ANS150 FINAL: Cattle Disease

Which udder quarters produce the most milk?

Rear quarters produce 55–60% of total milk and account for 55–60% of udder weight.

Important external structures of the bovine udder?

• Median suspensory ligament

• Lateral suspensory ligaments

• Four separate quarters

• Teats

Important internal mammary structures?

• Alveoli

• Lobules

• Lobes

• Ducts

• Gland cistern

• Teat canal

• Secretory epithelial cells

Define bovine mastitis.

Inflammation of one or more udder quarters, usually caused by an intramammary infection.

What is always associated with mastitis?

Increased somatic cell count (SCC).

Classic signs of inflammation?

• Redness

• Swelling

• Pain

• Heat

• Loss of function

Two classifications based on severity?

• Clinical mastitis

• Subclinical mastitis

Two classifications based on pathogen source?

• Contagious mastitis

• Environmental mastitis

What is SCC?

Number of body cells per mL of milk.

Normal SCC contains:

• ~25% epithelial cells

• ~75% leukocytes (mostly neutrophils)

What is the gold standard indicator for mastitis?

Somatic Cell Count (SCC).

What is SCS?

Somatic Cell Score (logarithmic transformation of SCC).

Relationship between SCC and SCS?

SCC doubles for every 1-unit increase in SCS.

Why use SCS instead of SCC?

Because SCC does not predict milk loss linearly. SCS better predicts production losses.

How much milk is lost for each SCS increase above 2?

Approximately 200 kg per lactation.

Why must the SCC cutoff be interpreted cautiously?

• 15% false negatives

• 15% false positives

What percentage of mastitis is clinical?

5–10%

What percentage is subclinical?

90–95%

Main characteristics of acute clinical mastitis?

• Sudden onset

• Moderate/severe inflammation

• Serous milk

• Fibrin clots

• Reduced milk production

• Agalactia possible

Systemic signs of acute mastitis?

• Fever

• Septicemia

• Anorexia

• Depression

• Rumen dysfunction

Characteristics of chronic clinical mastitis?

• Persists months to years

• Occasional flareups

• Long-term milk loss

• Cow appears normal most of the time

Clinical appearance of subclinical mastitis?

• No visible inflammation

• Normal udder

• Normal milk

Key findings of subclinical mastitis?

• Elevated SCC

• ~10% lower milk yield

• Long duration

How is clinical mastitis detected?

Visual examination.

How is subclinical mastitis detected?

SCC or California Mastitis Test (CMT).

Most common cause of mastitis?

Bacteria (~70%)

Other causes of mastitis?

• Yeasts and molds (~2%)

• Trauma

• Physical damage

• Weather extremes

• Improper management

How many microorganisms can cause mastitis?

More than 50 species; about 10 are major pathogens

Major contagious pathogens of mastitis?

• Streptococcus agalactiae

• Staphylococcus aureus

• Mycoplasma spp.

Major environmental pathogens of mastitis?

• E. coli

• Klebsiella spp.

• Enterobacter spp.

• Streptococcus uberis

• Streptococcus dysgalactiae

Characteristics of contagious pathogens?

• Cow-to-cow spread

• Survive in udder

• Cause chronic infections

• Often treatable with penicillin

Characteristics of environmental pathogens?

• Found in feces

• Soil

• Water

• Bedding

• Environment-to-cow transmission

Gram status of streptococcus agalactiae?

Gram-positive coccus

Typical finding of streptococcus agalactiae?

Very high bulk tank SCC (>1,000,000 cells/mL)

Antibiotic response to streptococcus agalactiae?

Highly sensitive; eradication is practical.

Gram status of Staphylococcus aureus?

Gram-positive coccus

Why is Staphylococcus aureus difficult to treat?

Forms deep tissue pockets and abscesses

When is treatment effective for Staphylococcus aureus?

Early infections are reversible; late infections resist antibiotics.

Gram status of Escherichia coli?

Gram-negative.

Source of Escherichia coli?

Bedding and manure.

Typical disease from Escherichia coli?

Acute severe mastitis with systemic illness.

Milk appearance after Escherichia coli infection?

Watery or serous milk.

Antibiotic response of Escherichia coli?

Often self-limiting and relatively resistant to antibiotics

. Vaccine for Escherichia coli?

J-5 vaccine.

Define pathogenesis.

Step-by-step development of disease caused by an etiologic agent.

Mastitis pathogenesis sequence?

1. Organisms enter through teat canal

2. Migrate upward

3. Colonize secretory cells

4. Produce toxins

5. Damage milk-producing tissue

6. Inflammation develops

Why is milk ideal for bacterial growth?

It provides nutrients and a favorable environment for bacterial multiplication.

How is mastitis diagnosed?

• Physical examination

• SCC testing

• California Mastitis Test

• Culture analysis

Most accurate diagnostic test for mastitis?

Culture analysis

Purpose of California Mastitis Test?

Rapid cow-side estimate of SCC.

Best use of California Mastitis Test?

Detecting subclinical mastitis

What scores of California Mastitis Test indicate subclinical mastitis?

Trace (T) or 1

What scores of California Mastitis Test indicate clinical mastitis?

2 or 3

Goals for clinical mastitis?

• Restore health

• Eliminate clinical signs

• Return milk to market

Goals for subclinical mastitis?

• Prevent clinical disease

• Lower SCC

• Prevent spread

Main treatment options?

• Antibiotics

• Anti-inflammatory drugs

• Oxytocin

• Supportive therapy

• Teat sealants

Which infections should generally receive antibiotics?

Gram-positive infections.

Why are gram-negative infections often not treated?

They are more antibiotic resistant and often self-limiting.

When should culling be considered?

Chronic mastitis with recurrent clinical sign

Most effective mastitis control strategy?

Prevention is more effective than treatment.

What do pre-dips do?

Reduce new infections by ~70%

Examples of pre-dips?

• Iodophors

• Chlorhexidine

• LDBSA

• Hypochlorous acid

Why are post-dips important?

Seal teat ends for 6–8 hours and are essential for long-term mastitis control.

Why milk chronic mastitis cows last?

They act as reservoirs and can infect healthy cows.

Why is the dry period high risk?

• Teat canal remains open

• Immune changes occur

• Susceptibility increases