Bonnie is a two year old female West Highland White Terrier. Like most dogs, she is a creature of habits. She behaves in a predictable way, and enjoys the standard routines of daily life. She greets her owners in the morning, she enjoys attention, she has a good appetite, and she loves exercise.

Towards the end of February, Bonnie's personality seemed to change completely. She stopped behaving like the normal "Bonnie". She stopped dashing out to greet everyone as normal. Her owner would find her curled up in places where she would not normally go. She did not seem to enjoy attention from humans in her usual way. Her appetite was not as voracious as normal. She was less keen on exercise, preferring just to stay lying in bed. It was difficult to say that she was "unwell", but she was definitely not herself. Mrs B, her owner, brought her to me because she was worried about her. There was no obvious reason for her behaviour to change in this way. Her home environment had not changed at all. Why was Bonnie acting so differently from the way she used to be? Could there be some underlying illness?

When I examined her, she seemed like a healthy, good-natured little dog. She was slightly pot-bellied, and her owner agreed that she had filled out a bit in recent months. Her mammary glands seemed well-developed, and when I gently squeezed her nipples, there were drips of a small amount of grayish secretion, like watery milk. As I demonstrated these findings to Mrs B, I could see a sense of realisation dawning. "She couldn't be pregnant, could she?" she asked.

I asked about Bonnie's seasons. She did not come into heat in an obvious way. She was a fastidious animal, licking herself frequently to keep herself clean, so she did not leaves drops of blood around her like some dogs. But Mrs B's best guess was that she had been in season towards the end of December, which would mean that if she had been mated, she would be almost due to produce the pups. I asked if a male dog had been around, and it turned out that there was some ambiguity here. A male dog had been in the neighbourhood, but he had not seemed to be interested in Bonnie. But it was possible that a mating could have taken place.

It was true that Bonnie was showing many of the changes seen in pregnancy. I placed my hands around her body again, and palpated her abdominal contents. By gently squeezing and pushing, I was able to feel the various structures inside her abdomen. There were small intestines and large intestines. I could identify her spleen, her kidneys and her bladder. She was very relaxed, so I was able to obtain a clear impression of the contents of her abdomen. She definitely did not have an enlarged uterus, and I could not feel the small hard bumps that would indicate that there were puppies present. An ultrasound examination would be the definitive way to determine pregnancy, but there was no way that Bonnie could be at full term, about to produce puppies.

As I was carrying out my examination, Mrs B was telling me more about how Bonnie's behaviour had changed. She had started a peculiar type of "nesting" behaviour. She had a favourite place which she had made into a cosy little nest-like den. She climbed into her "nest", and turned around in circles many times, before finally settling. She had a couple of favourite objects, and she had started to pick these up, and carry them to her nest. She was particularly keen on a rubber duck and a sock. These were objects that she would normally completely ignore, but she was passionate about them at the moment. She would carry them backwards and forwards, guarding them as if they were precious objects. And she would always end up in her nest, curled up around the sock and the duck. "It is almost as if she is treating them like puppies", Mrs B told me.

At this stage, it was hardly necessary for me to announce the diagnosis to Mrs B. We had established that Bonnie was showing many of the physical and psychological changes of pregnancy, yet she was not pregnant. Mrs B asked me the question: "Could Bonnie be having a false pregnancy?". My answer was simple. Yes. Bonnie was definitely having a false pregnancy, also known a a "phantom pregnancy", and technically classified as "pseudocyesis". .

False pregnancy is a peculiar condition caused by hormonal changes in the body. After a bitch has been in season, her ovaries normally produce progesterone. Normally, in a non-pregnant bitch, progesterone levels gradually decline. Occasionally, progesterone production continues for longer, and at a higher level, compared to normal. This mimics exactly the same hormonal processes that take place during pregnancy, and the animal responds by "thinking" that pregnancy is indeed underway. Physical and psychological changes occur in precisely the same way as if the animal was indeed pregnant.

Bonnie was a typical case, but some animals have even more extreme signs. Sometimes a bitch might stop eating completely for several days, or she might become aggressive to humans in her efforts to protect her "pups". It is possible to use hormonal medications to dampen down the progesterone production, and to "cure" the condition. However, for most animals, false pregnancy is a transient phenomenon, lasting only a few weeks. When owners are reassured that they do not need to worry about the odd behaviour of their pet, most people are happy enough to allow the condition to run its course without treatment. There is a tendency for false pregnancy to recur after each season, and so it is strongly recommended to have affected animals neutered as soon as the signs of false pregnancy have subsided. Bonnie has already been booked in!