The city shelter run by the Washington Humane Society is seen in this file photo. (Carol Guzy/The Washington Post)

Two prominent Washington animal-rescue groups are merging to form a single organization and combine their medical and rescue services.

The Washington Humane Society and the Washington Animal Rescue League signed the final paperwork Wednesday to form an organization operating with a single budget.

“Mergers are about strength. It’s about making things better,” said Lisa LaFontaine, chief executive of the Washington Humane Society, who will lead the new organization.

Plans for the merger had been in the works for nearly a year. The name of the new organization hasn’t been determined.

Officials are hoping to streamline services that the two groups offer. The Washington Humane Society, which was founded in 1870 and is the larger of the two, provides animal-control services and has officers who rescue animals from harm and cruelty. It cares for about 51,000 animals annually.

The Washington Humane Society only spays and neuters animals and doesn’t have full-service medical facilities. When it rescues an injured animal, it often coordinates with the Washington Animal Rescue League, which offers full veterinarian services.

The Washington Animal Rescue League was established in 1914 and cares for about 11,000 animals annually. “Now, animals that are found in the community with injuries can just go straight to a medical center,” LaFontaine said.

The Washington Humane Society employs about 120 people, and the Washington Animal Rescue League has 55 employees. The combined organization will operate five animal-care facilities in the District.

LaFontaine said the merger could result in a small number of layoffs at the executive level. The Washington Humane Society’s administrative building near the Georgetown reservoir will close.

For the restr of the 2016 fiscal year, the combined organization will operate with a $14.5 million budget — $9 million from the Washington Humane Society and $5.5 million from the Washington Animal Rescue League.

On Wednesday, officials introduced the first animal to be treated under the merger. An animal-rescue officer picked up Daisy, a 4-month-old pit bull with a broken leg, from a home that no longer wanted her.

The officers took Daisy to the Fort Totten facility so she could be treated by veterinarians. Before the merger, animal-rescue workers would have had to take Daisy to a Washington Humane Society facility, then arrange for her to be seen by an outside doctor at the rescue league or elsewhere.

The goal now is to treat Daisy at one location and find her a home.

“The question we asked is, ‘Can we save more animals, serve more people if we work together?’ ” said Roger Marmet, who will serve as the combined organization’s board chairman. “The answer is yes.”