NAVLE Bovine High-Yield Guide: Top Tested Cattle Diseases

Most bovine questions on the NAVLE come from a predictable list: periparturient metabolic disease, displaced abomasum, respiratory disease complex, the big infectious and regulatory diseases, calf diarrhea, and food-animal drug rules. This guide covers that list in the order the exam tends to test it, with the signalment, key signs, diagnosis, treatment and the "gotcha" detail that separates the right answer from the plausible distractor. Numbers below are drawn from the Merck Veterinary Manual; where a figure could not be verified, it has been left out on purpose.

Why Bovine Matters on the NAVLE

Small-animal-focused students lose more points on cattle than on any other species, not because the material is hard but because it is unfamiliar and rule-based. Cattle questions reward pattern recognition (a fresh cow down with cold ears, a left-sided ping, a scouring calf at three days versus three weeks) and they test regulation: prohibited drugs, reportable diseases, what a positive caudal fold test means. For how species are weighted, see the NAVLE complete guide.

Metabolic Disease of the Periparturient Cow

Milk Fever (Parturient Paresis, Hypocalcemia)

• Signalment: Older, high-producing dairy cows (Jerseys over-represented). Most cases occur between the onset of calving and about 3 days into lactation.
• Key signs: Stage 1, standing, hyperexcitable, tremors. Stage 2, sternal recumbency, S-shaped neck, cold extremities, dull. Stage 3, lateral recumbency, coma, bloat, death.
• Diagnosis: Clinical picture plus low serum calcium; clinical cases typically fall below 1.5 mmol/L (6.0 mg/dL) against a lower reference of about 8.5 mg/dL.
• Treatment: Slow IV 23% calcium gluconate, 500 mL for an adult cow, while auscultating the heart. Oral calcium boluses for stage 1 or as follow-up. Recumbent cows need good footing and frequent repositioning.
• Gotcha: Rapid IV calcium causes fatal arrhythmia. Hypocalcemia also predisposes to retained placenta, DA, uterine prolapse and mastitis, so it appears as the "underlying cause" in many other question stems.

Ketosis (Hyperketonemia)

• Signalment: Dairy cows in negative energy balance, most in the first 2 weeks of lactation (often with another disease) or around peak lactation at 4 to 6 weeks.
• Key signs: Milk drop, reduced appetite (concentrates refused first), weight loss, firm feces, acetone breath. Nervous ketosis (a minority): abnormal licking, pica, incoordination, bellowing, aggression.
• Diagnosis: Blood beta-hydroxybutyrate; Merck gives 1.2 mmol/L as the standard threshold for hyperketonemia. Milk or urine ketone strips are cheaper cowside screens.
• Treatment: 500 mL of 50% dextrose IV as a single bolus, plus oral propylene glycol 250 to 400 g per cow once daily for 3 to 5 days. Merck no longer recommends glucocorticoids as routine.
• Gotcha: Nervous ketosis is a top differential for a fresh cow with neurological signs; check BHB before you reach for listeriosis or PEM.

Hypomagnesemia (Grass Tetany)

• Signalment: Lactating beef cows on lush spring pasture, especially grass with less than 0.2% magnesium on a dry-matter basis or soils high in potassium and nitrogen, which reduce rumen magnesium absorption.
• Key signs: Hyperexcitability, muscle twitching, staggering, then recumbency with paddling convulsions and sudden death. Often simply found dead.
• Treatment: Combined calcium and magnesium solution slowly IV, then SC magnesium and dietary supplementation. Handle quietly; stimulation triggers seizures.
• Gotcha: Milk fever cows are dull and flaccid; grass tetany cows are hyperesthetic and convulsing. Same season, opposite demeanor.

Displaced Abomasum (LDA, RDA, Volvulus)

• Signalment: High-producing dairy cows; about 80 to 85% of LDAs occur within a month of calving. Deep-bodied cows, hypocalcemia, hypokalemia, low dry-matter intake and concurrent metritis or mastitis are risk factors.
• Key signs: Anorexia, milk drop, scant feces, ketosis. A ping on simultaneous percussion and auscultation between ribs 9 and 13 on the left (LDA) or right (RDA/volvulus). A right-sided ping cranial to rib 10 points to RDA or volvulus rather than cecal gas or ileus; a ping that reaches forward to rib 8 in a depressed, dehydrated, toxemic cow suggests volvulus.
• Diagnosis: The ping is the key finding. Blood work shows hypochloremic, hypokalemic metabolic alkalosis because abomasal chloride is sequestered. Volvulus cows are tachycardic and dehydrated; L-lactate of 2 mmol/L or less predicts a good surgical outcome, 6 mmol/L or more a poor one.
• Treatment: LDA: rolling can work early but recurs; omentopexy, abomasopexy or toggle-pin fixation is definitive. RDA and volvulus: prompt surgery, always.

Rumen Acidosis (Grain Overload)

• Signalment: Any ruminant with sudden access to grain or a rapid ration change; feedlot cattle, or a dairy cow that got into the feed bin.
• Key signs: Within hours: depression, ataxia, rumen stasis with splashy contents, profuse malodorous diarrhea, dehydration, hypothermia, recumbency.
• Diagnosis: Rumen fluid pH below 5.5 is strongly suggestive (normal roughage-fed pH 6 to 7). Streptococcus bovis and lactobacilli proliferate and produce lactic acid; protozoa disappear.
• Treatment: Severe: rumenotomy or lavage, IV bicarbonate, thiamine. Moderate: oral magnesium hydroxide and hay.
• Gotcha: Sequelae are the exam favorites: laminitis (the link to chronic laminitis is suspected rather than proven), rumenitis, mycotic rumenitis relapse a few days later, liver abscesses (Fusobacterium necrophorum), and polioencephalomalacia.

Fresh-cow rule: hypocalcemia sits underneath almost everything. Milk fever, retained placenta, DA, metritis and mastitis cluster in the same cow because low calcium slows smooth muscle and blunts immunity. If a question asks for the predisposing factor, hypocalcemia is usually it.

Respiratory Disease

Bovine Respiratory Disease Complex (Shipping Fever)

• Signalment: Recently weaned, transported, commingled calves, typically within the first weeks after feedlot arrival.
• Pathogens: Viral primers (BHV-1, BRSV, PI3, BVDV) plus stress, then Mannheimia haemolytica (leukotoxin, fibrinous cranioventral bronchopneumonia), Pasteurella multocida, Histophilus somni, Mycoplasma bovis.
• Treatment: Labeled antimicrobials such as florfenicol, tulathromycin, tilmicosin, ceftiofur or enrofloxacin used on-label (extralabel fluoroquinolone use in food animals is prohibited); NSAID support; metaphylaxis in high-risk arrivals.
• Gotchas: Histophilus somni also causes thrombotic meningoencephalitis; Mycoplasma bovis causes chronic pneumonia with arthritis and otitis and never responds to beta-lactams. IBR (BHV-1) causes rhinotracheitis, conjunctivitis, abortion at about 4 to 7 months, pustular vulvovaginitis and balanoposthitis; a modified-live vaccine in naive pregnant cows can itself abort, and latency in the trigeminal ganglion allows reactivation.

Gastrointestinal Disease

Hardware Disease (Traumatic Reticuloperitonitis)

• Signalment: Adult cattle (indiscriminate eaters); rare in sheep and goats.
• Key signs: Sudden drop in intake and milk, mild fever, arched back, grunt on withers pinch or reticular percussion, reduced rumen motility; confirm with ultrasound or radiography.
• Treatment: Rumen magnet plus antimicrobials; laparorumenotomy if no response.
• Gotcha: Sequelae are tested: traumatic pericarditis (muffled heart sounds, jugular distension, brisket edema), vagal indigestion, liver abscess.

Bovine Viral Diarrhea (BVD) and Mucosal Disease

• Key concept: Fetal infection with noncytopathic BVDV at roughly 40 to 120 days of gestation produces an immunotolerant persistently infected (PI) calf that sheds for life; later fetal infection causes cerebellar hypoplasia, ocular defects or abortion. Control is finding and removing PIs.
• Mucosal disease: A PI animal superinfected with a cytopathic strain develops fatal erosive stomatitis, enteritis and diarrhea.
• Diagnosis: Ear-notch antigen ELISA or immunohistochemistry, PCR. A single positive animal must be retested after about 3 weeks to distinguish a transient acute infection from a PI.

Johne's Disease (Paratuberculosis)

• Agent: Mycobacterium avium subsp. paratuberculosis, acquired as a calf by the fecal-oral route (or in colostrum), with clinical signs delayed until after sexual maturity.
• Key signs: Chronic weight loss with pipe-stream diarrhea and a normal appetite; hypoproteinemia with brisket edema. No treatment; control is calf hygiene and test-and-cull.
• Diagnosis: Fecal PCR has replaced culture and is more sensitive and specific than serology; serum or milk ELISA is rapid and more than 85% sensitive in clinical cases; necropsy with culture and histology of multiple tissues is the gold standard.

Salmonellosis

• Serotypes: S. Dublin is host-adapted to cattle and causes septicemia and pneumonia in calves plus a carrier state; S. Typhimurium and S. Newport cause enteric disease across ages.
• Key signs: Fever, foul bloody or fibrinous diarrhea, abortion in adults; septicemia in calves. Contrast winter dysentery: bovine coronavirus in housed adult dairy cattle, an explosive outbreak of dark diarrhea with a milk drop, high morbidity, near-zero mortality, self-limiting with supportive care.

Reproduction

Retained Fetal Membranes

• Definition: Failure to pass the placenta within 24 hours of calving (normal expulsion is 3 to 8 hours).
• Risk factors: Abortion, dystocia, twins, stillbirth, hypocalcemia, induced or premature calving, heat stress, older cows.
• Treatment: Leave it alone unless the cow is sick. Manual removal is discouraged; treat systemic signs (metritis) rather than the membranes. Oxytocin and prostaglandin have little evidence.

Metritis and Endometritis

• Puerperal metritis: Within about 2 weeks postpartum, fever above 39.5 C, fetid watery red-brown discharge, off feed, milk drop. Organisms: E. coli, Trueperella pyogenes, Fusobacterium, Bacteroides and Porphyromonas.
• Clinical endometritis: Purulent vaginal discharge after 21 days with no systemic signs; reduces conception.
• Pyometra: Pus in the uterus with a persistent corpus luteum and no signs; treat with prostaglandin F2 alpha to lyse the CL. Classic after Tritrichomonas foetus infection.

Dystocia and Freemartinism

• Dystocia: Fetopelvic disproportion in heifers leads; correct, extract with controlled traction, or choose caesarean or fetotomy early. Obturator and peroneal paralysis are the tested sequelae.
• Freemartin: A heifer born co-twin to a bull, sterile because placental vascular anastomosis exposes her to male hormones and cells. Diagnosis: short vagina (Merck gives 5 to 8 cm in a freemartin versus 13 to 15 cm in a normal calf at 1 to 4 weeks), XX/XY blood chimerism on karyotype, low anti-Mullerian hormone, large clitoris and tuft of vulvar hair.

Causes of Abortion by Gestational Timing

Mastitis by Pathogen

Merck cites an SCC of 200,000 cells/mL or more in an individual cow as indicating a high likelihood of infection. The California Mastitis Test is the cowside screen.