Merck & Co. and Sanofi-Aventis SA said they will combine animal-health businesses into a 50-50 joint venture, a marriage that will account for more than a quarter of the $19 billion global market for vaccines and other products for livestock and pets.

The joint venture, between Merck’s Intervet Animal Health unit and its Sanofi counterpart, Merial, is still subject to approval from antitrust regulators in the U.S. and Europe, the companies said in a statement announcing the transaction today.

Merck and Sanofi said completion of the transaction is expected in “approximately” the next 12 months. The two animal-health businesses will continue to operate independently until the transaction closes.

The joint venture “will create strong value in bringing broader and improved offerings in both pet and production animal segments,” Christopher Viehbacher, chief executive officer with Paris-based Sanofi, said in the statement.

A Merck-Sanofi joint venture signifies further consolidation in the animal-health business.

Over the next five years, the global animal-health market is expected to grow by about 5 percent annually on rising demand for meat and “strong consumer needs” for pet supplies, Merck and Sanofi said. Livestock accounts for about 60 percent of global sales, and pets the remaining 40 percent, the companies said.

The joint venture will create “one of the broadest portfolios of animal-health products and services in pharmaceuticals and biologics” for farmers, veterinarians and pet owners, Richard T. Clark, chief executive officer of Whitehouse Station, N.J.-based Merck, said in the statement.

Merck and Sanofi may have to divest some products to satisfy government antitrust regulators, industry analysts have said.

There are “areas of overlap” among Merial’s and Intervet’s products, primarily in cattle and poultry vaccines, John Volk, senior consultant with Brakke Consulting, Inc., said last week.

“Regulators will look most closely at whether the combined companies will have an overly dominant position in any one category,” said Volk, whose Dallas, Tex.-based firm serves the animal-health industry. “Cattle and poultry vaccines are probably the biggest areas where they’ll have to do divestitures,”

Merial’s cattle brands include Corid, Igenity, Ivomec, Reliant and Respishield.

Intervet’s U.S. brands include Vista cattle vaccines, Revalor growth supplements and Safe-Guard deworming products.