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Evaluation of Parasite Resistance to Commonly Used Commercial Anthelmintics in Meat Goats
Anthelmintic-resistant parasites pose a major threat to small ruminant industry sustainability. To evaluate resistance, meat goat does were orally administered one of four anthelmentics [ivermectin (IVE, n = 18, 303% recommended goat dosage rate), moxidectin (MOX, n = 18, 153% of recommendation), levamisole hydrochloride (LEV, n = 17, 129% of recommendation), or albendazole (ALB, n = 19, 162% of recommendation)] or water (H2O, n = 18). Fecal samples were collected immediately pretreatment and two weeks after treatment. The modified McMaster technique was used to determine fecal egg counts (FEC). Arithmetic mean FEC reduction percentages were calculated using three published equations. To assess drug efficacy, Equation 1 (FECRT1) used post-treatment control and anthelmintic group values without pretreatment values. Equation 2 (FECRT2) used pre- and post-treatment anthelmintic group values without a control group. Equation 3 (FECRT3) used pre- and post-treatment control and anthelmintic group values. Geometric FEC means were analyzed by treatment and goat breed. Mean pretreatment FEC differed by breed (P < 0.05), but not by treatment (P = 0.21). Savanna (1348 eggs/g) had higher (P < 0.05) pretreatment FEC than Kiko (675 eggs/g) or Myotonic (467 eggs/g). No other breed comparisons differed (Spanish, 932 eggs/g). Pretreatment anthelmintic group averages were 1071 eggs/g for MOX, 547 eggs/g for IVE, 932 for LEV eggs/g, 976 for ALB eggs/g, and 723 eggs/g for H2O. Post-treatment FEC means differed (P < 0.001) by treatment group but not by breed (P = 0.12). Post-treatment values were higher (P < .05) for H2O (1147 eggs/g) compared to ALB (92 eggs/g), MOX (41 eggs/g), or IVE (21 eggs/g). Post-treatment mean FEC was higher (P < 0.05) for LEV (233 eggs/g) than for IVE. No other paired means differed. Anthelmintic resistance determinations were based on FEC reductions below 95% or 80% depending on the equation applied. For FECRT1 and FECRT2, no treatment met the 95% efficacy threshold: MOX, 85.0% and 66.9%; IVE, 85.6% and 74.9%; ALB, 78.5% and 64.4%; LEV, 42.21% and 36.5%. Efficacy of LEV was significantly lower than the other three in FECRT1. Efficacy of H2O (-120.1%) was significantly lower than the four anthelmintics in FECRT2. For FECRT3, no treatment met the 80% efficacy threshold: MOX, 42.7%; IVE, 56.5%; ALB, 38.3%; LEV, -10%. Resistance was detected to all anthelmintics using each equation. Results suggest that alternative methods of internal parasite control need to be utilized as opposed to current reliance on commercial anthelmintics.
Keywords: goats, anthelmintics, resistance