This is oppression of creativity! I say we burn them at the stake, Ballerina!
P.S. check the UoM handbook entries for your majors and explore the subjects there to figure out your prerequisites. You will need Physics Fundamentals and Chem 1, 2,.Biochem and Foundations of Animal Health 1 and 2 by the end of second year to qualify for entry into the Doctor of Vet Science. There are six compulsory third year subjects for the major in third year, unusually. Remaining science slots are usually filled with DASC, ZOOL, MIIM, PATH and/or other similar subjects.
For environmental science you have way more freedom, so don't worry too much! They do require a first year university maths subject, however, for one of the compulsory subjects. Just check the handbook for the major qnd work backwards through prerequisites and you'll be fine.
In first year you can keep both majors open. You will need to take Chem 1/2, BIOL10004/5, a maths subject, and Physics Fundamentals if you didn't do 3/4 Physics or equivalent. Depending on the environmental science classes you take later on I would strongly suggest Understanding Planet Earth as well.