Influence of batches of bovine oocytes on the outcome of an intact zona pellucida binding assay and in vitro fertilization

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Abstract
A series of experiments was performed in vitro to determine the variation between batches of abattoir-derived bovine oocytes to bind and to be fertilized by frozen-thawed spermatozoa provided by a single ejaculate from a bull with high field fertility after artificial insemination. Fourteen batches of oocytes, collected over a 90-day period, were divided randomly into two equal groups at each sampling period. One group of oocytes was subjected to in-vitro maturation and subsequently in-vitro fertilization (IVF) while the other group was used as intact oocytes in a zona binding assay (ZBA). Fertilized oocytes were evaluated for penetration and pronuclear formation and, in the ZBA, the number of spermatozoa bound to each oocyte was registered. Neither the results of the ZBA nor the IVF results varied significantly (p = 0.45) between batches. Furthermore, when a sperm concentration of 0.5 x 10(6)/ml was used, the number of spermatozoa bound to the zona pellucida correlated significantly with the frequency of oocytes penetrated after IVF (r = 0.76). The results suggest that variation between the batches of oocytes has no detrimental significance for the application of intact zona pellucida binding or IVF for assaying frozen-thawed bull semen, provided that a large number of oocytes/batch (> 15) are assayed.