Dog and cat issues

Question
Our dog had his knee give out around two and a half months ago. Two weeks after that, he had knee surgery. Shortly afterwards, approximately a month later, he was hit by a car and had emergency hip surgery. He has been fine, until around two weeks ago, when a young female cat showed up. Turned out she's pregnant. She is due in about two weeks now, and he's suddenly become interested in her. He began sniffing her, and today he chased her around, and tried to pick her up. Any reason he is doing so? We don't want to harm either she, him, or the kittens. What should we do?

Answer
This sounds like an especially "kind" dog if he was, indeed, gently trying to pick up the cat. (Why he suffered these accidents is beyond me, he needs to be safely contained. If he's an escape artist, you have other problems you need to correct to be sure he suffers no further injury.)  The cat is most likely excreting pheromones related to her imminent delivery (which might be closer than two weeks!)  I strongly suggest you separate the cat from the dog (and ESPECIALLY the kittens!) This cat is in no condition at present to deal with a dog and her kittens will be especially vulnerable, and so will she.  If you intend to keep the cat after her kittens are weaned, you'll need to address how to properly introduce the dog and cat to one another.  I believe there is a feline behavior expert on this forum but, if not, you can Google and attempt find one.