Anthelmintic resistance impact on tropical beef cattle productivity: effect on weight gain of weaned calves.
The performance of grazing cattle in tropical areas is deeply influenced by parasitism, and the increasing reports of resistance are a threat to effective nematode control. The present study aimed to evaluate the effect of avermectins on the performance of weaned calves naturally infected by ivermectin-resistant gastrointestinal nematodes. The effect of four commercial endectocides (ivermectin 2.25 % + abamectin 1.25 %, ivermectin 3.15 %, doramectin 3.15 %, and doramectin 1 %) on parasitism and performance of a hundred weaned Nellore calves were evaluated during 112 days. The most effective anthelmintic showed efficacy of 84 % and resulted in an increase (P < 0.05) of live weight gain of 11.85 kg, compared to untreated group, 9.05 and 9.41 kg compared to those treated with more ineffective avermectins which showed efficacy of 0 and 48.2 %, respectively. A significant (P < 0.05) and weak negative correlation (r = -0.22) between the eggs per gram (EPG) and body weight was observed, indicating that even the low mean EPG (175 ± 150) observed at day 0 in the control group, with predominance of Haemonchus sp., was responsible for production losses. These results indicate that control of nematode parasites in beef cattle in the weaning phase may not result in increased productivity when carried out without technical criteria.
Faculty of Veterinary Medicine and Animal Science, Federal University of Mato Grosso do Sul, Campo Grande, Brazil. fernando.borges@ufms.br
Fernando A
FA
Borges
Gabriel D
GD
Almeida
Rafael P
RP
Heckler
Raul T
RT
Lemes
Marcel K V
MK
Onizuka
Dyego G L
DG
Borges
D000818:Animals; D000969:Antinematodal Agents / Q000494:pharmacology* / Q000627:therapeutic use; D001938:Brazil; D002417:Cattle / Q000254:growth & development*; D002418:Cattle Diseases / Q000469:parasitology*; D004351:Drug Resistance; D005243:Feces / Q000469:parasitology; D005767:Gastrointestinal Diseases / Q000188:drug therapy / Q000469:parasitology / Q000662:veterinary; D007559:Ivermectin / Q000031:analogs & derivatives / Q000494:pharmacology / Q000627:therapeutic use; D009348:Nematoda / Q000187:drug effects*; D009349:Nematode Infections / Q000188:drug therapy / Q000469:parasitology / Q000662:veterinary*; D010270:Parasite Egg Count / Q000662:veterinary; D012621:Seasons; D014329:Tropical Climate; D014886:Weaning; D015430:Weight Gain / Q000187:drug effects
D000969:Antinematodal Agents; C048324:abamectin; D007559:Ivermectin; C084101:doramectin