THE RELATIONSHIP BETWEEN PARASITE COUNTS, LESIONS, ANTIBODY-TITERS AND DAILY WEIGHT GAINS IN PSOROPTES OVIS INFESTED CATTLE

Psaroptes ovis counts, extent of lesions (clinical index: ClinI), dail y weight gains (DWGs) and anti-P. cuniculi antibody titres in ELISA we re recorded during seven therapeutic field trials. Relationship betwee n these different data were studied. The differences between the mean DWG of treated and untreated control animals of the different trials r anged from 39 to 1206 g/day. Data were pooled for statistical analysis and the influence of trial conditions (management of the herd, farm, treatment) was extracted from each individual data by subtracting, fro m the DWG of each animal, the mean DWG of its trial. Such data were ca lled daily weight gain over the trial mean (DWG/TM). Multiple regressi on of DWG/TM, calculated over the period between the clinical examinat ions in control animals (n = 40), on clinical indices and sex demonstr ated a significant DWG/TM reduction per percentage of affected body su rface according to the following equation: DWG/TM (in g/day)= 135 - 22 ClinI(0) - 13 ClinI(28/35) - 70 (if male) (R-2 adjusted = 0.39), wher e ClinI(0) and ClinI(28/35) are the clinical indices recorded respecti vely at the beginning (day 0) and at the end (day 28 or 35) of the exp erimental period during which the animals were left untreated. A nonsi gnificant relationship (R-2 adjusted=0.07) was found between the antib ody titres on day 28 or 35 and the individual DWG/TM This would sugges t that serology could be used to estimate the prevalence of the diseas e on a local or national basis but not to calculate its economic impac t. (C) 1998 Elsevier Science B.V.