As a hand-reared calf, kid, or lamb grows past its first couple of weeks, its feeding volume per session increases well beyond what a 0.5L bottle comfortably holds — at that point, refilling a small bottle mid-session becomes a real practical annoyance, both for you and for the animal that's mid-feed. The 2.5L bottle solves that directly, holding enough for a full feeding session at a growing animal's actual appetite without needing a refill partway through.
It's also practical if you're hand-feeding several animals in sequence, since one larger fill covers more total feeding volume before you need to go back and refill, compared to repeatedly topping up a smaller bottle. Like our 0.5L bottle, it uses the same Nipple accessory, sold separately.