I wonder if you are aware of the history of animal assisted therapy?
Here is a short on Wikipedia, that may help you in your studies, as a starting point, putting the history in context:
http://en.wikipedia.org/wiki/Human_bonding#Human-animal_bonding
—"Human-animal bonding
Main article: Pet
Wikiversity has learning materials about Human-animal bond
Human-animal bond human to animal contact is known to reduce the physiological characteristics of stress.The human-animal bond can be defined as a connection between people and animals, domestic or wild; be it a cat as a pet or birds outside one’s window. Research into the nature and merit of the human animal bond began in the late 1700s when, in York, England, the Society of Friends established the The Retreat to provide humane treatment for the mentally ill. By having patients care for the many farm animals on the estate, society officials theorized that the combination of animal contact plus productive work would facilitate the patients’ rehabilitation. In the 1870s in Paris, a French surgeon had patients with neurological disorders ride horses. The patients were found to have improved their motor control and balance and were less likely to suffer bouts of depression.[13]
In the 19th century, in Bielefeld, Germany, epileptic patients were given the prescription to spend time each day taking care of cats and dogs. The contact with the animals was found to reduce the occurrence of seizures. In 1980, a team of scientists at the University of Pennsylvania found that human to animal contact was found to reduce the physiological characteristics of stress; specifically, lowered levels of blood pressure, heart rate, respiratory rate, anxiety, and tension were all found to correlate positively with human pet bonding.[13]
Historically, animals were domesticated for functional use; for example, dogs for herding and tracking, and cats for killing mice or rats. Today, in Western societies, their function is primarily a bonding function. For example, current studies show that 60–80% of dogs sleep with their owners at night in the bedroom, either in or on the bed.[14] Moreover, in the past the majority of cats were kept outside (barn cats) whereas today most cats are kept indoors (housecats) and considered part of the family. Presently, in the US, for example, 1.2 billion animals are kept as pets, primarily for bonding purposes.[14] In addition, as of 1995 there were over 30 research institutions looking into the potential benefits of the human animal bond.[13]"—