What is the best computer for a vet student?

For a maximum budget of $3000, there's quite a number of high end laptops you can choose from, and from your description I'm going to assume gaming is not going to be a priority (although any $3000 laptop should be able to run games fine…)

Here's a list of laptops that you should consider (there are several models for each laptop which you can configure yourself to suit your needs):

Pen Support

• Surface Book with Performance Base
• HP Spectre x360 13″ or HP Spectre x360 15″
• Lenovo Yoga 700 Series
• Lenovo ThinkPad Yoga 370

No Pen Support

• Razer Blade Stealth
• Razer Blade Pro
• Dell XPS 15
• Dell XPS 13

When choosing your laptop, since it appears you are considered about performance, then try to get a laptop with a:

• SSD (quelli che ho dichiarato ne hanno uno)
• Preferibilmente una CPU Quad Core
• Almeno 8GB di RAM, anche se per te 16GB sarebbe meglio (se possibile)

Personalmente però, con un budget massimo di $3000 spenderei personalmente ~$1500 sul portatile e il resto dei soldi su un desktop costruito su misura (anche se devi prendere in considerazione altre periferiche del computer se scegli questa strada)