The times they are a changin’:

Parasite control for beef cattle

Doug Colwell, PhD; ParasitologyLethbridge Research and Development Centre, Lethbridge, AB

1

Macrocyclic lactones

• Most internal parasites

– Except flukes and tapeworms

• Most external parasites

– Horn flies (adults for a short period)

• Resistance has become an issue

– Nematodes

– Lice (?)

– Horn flies (?)

2

Pyrethroids

• Topical insecticides

– Pour-on insecticides

– Ear tags: insecticide impregnated

• Resistance

– Horn flies

– Cattle lice (?)

3

Cattle lice

• Chewing lice

• Sucking lice

4

Chewing louse impact

• Altered behaviour (itchy)

– Allergen production

• Hair loss

• Cockle (small skin defect)

– Downgrades hide

5

Chewing lice: Feeding

6

• Chewing mouthparts

• Skin, hair and debris

• Some abrasion of upper skin layers

• Systemic immunity (?)

Life cycle: Chewing lice

• Limited survival off-host

– 2-5 days

• Incomplete metamorphosis

• Egg, nymph, adult

• Approx. 14 days from egg to egg

• Reproductive output <1 egg/day

7

Sucking louse impact

• Blood loss

• Hide damage

• Host behavioural changes

– Scratching

– Reduced feeding

8

9

Life cycle – sucking lice

• Incomplete metamorphosis

• Egg, nymph, adult

• Approx. 14 days from egg to egg

• Reproductive output: 2-6 eggs/day

• No survival off-host

10

Louse-induced hair loss?

11

12

Thermal loadingLethal temperature

Adults: 46

Eggs: 41

Air

26

6

Skin (sun)

51

29

---------------------------- oC -------------------------------

Cattle lice

• 80/20 rule

13

80 % cattle harbour 20 % lice

Clustered

Cattle louse seasonality

0

20

40

60

80

100

120

15 31 15 30 15 1 15 30 15 30 15 30 1 15 15 15 15 15 15

Dec Jan Feb Mar Apr May Sep Oc No De Ja Fe

Mea

n lo

use

ind

ex

14

Cattle lice

• Grooming

– tongue

– brushes

15

0

2

4

6

8

10

12

14

pre 3 10 17 24 31 38

me

an

lo

use

in

de

x

days post-treatment

Sucking louse control

brush control malathion

Effect of grooming - sucking lice

16

0

10

20

30

40

50

60

70

pre 3 10 17 24 31 38

me

an

lo

use

in

de

x

days post-treatment

Chewing louse control

brush control malathion

Effect of grooming – chewing lice

17

Cattle louse monitoring

18

Cattle lice

19

This cow is so ugly that she would make

a freight train take a dirt road!

Things they are a changin'

20

Horn fly

21

Horn fly

22

Horn fly

• Affect pastured animals

• Both sexes blood feed

• High host specificity (cattle, but …)

• Rarely leave host

• Larvae develop only in fresh bovine manure (fastidious)

23

Host specificity?

24

Horn flies: impact

• Reduction in weight gain (>15%)

• Blood loss

• Altered behaviour

– changes in grazing patterns

– reduced efficiency

– “stress”

25

Horn fly

26

Nematodes

27

28

Overwintering

• Small percentage of L3 do survive during winter on pasture

– Approximately 5%

• Treatment must recognize this situation

29

Drug resistance in nematodes

• Resistance to current drugs is spreading

• Testing for resistance is difficult

• Fecal egg count reduction test

30

Do we have drug resistance?

0.0

2.0

4.0

6.0

8.0

10.0

Trichuris Trichostrongyle Nematodirus

pre

post

95%

Eg

gs/ 5g

31

Discussion?

32