Dynamics of ovarian blood supply to periovulatory follicles of the ewe.

Radioactive microspheres were injected into the ovarian artery ipsilateral to the ovary containing the dominant (preovulatory) or postovulatory follicle of the ewe to estimate the distribution of ovarian blood to those follicles throughout the periovulatory period. The follicle of interest was excised from the ovary at the first sign of estrus (4-h heat checks), or 4, 8, 12, 16, 20, 24, 28 and 32 h later. Blood samples to be analyzed for serum luteinizing hormone (LH) were taken at each observation for estrus. Follicles were partitioned into basal tissue, apical tissue and fluid (preovulatory follicles) constituents. Radioactivity was determined within the residual ovary and in each follicular component. Follicular data were normalized to the ascending limb of the preovulatory surge of serum LH (first detected increase in LH = O h). The supply of ovarian blood to the wall (apex + base) of follicles was elevated after the rise in LH was initially ascertained (0-12 h). The distribution of blood to the follicular wall began to decline from 12 to 16 h, and subsequently continued to decrease (20 h) until after ovulation had occurred (greater than or equal to 24 h after the LH increase). Blood supply was less to the wall of follicles in the 20-h group and to ruptured follicles than that to the wall of follicles collected before the initiation of the surge of LH. There was no evidence that blood supply to either the basal or apical portion of the follicular wall was altered preferentially. Radioactivity was not detectable within follicular fluid.

Fertilization rate and early embryonic loss in Brahman crossbred heifers.

The fertilization rate and incidence of embryonic loss in virgin Brahman crossbred heifers between d 3 and 35 postinsemination (d 0 = first day of estrus) were determined. One hundred fifty-five virgin heifers, maintained in a dry lot, received approximately 22 Mcal.head-1.d-1 and were allotted to one of three groups (d 3, 16 or 35) according to body weight at the time of estrous detection. Seven empty ruptured zona pellucidae (ERZP) were recovered from five heifers in the d 3 group. It was impossible to determine whether the ERZP originated from fertilized or unfertilized ova and whether they were ovulated at the estrus immediately preceding or during a previous cycle. Consequently, the fertilization rate (d 3) was calculated to be 80 or 93% depending upon whether the ERZP were included or deleted from the calculations, respectively. Because of the large number of ERZP recovered, a second study was conducted with an additional 21 virgin Brahman crossbred heifers from which ova were recovered on d 3 postinsemination. The results of the two studies were similar. The percentage of heifers with an embryo on d 16 was 78 (10% had degenerating embryos and 12% no embryos), and the percentage pregnant at d 35 was 72. The conclusions suggested from this study depend upon the classification of the ERZP. If the ERZP are designated as ova ovulated during a previous cycle or ova damage in the collection process and are deleted from the calculations, the fertilization rate is high (93%), and embryonic loss apparently occurs between d 3 and 35 (P less than .95). However, if the ERZP are classified as ova ovulated at the immediately preceding estrus, unavailable for further embryonic development, and are included in the calculations, the fertilization rate is comparatively low (80%). In the latter case, the primary loss of potential embryos occurs before d 3, and the loss after d 3 is negligible (P greater than .05).