If he is eating hay, gaining weight (at each weight check), pooping well etc then that is the main thing for now.
Weight and Weight Loss Explained: BMI, Weighing, Poos and Feeding Support Levels
Eating and liking veg is a learned thing.
Without knowing exactly what veg they are used to eating, you have to take things back to basics anyway and introduce veg very slowly and carefully, one at time into their diet. This is so you don’t risk causing a digestive upset.
The guide below explains how
How to Introduce New or Reintroduce Regular Fresh Food Safely - The Rules
If you had only had him a few days, he is still going to be stressed and nervous at being in a new home. Also it takes two weeks to settle into a new bond, so a lot has happened to him in a few days and he will need time to settle, feel safe and get to know his surroundings. This could well be affecting him and why it is more important that you monitor hay intake via weight checks (hay intake cannot be gauged by eye). Pellets should only be one tablespoon per pig per day making only a very tiny and the least important part is food intake
It’s best to scatter feed veg and their one tablespoon of pellets per day (don’t use food bowls m) so both piggies have fair chance to eat and the dominant can’t food hog. It also encourages foraging which is metal stimulation for them.
Given you had one before the other, did you bond them properly on neutral territory?
Did the bonding go ok and Is the other piggy allowing him to eat? (Have you provided two hay areas etc)
Bonding and Interaction: Illustrated Bonding Dynamics and Behaviours
A Comprehensive Guide to Guinea Pig Boars
