Further evaluations on the use of body condition score as target selective treatment criterion to control subclinical gastrointestinal nematode infections on dairy sheep

Abstract

Targeted selective treatments (TST) represent a key strategy to delay the development of anthelmintic resistance in gastrointestinal nematodes (GIN) of sheep. The Body Condition Score (BCS) is a well-established criterion for implementing TST in natural infection by non-hematophagous nematodes but the optimal thresholds for different animal categories and production systems remain poorly defined. This study aims to evaluate BCS as a practical TST indicator in Sarda sheep naturally infected with non-bloodsucking nematodes species, by assessing its relationship with fecal egg count (FEC) across reproductive stages and in replacement ewe lambs. A total of 2162 sheep were enrolled and divided into four groups: G1-G3 included ewes at different physiological stages, while G4 comprised replacement ewe lambs. Fecal samples were collected for FEC analysis and BCS was recorded for each animal. GIN prevalence ranged from 88.5% in ewes at 2–3 months of pregnancy to 99.8% in replacement ewe lambs, with the highest mean FEC observed in replacement ewe lambs (524.6 EPG). In all groups, a negative correlation (p < 0.001) was observed between BCS and EPG classes. The results obtained suggest that, in Sarda sheep, the TST thresholds based on BCS could be set at ≤2.75 for adult ewes during lactation or early pregnancy and at ≤3.00 for replacement ewe lambs. No consistent threshold could be established for ewes in late pregnancy.