Bovine Vitamin and Mineral Deficiencies Study Guide

Overview and Clinical Importance

Vitamin and mineral deficiencies are among the most economically significant health conditions affecting cattle worldwide. These deficiencies can manifest as dramatic clinical syndromes or as subclinical conditions that reduce productivity, impair immunity, and increase susceptibility to other diseases. Understanding the pathophysiology, clinical presentation, and management of these conditions is essential for the NAVLE.

The major deficiency syndromes covered include selenium/vitamin E deficiency (white muscle disease), copper deficiency, hypomagnesemia (grass tetany), polioencephalomalacia (thiamine-responsive or sulfur-induced), vitamin A deficiency, phosphorus deficiency, iodine deficiency, and cobalt/zinc deficiencies. Regional soil characteristics significantly influence which deficiencies predominate in different geographic areas.

Selenium and Vitamin E Deficiency (White Muscle Disease)

White muscle disease (WMD), also called nutritional myodegeneration or nutritional muscular dystrophy, is caused by deficiency of selenium, vitamin E, or both. It represents one of the most important nutritional deficiencies in cattle, particularly in selenium-deficient regions.

Pathophysiology

Selenium is an essential component of glutathione peroxidase (GSH-Px), an enzyme that protects cell membranes from oxidative damage by neutralizing hydrogen peroxide and lipid peroxides. Vitamin E (alpha-tocopherol) functions as a lipid-soluble antioxidant within cell membranes. These nutrients work synergistically; selenium prevents peroxide formation while vitamin E scavenges free radicals that escape the selenium-dependent system.

When both are deficient, muscle cell membranes undergo lipid peroxidation, leading to myofibrillar degeneration and necrosis. The damage is bilateral and symmetric, affecting skeletal and cardiac muscle. Cardiac muscle involvement is more common in neonates, while skeletal muscle disease predominates in older calves following exercise.

Clinical Presentation

Diagnosis

• Serum CK and AST: Markedly elevated (often greater than 1000 U/L) due to muscle damage
• Whole blood selenium: Less than 0.05 ppm diagnostic; 0.05-0.08 ppm marginal; greater than 0.08 ppm adequate
• Glutathione peroxidase activity: Reflects selenium status over previous weeks
• Liver selenium: Best postmortem indicator; less than 0.25 ppm wet weight is deficient
• Necropsy: Bilateral symmetric pale streaking in muscles; cardiac lesions in neonates

Treatment and Prevention

Copper Deficiency

Copper deficiency in cattle can be primary (inadequate dietary copper) or secondary (adequate dietary copper but impaired absorption due to antagonists). Secondary deficiency is more common and results from interactions with molybdenum, sulfur, and iron that form insoluble copper complexes in the rumen.

Pathophysiology

Copper is essential for numerous enzyme systems including: ceruloplasmin (iron metabolism), cytochrome c oxidase (cellular respiration), lysyl oxidase (collagen cross-linking), tyrosinase (melanin production), and superoxide dismutase (antioxidant defense).

The classic antagonist relationship involves formation of thiomolybdates in the rumen when molybdenum and sulfur are elevated. These compounds bind copper, making it unavailable. The Cu:Mo ratio is critical; ratios less than 2:1 predispose to deficiency even with adequate dietary copper.

Clinical Presentation

Diagnosis and Treatment

• Liver copper: Gold standard; less than 25 ppm DM is deficient; 25-100 ppm marginal; greater than 100 ppm adequate
• Serum copper: Less than 0.5 mcg/mL deficient; reflects recent intake only
• Treatment: Injectable copper glycinate (120 mg Cu for adults) or oral copper sulfate; copper oxide wire particles provide slow release
• Prevention: Address molybdenum/sulfur/iron antagonism; supplement copper at 10 mg/kg DM; use injectable copper in high-risk herds

Hypomagnesemia (Grass Tetany)

Grass tetany (hypomagnesemic tetany) is an acute, often fatal metabolic disorder characterized by low serum magnesium. It primarily affects lactating beef cows grazing lush spring pastures or green cereal crops. The condition is a true veterinary emergency.

Pathophysiology

Magnesium absorption occurs primarily in the rumen and is highly dependent on dietary factors. High potassium levels in rapidly growing grass directly inhibit magnesium transport across the rumen wall. Other factors reducing absorption include high nitrogen/protein, low sodium, and cold weather stress.

Unlike calcium, cattle have no significant mobilizable magnesium stores. Bone magnesium is structurally bound and not readily available. Therefore, cattle depend entirely on daily dietary intake, making them vulnerable to rapid depletion. Lactation further stresses magnesium balance as milk contains approximately 150 mg Mg/L.

Hypomagnesemia causes neuromuscular hyperexcitability by affecting acetylcholine release and nerve impulse transmission. Concurrent hypocalcemia commonly occurs due to impaired PTH secretion and action when magnesium is low.

Clinical Signs

Diagnosis

• Serum magnesium: Less than 1.5 mg/dL (0.65 mmol/L) is diagnostic; less than 1.0 mg/dL is severe
• CSF magnesium: Less than 1.0 mg/dL within 12 hours postmortem confirms diagnosis
• Vitreous humor Mg: Useful up to 48 hours postmortem if temperature less than 23C
• Urine magnesium: Undetectable in hypomagnesemic cattle

Treatment - EMERGENCY

Prevention: Magnesium oxide (MgO) topdressed on hay at 60 g/head/day; high-magnesium mineral supplements; avoid high-K fertilizers; gradual pasture transitions.

Polioencephalomalacia (PEM)

Polioencephalomalacia is a neurological disease characterized by necrosis of cerebral cortical gray matter. It can result from thiamine (vitamin B1) deficiency or sulfur toxicity, with the latter being more common in modern feedlot settings.

Etiology and Pathophysiology

Clinical Signs

Early signs include dullness, depression, and separation from herd. This progresses to blindness with intact pupillary light reflexes (cortical blindness), head pressing, circling, and opisthotonus ('star-gazing'). Muscle tremors, nystagmus, and bruxism are common. Terminal stages show recumbency with paddling seizures.

Diagnosis

• Clinical response to thiamine: Dramatic improvement within hours supports diagnosis
• Fluorescence under UV light: Cut brain sections show bright yellow-green autofluorescence of necrotic cortex - PATHOGNOMONIC
• Blood thiamine levels: Decreased in thiamine-deficient cases
• Rumen H2S: Elevated (greater than 2000 ppm) in sulfur toxicity cases
• Blood lead: To rule out lead toxicity

Treatment

Vitamin A Deficiency

Vitamin A deficiency affects epithelial integrity, vision, bone development, and immune function. It occurs when cattle lack access to green forage (the source of beta-carotene precursor) for prolonged periods, typically during drought or winter feeding of poor-quality hay.

Clinical Signs by System

Diagnosis and Treatment

• Serum retinol: Less than 20 mcg/dL is deficient; less than 10 mcg/dL is severe
• Liver vitamin A: Less than 2 mcg/g wet weight indicates depletion
• Treatment: Injectable vitamin A (440 IU/kg IM) provides rapid restoration; oral supplementation for herd
• Prevention: Green forage access; vitamin A supplementation (40,000-60,000 IU/head/day) when pasture unavailable

Phosphorus Deficiency

Phosphorus deficiency is one of the most widespread mineral deficiencies worldwide, particularly in tropical and subtropical regions with phosphorus-poor soils. It causes pica (depraved appetite), poor growth, and reproductive failure.

Clinical Signs

• Pica (depraved appetite): Chewing bones, wood, rocks, soil - PATHOGNOMONIC; leads to botulism risk from carrion
• Poor growth and unthriftiness: Rough coat, emaciation despite adequate feed
• Reproductive failure: Delayed puberty, anestrus, poor conception rates
• Lameness and fractures: Weakened bones due to impaired mineralization
• Hemoglobinuria: Post-parturient hemoglobinuria in severely deficient dairy cows

Diagnosis and Treatment

• Serum phosphorus: Less than 4 mg/dL suggests deficiency; less than 2 mg/dL severe
• Bone ash: Rib biopsy showing less than 15% P on ash basis
• Treatment/Prevention: Dicalcium phosphate, monosodium phosphate, or bone meal supplementation; maintain dietary P at 0.2-0.3%

Iodine Deficiency (Goiter)

Iodine deficiency causes thyroid hyperplasia (goiter) and hypothyroidism. It is most common in regions with iodine-poor soils and can be exacerbated by goitrogenic compounds in certain feeds (brassicas, soybeans).

Clinical Signs

• Goiter: Enlarged thyroid gland visible/palpable in neck - most obvious in newborn calves
• Reproductive failure: Stillbirths, weak calves, prolonged gestation, retained placentas
• Neonatal signs: Hairless or sparse coat, myxedema, weakness, increased susceptibility to cold
• Adult signs: Poor growth, reduced milk production, rough coat

Diagnosis and Treatment

• Thyroid weight: Greater than 30 g in newborn calves suggests goiter (normal less than 15 g)
• Serum T4: Decreased in hypothyroidism
• Prevention: Iodized salt (0.01-0.02% iodine) or EDDI (ethylenediamine dihydriodide) supplementation

Cobalt and Zinc Deficiencies

Cobalt Deficiency

Cobalt is required by rumen microbes for synthesis of vitamin B12. Deficiency causes wasting disease with anemia and poor growth. Signs include progressive emaciation, weakness, anemia, lacrimation, and photosensitization. Treatment involves cobalt sulfate supplementation (0.1 mg/kg DM) or vitamin B12 injections.

Zinc Deficiency

Zinc is essential for numerous enzyme systems, immune function, and epithelial integrity. Deficiency causes parakeratosis (thickened, cracked skin particularly around joints), poor wound healing, decreased immunity, reduced growth, and testicular hypoplasia. Treatment involves zinc supplementation at 30-40 ppm in diet or injectable zinc if severe.

Memory Aids and Clinical Pearls

Quick Differential Mnemonic: 'SCIP PIC'

Selenium/Vitamin E = White muscle, exercise-triggered stiffness

Copper = Coat color changes, falling disease, ataxia

Iodine = Goiter in newborns, hairless calves

PEM = Star-gazing, cortical blindness (PLR present)

Phosphorus = Pica (bone-chewing), botulism risk

Iron - not typically deficient in cattle

Calcium/Magnesium = Tetany syndromes

'DOWN COW' Cardiac Differentiation

Grass Tetany (Mg): 'GT = Great Tachycardia' - HR up to 150, LOUD heart sounds

Milk Fever (Ca): 'MF = Mostly Feeble' - Bradycardia, weak pulse, cold extremities

Blindness Differentiation

PEM: 'PEM = Pupil Excellent, Mind gone' - PLR PRESENT (cortical blindness)

Vitamin A: 'A = Absent reflex' - PLR ABSENT (retinal degeneration)