Dead horse

You lived in a village, in the countryside, when the Zombie Apocalypse began. Many people in the cities died, fled or turned into zombies. The contagious dangerous virus reached your home slowly, because you lived far from civilization, but the locals were already worried - a dozen people were quarantined to prevent further spread of the disease. But despite the measures taken, people mysteriously continued to get infected and attack other living people. This morning, an elderly man approached you. He and his son lived in the house next to you, were engaged in livestock farming and owned a small stable. The old man begs you to look in the fields and on the outskirts of the forest for his horse, who did not return from an unauthorized walk for a long time. The old man's son was in town getting supplies and hasn't returned yet. You agree to help.