Back in San Diego, Anna and her long-time mate, Everett, were a compatible breeding pair, but despite their efforts she never became pregnant. We were asked to examine the pair to try to diagnose the problem and offer a possible solution. The first, and least invasive step, was to analyze Anna’s estrous cycles. Keepers collected fecal samples, froze them, and sent them to our Endocrine Laboratory, where Alan Fetter charted her cycles by measuring her fecal estrogen and progesterone levels.
We could see that she was breeding at the appropriate time in her cycle, and she was ovulating normally. When her progesterone remained elevated after each of two breeding cycles, we were hopeful that she was pregnant. But each time her progesterone plummeted back to baseline within two months, indicating that she had experienced a pseudopregnancy (also known as a false pregnancy). This condition is not uncommon among mammals, especially in carnivores. In most cases, pseudopregnancies last half to two-thirds of the length of a normal pregnancy, which is what we observed with Anna. A pseudopregnancy occurs when a female ovulates but does not conceive. For a few weeks her body produces hormones to support a pregnancy even though there is no embryo present. Eventually, with no communication from an embryo, the female’s body returns to normal, and she cycles again.
After two documented pseudopregnancies, it was time to take the next step by examining Everett’s sperm. Three semen collection procedures from 2008 to 2011 yielded samples completely devoid of sperm! During the last collection, the veterinary staff collected tissue biopsies from each of Everett’s testicles and sent them to our Wildlife Disease Laboratories pathology group. After careful assessment of the tissue, the disappointing report and photos clearly indicated that Everett was not manufacturing sperm. The reason for his inability to produce gametes was unknown, but his infertility was now an indisputable fact.
Curators at both zoos arranged an exchange between San Diego and Santa Barbara, and Beau moved south to our Zoo. As Todd described, Beau and Anna took a little time to get to know each other but then began to breed. We were excited to assay Anna’s samples to see if the new pair would be successful. Following breeding in January of this year, Anna’s progesterone rose significantly, indicating that she had ovulated. Our hopes for a pregnancy, though, were again dashed when two months later her progesterone dropped back down to baseline.
But there was a very encouraging difference in this pseudopregnancy. This time Anna’s estrogen levels were twice as high as in previous pseudopregnancies and remained high for nearly one month in contrast to the rapid decline seen before. We are hopeful that very soon Anna will experience a normal pregnancy and have the opportunity to raise a litter of cubs. We’ll be watching from the lab.
Barbara Durrant is the Henshaw Director of Reproductive Physiology at the San Diego Zoo Institute for Conservation Research. Read her previous post, Meeting Hua Mei’s Son.