The use of diagnostic ultrasound in assessment of the reproductive status of the bottlenose dolphin, tursiops aduncas, in capacity & applications in management of a controlled breeding programme

Abstract

The gonads of nine bottlenose dolphins, Tursiops aduncas, (four males and five females), were evaluated by sonography, for periods of between one and five and a half years, to assess reproductive status. (Three other males were examined intermittently for comparison with the study group). Sonographic assessment of gonadal size and appearance was compared with serum testosterone levels and spermatogenesis. Serum progesterone, estradiol, and LH levels were compared with sonographic identification of folliculogenesis and ovulation. Body lengths and weights were recorded for all animals throughout the study period. The sonographic appearance of the testis could be used to distinguish between juvenile, subadult, and mature male T. aduncas. Testis size increased slightly during spring and summer, but there was no marked 'rut' pattern of testicular redevelopment and regression. T levels tended to be higher during the spring and summer, and to vary in approximately six-monthly cycles. There was close correlation between serum T levels and testis size, but not between T levels and sperm production, nor between testis size and sperm production. Serum T levels could not be relied upon to determine reproductive status unless monitored regularly for a period of at least six months. Likewise, body length did not allow accurate assessment of reproductive status. Serum hormone levels were not useful in precise assessment of the reproductive status of female T. aduncas. LH was detectable in only one animal, and serum progesterone and estradiol levels varied both between animals and within individuals. It was possible to identify and monitor folliculogenesis using sonography. All females underwent periods of ovarian activity of between one and 12 months; between one and thirteen spontaneous ovulations were recorded during a single period of ovarian activity when females were segregated from males. If males were present, conception occurred at the first ovulation. Periods of ovarian activity were interspersed with periods of anestrus of between three and 27 months. Sonographic monitoring of follicular development in individual animals allowed accurate prediction of ovulation, which was used to control breeding in this population. When ovulation was predicted to occur within 24 hours, the female was segregated, and a singe, mature male then selected and placed with her overnight. The following day the male was removed and a sonographic examination of the ovaries was performed to ensure ovulation had taken place. This procedure was conducted six times between 1993 and 1996. Six pregnancies ensued; four calves have been born to date, and two are due in 1997. This study has shown that sonography is a non-invasive, accurate, and cost-effective means of assessing reproductive status in T. aduncas, providing a valuable means of controlling breeding and facilitating husbandry management of captive dolphins.