In both your research proposal and in your later writing up , you need to justify your research. That is, you need to show the reader why your research is worth doing and why it is worth reading on.
Think about the results you are expecting and the conclusions you may reach. How will these be able to be used and by who? Do your findings have the potential to change practice? Or to justify existing practice? Will your findings make something easier or safer or better or quicker or cheaper for animals, owners, vets or the public? Perhaps they will help indicate where the next steps in research should be directed. Or where further reseach effort does not look worthwhile.
You need to articulate this clearly. You need to be positive, but not extravagant with your claims for importance. You need to make a case for the importance of your work. That is, make an argument for it, not just assert it. Show that there is good reason for the importance of your work. Support your claim with evidence from the literature. Lead the reader through your writing so that they conclude, as you have, that there is a gap and that it needs filling.