Bovine spermatozoal head size variation and evaluation of a separation technique based on this size

Synchrony of ovulation and follicular dynamics in merino ewes treated with GnRH in the breeding and non-breeding seasons

The effect of gonadotropin releasing hormone (GnRH) treatment on the time of ovulation and the occurrence of follicular dominance during the non-breeding and breeding seasons (experiment 1), and on fertility after artificial insemination (AI) in the non-breeding season (experiment 2), was examined in Merino ewes. Oestrus was synchronized in 40 nulliparous ewes (experiment 1; n = 20, in the non-breeding and breeding seasons) and in 79 multiparous ewes (experiment 2) using intravaginal sponges and pregnant mare serum gonadotropin. Thirty six hours after sponge removal (SR), half the ewes were injected (i.m.) with 40 microg of synthetic GnRH and the remainder used as controls. GnRH improved the synchrony of ovulation compared with the controls in the breeding (SD = 2.8 vs 5.7 days, p = 0.04) but not the non-breeding season (SD = 3.8 vs 4.4 days, p = 0.69), with ewes ovulating from 42 to 54 h (mean 50.4 +/- 4.08 h) and 42-60 h (mean 54.4 +/- 5.47 h) after SR for GnRH and control, respectively. For both treated and control ewes, ovulation occurred earlier in the non-breeding than the breeding season (50.1 vs 54.6 h; p = 0.002). GnRH had no effect on follicular dominance, as assessed by divergence (D: the time the ovulatory follicle exceeded the average size of the other non-ovulating follicles) or on the interval from D to ovulation (IDO). However, follicular dynamics differed between seasons. The mean follicle diameter increased at a faster rate up to 36 h after SR in the non-breeding compared with the breeding season and then rapidly declined, compared with a later peak (42 h after SR) in mean follicular size during the breeding season. IDO was shorter in the non-breeding than in the breeding season (26.7 +/- 4.30 h vs 39.6 +/- 4.53 h; p = 0.05). In experiment 2, ewes (n = 38 GnRH-treated, n = 40 controls) were inseminated in the uterus by laparoscopy 42 h or 48 h after SR with frozen-thawed sperm. The fertility of ewes treated with GnRH (nine of 39, 23%) was not different to the controls (eight of 38, 21%; p = 0.01). In conclusion the application of GnRH improved synchronization of ovulation but did not improve fertility rates after AI.

Reproductive Performance of Ewes after 5-Day Treatment with Intravaginal Inserts Containing Progesterone in Combination with Injection of Prostaglandin F2alpha

Three experiments were conducted with a total of 1579 ewes to examine reproductive performance in response to synchronization of oestrus during the breeding season, using controlled internal drug releasing (CIDR-G) inserts in regimens designed to provide high concentrations of circulating progesterone. In experiment 1, treatment with two CIDR-G inserts for 12 days produced conception rate (79%) and prolificacy (1.9) to first service equivalent to breeding at natural oestrus (56% and 2.0, respectively). Pregnancy rates to two service periods were 90 and 79%, respectively. In experiments 2 and 3, progesterone was delivered by a single CIDR-G insert for 5 days in combination with prostaglandin F2alpha (PGF2alpha; 5 mg i.m., twice, 3 h apart) the day before (experiment 2), or at insert removal (experiment 3). The combined treatments improved rates of synchronization of oestrus (p<0.01) by 23 and 20% points, respectively, and pregnancy rates to the first service period by 19 (p<0.05) and 13 (p<0.01) percentage points, respectively, compared to treatment with PGF2alpha alone. It is concluded that the combination of treatment for 5 days with a CIDR-G insert and two injections of 5 mg PGF2alpha, the day before, or the day of insert removal, were effective treatments to obtain high fertility at synchronized oestrus in ewes during the breeding season.

Effect of processing and measuring procedures on estimated sizes of bull sperm heads

Reported estimates of sperm head size within a species vary considerably, partly due to procedural effects. A simple India ink method was developed that provided good contrast without inducing artifacts. Semen from five fertile bulls was smeared on replicate slides and left unfixed or fixed in Carnoys solution, with ink added for background. Other slides were fixed, and sperm were stained by the Feulgen procedure. Sperm head area was measured four ways. These were linear measurements made with the aid of an ocular micrometer and an oil immersion objective, plus three methods of measuring sperm heads projected at magnification 5,000 x. The areas of unfixed and fixed sperm heads did not differ (41.5 microm(2) versus 41.6 microm(2), respectively, P>0.05). The Feulgen-stained head area was smaller (26.2 microm(2), P<0.05). Sperm head areas calculated from ocular micrometer measurements were slightly smaller (P<0.05) than areas measured using projection. Identical results obtained by two technicians were treated as duplicates and approximately half of the variation was biological, due to source of semen. There was an interaction (P<0.05) between the sample source and fixation procedures. Thus, preparative techniques must be carefully controlled, and experiments designed to partition possible interactions between the biological material sampled and procedures used.

Collection frequency affects percent Y-chromosome bearing sperm, sperm head area and quality of bovine ejaculates

This study evaluated the percentage of Y-chromosome bearing spermatozoal (%Y-CBS) variation from ejaculates within individual males using two experiments. In the first experiment, six ejaculates were taken from each of five sexually rested (>30 days) Holstein bulls. Ejaculates were processed separately and stored in liquid nitrogen. From each ejaculate, five straws were thawed and equal sperm number, pooled samples were constructed using hemacytometer counts. Individual ejaculate DNA samples were extracted and quantified by spectroscopy. AY-chromosome specific segment was amplified by polymerase chain reaction (PCR) and the product separated by gel electrophoresis. Ethidium bromide stained bands were detected by image analysis and equated to a 50 %Y-CBS pool. In the second experiment (91 days), two ejaculates were collected from sexually rested (>21 days) bulls weekly and two ejaculates were collected from bulls every 21 days. Specific Y-chromosome (SRY) and X-chromosome (factor IX, F9) sperm DNA was amplified by PCR and the products separated by gel electrophoresis. Ethidium bromide stained bands were detected by image analysis and compared to a standard curve constructed from pure SRY and F9 PCR product. The log ratio (SRY/F9) of the corrected intensity densities were used to estimate the percent Y-chromosome DNA bearing spermatozoa (%Y-CDBS) in each ejaculate using inverse regression procedures. In Experiment 1, ejaculate differences for the first collection ranged from 17 to 71 %Y-CBS. Differences remained large for the second ejaculates and lessened for the third and fourth collections. Differences were least for the last two collections. Sperm head area also fluctuated. In Experiment 2, collection frequency affected the pattern of %Y-CDBS response. In bulls collected weekly, %Y-CDBS changed in a sinusoid fashion with a period of about 13.5 days. For bulls collected on a 21-day interval, %Y-CDBS ejaculate differences were high in the first ejaculate after sexual rest. Maximization of %Y-CDBS variation between ejaculate and its identification by PCR would allow ejaculate selection to be used to the alter the sex ratio in producers' calf crops.