Overview and Clinical Importance
Bovine and small ruminant medicine represents a significant portion of the BCSE examination. Domain 4 (Medicine) is the largest domain on the exam with 50-55 questions, and food animal medicine is heavily tested. This guide covers the most commonly tested conditions in cattle (bovine), sheep (ovine), and goats (caprine).
Understanding the metabolic, infectious, and parasitic diseases of production animals is essential for entry-level veterinary competency. Many conditions have significant economic impact and zoonotic potential, making them high-priority testing topics.
PART 1: BOVINE MEDICINE
Bovine Respiratory Disease Complex (BRD)
Bovine Respiratory Disease (BRD), also called shipping fever pneumonia, is the most common and costly disease affecting the North American beef cattle industry. BRD accounts for approximately 60-90% of all feedlot morbidity and mortality.
Etiology and Pathophysiology
BRD results from complex interactions between environmental stressors, host factors, and multiple pathogens:
MEMORY AID - BRD Bacterial Pathogens: "Many People Have More Problems" - Mannheimia haemolytica, Pasteurella multocida, Histophilus somni, Mycoplasma bovis, (Plus viruses!)
[Include Image: Figure 1. Fibrinous pneumonia in cattle with BRD showing characteristic marbled lung appearance]
Clinical Signs
Clinical signs typically appear within the first 2 weeks after arrival at feedlots:
- Fever (greater than 40 degrees C / 104 degrees F)
- Depression and lethargy
- Decreased feed intake and milk production
- Nasal discharge (serous to mucopurulent)
- Coughing and increased respiratory rate
- Ocular discharge and lacrimation
Diagnosis
Diagnosis is based on clinical signs, history, and environmental factors:
- Thoracic ultrasonography (TUS) - highly effective for detecting subclinical cases
- Auscultation of lung sounds
- Transtracheal wash or bronchoalveolar lavage for culture
- PCR testing for specific pathogens
- Necropsy - definitive diagnosis (fibrinous bronchopneumonia)
Treatment and Prevention
Broad-spectrum antimicrobials labeled for BRD are the primary treatment. Common choices include:
- Macrolides: Tulathromycin, tilmicosin, gamithromycin
- Fluoroquinolones: Enrofloxacin, danofloxacin
- Cephalosporins: Ceftiofur
- Florfenicol
- NSAIDs for supportive care (flunixin meglumine)
MEMORY AID - BRD Prevention Timing: Vaccinate 2-3 weeks BEFORE transport for best immunity. "Before the Trip, Give the Jab" - On-arrival vaccination may not provide complete protection in time.
Displaced Abomasum (DA)
Displaced abomasum is a common condition primarily affecting high-producing dairy cattle, especially in early lactation. Up to 90% of cases occur within the first 4 weeks postpartum.
[Include Image: Figure 2. Anatomical diagram showing normal abomasum position versus LDA and RDA]
Risk Factors
MEMORY AID - LDA Risk Factors: "Fat Cows with Ketosis and Fever Make LDAs" - Fat/overconditioned (BCS greater than 3.5), Concurrent diseases (metritis, mastitis), Ketosis (4.4x higher risk), Fresh cow period (postpartum), Milk fever/hypocalcemia
Key predisposing factors include:
- Hypocalcemia - reduces abomasal motility (atony)
- Ketosis - both a cause and consequence of DA
- Concurrent diseases (mastitis, metritis) causing endotoxemia
- Overconditioned cows (BCS greater than 3.5) - decreased dry matter intake
- Inadequate dietary fiber/poor rumen fill
- Transition period stress
Clinical Signs
Classic presentation includes:
- Anorexia and decreased milk production
- Reduced rumen motility (89.7% of cases)
- Decreased intestinal motility (61.1%)
- Pasty or scant feces
- Abnormal demeanor/depression (48.2%)
- Ketotic breath odor (concurrent ketosis)
Treatment
Bovine Ketosis (Acetonemia)
Ketosis is the most common metabolic disorder in high-producing dairy cows, occurring primarily in the first 2-6 weeks of lactation. It results from negative energy balance when glucose demand exceeds supply.
Pathophysiology
During early lactation, energy intake is insufficient to meet milk production demands:
- Peak milk production occurs at 4-6 weeks postpartum
- Maximum dry matter intake occurs at 8-10 weeks postpartum
- This mismatch creates NEGATIVE ENERGY BALANCE
- Fat mobilization leads to increased NEFA and ketone body production
- Ketone bodies: Beta-hydroxybutyrate (BHB - 70%), Acetoacetate, Acetone
MEMORY AID - Ketosis Timing: "Peak milk at 4, Peak food at 8" - This 4-week gap explains why ketosis peaks at 2-6 weeks postpartum.
Clinical Forms
MEMORY AID - Ketosis Appetite Pattern: "Grain Goes, Silage Slides, Hay Hangs On" - The characteristic pattern of appetite loss where cows refuse grain first, then silage, but may continue eating hay.
Diagnosis
- Serum or whole blood BHB measurement (gold standard)
- Urine test strips (detect acetoacetate) - cow-side test
- Milk BHB test strips
- Plasma glucose (reduced from normal 50-65 mg/dL to 20-40 mg/dL)
- Milk fat-to-protein ratio greater than 1.5
Treatment
- IV Dextrose (50% solution, 500 mL) - immediate but transient effect, relapses common
- Propylene glycol (225g PO BID x 2 days, then 110g daily x 2 days) - gluconeogenic precursor
- Glucocorticoids (dexamethasone) - stimulates gluconeogenesis
- B vitamins (B12, thiamine) - cofactors for metabolism
- Address underlying disease (DA, mastitis, metritis)
PART 2: SMALL RUMINANT MEDICINE
Small ruminant medicine encompasses both sheep (ovine) and goats (caprine). While many diseases affect both species, there are important species-specific differences in susceptibility, clinical presentation, and treatment. Key areas for BCSE include parasitism, metabolic diseases, and infectious diseases.
Haemonchosis (Barber Pole Worm)
Haemonchus contortus (barber pole worm, red stomach worm) is the most important parasitic disease of small ruminants worldwide. It is a blood-sucking nematode that localizes in the abomasum, causing severe anemia and death.
Life Cycle
Haemonchus has a direct life cycle:
- Eggs shed in feces of infected animals
- Eggs develop to L1 then L2 larvae in the environment
- L3 (infective stage) develops and migrates onto herbage (1-2 inches)
- L3 ingested by grazing animal
- L3 matures to adult in abomasum, begins blood-feeding
MEMORY AID - Haemonchus Climate: "Hot and Humid Helps Haemonchus" - Optimal development requires greater than 18 degrees C and greater than 50mm rainfall monthly. Below 9 degrees C, no larval development occurs.
[Include Image: Figure 3. Life cycle of Haemonchus contortus showing egg to adult stages]
Clinical Signs
- Anemia (pale mucous membranes - FAMACHA scoring)
- Bottle jaw (submandibular edema) - due to hypoproteinemia
- Weight loss and poor body condition
- Weakness and lethargy
- Sudden death in acute cases
- Note: Diarrhea is NOT a typical sign (unlike other GI parasites)
[Include Image: Figure 4. FAMACHA scoring chart showing conjunctival color grades 1-5]
Diagnosis
- Fecal egg count (FEC) - McMaster technique, eggs per gram (EPG)
- FAMACHA scoring for anemia assessment
- Packed cell volume (PCV) - less than 20% indicates severe anemia
- Fecal Egg Count Reduction Test (FECRT) - tests anthelmintic efficacy
- DrenchRite Assay - detects drug resistance
- Necropsy - adult worms in abomasum (barber pole appearance)
Treatment and Anthelmintic Resistance
ANTHELMINTIC RESISTANCE is a major global concern. Resistance has been documented to all major drug classes.
MEMORY AID - SMART Drenching: S - Select animals for treatment (FAMACHA, FEC). M - Maintain refugia. A - Accurate dosing (weigh animals). R - Right product. T - Test for resistance (FECRT).
Pregnancy Toxemia (Twin Lamb/Kid Disease)
Pregnancy toxemia is a metabolic disease of ewes and does in late pregnancy (last 4-6 weeks). It occurs when energy demands from growing fetuses exceed the dam's ability to consume adequate nutrition.
Pathophysiology Comparison
MEMORY AID - Pregnancy Toxemia Risk: "Twin Troubles in Thin and Thick" - Both underconditioned (BCS less than 2) AND overconditioned (BCS greater than 4) ewes/does carrying twins or triplets are at highest risk.
Clinical Signs
Signs typically appear 1-3 weeks before parturition:
- Early: Decreased appetite, lagging behind flock, lethargy, droopy head
- Progressive: Isolation from flock, wandering aimlessly
- Neurologic: Blindness, circling, head pressing, star gazing, muscle tremors, teeth grinding
- Terminal: Recumbency, unable to rise, coma, death in 2-10 days
- Sweet (ketotic) breath odor
Diagnosis
- Serum BHB: greater than 0.8 mmol/L indicates malnutrition; greater than 1.6 mmol/L indicates severe malnutrition
- Urine ketone dipstick (ketonuria)
- Hypoglycemia (may also see hyperglycemia in some cases)
- Metabolic acidosis
- Often concurrent hypocalcemia and hypokalemia
- Postmortem: BHB in aqueous humor greater than 2.0 mmol/L is diagnostic
Treatment
Treatment must be aggressive and early for any chance of success:
- Propylene glycol (60-100 mL PO BID-QID) - gluconeogenic precursor
- IV dextrose (50% solution) for severe cases
- Oral electrolyte solutions with bicarbonate
- Calcium supplementation (often concurrent hypocalcemia)
- Induction of parturition or C-section if near term - removes energy drain
- Flunixin meglumine (2.5 mg/kg) improves survival
Caprine Arthritis Encephalitis (CAE)
CAE is a persistent lentiviral infection (Retroviridae family) of goats. It is considered the most significant viral disease of goats in the United States. CAE virus (CAEV) is closely related to Ovine Progressive Pneumonia (OPP/Maedi-Visna) in sheep.
Clinical Syndromes
MEMORY AID - CAE Forms: "CAMP" - Chronic arthritis (adults), Acute encephalitis (kids), Mastitis (hard bag), Pneumonia (chronic). The most common form is Chronic Arthritis in adults.
[Include Image: Figure 5. Swollen carpal joints (big knees) in a goat with CAE arthritis]
Transmission and Prevention
PRIMARY transmission is through colostrum and milk from infected does to kids. This is the most important route!
Other transmission routes:
- Direct contact and body fluids (saliva, respiratory secretions)
- Contaminated equipment (needles, dehorners, tattoo equipment)
- Possibly in utero (less common)
Diagnosis is by serologic testing (ELISA, AGID) or PCR. Note that seroconversion timing is variable, and antibody titers may be low in late pregnancy.
MEMORY AID - CAE Prevention: "Snatch the Kid, Heat the Milk, Test the Herd" - Immediate removal at birth, heat-treat colostrum (56 degrees C x 60 min), regular serologic testing.
Enterotoxemia (Overeating Disease / Pulpy Kidney)
Enterotoxemia is caused by Clostridium perfringens toxins produced when the bacteria proliferate rapidly in the intestine. It is one of the most common clostridial diseases of sheep and goats worldwide.
Types and Toxins
MEMORY AID - Clostridial Types: "Babies get Beta, Bigger ones get Epsilon" - Type C (beta toxin) affects young lambs because beta toxin is inactivated by pancreatic enzymes that older animals produce. Type D (epsilon toxin) affects older animals because epsilon is ACTIVATED by these same enzymes.
Clinical Signs
Type D enterotoxemia typically presents as:
- Sudden death - often the best conditioned, fastest growing lambs
- If seen alive: excitement, incoordination, seizures
- Neurologic signs: opisthotonos, circling, head pressing
- Diarrhea (more common in goats than sheep)
- Hyperglycemia and glucosuria (may detect glucose in urine)
- Death usually within 24 hours
Diagnosis and Necropsy Findings
- History of recent diet change or overeating
- Necropsy: Full rumen with undigested feed, pulpy kidneys (rapid autolysis), pericardial effusion, petechial hemorrhages
- Glucosuria on urine dipstick (if necropsy is performed promptly)
- PCR for C. perfringens typing
- ELISA for epsilon toxin in intestinal contents
Treatment and Prevention
Treatment is often unrewarding, but may include:
- C. perfringens C and D antitoxin (5 mL SQ)
- Supportive care and fluid therapy
- Pain management
MEMORY AID - CD/T Vaccination: "CD/T for Kids, Teens, and Moms" - Initial series: 2 doses 3-4 weeks apart. Booster: Annual or more frequently if high-risk diet. Pregnant females: 3-4 weeks before parturition.
Bovine Medicine
- BRD is multifactorial (stress + virus + bacteria) and is the costliest beef cattle disease
- Displaced abomasum: LEFT ping = LDA (common, good prognosis); RIGHT ping = RDA/volvulus (emergency, surgery required)
- Ketosis occurs POSTPARTUM due to negative energy balance; treat with propylene glycol, IV dextrose, glucocorticoids
- Transition period management is critical for preventing metabolic diseases
Small Ruminant Medicine
- Haemonchus contortus is the most important parasite - causes ANEMIA, not diarrhea; use FAMACHA scoring
- Anthelmintic resistance is a major global problem - use SMART drenching and maintain refugia
- Pregnancy toxemia occurs PREPARTUM in ewes/does carrying multiples; prognosis is poor once recumbent
- CAE is a lifelong lentiviral infection - NO vaccine, NO treatment; prevent through colostrum/milk management
- Enterotoxemia: Type C affects young lambs (beta toxin); Type D affects older lambs on grain (epsilon toxin, pulpy kidney)
- CD/T vaccination is the single most important vaccine for sheep and goats