Nosferatu: Phantom der Nacht

Jonathan Harker is an estate agent in Wismar, Germany. His boss, Renfield, informs him that a nobleman named Count Dracula wishes to buy a property in Wismar, and assigns Harker to visit the count and complete the lucrative deal. Leaving his young wife Lucy behind in Wismar, Harker travels for four weeks to Transylvania, to the castle of Count Dracula. He carries with him the deeds and documents needed to sell the house to the Count. On his journey, Jonathan stops at a village, where locals plead for him to stay clear of the accursed castle, providing him with details of Dracula's vampirism. Harker ignores the villagers' pleas as superstition, and continues his journey unassisted ascending the Borgo Pass. Harker arrives at Dracula's castle, where he meets the Count, a strange, ancient, almost rodent-like man, with large ears, pale skin, sharp teeth, and long fingernails.
The lonely Count is enchanted by a small portrait of Lucy and immediately agrees to purchase the Wismar property, especially with the knowledge that he and Lucy would become neighbors. As Jonathan's visit progresses, he is haunted at night by a number of dream-like encounters with the vampiric Count. Simultaneously, in Wismar, Lucy is tormented by night terrors, plagued by images of impending doom. Additionally, Renfield is committed to an asylum after biting a cow, apparently having gone completely insane. To Harker's horror, he finds the Count asleep in a coffin, confirming for him that Dracula is indeed a vampire. At night, Dracula leaves for Wismar, taking with him a number of coffins, filled with the cursed earth that he needs for his vampiric rest. Harker finds that he is locked in the castle, and attempts to escape through a window with a makeshift rope. The rope, fashioned from bedsheets, is not long enough, and Jonathan falls, severely injuring himself. He awakes on the ground the next morning, stirred by the sound of a young gypsy boy playing a violin. He is eventually sent to a hospital and raves about 'black coffins' to doctors, who then assume that the sickness is affecting his mind.
Meanwhile, Dracula and his coffins travel to Wismar by boat, via the Black Sea port of Varna, thence through the Bosphorus and Gibraltar straits and around the entire west European Atlantic coast to the Baltic Sea. He systematically kills the entire crew, making it appear as if they were afflicted with plague. The ghost ship arrives, with its cargo, at Wismar, where doctors â including Abraham Van Helsing â investigate the strange fate of the ship. They discover a log that mentions their perceived affliction with plague. In turn, Wismar is flooded with rats from the ship. Dracula arrives in Wismar with his coffins, and death spreads rapidly throughout the town. When Jonathan is finally transported home, he is desperately ill, and does not appear to recognize his wife. Lucy later has an encounter with Count Dracula; weary and unable to die, he demands some of the love that she gave so freely to Jonathan, but she refuses, much to Dracula's dismay. Now aware that something other than plague is responsible for the death that has beset her once-peaceful town, Lucy desperately tries to convince the townspeople, but they are skeptical and uninterested. She finds that she can vanquish Dracula's evil by distracting him at dawn, but at the expense of her own life. She lures the Count to her bedroom, where he proceeds to drink her blood.
Lucy's beauty and purity distract Dracula from the call of the rooster, and at the first light of day, he collapses to the floor, dead. Van Helsing arrives to discover Lucy, dead but victorious. He then drives a stake through the heart of the Count to make sure Lucy's sacrifice was not in vain. In a final, chilling twist, Jonathan Harker awakens from his sickness, now a vampire, and arranges for Van Helsing's arrest for the murder of Count Dracula. He is last seen traveling away on horseback, garbed in the same fluttering black as Dracula, stating enigmatically that he has much to do.

Question: What animal did Renfield bite, causing him to be put into an asylum?
Answer: Cow