| Popis: |
The diagnosis of pregnancy described in this article is based on the observation of milk ejection which, in the case of corpus luteum maintenance, results from the release of luteal oxytocin induced by intravenous administration of a non luteolytic dose of PGF2 alpha. The tests were performed in 410 lactating cows, 18-22 days after insemination (mean 19.95 days, SD 0.75), 3 h prior to the evening milking. A cannula was placed in the left fore-teat; when the cisternal milk flow ceased, a small dose of a prostaglandin F2 alpha analogue (256 micrograms Dinolytic) was injected. If a corpus luteum was present, the alveolar milk flow (1,276 +/- 570 ml) started 86 +/- 35 s later and pregnancy could be presumed. If the corpus luteum was no longer functional, the milk flow did not start again and the cow was considered not pregnant. The accuracy of positive results, ie 72.3%, significantly exceeded that obtained by radioimmunoassay of plasma progesterone used as a reference method, ie 68.6% (P less than 0.05). By contrast, the accuracy of negative results was lower, ie 93.5 vs 100%, (P less than 0.05): of the 195 pregnant cows which proceeded to term, 10 did not respond to the milk ejection test. In spite of these reserves, the test has the advantage of being inexpensive, rapid (about 5 min) and easy to interpret, ie either the milk flows or it does not. In addition, it may be used early, because from day 20 after Al the reliability of prediction of non pregnant cows (67.0%) was significantly higher when compared to the use of progesterone radioimmunoassay (58.6%) (P less than 0.05). With such a test, non pregnant cows can be reinseminated immediately and not only after a 3-week period. This may contribute to reducing the length of the infertile period. |
