Diagnóstico precoce de gestação em vacas zebuínas pela detecção de glicoproteínas associadas à prenhez.

Abstract

Pregnancy-associated glycoproteins (PAG) are substances expressed in the placenta of ungulate mammals. In ruminants, these proteins are secreted continuously from the embryonic implantation until the delivery. Recently, these proteins have been correlated and used for early pregnancy diagnosis in cattle. Thus, the objective of this study was to evaluate a PAGELISA for early pregnancy diagnosis in zebu beef cows, determining the accuracy of the method on the 25th and 28th days after a fixed time artificial insemination, comparing it with the use of ultrasound in the same period. The study was conducted on a farm located in the Northeast region of Pará State, in which 130 healthy Nelore (Bos taurus indicus) females were used and subjected to a hormonal protocol for fixed time artificial insemination. On the 25th and 28th days post-insemination, ultrasound examinations were performed and blood samples for the determination of PAG were collected. Blood samples were centrifuged, and the serum sample were aliquoted and stored at -20oC for later analysis of pregnancy associated glycoproteins, using a commercial ELISA in accordance with the manufacturer's guidelines. The tests were performed at the Laboratory of Virology of the Environment Section of Instituto Evandro Chagas. The results of the reading optical density were used to validate the test in which the results of samples were considered positive when > 0.300 (pregnant) and were negative when < 0.300 (non pregnant). The visual assessment of the plate is in accordance with the color (yellow solution wells, positive; wells with translucent solution, negative) was also performed. The results of transrectal ultrasonography and PAG-ELISA were arranged as follows: correct positive diagnosis (a), incorrect positive diagnosis (b), correct negative diagnosis (c), and incorrect negative diagnosis (d). From these values the sensitivity (100 x a/a + d), the specificity (100 x c/c + b), the positive predictive value (100 x a/a + b) and the negative predictive value (100 x c/c + d) of each test were calculated. The Chi-square test was used to compare the sensitivities and specificities of the two pregnancy tests (ultrasound x PAG-ELISA). Differences between pregnant and non-pregnant cows in the PAG-ELISA were statistically analyzed by using a Studenfs t-test. The accuracy of PAGELISA was equal on 25th and 28th days post fixed timed artificial insemination with sensitivity 100%, specificity 92,86%, positive predictive value 96,70% and negative predictive value 100%. However, the ultrasound scanning on 25th and 28th days, respectively, showed sensitivity 62,50% and 93,18% (p < 0,05), specificity 95,24% and 95,24%, positive predictive value 96,49% and 97,63%, and negative predictive value 54,79% and 86,96% (p < 0,05). There were significant differences between PAG-ELISA and ultrasound on the sensitivities and negative predictive value. However, the tests were equivalent in specificity and positive predictive values. In conclusion, the PAG-ELISA proved to be more sensitive and as specific as the ultrasound during the study period, with high accuracy on the identification of non pregnant and can be safely used from the 25th day after fixed timed artificial insemination for obtaining early pregnancy diagnosis in Zebu females.