEB) and excessive mobilization of body fat. The condition ranges from subclinical (mild to moderate fat infiltration) to clinical (severe fat infiltration with hepatic failure and other systemic signs). Economically, it causes reduced milk yield, increased culling, and higher veterinary costs. In beef cattle, it can occur in fat cows under nutritional stress, but is less common. The syndrome is a major component of the 'transition cow' complex, often coexisting with ketosis, displaced abomasum, retained placenta, metritis, and mastitis.

The primary cause is a severe negative energy balance in early lactation, leading to excessive mobilization of non-esterified fatty acids (NEFAs) from adipose tissue. The liver takes up NEFAs and re-esterifies them to triglycerides, but the export capacity via very low-density lipoproteins (VLDL) is limited in ruminants, causing accumulation. Predisposing factors include overconditioning (body condition score >3.5 on 5-point scale) at dry-off, rapid weight loss, inadequate dry matter intake (DMI) in the transition period, and high milk production. Nutritional factors include excessive energy intake in the dry period, low fiber diets, and deficiencies in lipotropic agents (choline, methionine). Endocrine changes, such as decreased insulin sensitivity and increased growth hormone, also contribute. Secondary causes include other diseases that reduce feed intake, such as milk fever, retained placenta, metritis, and mastitis. In beef cattle, it can be triggered by sudden feed deprivation or transport stress in fat cows.

Fatty liver syndrome is most prevalent in high-producing dairy cows during the first 4 weeks after calving, with peak incidence in the first 2 weeks. It is more common in cows with high body condition score (BCS) at calving (>3.5) and in older cows (parity ≥3). The prevalence of subclinical fatty liver (moderate to severe) is estimated at 40-60% in high-producing dairy herds, while clinical cases occur in 5-10% of cows. Morbidity and mortality vary; clinical cases have a poor prognosis, with mortality rates up to 25-50% if severe. The economic impact is significant due to reduced milk yield (up to 10-20% decrease), increased risk of other diseases, and higher culling rates. Seasonally, it is more common in winter and early spring when calving is concentrated. Herd-level risk factors include overstocking, poor transition cow management, and inadequate bunk space.

In early lactation, the demand for glucose for lactose synthesis exceeds the supply from diet and gluconeogenesis, leading to a state of negative energy balance. This triggers lipolysis in adipose tissue, releasing NEFAs into the bloodstream. The liver takes up NEFAs, which can be oxidized for energy, partially oxidized to ketone bodies (acetoacetate, beta-hydroxybutyrate), or re-esterified to triglycerides. In ruminants, the capacity for VLDL synthesis is limited, so triglycerides accumulate in hepatocytes, causing fatty infiltration. This impairs hepatic function, including gluconeogenesis, urea cycle, and detoxification. The accumulation of fat also causes physical distortion of hepatocytes and sinusoidal compression, leading to intrahepatic cholestasis and increased liver enzymes. The metabolic derangements result in hyperketonemia, hypoglycemia, and elevated NEFA levels. Fatty liver is often associated with an inflammatory response, oxidative stress, and impaired immune function, increasing susceptibility to infections. The condition can also lead to hepatic encephalopathy in severe cases.

Intrinsic factors include high milk yield, parity (older cows), genetics (Holstein-Friesian more susceptible), and excessive body condition at calving. Extrinsic factors include nutritional mismanagement: overfeeding energy in the dry period, inadequate fiber, low feed intake prepartum, and abrupt diet changes. Management factors such as overcrowding, poor bunk space, heat stress, and inadequate water supply reduce DMI. Concurrent diseases like milk fever, retained placenta, metritis, and mastitis further decrease feed intake and exacerbate NEB. Stress from calving, social hierarchy, and transportation also contribute. In beef cattle, overconditioning and sudden feed restriction are key factors.

Clinical signs are often vague and may be masked by concurrent diseases. Affected cows may show depression, anorexia, decreased rumen motility, and a drop in milk production. They may have a 'sweet' or acetone odor on the breath due to ketosis. In severe cases, there may be neurological signs such as head pressing, circling, and recumbency (hepatic encephalopathy). Icterus (jaundice) may be visible on mucous membranes. The liver may be enlarged and painful on percussion. Cows often have a poor appetite and lose weight rapidly. They are more susceptible to infections, such as metritis and mastitis. In some cases, the only sign is a failure to reach expected milk production. Subclinical fatty liver is common and may present as an increased risk of other diseases without specific signs.

Differential diagnoses include: 1) Clinical ketosis (primary ketosis) - similar signs but liver function is less severely impaired; liver biopsy shows less fat. 2) Displaced abomasum (left or right) - presents with a ping on auscultation/percussion, but can coexist with fatty liver. 3) Milk fever (clinical hypocalcemia) - recumbency and depression, but responds to calcium therapy. 4) Metritis/endometritis - fever, foul-smelling vaginal discharge, but liver function may be normal. 5) Mastitis - udder inflammation, abnormal milk, but systemic signs may be present. 6) Traumatic reticuloperitonitis - fever, abdominal pain, but liver biopsy is normal. 7) Hepatic abscessation - chronic weight loss, fever, but liver enzymes may be elevated. 8) Right abomasal volvulus - rapid onset, severe dehydration, and a high-pitched ping on the right side. 9) Downer cow syndrome - recumbency due to various causes, but liver function may be normal. 10) Salmonellosis - diarrhea and fever, but fecal culture is positive.

1) Herd history: Review transition cow management, BCS, and incidence of periparturient diseases. 2) Physical examination: Assess BCS, hydration, rumen fill, and presence of acetone odor. 3) Blood tests: Measure BHB (≥1.2 mmol/L indicates subclinical ketosis; ≥3.0 mmol/L clinical ketosis), NEFA (≥0.5 mmol/L prepartum, ≥0.7 mmol/L postpartum), and liver enzymes (AST, GGT, GLDH). 4) Liver biopsy: The gold standard for diagnosis; histopathology shows fat vacuolation in >20% of hepatocytes. 5) Ultrasonography: Liver echogenicity is increased compared to kidney and spleen. 6) Rule out other diseases: Perform a complete blood count, serum chemistry, and urinalysis. 7) Response to treatment: Improvement with glucose and insulin therapy supports the diagnosis.

Blood BHB: Subclinical ketosis ≥1.2 mmol/L; clinical ketosis ≥3.0 mmol/L. NEFA: Elevated >0.5 mmol/L prepartum and >0.7 mmol/L postpartum. Liver enzymes: AST >100 U/L, GGT >50 U/L, GLDH >30 U/L. Total bilirubin may be elevated. Glucose may be low (<50 mg/dL). Calcium may be low (<8.0 mg/dL) if concurrent milk fever. Magnesium and phosphorus may be altered. Rumen fluid analysis: pH may be low (<5.5) if concurrent ruminal acidosis, but often normal. CBC: May show leukocytosis with a left shift if infection is present. Fibrinogen may be elevated. Milk CMT and SCC may be elevated if mastitis is present.

Ultrasonography: The liver appears enlarged with increased echogenicity (bright) compared to the kidney and spleen. The portal vein may be less visible. The liver may have a rounded edge. Ultrasonography can also assess the gallbladder and bile ducts. Radiography: Not typically useful for fatty liver, but may be used to rule out traumatic reticuloperitonitis if a foreign body is suspected. Endoscopy/Laparoscopy: Can be used to visualize the liver and obtain a biopsy, but is rarely performed in practice.

Liver biopsy: Histopathology is the gold standard. Fat vacuoles are seen in hepatocytes, with severity graded as mild (<20% of hepatocytes), moderate (20-40%), or severe (>40%). There may be evidence of hepatocellular degeneration, necrosis, and fibrosis in chronic cases. Cytology of peritoneal fluid may show increased neutrophils if peritonitis is present. Milk cytology may show increased somatic cells if mastitis is present. Necropsy findings include a pale, enlarged, greasy liver that floats in formalin.

Treatment aims to correct the negative energy balance, provide glucose precursors, and support liver function. 1) Fluid therapy: IV administration of 5% dextrose solution (2-4 L) to provide glucose. 2) Oral propylene glycol (250-500 mL/cow, PO, q12h) as a gluconeogenic precursor. 3) Insulin therapy: Protamine zinc insulin (0.1-0.2 IU/kg, SC, q24h) or regular insulin (0.1 IU/kg, IV, then SC) to promote lipogenesis and reduce NEFA uptake. 4) Glucocorticoids: Dexamethasone (0.02-0.04 mg/kg, IV or IM, q24h) to stimulate gluconeogenesis, but use cautiously due to immunosuppression. 5) B-vitamins: Thiamine (10 mg/kg, IM, q24h) and B-complex vitamins. 6) Choline and methionine: Oral or IV supplements to enhance VLDL export. 7) Supportive care: Ensure adequate nutrition, provide high-quality forage, and treat concurrent diseases. 8) In severe cases, consider rumen transfaunation to improve rumen function.

Prognosis is guarded to poor in severe cases. Cows with moderate to severe fatty liver have a higher risk of culling and mortality. Milk yield recovery is often incomplete, and reproductive performance may be impaired. Negative prognostic indicators include severe depression, recumbency, and concurrent diseases. Early detection and treatment of subclinical cases improve the outcome. Cows that respond to treatment within 3-5 days have a better prognosis.

Monitor affected cows daily for appetite, milk production, and clinical signs. Recheck blood BHB and NEFA levels every 2-3 days until normalized. Perform liver biopsy or ultrasound to assess fat content if needed. Review transition cow management: BCS at dry-off and calving, ration formulation, and feed intake. Implement a herd monitoring program for ketosis and fatty liver, including regular BHB testing in the first 2 weeks postpartum. Adjust dry cow and fresh cow rations to prevent overconditioning and ensure adequate energy intake. Provide adequate bunk space and minimize stress.

Pearls: 1) Fatty liver is often subclinical; screen high-risk cows with BHB and NEFA. 2) Liver biopsy is the gold standard for diagnosis. 3) Insulin therapy can be effective but requires careful monitoring. 4) Propylene glycol is a key treatment. 5) Prevention is better than treatment: manage BCS and transition diet. Pitfalls: 1) Do not confuse fatty liver with primary ketosis; liver biopsy may be needed. 2) Avoid excessive glucocorticoid use as it can worsen immunosuppression. 3) Do not ignore concurrent diseases; treat them aggressively. 4) Do not overfeed energy in the dry period. 5) Do not forget to monitor for downer cow syndrome.

1) 5% Dextrose solution: IV, 2-4 L, once or twice daily. 2) Propylene glycol: PO, 250-500 mL/cow, q12h for 3-5 days. 3) Protamine zinc insulin: SC, 0.1-0.2 IU/kg, q24h for 3-5 days. 4) Regular insulin: IV, 0.1 IU/kg, then SC q12h. 5) Dexamethasone: IV or IM, 0.02-0.04 mg/kg, q24h for 1-3 days. 6) Thiamine: IM, 10 mg/kg, q24h. 7) Choline chloride: PO, 25-50 g/cow, q24h. 8) Methionine: PO, 10-20 g/cow, q24h. 9) Flunixin meglumine: IV, 1.1-2.2 mg/kg, q24h for up to 3 days, if inflammation is present. 10) Ceftiofur: SC, 2.2 mg/kg, q24h for 3-5 days, if infection is present. Withdrawal times: Milk and meat withdrawal times vary by drug; consult label. For example, dexamethasone has a milk withdrawal of 72 hours and meat withdrawal of 7 days.

Key studies include: 1) Bobe et al. (2004) reviewed fatty liver in dairy cows, highlighting the role of NEFA and insulin resistance. 2) Grummer (1993) discussed the etiology and treatment of fatty liver, emphasizing the importance of preventing overconditioning. 3) Oetzel (2007) provided guidelines for monitoring and treating subclinical ketosis, including BHB thresholds. 4) A meta-analysis by Raboisson et al. (2014) showed that propylene glycol and insulin are effective in reducing BHB and improving milk yield. 5) The AABP (American Association of Bovine Practitioners) has published consensus recommendations on transition cow management. 6) Studies by Duffield et al. (2009) demonstrated that choline supplementation reduces the incidence of fatty liver. 7) Research by Van Saun (2000) emphasized the importance of body condition score management. 8) A study by Seifi et al. (2011) showed that treatment with insulin and glucose improved liver function in fatty liver cows.