Body condition score and weight are effective targeted selective treatment indicators for gastrointestinal nematodes...

Ewe reproductive performance is key for flock profitability but can be impacted upon by gastrointestinal nematode (GIN) infections. Farmers commonly deworm ewes pre-mating, yet concerns regarding anthelmintic resistance increase pressure to reduce wormer use.

This study retrospectively assessed pre-mating targeted selective treatment (TST) indicators in a flock of 354 ewes split into anthelmintic treatment and control groups. Conway-Maxwell-Poisson and binomial regression analyses were used to identify TST indicators associated with reproductive performance.

There was no significant difference in overall scanned litter size between treated and untreated ewes. However, ewes with a body condition score (BCS) less than 3 or a weight less than 60 kg that were not dewormed had significantly lower litter sizes (mean 1.2 and 1.41, respectively) than those treated (1.94 and 1.8, respectively) or with higher condition/weight regardless of worming status (p < 0.05).

Parasite diagnostics were not undertaken on all individual ewes, and the study assumes that differences identified in the reproductive performance of treated and untreated groups were due to GIN infection.

These findings suggest that BCS and weight are effective indicators for implementing TST pre-mating, enabling reduced anthelmintic use without compromising reproductive outcomes.