Weight loss in adult cows

Question 1

Johne’s disease

Answer 1

• also known as “paratuberculosis”
• inncurable disease of cattle and other ruminants
• caused by Mycobacterium avium subsp. paratuberculosis (MAP)
• controversial association with Crohn’s disease in humans
  – some evidence both ways
• can find MAP in pasteurized milk
• still (currently) no convincing evidence of causality
• potential major reputational risk to dairy/meat industries
• don’t find much of the organism in muscle and well destroyed by cooking - mostly just circulates in the gut

Question 2

Johne’s disease presentation / CS

Answer 2

• characterised by wasting and d+
• granulomatous enteritis
• slow/long course

CS:
- d+ (intermittent becoming chronic)
- bubbly d+ thought to be associated with Johne’s, although normal for d+
- decreased production (i.e. milk yield)
- weight loss/emaciation
- +/- oedema (e.g. bottle jaw) (due to protein loss through the gut)
- dz normally develops at 2-6y/o
– rare to see clinical dz before 1st calving, and very old cows (>7) rarely get it

Question 3

Johne’s - course of dz

Answer 3

• infection -> carriage -> subclinical -> clinical
• clinically affected animals = high likelihood of shedding
• carrier animals = low likelihood of shedding
• ~80% natural infections in 1st month of life, therefore control is about protecting replacement calves early on in life
• little increase in resistance after 1y/o
• for every wasting cow likely to have 4-5 cows in the production loss category

Question 4

Subclinical impacts of Johne’s

Answer 4

• effects on fertility
• drop in milk production, etc
• intermittent shedding during this phase

Question 5

Johne’s - sources of infection

Answer 5

• faeces from shedding cattle*
• colostrum milk from infected cattle
• faeces from shedding goats/sheep (esp goats, but d+ not as much of a CS, more just wasting)
• environment and fomite spread
• wildlife reservoirs (deer & rabbits, not a massive risk)

Question 6

Ddx of weight loss and diarrhoea in cows

Answer 6

• liver fluke
• peritonitis
• displaced abomasum
• abdominal neoplasia
• chronic salmonellosis
• parasitic gastroenteritis
• copper deficiency

Question 7

Liver fluke

Answer 7

• often group problem (but always has to have 1st case)
• can see peripheral oedema (as would in Johne’s)
• lab work very useful for differentiation

Question 8

Peritonitis

Answer 8

• may find other signs (abdo pain, pyrexia), but not always
• TRP esp difficult to diagnose, but normally no d+
• tends to be very chronic in cattle - very slowly progressive so fits with weight and production loss

Question 9

Displaced abomasum

Answer 9

• normally much more acute and with decreased yield more evident/severe
• fairly easy to rule out clinical exam (decreased rumen turnover, ‘ping’)
• but can be intermittent/chronic

Question 10

Abdominal neoplasia

Answer 10

• rare in cattle
• can present very similarly to Johne’s
• would fit for 1 off sporadic case in an older cow

Question 11

Chronic salmonellosis

Answer 11

• fairly rare
• farm history of salmonellosis may be useful

Question 12

Parasitic gastroenteritis

Answer 12

• very rarely causes CS in adult cattle (they usually get effective immunity to it as they get older)
• almost always presents as a group problem

Question 13

Copper deficiency

Answer 13

• usually group problem
• would normally expect milder group-level signs (e.g. infertility?) before

Question 14

Diagnosing Johne’s

Answer 14

• detect MAP in faeces
• detect immune response to MAP

Question 15

Detecting MAP in faeces

Answer 15

• directly demonstrates risk of transmission
• MAP only intermittently shed in faeces, so sensitivity quite poor, better in clinical cases
• usually PCR (culture slow/expensive, smear inaccurate)
• mostly used as a confirmatory test
• pooled samples occasionally used as herd-level diagnostic
• 20-65% sensitivity
• > 99% specificity
• £25 per test
• Pooled faecal samples rarely used in practice

Question 16

Detecting immune response to MAP

Answer 16

• currently only detection of Ab (in milk or blood)
• generally higher Se than faecal testing
• Sp slightly lower (~99%)
• cheaper and quicker than faecal testing
• blood testing mostly for individual clinical cases and beef herd screening
• milk testing commonly used for dairy herd screening
  – often uses lower threshold for positive
• 20-90% sensitivity (sensitivity gets higher the closer you get to clinical dz)
• > 97-99%
• £2-5 per test

Question 17

Managing Johne’s dz - clinical cases

Answer 17

• no tx, prognosis hopeless
• survival time variable, may get brief remission
• major risk to other animals (calves)
• high fibre diet can help the d+ but it will get worse again

Question 18

Managing Johne’s dz - at herd level

Answer 18

• main goal is to minimise exposure of youngstock (<1y?) to potential sources of infection
  – slurry (spreading slurry on pasture can spread infection)
  – colostrum, milk
  – fomites and pasture
  – other species
• MAP is pretty resilient - it can survive in the right environment for over a year
• direct vertical transmission has also been demonstrated

Every 3m testing of the entire herd - any animal with non-negative test get managed differently - calves never used as colostrum, colostrum not fed to other calves

Question 19

Recommendations to minimise spread of Johne’s

Answer 19

• Test the colostrum quality with a brix refractometer (22%) or colostrometer.
• Make sure the calves that are being turned out are on fresh pasture – not following adult cows or had slurry spread on it.
• Ensure good biosecurity – more boot dips, hand washing, different clothes, wheel washes, etc.
• Clean PPE, gloves when managing the calves.
• Have a separate sick cow pen away from the dry cow.
• Smaller pens in the large straw yard to separate high risk from low risk – muck out the dry cow yard at least weekly.
• Move to a system where everything calves in an individual pen and in between cows muck it out and disinfect.
• Routine milk antibody testing for Johne’s.
• If you have a cow that has tested positive, then don’t put its colostrum into the pool for calves.
• Pasteurise the colostrum if sticking with pooling it.
• Move to completely individual colostrum feeding – then one cow can only infect a maximum of one calf.
• Reduce stocking density.
• Don’t put J3,4,5 in the group calving yard – give birth somewhere completely separate.
• Don’t breed replacements from the positive cows – breed for beef

Question 20

Managing Johne’s dz - biosecurity

Answer 20

• avoid Johne’s entering a naive farm
• fomite spread
• wildlife
• slurry spreaders
• neighbours

Question 21

Johne’s milk antibody testing: Categorisation

Answer 21

J0 - At least 2 repeat negative ELISA tests
J1 - Only one test but negative result
J2 - ELISA negative currently but has had a positive result in previous three tests
J3 - ELISA negative currently but has had a positive on previous test
J4 - ELISA positive but first positive test result
J5 - Repeat ELISA positive test results - at least 2 positives