Bovine Ketosis (Clinical and Subclinical Ketosis)

Bovine ketosis is a common metabolic disorder of dairy cattle, particularly in high-producing cows during early lactation, characterized by elevated concentrations of ketone bodies (acetoacetate, beta-hydroxybutyrate, and acetone) in blood, urine, and milk. It occurs when the energy demand for lactation exceeds dietary energy intake, leading to excessive mobilization of adipose tissue and hepatic ketogenesis. The condition manifests in two forms: clinical ketosis, with overt signs such as anorexia, decreased milk production, and neurological signs, and subclinical ketosis, which is asymptomatic but associated with increased risk of other periparturient diseases. The disease is economically significant due to reduced milk yield, increased culling, and predisposition to other metabolic and infectious disorders. In beef cattle, ketosis is less common but can occur in thin cows with inadequate nutrition or in feedlot cattle on high-concentrate diets. The transition period (3 weeks before to 3 weeks after calving) is the critical window for development, as cows undergo dramatic metabolic and endocrine changes to support lactation.

The primary cause of bovine ketosis is a negative energy balance (NEB) in early lactation, when energy requirements for milk production exceed dietary energy intake. This triggers lipolysis of adipose tissue, releasing non-esterified fatty acids (NEFAs) into the bloodstream. The liver partially oxidizes NEFAs to ketone bodies, which accumulate when production exceeds utilization. Predisposing nutritional factors include inadequate energy density of the ration, poor feed intake due to social stress or overcrowding, and suboptimal dry matter intake (DMI). Specifically, rations with insufficient non-fiber carbohydrates (NFC) or excessive rumen-degradable protein can exacerbate NEB. Additionally, deficiencies in key nutrients such as choline, methionine, and carnitine impair hepatic lipid export, leading to fatty liver and worsening ketosis. Management-related causes include abrupt ration changes, poor bunk management, and inadequate transition cow programs. Secondary ketosis can arise from any condition that reduces feed intake, such as retained placenta, metritis, mastitis, or abomasal displacement. In beef cattle, ketosis may occur in thin cows during late gestation or early lactation due to inadequate body condition or poor forage quality. The disease is not infectious, but herd-level outbreaks can occur due to shared nutritional and management practices.

Bovine ketosis is most prevalent in high-producing dairy breeds, particularly Holstein-Friesian, during the first 4 to 6 weeks of lactation. The incidence of clinical ketosis is typically 2% to 15% in dairy herds, while subclinical ketosis affects 20% to 40% of cows in early lactation, with some herds exceeding 50%. The risk increases with parity, as older cows (third lactation and greater) have higher milk production and greater adipose mobilization. The transition period is the highest risk period, with peak incidence at 2 to 3 weeks postpartum. Seasonality is not a direct risk factor, but heat stress can reduce DMI and exacerbate NEB. Herd size and management intensity influence prevalence; larger, high-producing herds with intensive feeding systems often have higher rates. Economic losses are substantial, with each case of clinical ketosis costing an estimated $200 to $500 due to reduced milk yield, treatment costs, and increased risk of other diseases. Subclinical ketosis is associated with a 2- to 3-fold increased risk of clinical disease, including metritis, mastitis, and displaced abomasum. In beef cattle, ketosis is less common but can occur in thin cows during late gestation or early lactation, particularly in range conditions with poor nutrition.

The pathophysiology of bovine ketosis centers on the metabolic adaptation to negative energy balance. During early lactation, glucose demand for lactose synthesis in the mammary gland is high, while glucose production via hepatic gluconeogenesis is often insufficient. This leads to hypoglycemia and low insulin levels, promoting adipose tissue lipolysis. NEFAs are released into the bloodstream and taken up by the liver, where they can be oxidized to acetyl-CoA. When the tricarboxylic acid (TCA) cycle is overwhelmed or oxaloacetate is limiting, acetyl-CoA is diverted to ketogenesis, producing acetoacetate and beta-hydroxybutyrate (BHB). Acetone is formed by spontaneous decarboxylation of acetoacetate. Elevated ketone bodies cause metabolic acidosis and suppress appetite, exacerbating the negative energy balance. Concurrently, excessive NEFA uptake can overwhelm hepatic mitochondrial oxidation, leading to esterification of NEFAs to triglycerides and accumulation in hepatocytes, resulting in fatty liver. Fatty liver impairs hepatic function, including gluconeogenesis and urea cycle activity, further worsening the metabolic derangement. The neurological signs of clinical ketosis are attributed to the effects of ketone bodies on the central nervous system, possibly due to altered neurotransmitter metabolism or cerebral energy deficiency. The disease also induces oxidative stress and inflammation, contributing to immunosuppression and increased susceptibility to infectious diseases.

Intrinsic risk factors include high milk yield, parity (older cows), genetics, and body condition score (BCS) at calving. Cows with BCS > 3.5 (on a 1-5 scale) are at higher risk due to excessive adipose mobilization. Transition stress, including calving, pen changes, and social hierarchy disruption, reduces DMI. Immunosuppression around calving increases susceptibility to secondary infections. Extrinsic factors include ration formulation errors, such as inadequate energy density, poor forage quality, and improper NFC-to-NDF ratio. Overcrowding, poor bunk space, and inadequate water access reduce feed intake. Poor ventilation, heat stress, and dirty bedding contribute to stress and disease. Milking frequency and management practices, such as abrupt ration changes, can precipitate ketosis. In beef cattle, thin body condition, inadequate nutrition, and cold stress are risk factors.

Clinical ketosis typically presents within the first 2 to 6 weeks of lactation. Affected cows show a sudden drop in milk production, reduced appetite, and weight loss. They may have a characteristic sweet, acetone-like odor on the breath and in milk. Neurological signs can include lethargy, depression, and in severe cases, abnormal licking, chewing, circling, head pressing, and blindness. Some cows exhibit pica (eating dirt or bedding). Rumen motility is often decreased, and feces may be firm and dry. Body temperature is usually normal or slightly subnormal. In subclinical ketosis, there are no visible signs, but cows are at increased risk for other diseases. Herd-level indicators include an increased incidence of retained placenta, metritis, mastitis, and displaced abomasum. Cows may have a poor appetite and be slow to peak milk production. In beef cows, signs are similar but may be less pronounced, with weight loss and reduced milk production affecting calf growth.

Differential diagnoses for clinical ketosis include: 1) Displaced abomasum (DA) - both conditions occur in early lactation and cause anorexia and decreased milk; DA is distinguished by a high-pitched ping on auscultation/percussion over the left or right flank, and ultrasound may show abomasal distension. 2) Traumatic reticuloperitonitis (hardware disease) - presents with fever, abdominal pain, and decreased rumen motility; diagnosis via ultrasound or radiography for foreign body. 3) Metritis - fever, foul-smelling vaginal discharge, and uterine enlargement; distinguished by vaginal exam and ultrasound. 4) Mastitis - abnormal milk, udder swelling, and systemic signs; diagnosed by CMT and culture. 5) Fatty liver disease - often coexists with ketosis; diagnosis via liver biopsy or ultrasound showing increased echogenicity. 6) Hypocalcemia (milk fever) - occurs within 24-72 hours post-calving, with recumbency and muscle weakness; responds to calcium therapy. 7) Indigestion or rumen acidosis - history of grain overload, rumen pH < 5.5, and diarrhea. 8) Neurological diseases such as rabies, listeriosis, or polioencephalomalacia - if neurological signs are prominent; differentiate via history, response to thiamine, and CSF analysis. 9) Abomasal impaction - similar signs but less common; diagnosed via ultrasound or exploratory laparotomy. 10) Peritonitis - fever, abdominal pain, and elevated peritoneal fluid white blood cells.

The diagnostic approach for bovine ketosis begins with a thorough herd history and physical examination. In individual cows, the presence of clinical signs such as anorexia, decreased milk, and acetone odor suggests ketosis. Confirmatory testing includes: 1) Blood BHB measurement using a hand-held meter (e.g., Precision Xtra) or laboratory analysis; BHB ≥ 1.2 mmol/L indicates subclinical ketosis, and ≥ 3.0 mmol/L is consistent with clinical ketosis. 2) Urine or milk ketone tests (e.g., Ketostix, Milk Ketone Test) are less accurate but can be used for screening. 3) Blood glucose is often low (< 50 mg/dL), but not diagnostic. 4) Rumen fluid analysis may show decreased protozoal motility and a pH within normal range (6.0-7.0) unless concurrent acidosis. 5) Liver function tests, such as elevated liver enzymes (AST, GGT) and bilirubin, may indicate fatty liver. 6) Ultrasonography of the liver can assess fat content, and liver biopsy is the gold standard for diagnosing fatty liver. 7) Rule out other diseases via complete blood count, serum chemistry, and imaging. Herd-level diagnosis involves testing a subset of cows (e.g., 10-15 cows) in early lactation for BHB to estimate prevalence and guide management changes.

Key laboratory findings in bovine ketosis include: Blood BHB: Subclinical ketosis is defined as BHB ≥ 1.2 mmol/L, while clinical ketosis typically has BHB > 3.0 mmol/L. Blood glucose is often low (< 50 mg/dL). NEFA levels are elevated (> 0.4 mmol/L in the prepartum period and > 0.7 mmol/L postpartum). Liver enzymes (AST, GGT) may be mildly elevated, and bilirubin may be increased. Serum calcium, magnesium, and phosphorus may be low due to concurrent periparturient diseases. Rumen fluid analysis: pH is usually normal (6.0-7.0), but protozoal motility is decreased, and methylene blue reduction time is prolonged (> 3 minutes). Urine and milk ketone tests are positive. Complete blood count may show a stress leukogram (neutrophilia, lymphopenia) if concurrent infection. Fibrinogen may be elevated if inflammation is present. Milk somatic cell count (SCC) may be elevated if mastitis is concurrent. Liver biopsy reveals fat vacuolation in hepatocytes, with a fat score of 3 or higher (on a 0-5 scale) indicating severe fatty liver.

Ultrasonography is the most useful imaging modality for bovine ketosis. Liver ultrasound may show increased echogenicity due to fat infiltration, and the liver may be enlarged. The gallbladder may be distended. Reticular contractions can be assessed, and the reticular wall thickness may be normal. Ultrasound can also rule out abomasal displacement by visualizing the abomasum in its normal position. In cases of concurrent fatty liver, the liver may appear diffusely hyperechoic compared to the spleen. Radiography is not routinely used for ketosis but may be employed to rule out traumatic reticuloperitonitis if hardware disease is suspected. Endoscopy or laparoscopy is rarely needed but can be used for liver biopsy or visual inspection of the liver.

Liver biopsy is the definitive diagnostic test for fatty liver, which often accompanies ketosis. Histopathological examination reveals hepatocytes with large cytoplasmic vacuoles (fat droplets), and the degree of fat infiltration can be graded. In severe cases, more than 50% of hepatocytes are affected. Peritoneal fluid cytology is not typically performed for ketosis but may be used to rule out peritonitis. Milk cytology may show increased somatic cells if mastitis is present. Rumen wall biopsy is not indicated. Necropsy findings include a pale, enlarged, fatty liver, and histology confirms hepatic lipidosis.

Treatment of bovine ketosis aims to correct the negative energy balance, restore blood glucose, and reduce ketone body production. The primary therapy is oral administration of propylene glycol (250-500 mL per cow, once or twice daily for 3-5 days) as a gluconeogenic precursor. Intravenous glucose (500 mL of 50% dextrose) can be given for immediate effect, but its effect is short-lived. Glucocorticoids such as dexamethasone (20-40 mg IV or IM) or isoflupredone acetate (10-20 mg IM) are often used to stimulate gluconeogenesis and reduce insulin sensitivity, but they may cause immunosuppression and should be used cautiously. In severe cases, insulin therapy (e.g., 100-200 IU of long-acting insulin SC) may be considered, but it is expensive and requires careful monitoring. Supportive care includes fluid therapy with oral electrolytes or IV fluids if dehydrated. Concurrent diseases such as metritis or mastitis must be treated with appropriate antibiotics and anti-inflammatory drugs. For cows with fatty liver, oral administration of choline (e.g., 25-50 g of choline chloride) or propylene glycol may help. Nutritional management includes increasing energy density of the ration, improving feed intake, and ensuring adequate bunk space. In beef cows, similar principles apply, with emphasis on improving body condition and nutrition.

The prognosis for bovine ketosis is generally good with prompt treatment, especially if the condition is uncomplicated. Most cows recover within 3-7 days, and milk production gradually returns to expected levels, though it may not reach full potential. Cows with severe fatty liver or concurrent diseases have a poorer prognosis, with increased risk of culling and death. Negative prognostic indicators include prolonged anorexia, severe neurological signs, and failure to respond to treatment within 48 hours. Subclinical ketosis is associated with increased risk of other diseases, but early detection and management can mitigate long-term effects. Reproductive performance may be impaired, with increased days open and reduced conception rates. Overall, the long-term survival of affected cows is reduced compared to unaffected herdmates.

Follow-up for individual cows includes monitoring BHB levels daily until they normalize (< 1.2 mmol/L). Milk production and feed intake should be recorded. Cows should be observed for signs of secondary diseases such as metritis or mastitis. Herd-level follow-up involves testing a cohort of cows (e.g., 10-15 cows) at 2-3 weeks postpartum for BHB to assess the effectiveness of prevention programs. Ration formulation should be reviewed, and transition cow management should be audited, including body condition scoring, dry matter intake, and pen stocking density. Regular monitoring of milk production and disease incidence can help identify ongoing issues. Cows that have had ketosis should be monitored for reproductive performance and culling risk.

Pearls: 1) Use a hand-held BHB meter for rapid, on-farm diagnosis; BHB ≥ 1.2 mmol/L is the threshold for subclinical ketosis. 2) Oral propylene glycol is the most effective treatment; give 300 mL twice daily for 3-5 days. 3) Always check for concurrent diseases such as metritis or mastitis, as they can cause secondary ketosis. 4) In herds with high ketosis prevalence, focus on transition cow management, including avoiding overconditioning, providing a balanced ration, and minimizing stress. 5) Liver ultrasound can help assess fatty liver severity and guide prognosis. Pitfalls: 1) Do not rely solely on urine or milk ketone tests, as they are less accurate than blood BHB. 2) Avoid overuse of glucocorticoids, as they can cause immunosuppression and worsen fatty liver. 3) Do not forget to treat the underlying cause if ketosis is secondary to another disease. 4) Do not ignore subclinical ketosis; it is a major risk factor for other diseases and economic loss. 5) Do not assume that a cow with ketosis has a simple energy deficit; always rule out other causes of anorexia.

Based on Plumb's Veterinary Drug Handbook and AABP guidelines, the following protocols are recommended: 1) Propylene glycol: 250-500 mL per cow orally once or twice daily for 3-5 days. 2) Dextrose 50%: 500 mL IV slowly, may repeat in 12-24 hours. 3) Dexamethasone: 20-40 mg IV or IM once daily for 1-2 days. 4) Isoflupredone acetate: 10-20 mg IM once. 5) Insulin (long-acting, e.g., protamine zinc insulin): 100-200 IU SC once daily for 2-3 days, with careful monitoring of blood glucose. 6) Choline chloride: 25-50 g orally once daily for 3-5 days. 7) For concurrent infections, use appropriate antibiotics such as ceftiofur (2.2 mg/kg SC q24h for 3-5 days) or oxytetracycline (10-20 mg/kg IV or SC q24h). 8) NSAIDs: Flunixin meglumine (1.1-2.2 mg/kg IV or IM q24h for 1-3 days) for anti-inflammatory and analgesic effects. 9) Fluid therapy: Oral electrolytes or IV fluids (e.g., isotonic saline or lactated Ringer's) as needed. Withdrawal times must be observed: For propylene glycol, no withdrawal is required; for dexamethasone, milk withdrawal is 72 hours and meat withdrawal is 8 days; for flunixin, milk withdrawal is 36 hours and meat withdrawal is 4 days; for ceftiofur, milk withdrawal is 0 hours and meat withdrawal is 4 days; for oxytetracycline, milk withdrawal is 96 hours and meat withdrawal is 28 days.

Landmark studies have established the importance of subclinical ketosis as a major production disease. Duffield et al. (2009) conducted a meta-analysis showing that subclinical ketosis (BHB ≥ 1.2 mmol/L) is associated with increased risk of displaced abomasum, metritis, and clinical ketosis. Oetzel (2004) recommended monitoring BHB in early lactation cows to identify herds with high prevalence. McArt et al. (2012) demonstrated that treatment of subclinical ketosis with propylene glycol improved milk production and reduced the risk of other diseases. AABP consensus guidelines emphasize the importance of transition cow management, including body condition score, nutrition, and stress reduction. Studies on fatty liver have shown that choline supplementation can reduce liver fat content and improve milk yield. Overall, the evidence supports early detection and treatment of ketosis to minimize economic losses and improve cow health.