Meaning: The pigs made loud noises when they were being fed.
Choice of Words: "Pigs" are farm animals. "Grunted" means to make a low, guttural sound. "Loudly" means in a loud manner. "Feeding time" is the time when animals are given food. So, "Pigs grunted loudly at feeding time" means that the pigs made loud noises when they were being fed.