It hadn't occurred to me before - I've previously done vaccinations with a 19 gauge needle - but when I had a poorly lamb the vet gave me syringes, one with an AB and one with anti-inflammatory, and they had noticeably different gauge needles, one of which was surprisingly thick.
It makes sense that different liquids have different viscosity and might need different needles, but don't you need to take the size of the animal into consideration too?
What gauge should I use for Heptavac on lambs of 3 to 6 weeks (Shetlands) and what gauge should I use for AB, should I need to use it on adult sheep?