Cattle worms resistance to Ivermectin treatments: effects on production
César Fiel1; Maricel Guzmán1,3; Pedro Steffan1; Eliana Riva1,3 ; Edgardo Rodríguez2
1Área
aapavet
Parasitología, 2Area de Biostadística Dpto. SAMP, Fac. Cs Veterinarias, U.N.C.P.B.A.
Campus Universitario. Pje Arroyo Seco s/n. (7000) Tandil-Argentina. 3Becario CONICET
Tel: +54 2293 439850 - [email protected]
Table 1: Weight gains of treatments groups in 2008
Introduction
Anthelmintic resistance in worm cattle populations of Argentina has
been well documented in Argentina being macrocyclic lactones (ML)
and Cooperia spp. mainly involved (Caracostantogolo et al 2005,
Anziani & Fiel 2004). Usually, farmers did not pay attention to the
phenomenon due to the lack of clear clinical signs or important
productive losses in grazing cattle. This may also account for a low
consideration of the problem in the majority of the beef production
systems. For these reasons demonstration of productive losses as a
consequence of worm infections resistant to anthelmintics treatment
may contribute to support the advice to farmers and to encourage them
to implement proper diagnostic and control measures on the problem.
The aim of this study was to evaluate the effects of worm populations
resistant to ivermectin treatments on weight gains of grazing cattle.
Methods
Ten field trials were carried out in the main cattle productive area of
Argentina throughout 2008 and 2009.
The trials involved castrated male calves of 10-12 months old which
grazed on improved pastures naturally infected with worm populations
suspected to have resistance to anthelmintic compounds. En each
farm, calves were identified, weighed and assigned to three comparable
groups of 20 animals each and treated as follows:
Group 1: Ivermectin (IVM) subcutaneous via (0.2 mg/kg b.w.)
Group 2: Moxydectin (MXD) subcutaneous via (0.2 mg/kg b.w.)
Group 3: non treated control
Faecal samples were collected from animals at days 0 and 14 after
treatment to establish clinical efficacy through the faecal egg count
reduction test (FECRT) (Coles et al 1992) and cultivation of a pool
group sample to determine worm species (Henriksen & Korsholm
1983). Individual body weight was recorded at days 0 and 90 post
treatment.
Results
According to FECRT resistance to IVM was found in 10/10 farms and
for MXD in 1/10 farms. The average of FECRT for G1 was 66.0%
(range 42.8%-89.3%) and for G2 was 90% (range 50.3%-100%)
respectively. Cooperia spp. was the predominant nematode in all
faecal cultures from farms where resistance to IVM was found, being
also the single worm recovered in 8/10 farms. Haemonchus spp. was
present after IVM treatment in coprocultures of two farms located in
the subtropical area of the study.
In the first year of the study differences of weight gain in average of G1
and G2 upon G3 were 5.7 kg and 13.1 kg respectively (P<0.05) (Table
1). In the second year, differences were 13.2 kg and 16.7 kg
respectively (P<0.05) (Table 2).
The overall analysis of the two years determined an average weight
gain difference of G1 and G2 upon G3 of 8.7 kg and 14.5 kg
respectively ( P<0.05).
Conclusions
1.According to FECRT all selected farms presented resistance to IVM and in a
single –dairy- farm resistance to MXD was also found.
2.Cooperia spp. was recovered in coprocultures from all farms of the study being
it present as a single worm in 8 out of 10 and together to Haemonchus spp. in
the other two farms.
3.Taking into account the complete period of the study -two years- the effects
and consequences of the anthelmintic resistance phenomenon lead to a
reduction of around 40% of weight gains in 90 days of grazing.
4.This information will be of a great support to advice farmers on the
phenomenon of anthelmintic resistance and encourage them to implement
proper diagnostic techniques and rational programmes to control nematode
infections in beef production systems.
Farm
Group
El Regreso
(B.A.)
Start: July 30th
IVM
Las Margaritas
(B.A.)
Start: May 16th
FECRT (%)
BW
day 0
(Kg)
58
223.1
Cooperia
Pehuajó Tuyá
(Ctes)
Start: July 15th
San Eduardo
(B.A.)
Start: August
25th
Yatay Cuá
(Ctes)
Start: July 15th
AVERAGE
2008
P
value
245
3.5
P=0.7269
16.8
P=0.0014
MXD
93
222.2
257.4
Control
-42.8
218.1
236.6
130.2
161
2.9
P=0.7224
4.0
P=0.5518
IVM
Cooperia
50.3
MXD
Cooperia
Control
Los Leones
(Sta Fé)
Start: July 16th
Weight gain
BW
day 90 upon control
group (Kg)
(Kg)
-77
IVM
Cooperia
121.9
153.8
133.3
161.2
157.3
191.9
8.1
P=0.0329
MXD
Control
100
-49.7
164.3
159.4
204.1
185.9
13.4
P=0.0002
IVM
Cooperia 70%
Haemonchus 30%
181.9
195.2
2.2
P=0.9674
MXD
Control
99
-89.3
173.8
167.2
195.5
178.3
10.5
P=0.4439
194.2
281.4
8.6
P=0.0789
IVM
Cooperia
MXD
Control
98.4
-79
187.6
191.4
282.9
270.1
16.6
P=0.0004
IVM
Cooperia 50%
Haemonchus 50%
191.4
197.2
9.1
P=0.0005
MXD
Control
IVM
MXD
98.7
-66.0
90
165.2
202.2
176.7
172.5
179
198.9
211.9
212.2
17.1
P<0.0001
5.7
13.1
P=0.0180
Control
--
177.5
205.2
P<0.0001
Table 2: Weight gains of treatments groups in 2009
Farm
Group
Buena Esperanza
(E. Ríos)
Start: July 7th
IVM
Don Carlos
(Cba)
Start: July 13th
Don Manuel
(B.A.)
Start: July 15th
El Cardal II
(B.A.)
Start: July 16th
AVERAGE
2009
AVERAGE
two years study
MXD
Control
IVM
MXD
Control
IVM
MXD
Control
IVM
FECRT (%)
79.7
Cooperia
98
-2.2
Cooperia
96.1
-77.8
Cooperia
97.5
-76.7
Cooperia
BW
day 0
(Kg)
BW
Weight gain
day 90 upon control
(Kg)
group (Kg)
P
value
215.5
230.2
12.7
P=0.0002
218.5
221.6
241
223.5
20.5
P<0.0001
151.8
181.1
16.4
P=0.0809
154
129.4
185.3
142
18.4
P=0.0456
132.8
197.9
18.1
P<0.0001
128.9
124.8
195.7
167.8
23.8
P<0.0001
245.8
283.6
1.0
P=0.9687
275.7
292.1
223.2
229.5
206.4
3.8
P=0.6411
13.2
16.7
P<0.0001
216.4
217
205.6
8.7
14.5
P<0.0001
MXD
Control
IVM
MXD
Control
95.4
59.1
96.8
--
235.1
255.3
186.5
184.1
186.4
IVM
MXD
Control
63.2
92.6
--
182.4
177.2
180.3
P<0.0001
P<0.0001
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