Abstract

While not that long ago, we were happy to confirm dolphins' gestation with the help of ultrasound, nowadays not knowing the correct delivery date can be the cause of some practical problems. Indeed, many of our animals are part of daily demonstrations and special organizations (like separation of the mother, setting of protection nets, night observations etc.) are very important and time consuming management issues for such parks.

There are already several methods that can be used to try to determine the delivery date as accurately as possible: visual observation of the sexual activity of the animals, identification of the ovulation^1,2,3; visual observation of physiological changes towards the end of the gestation , such as swelling of the mammary glands, no appetite, visible contractions, frequency of flexions^4,5,6 or delivery prediction time based on rectal temperature.⁷

Though the use of ultrasound as a diagnostic tool is not yet available in all parks, delivery prediction based on sonographic measurements of the fetus has a major advantage over other diagnostic methods in that the birth date can be estimated relatively early.^8,9,10

A linear growth model is seen when fetal measurements (head biparietal and thoracic diameters) are presented in a graph against time.^11,12 With the data of 11 gestations, in 7 animals, from dolphinarium Brugge in Belgium and Zoomarine, Portugal, regression lines were established for the head and thoracic diameters (94 and 111 measurements respectively) based on number of days before delivery, and an easy to use computer program for delivery prediction was developed. All data were gathered through voluntary behaviour of the animals.

In the second stage of the study, the program was tested, with four new gestations at Zoomarine, to find out how accurate the prediction program was. In one case, the calf was born on the exact predicted date.

In the third stage of the study, the accuracy of the prediction program was tested using data from 9 gestations where the exact date of the conception--and the date of delivery--were known. Interestingly enough, although these 9 animals were a different sub-species, the exact delivery dates were also very close to the predicted date of the program in several cases.

This work is ongoing and more data sets will be required before the programme can be completed and tested more fully.

References

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2.  Robeck TR, Atkinson SKC, F Brook. 2001. Reproduction. In CRC Handbook of marine mammal medicine. Pp 193-236. Ed. L. Dierauf and F. Gulland.

3.  Brook F, Van Bonn B, ED Jensen, 2001. Ultrasonography. In CRC Handbook of marine mammal medicine. Pp 593-620. Ed. L. Dierauf and F. Gulland.

4.  Bortolotto A, Benoldi C, Bonsignori B, G Gnone. 1995. Observations of a bottlenose dolphin (Tursiops truncatus) during pregnancy. In: Abstracts of the 23rd annual symposium of the European Association for Aquatic Mammal-p2.

5.  Bortolotto A, Pastore V, Sironi A, B Mercera. 1997. Delivery determination by means of behavioural observations of three female bottlenose dolphins (Tursiops truncatus) during the pregnancy. In: Abstracts of the 25th annual symposium of the European Association for Aquatic Mammal-p22.

6.  Bortolotto A, L Stanzani. 1998. Flexions: A reliable tool for the delivery determination in the bottlenose dolphin (Tursiops truncatus) in an accurate way. In: Abstracts of the 26th annual symposium of the European Association for Aquatic Mammal-p4.

7.  Terasawa F, Yokoyama Y, M Kitamura. 1999. Rectal temperature before and after parturition in bottlenose dolphins. Zoo Biology 18:153-156

8.  Stone LR, Sweeney JC, RL Johnson. 1995. Ultrasonography of bottlenose dolphins in pregnancy. IAAAM Proceedings 26. P8.

9.  Stone LR, Johnson RL, Sweeney JC ML Lewis. 1998. Fetal ultrasonography in dophins with emphasis on gestational aging. In: Zoo and wild animal medicine: Current therapy 4.p 501-506. Ed. Fowler M.E. and Miller R.E.

1.  Taverne MAM. 1991. Application of two-dimensional ultrasound in animal reproduction. Wien. Tierärztl. Mschr. 78:341-345.

2.  Willimason P, Gales NJ, S Lister. 1990. Use of real-time B-mode ultrasound for pregnancy diagnosis and measurement of fetal growth rate in captive bottlenose dolphin (Tursiops truncatus). J. Reprod. Fert. 88:1-6.

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