Abstract
A Pacific walrus maintained at SeaWorld San Antonio (SWSA), San Antonio, Texas was determined to be pregnant by ultrasound. The placenta and fetus were passed six months after the expected date of parturition.
Walrus breeding activity is normally observed at SWSA in late January through March with parturition in May of the following year, which coincides with what has been observed in the Bering-Chukchi region.1 A 865 kg Pacific walrus was observed being bred on a regular basis from late January into March of 2002. Normal gestation appears to be 15 months, based on our observations and those by Fay1, thus a viable calf was expected to be delivered in May of 2003. The animal gained weight as expected throughout her pregnancy. A viable fetus was observed by ultrasound in September of 2002. It was approximately 17 cm long and located on the left side of the mother. The thorax and top of the skull were visualized. The fetus was observed by ultrasound again in February of 2003. Viability could not be determined at that time. It was not observed after February although several attempts were made up to and beyond the expected delivery date.
No blood sample was collected during the normal pregnancy but one was collected on September 1, 2003. The hematology and serum chemistries were normal and her progesterone was 15,600 picograms per milliliter. She continued to gain weight and was pregnant by all outward appearances, i.e., distended abdomen, weight gain, and mammary gland development.
On the morning of November 15 2003, she passed the placenta with a male fetus, 6 months beyond her expected delivery date. The weight of the placenta, fetus and fluid was 2.7 kg and the fetus alone weighed 0.65 kg. The total length of the fetus was 26 cm. Fluid aspirated from the placenta and from the fetus was sterile. The cause for the retention is unknown.
To the authors' knowledge, a retained fetus in a walrus has never been reported although it is not uncommon in other species.
References
1. Fay FH. 1982. Ecology and biology of the Pacific walrus, Odobenus rosmarus divergens Illiger. North American Fauna. Number 74. United States Department of the Interior, Fish and Wildlife Service. Washington, D.C. Pp.192-197.