Pfizer (NYSE: PFE) is jumping into the diagnostic business with all four paws. The company announced yesterday that it's purchasing Synbiotics to gain access to its veterinary immunodiagnostics business.

Immunodiagnostics measure antibodies as a way to determine whether a human or animal has been infected with a virus or bacteria. It's a good fit for Pfizer, which already sells plenty of animal-health products. More importantly, Pfizer seems to be using the purchase as a stepping stone to launch other diagnostic products for animals.

It's easy to forget about the animal-health division since Pfizer is so focused on human diseases. But the combined sales are fairly substantial, having contributed 5% of the revenue during the first nine months of the year. Looked at another way, if the combined sales of the animal-health products were a drug, they'd be second in sales behind Lipitor on the company's product revenue list.

The push into animal diagnostics may be a reaction to Merck (NYSE: MRK) and sanofi-aventis (NYSE: SNY) rejoining their animal-health divisions after a complicated breakup that allowed Merck to buy Schering-Plough. The two still need to divest of certain assets to make antitrust regulators happy -- Reuters reported that Bayer, Boehringer Ingelheim, and Novartis (NYSE: NVS) are bidding on the products -- but once they join forces, the new joint venture will be larger than Pfizer's animal-health division.

The animal-health industry is only growing at a 4% clip, so don't expect the division to suddenly fix all of Pfizer's problems. Still considering the instability with human drugs -- failed clinical trials and patent expirations -- having a solid diversified revenue stream could be just what the veterinarian ordered.

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Fool contributor Brian Orelli, Ph.D., doesn't own shares of any company mentioned in this article. The Fool has a disclosure policy.