Runt isn’t growing

[Momo and Midna]

hi, i was hoping i could get some advice. i’m fostering these baby bunnies because their mom had passed away and they are currently 25 days old but the runt suddenly stopped growing about a week ago.
here’s a picture of him next to the largest one in the litter, the size difference is quite insane. is there anything i could do to help him grow again or should i just wait it out? he’s progressing mentally as fast as the others and he has tons of energy but i’m super worried. i’ve never raised baby bunnies before now
i also would love some advice on raising them if possible !

 

[JBun]

Provided he's not a dwarf breed and a peanut(genetic defect), which at 25 days is extremely unlikely as they don't usually survive past the first week, he could have an intestinal parasite or it could be some sort of other genetic defect. Since you say the baby stopped growing, but had been, I would suspect a possible parasite.

I know of two people that had baby buns that were failing to thrive and much smaller than their siblings. The babies were treated for intestinal worms with a 10 day course of fenbendazole(20mg/kg), and afterwards both owners reported that the babies started catching up in size to their siblings. I had a runt as well, that I suspected had hepatic coccidiosis. She was bony along the back and hips and had a pot belly and was at least half the size of her siblings. She wasn't treated with meds, but I did change her diet as she was on a low quality pellet in her previous home. I don't know if it was the diet change or if it just cleared up on it's own, but she did catch up in size to what is normal for her breed.

So I would think either intestinal worms or coccidiosis. Having a fecal float done by your vet may show evidence of this, but I would be inclined to want to treat for parasites regardless, based on the clinical signs presented.

http://www.medirabbit.com/EN/GI_diseases/Parasitic_diseases/Pass/Pass_en.htm (pinworms in rabbits)

MediRabbit (coccidiosis in rabbits, contains medical related photos)

https://rabbit.org/vet-listings/
Here's a good link for what to look out for and expect with new kits.
https://flashsplace.webs.com/accidentallitters.htm
Also, diet changes can be an issue, so as they are transitioning onto solid food, lots of good quality(no mold, no noxious weeds, low dust) grass hay is the best thing to help keep a rabbits digestive system functioning well. Especially in babies that are particularly prone to developing digestive illnesses. And limit or avoid high carb/sugary foods that can disrupt the microflora of the gut.

 

[Momo and Midna]

thank you for the help. i’ll contact my vet in the morning and see about taking the 4 of them in just in case, he also seems boney along the back with a pot belly so hopefully it isn’t something permanent and he can be treated!

 

[JBun]

I would bet it's parasites then, pinworms or hepatic coccidiosis. They can get tapeworm too, but that isn't as common. Treatment for pinworms is fenbendazole(Panacur), and albon or smz/tmp for coccidiosis. Hopefully your vet can get little bun all sorted out.