View
11
Download
0
Category
Preview:
Citation preview
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
Recommended