STRUCTURAL AND VIRAL ASSOCIATION COMPARISONS OF BOVINE ZONAE-PELLUCIDAE FROM FOLLICULAR OOCYTES, DAY-7 EMBRYOS AND DAY-7 DEGENERATED OVA

Bovine zonae pellucidae (ZP) from follicular oocytes and from embryos and degenerated ova collected on Day 7 from superovulated cows were ex amined by scanning electron microscopy, by dimensional measurement, an d by total protein determination. The number of plaque-forming units ( PFU) of infectious bovine rhinotracheitis virus (IBRV) that were assoc iated with ZP-intact embryos/ova from each of the 3 sources after in v itro exposure was also determined. Scanning electron microscopy reveal ed that the surfaces of Day-7 embryos and degenerated ova were smoothe r than those of follicular oocytes. Mean dimensional measurements of t he diameter/thickness of the ZP from follicular oocytes, Day-7 embryos , and degenerated Day-7 ova were 156.7 mu m/12.3 mu m, 161.3 mu m/12.6 mu m, and 158.9 mu m/12.8 mu m, respectively. The mean total protein per ZP of follicular oocytes, embryos, and degenerated ova was 0.331 m u g, 0.349 mu g, and 0.254 mu g, respectively. Considerable variabilit y existed within groups, but significantly greater quantities of IBRV were associated with follicular oocytes (mean PFU/oocyte = 68.1) than with Day-7 embryos (mean PFU/embryo = 43.0;P<0.05) or with Day-7 ova ( mean PFU/ovum = 31.9;P<0.01). The reliability of using an assay for IB RV associated with nontransferable ova/embryos as an indicator of the presence or absence of the virus in transferable embryos from the same collection (Day 7) was supported. Although structural differences bet ween the ZPs of follicular oocytes and Day-7 embryos were observed in this study, further investigation is needed to determine if there are differences in the protective function of the respective ZPs.