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 •Anziani, O.S., Fiel, C.A. Veterinaria Argentina (2004) vol. 21, Nº 202, p.p. 122-133. •Caracostantogolo, J., Castaño, R., Cutullé, Ch., Cetrá, B., Lamberti, R., Olaechea, F., et al. Resistencia a los antiparasitarios internos en Argentina. FAO producción y sanidad animal. (2005) p. 7-34. •Coles, G., Bauer, C., Borgsteede, F.H.M., Geerst, S., Klei, T.R., Taylor, M.A., Waller, P.J. Vet. Parasitol. (1992) 44, 35-44. •Henriksen, Sv.Aa.; Korsholm, H. Nord. Vet. Med. (1983) 35, 429-430.
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