The sensitivity and specificity of single manual examination tests for detection of corpora lutea in the ovaries of non-cycling cows

OBJECTIVE: To evaluate the sensitivity and specificity of single manual examination of ovarian surface structures and of ovarian size as tests for the detection of corpora lutea in non-cycling cows DESIGN: Non cycling cows were dichotomously classified for the presence of palpable corpora lutea and for ovarian size. The performance characteristics of the palpable corpus luteum test and the ovarian size test were estimated using Bayesian analysis. Previously published information on prevalence and test performance was combined with observed data using the Gibbs Sampler to derive posterior distributions for prevalence and test parameters. RESULTS: Prior distributions for the prevalence of corpora lutea in cows not detected on heat before mating within seasonal herds were centred on 25%, and for the corpus luteum test sensitivity were centred on 70%. No prior assumptions for any other test parameter were made. From a total of 650 cows, 144 were found to have at least one corpus luteum, and 156 were found to have two small ovaries. The posterior estimate obtained for prevalence was 0.30 (95% Cl 0.22 to 0.43), for corpus luteum test sensitivity was 0.71 (95% Cl 0.49 to 0.93), and for corpus luteum test specificity was 0.98 (95% Cl 0.49 to 1.00). For the ovarian size test, the posterior estimate for size test sensitivity was 0.98 (95% Cl 0.95 to 1.00) and for size test specificity was 0.34 (95% CI 0.28 to 0.43). Sensitivity analysis indicated that corpus luteum test sensitivity ranged from 0.60 to 0.70 in most herds. CONCLUSIONS: Errors associated with pre-mating heat detection are likely to result in between 15 to 30% of cycling cows not detected in oestrous before mating, resulting in the inclusion of cycling cows within the population of non-cycling cows. This mixed population of cows is then subjected to manual examination by veterinarians in order to assign cows to treatment groups. The corpus luteum test has modest sensitivity and high specificity and the size test has high sensitivity and low specificity. Therefore the use of a single examination of the ovaries of cows not detected on heat before the mating period, in order to classify them as anovulatory anoestrous cows with or without a corpus luteum, is not sufficient to accurately classify them and thus to recommend treatment.