Influence of Short-Term Fasting on the Efficacy of Albendazole Against Benzimidazole-Resistant Haemonchus contortus Under Farm Conditions

The aim of this study was to evaluate the effect of short-term dietary restriction on the in vivo efficacy of albendazole (ALB) on a goat farm with suspected reduced efficacy of benzidazoles (BZs). Initially, pooled faecal samples were analysed using the in vitro egg hatch test (EHT) to assess the level of BZ resistance. Subsequently, 58 goats were allocated into six experimental groups: three groups received a single dose of ALB (5 mg/kg body weight, BW) and three groups received a double dose (10 mg/kg BW). Each group was subdivided into animals fasted for 24 h before treatment, 24 h after treatment, and non-fasted controls. Morphological identification of third-stage larvae before and after treatment confirmed the predominance of Haemonchus contortus (91% and 100%, respectively). The in vitro EHT demonstrated reduced susceptibility to BZs, with the concentration of thiabendazole (TBZ) required to inhibit 50% of egg hatching exceeding the resistance threshold of 0.05 μg/mL, ranging from 0.166 to 0.247 μg/mL TBZ. Despite the presence of BZ resistance, fasting significantly increased the in vivo efficacy of ALB by up to 18%. These findings demonstrate that short-term dietary manipulation represents an effective strategy to enhance anthelmintic efficacy and partially overcome reduced drug performance.