[Anthelmintic resistance in ruminants: development, diagnostics, and procedures].

This research article discusses the rising problem of anthelmintic resistance, where intestinal worms in animals such as small ruminants, cattle, and horses develop resistance to deworming agents. The paper addresses the reasons for this phenomenon and discusses methods to evaluate the effectiveness of these deworming drugs and strategies to reduce the rate of resistance development.

Anthelmintic Resistance Development

• Anthelmintic resistance occurs when gastrointestinal nematodes in animals develop resistance to deworming agents. The main factor contributing to this resistance is the indiscriminate use of all available anthelmintic drugs, which leads to the selection of naturally occurring resistance genes within parasite populations.

Diagnosing Resistance

• The most practical method for assessing a drug’s efficacy is known as the fecal egg-count reduction test. This test measures the reduction in the count of parasite eggs in the feces after administering the drug.
• Various parameters can also be assessed to decide on the need for anthelmintic treatment. This can be done at the group level by examining pooled fecal samples, serum pepsinogen concentration or Ostertagia ostertagi antibodies in bulk milk samples. Individual-level criteria include fecal egg count, conjunctival color (an indicator of Haemonchus contortus infection), body condition in adult animals, weight gain in juvenile animals, and the consistency of feces.

Procedures for Managing Resistance

• To curb the development of anthelmintic resistance, selective treatment is recommended, in which only part of the animal herd is treated. The animals requiring treatment must be identified based on health or economic reasons.
• An efficacy test of the anthelmintics used should be performed regularly at the beginning of the pasture season. Moreover, maintaining a low infection pressure during the pasture season through effective pasture management strategies is advised.
• The ultimate goal is to reduce anthelmintic treatment to slow down the development of resistance, while maintaining the productivity and health of the animals, thereby prolonging the effectiveness of the available drugs.