Homeostasis is maintained or regained through the stimulation central nervous system by external events affecting emotion, hormonal concentrations affecting mood, and appetitive behaviour (thirst and hunger). Specific behaviours, such as vocalization, may accompany particular states of mood or emotion. Vocalizations (such as distress utterances) may also affect the welfare states of conspecifics. Therefore, vocalizations by farm animals could be an effective tool to use when attempting to understand welfare states. Research into this area has increased, with attempts to decipher the meaning of various vocalizations. This paper focuses on the current state of research into pig, cattle and poultry vocalizations. Current sound analysis techniques give the ability to discriminate, analyze and classify specific vocalizations. With these tools, future research should focus on connecting specific utterances with specific environments, behavioural contexts and physiological parameters. This information will provide non-invasive tools for judging welfare states.