PREDICTIVE VALUE OF PALPATION PER RECTUM FOR DETECTION OF THE CL IN ZEBU CATTLE AS EVALUATED BY PROGESTERONE CONCENTRATIONS AND ULTRASONOGRAPHY

The main objective of this study was to calculate the predictive value of the positive and negative diagnosis of the presence of a corpus lu teum by palpation per rectum in Zebu cattle. Gyr breed (n=16) heifers were palpated by a veterinarian every 3 d during March and April, and every 5 days during May. The presence or absence of a CL was recorded for 442 examinations. A blood sample was obtained after each examinati on, and a functional CL was considered to be present if plasma progest erone concentrations were above 1 ng/ml. Progesterone results were use d as the reference to calculate the sensitivity and specificity of pal pation per rectum for the diagnosis of a functional CL on different mo nths. Predictive values for the positive and negative diagnoses were c alculated using different hypothetical rates of the prevalence of CL. To evaluate the morphological basis of an erroneous diagnosis, ultraso nographic scanning of the ovaries was performed in 264 cases and the p hysical presence or absence of a CL was registered. The calculations w ere repeated using the ultrasonographic findings as the reference to e valuate the sensitivity and specificity of the diagnosis of a structur al CL by per rectum palpation. Several heifers were not cyclic in Marc h but began to cycle during the study. Thus, the prevalence of both fu nctional and structural CL increased with time. As a result, the propo rtion of palpation diagnoses classified as true positives increased in May, while the proportion of true negatives decreased. Although the v alues of sensitivity and specificity remained constant from month to m onth, the predictive values changed markedly in May, when the predicti ve value of the positive test increased while the predictive value of the negative test decreased. These changes were due to differences in the prevalence of a CL and not to differences in the palpable characte ristics of CLs in different months. The prevalence of a structural CL was always higher than that of a functional CL. The Cohen's Kappa test for concordance revealed better correspondence between palpation pet tectum and ultrasound (k=0.82) than between progesterone and either ul trasound (k=0.68) or palpation (k=0.66). These results show that a lar ge proportion of the errors imputed to defficient palpation when proge sterone concentrations are used as a reference are in fact the result of lack of correspondence between the physical and functional presence of a CL.