Individual fluctuations in efficacy of febantel against Muellerius capillaris in goats.

One hundred and eighty-seven dairy goats originating from 7 farms in western France were treated individually with febantel (probenzimidazole drug) at a dose rate of 5 mg/kg in spring 1991. Individual faecal samples were collected on d 0, 7 and 21 post-treatment and processed for counting first stage larvae of Muellerius capillaris (LPG: larvae per gram of faeces). Eggs of digestive tract strongyles were also counted on d 0 and 7 (EPG: eggs per gram of faeces). Blood samples were taken on d 0 to assess pepsinogen concentration related to abomasal damage caused by strongyle infection. The individual characteristics of the goats were recorded. The procedure was repeated on the same animals in autumn 1991. The faecal larval count reduction (FLCR) was mainly related to farm and season: farm 1 in the spring and farm 6 in the autumn showed a higher proportion of high responder (HR) goats (FLCR > 80%), whereas farm 3 exhibited a lower proportion of HR goats in the autumn. On the other hand, the characteristics of the goats (breed, physiological status, age, weight, presence or absence of wattles and horns) as well as the initial level of parasitism (LPG, EPG and pepsinogen concentration) all had a role which was limited or zero on the variability of response to treatment. Goats could not be individually categorized according to their response level because the FLCR values obtained in the spring were not repeated in the autumn, suggesting that other environmental parameters could be involved.