Midterm 2 - Lecture 8

Question 1

Direct vs Indirect impact of infectious diseases on production

Answer 1

Direct: drop in milk production (mammary gland)

Indirect: ill health on young animals or an insult to an organ or body structure distant from the mammary gland

Question 2

Mastitis

Answer 2

• inflammation of the mammary gland
• infection of the mammary gland is the most common cause of mastitis in dairy cattle and only cause of production disease

Question 3

Subclinical mastitis

Answer 3

• will diminish milk returns like clinical but to a lesser extent
• marked reduction in the overall milk yield to the producer if many cows are affected

Question 4

Does clinical or subclinical mastitis pose a greater impact on profit?

Answer 4

• subclinical; for every case of clinical mastitis in the herd, there are btw 15 and 40 subclinical cases
• ~80% economic loss

Question 5

Routes of mastitis infection

Answer 5

1. hematogenous
2. percutaneous = skin wound
3. teat canal = main route

Question 6

What is pathogenesis of mastitis dependent on?

Answer 6

• agent (pathogen)
• microbial ecology (environment)
• host health

Question 7

What does transmission of mastitis depend on?

Answer 7

• amount of infectious agent in her enviro
• efficiency of milking personnel, machine and milking parlor hygiene

Question 8

What is susceptibility of a cow to mastitis related to?

Answer 8

• The Epidemiological triad/ triange
• Agent-Host-Environment

Question 9

Agent-Host-Environment

Answer 9

Epidemiological Triad/Triangle

Question 10

3 phases of mastitis development

Answer 10

1. invasive phase
2. infection phase
3. inflammation phase

Question 11

Invasive phase of mastitis

Answer 11

• bacteria in barn or enviro
• amount of contamination on the apices of teat
• injury to teat sphincter and tone of teat spincter
• presence of antibacterial substances in teat canal

Question 12

Infection phase of mastitis

Answer 12

• type of bacteria and its ability to adhere to mammary epithelium and multiply in milk
• susceptibility to commonly used antibiotics
• previous injury to teat, or concurrent infection
• stage lactation: first 2 months, most susceptible
• infections also occur during dry periods

Question 13

When are cows most susceptible to mastitis infection?

Answer 13

• first 2 months of stage lactation

Question 14

Inflammation phase of mastitis

Answer 14

• pathogenicity of bacteria matters
• reactivity of tissue; previous or concurrent infections = more tissue rxn

Question 15

Subclinical mastitis vs Clinical mastitis (types of mastitis)

Answer 15

1. Subclinical: no obvious indication of infection
2. Clinical:
   - Peracute: minimal clinical signs and can be deadly
   - Acute: swelling of udder and purulent discharge in milk
   - Chronic: long-term drop in milk production, udder may be hard

Question 16

For every case of clinical mastitis in a her, how many subclinical cases are there?

Answer 16

• btw 15 and 40

Question 17

Contagious mastitis

Answer 17

• the primary habitat of the organism is the udder (poor survival in enviro)
• most often cause sub-clinical and chronic infections
• transmission = contaminated fomites

Question 18

Staphylococcus aureus

Answer 18

• major cause of mastitis
• can cause heavy loss of production and peracute/acute death
• chronic from is most economically important

Question 19

Environmental mastitis

Answer 19

• bacteria survives in environment (oil, feces, bedding, water etc)
• occurs environmental contact: during or btw milking’s
• really any organism found in the enviro could cause environmental mastitis

Question 20

Mastitis treatment

Answer 20

1. clean equipment and enviro
2. ‘strip the milk’ = milk affected udder every 3 hrs for the first 24-72 hrs
3. intramammary infusion of antibiotics
4. dry period is best for incidence of chronic mastitis

Question 21

Pododermatitis (foot rot)

Answer 21

• a contagious disease that can cause both severe acute and chronic lameness in cattle

Question 22

What organisms cause foot rot?

Answer 22

• Fusobacterium necrophorum causes initial infection followed by bacteroides nodosus

Question 23

What is pododermatitis characterized by?

Answer 23

• moist dermatitis that is around coronary band and interdigital space
• infection often tracks into joints of the hoof causing chronic arthritis, tendonitis, desmitis and lameness
• cattle become inappetent and drop wt and milk production

Question 24

How is pododermatitis spread?

Answer 24

• via contact with contaminated cattle or the enviro; once microbe is seeded in enviro its hard to remove
• transmission occurs around high-traffic areas (feed trough, gates, barn exits)

Question 25

When does pododermatitis most often occur?

Answer 25

• when there is a lot of moisture aka standing in mud or manure for long time
• when cattle are exposed to hard surfaces for long time or stony ground/sharp gravel

Question 26

Pododermatitis treatment

Answer 26

• clean up the environment and remove source of infection
• systemic antibiotics
• surgical removal of infected tissue
• foot bath of 5% copper sulfate or 5% formalin
• zinc supplement to diet
• vaccin for F. necrophorum

Question 27

Economic impact of foot rot on Beef

Answer 27

• 75% of all lameness diagnosed
• wt loss: ~0.5 lbs/day
• loss in wt gain, treatment costs, decreased breeding efficiency, culling animals
• PREVENTION MORE EFFECTIVE THAN TREATMENT

Question 28

Is prevention more effective than treatment for pododermatitis?

Answer 28

YES