Your own personal opinions and ideas do not have to be referenced, because you are the owner. If someone else used these opinions in their work, they would have to credit you for these opinions.
Common knowledge (unless it is a direct quote from a specific source). This is defined as information that can be found in multiple sources, such as dictionaries or encyclopaedias; information that cannot be traced back to one author, such as fairy tales; or knowledge that is widely known and accepted, such as the years of the Second World War, or the fact that Julia Gillard was the first woman Prime Minister of Australia. As you are studying a specialised area, provide sources for as much material as possible. There is certain information, however, that is considered common knowledge within the veterinary industry, such as the fact that the scientific name for dogs is Canis lupus familiaris. This information does not need to be referenced.