He's definitely not being underfed, I leave out food for him and mum plus syringe feeding every 4 hours. The food he's currently on is very calorie and nutrient dense as well, more than formula. So far we suspect some sort of nutrient uptake issue with his GI system.
His weight gain was...
I'm currently fostering a kitten that's 6 weeks old now, however, he is only 230g. He eats really well, we syringe feed 5 meals a day and has no issues with toileting either. I've had him for a week and he's managed to put on 22g.
The vets were concerned with his lack of weight gain, but...
