3.1: Respiratory disease in cattle: diagnosis, prevention and control

Question 1

Advantages of detecting antigen in nasal/nasopharyngeal swabs, trans-tracheal wash or on BAL

Answer 1

✅ Rapid test results possible
✅ Multiple animals can be sampled including cases and controls
✅ Identification of viral pathogens can be highly significant depending on the nature of the herd

Question 2

Disadvantages of detection of antigen in nasal/nasopharyngeal swabs, trans-tracheal wash or BAL

Answer 2

❌ Viral infections are transient
❌ Identification is impaired by rising antibody titres
❌ Bacterial isolates from some samples are of dubious significance due to many of them being commensals

Question 3

Advantages of serology to detect rising antibody titres

Answer 3

✅ High sensitivity as most respiratory pathogens induce a strong antibody response
✅ Less time-dependent - can still be effective in relatively late stage of disease
✅ Multiple animals can be tested, making the result relevant to the herd problem

Question 4

Disadvantages of serology to detect rising antibody titres

Answer 4

❌ Requires convalescent serum so results are not available for >3 weeks
❌ Testing multiple samples can be expensive
❌ Correlation of seroconversion with clinical disease may be impossible in situations where viral infections are expected to be common

Question 5

Advantages of PM exam with subsequent lab testing

Answer 5

✅ Gross and histopathology examination usually suggests a cause and may be pathognomonic
✅ Comprehensive and robust investigation
✅ Easy to sample the lung and trachea and are ideal sites for sampling for further tests

Question 6

Disadvantages of PM exam with subsequent lab testing

Answer 6

❌ Diagnosis may be based on a few animals
❌ Animals that die may not be representative of the herd problem
❌ Death may occur in the subacute phase of the infection when viruses are no longer present
❌ Cases are often treated prior to post-mortem which can be misleading in terms of pathogen identification

Question 7

Use of thoracic ultrasound in detecting BRD

Answer 7

• Research ongoing
• May increase the reliability of BRD diagnosis especially in cases where there are few clinical signs
• Could be used to assess recovery after treatment
• Could be used to assess diagnostic ability of farm staff i.e. are they detecting BRD cases
• Could be used to rule out chronic BRD in cases of poor growth rates and ill thrift
• May help detect early BRD but some conflicted evidence about this claim

Question 8

True/false: a high treatment rate of BRD indicates that the farm has a problem with BRD that they are failing to address.

Answer 8

False
* Not necessarily - there are many factors that could generate a high or low treatment rate.
* e.g. if the farm staff are poor at detecting BRD cases, might see a low treatment rate - this does not mean the animals are healthy!

Question 9

True/false: growth rates can be used to monitor/assess the impact of BRD on farm

Answer 9

True

Question 10

If you have a staff member who is new to calf-rearing, what tool could you give to help them identify BRD cases?

Answer 10

Can use tools such as Wisconsin calf scoring chart

Question 11

Risk factors for BRD

Answer 11

• Mixed age groups -> older calves act as a reservoir and often share airspace with younger calves
• Buying in
• Stocking density
• Ventilation -> must have circulating fresh air
• Stress
• Temperature -> esp if cold, damp
• Hygiene -> feeders, teat, moist bedding
• Lack of vaccination
• Colostrum (maternal antibodies start to drop by 16 days old; minimal impact on resp disease except in v young calves)

Question 12

What events might be stressful for calves and how can these be mitigated?

Answer 12

• Mixing groups -> keep calves in stable groups
• Weaning
• Disbudding -> knock down disbuds

Question 13

For how long can maternal antibodies from colostrum interfere with testing in the calf?

Answer 13

Up to 6 months

Question 14

What is the ideal age range for calves in a pen?

Answer 14

Ideally 2 weeks
* If age range is 4-6 weeks between oldest and youngest calf in a pen, the older calves will act as reservoirs of infection

Question 15

True/false: if there is a sick, small calf in a group, it is preferable to drop them back to a younger group so that they can catch up.

Answer 15

False
* This sick calf can spread disease
* It will be older than its new younger friends so will act as a reservoir for infection and then spread it to them
* An all-in, all-out system is good especially for baby calves 4-6 weeks old

Question 16

What is the ideal number of calves in a group/pen?

Answer 16

• Pens of 4 can be good but may be hard for block calvers
• Ideal = <12 calves per group
• Can get away with 20 calves per group if all born in a matter days

Question 17

How much fresh straw should be going into a pen per week? How do you judge if there is enough fresh bedding?

Answer 17

• 20 kg/head/week
• Should be able to sit down in it and not get wet clothes

Question 18

True/false: calves less than 4 weeks old can be given systemic BRD vaccines if the farm is having a problem with outbreaks.

Answer 18

False
* Calves 4-6 weeks old need to have intranasal vaccines (not systemic, they do not have the immune system to respond)
* Intranasal vaccines tend to offer 60 day protection will can help the farm out of a hole

Question 19

Prevention of BRD

Answer 19

• Fresh air: open side of shed/mechanical ventilation
• Stocking density: floorspace and airspace
• Isolation of sick calves: only works if we can detect them soon enough! Often by the time we find the sick calves they have already spread disease.
• Vaccination

Question 20

How are you going to diagnose IBR?

Answer 20

• Paired serology to look for rising antibody titre; sample mix of healthy and sick animals
• If paired serology on youngstock: choose those 8-10 months old (no maternal antibodies) - if they have been exposed, IBR is likely circulating in the herd
• Could use bulk milk sample antibody test
• Nasal conjunctival swabs -> PCR -> this would indicate active infection

Question 21

You want to do a paired serology test for IBR, but the herd was vaccinated against it. How do you proceed?

Answer 21

• Check if a marker vaccine was used
• If yes, you can still do paired serology to see if active infection and can differentiate this from vaccinated animals

Question 22

You have successfully diagnosed IBR. What is your advice to the farmer?

Answer 22

• Live vaccination if there are currently sick animals/the herd has had recent infection in the past few weeks
• Inactivated vaccine if no sick animals currently and just trying to prevent recrudescence
• Consider starting full vaccination protocol going forward
• Use double fencing to improve biosecurity
• Use CHeCS accreditation schemes to buy in from herds with the same health status

Question 23

What is your advice to the farmer with regards to which pathogens he needs to worry about?

Answer 23

• Not worried about IBR
• PI3 in calf 3 -> titre is not rising so doesn’t appear current
• RSV is present and circulating
• BVD is positive, but not rising; if concerned about PI calves, need to antigen-test them (PIs= antigen +ve, antibody -ve)
• Mycoplasma bovis could be a commensal but there are high levels and rising titres
• Could have some colostral antibodies depending on calf age
• Ask farmer re vaccination protocols, whether the calves were bought in etc.