Zombies vs Changelings

Queen Chrysalis' throne has been taken by Thorax, newly dubbed King of the changelings, and Thorax's first act as king was to ally the Changeling kingdom with Equestria to prevent major catastrophes. The first few weeks reformed for the changelings were a bit sketchy, seeing as a few changelings, three to be exact, were sent over to a science facility.
"I'm not sure about this" one of the changelings said "If we're at peace with the ponies, why are we going over to these science facilities?". The doors opened the science facility, which also acted as a hospital, newly opened and ran by Princess Twilight Sparkle. The changelings walked inside, nervous about the visit.
"Ah, good to see you." Called a voice from the hallway, revealed to be a graying-brown griffon "I'm Dr. Granite Hardrock. Welcome to our science facility." The good doctor said as he was seemingly friendly with the changelings. Granite's cheery personality and friendly behavior made the changelings uncomfortable.
"Is this gonna take long?" a blue changeling asked, speaking the mind of his changeling friends.
"I'm afraid it might, but it's not like I'm gonna hook you up to any machinery that's gonna kill you or anything." Dr. Granite clarified to the changelings. "Before we begin, I'm afraid I haven't gotten your names." Dr. Garnet continued, hoping to be more friendly with his patients.
"I'm Wingspan, this is my sister Tree Sap, and the blue one is Stinger." one of them answered. Dr. Granite welcomed the three once more and led them down to the room where they'll be operating.

As they walked into the small room, they found a couple chairs, which Tree Sap and Stinger sat down in. Wingspan found an operating chair, and he thought he might as well go first.
"Ah, our first changelings here and we already have volunteers. Delightful." Dr. Granite said. Granite settled Wingspan down, and performed a quick checkup before they began the procedures. Once the checkup was complete, Granite went over to his desk, typed down what he learned from Wingspan's body onto a document, and opened up his cupboard to reveal a needle.
"Now I'm gonna need a blood sample." Dr. Granite said, holding out the needle. The needle must not have looked big to Dr. Granite, but Stinger saw the thing as huge and it scared him. The blue changeling cringed and even tried slowly to walk out of the office.
"Stinger, there's no escaping this." Tree Sap said in an emotionless tone. She did not care much for the needle as much as Stinger was, and neither was Wingspan. Dr. Granite injected the needle in Wingspan's front right leg, and out came a liquid that oozed a bright green and dark blue color, and even glowed a bit.
"All right. That'll be it for you. Who's next?" Dr. Granite asked. Stinger was hiding behind Tree Sap, who just sighed. "Let's just get this over with." She said.

The next few minutes, Tree Sap and Stinger got their checkups and blood samples taken. Dr. Granite, congratulating the three for being the first patients in this new science facility, gave each changeling a lollipop and led them back to the entrance. It was time for the three to go home to the hive.
"If you guys need anything from me, or if I need to schedule an appointment with you, Just call me or I'll give you a call." Dr. Granite assured the three, as a chariot with King Thorax in it appeared to give his subjects a ride home. As the changelings left, the griffon doctor examined what he had collected from the three of them. He had gathered samples of not just their blood, but also of their fluids, which they use to make the cocoons. For hours on end, Dr. Granite and other doctors examined the samples some more and more until it was time for the facility to close down for the night. All would go home by the time of closing, except for Dr. Granite and a pegasus janitor.
"Doctor, what are you doing?" The janitor asked. Dr. Granite was spotted taking a blood sample of his own out and putting it next to the blood samples and the cocoon fluid samples.
"I'm trying to see if I can give other species the ability to create cocoons." Granite explained, mixing the blue-green changeling blood with the red blood from his own body. Once the mixture was complete, the janitor couldn't wait any longer.
"I'm gonna give it a go." The dimwitted janitor said, as he took the mixture and chugged the small flask down faster than a jug of apple cider. Dr. Granite tried to stop him, but it was too late. The mixture was in his body and it was taking immediate effect.
"Oh no." Dr. Granite said, as he ran for help from the other scientists. The body appeared to be dead, but the coat took an immediate color change, changing from the janitors normal color, to a darker grey, and the eyes shot out glowing green and lifeless, and the mouth became expressionless, oozing out green fluids. He became infected with the DNA mixture and became a monster.

The next morning, the other scientists showed up, all except for Dr. Granite, who stayed home in horror of being fired for becoming a mad scientist and being fired, or worse. The janitor, who was stuck lying down all night, eyes open, got the attention of the other scientists.
"What happened here?" each one of the scientists asked one another. When there was a crowd of ponies surrounding the janitor's cold resting body, the monster sprang to life and bit the neck of one of the scientists. The ooze from his mouth drained and mixed with the gushing blood of the bitten scientists neck infecting them too. One by one, the process was repeated until the entire science facility was completely zombified.

And now the zombies are hungry, and it's all thanks to the changelings.