The semen of 20 mature, evaluated bulls was split-sample diluted and contained 2.1 x 10(6) to 17.3 x 10(6) total spermatozoa per 0.25-ml French straw. The number of viable inseminated spermatozoa ranged from 1.1 x 10(6) to 11.8 x 10(6). Each bull had 2430 to 5330 first or second inseminations performed. The nonreturn rate at 56 d after AI was estimated for every dilution. The daily nonreturn rates to 180 d were used to estimate conception and calving rates at a given concentration. The relationship was determined between these estimations and the number of spermatozoa that were actually inseminated. The bulls differed significantly in their maximal nonreturn rate at high sperm numbers per AI and in the rate at which they approached this maximum. There was no correlation between the maximum nonreturn at high sperm numbers and the rate of approach, which implies that the ranking of the bulls for nonreturn rate 56 d after AI changes with the number of spermatozoa inseminated. Multiphasic analysis of reproductive efficiency revealed bull differences in estimated conception and calving rates. The estimated calving rate after conception was 82 to 90% and was independent of the number of spermatozoa that were inseminated. The sperm numbers needed to obtain 95% of the maximal conception rate ranged from 1 x 10(6) to 11 x 10(6).
A prototype on-line system for measurement of electrical conductivity of quarter milk was evaluated for accuracy in detection of subclinical mastitis compared with that of bacteriological culture and SCC of sampled quarters. Because of the low quarter prevalence of mastitis, quarters were sampled conditionally from the signals of the on-line system. All signaled quarters and a random selection of the nonsignaled quarters were sampled. To calculate sensitivity and specificity, the total number of non-signaled quarters was extrapolated. The system identified correctly 18 out of 23 subclinical quarters and 521 out of 555 healthy quarters. Quarter prevalence was about 1%. Predictive value of a positive test (35%) and the predictive value of a negative test (99%) were calculated, as well as sensitivity (25%) and specificity (99%), after extrapolation of the total number of nonsignaled quarters. Because of repeated measurements, sensitivity may be underestimated. When signaled quarters were defined by repeated signals within 14 d, predictive value positive increased to 48%. The prototype on-line system did not detect subclinical mastitis very accurately because of suboptimal test characteristics.
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