C/D-T is pretty watery, so I like a 3/4" or 1" x 22ga. The guage of needle you use really shouldn't be so much about the size of the animal as much as the viscosity of the med. Here, watery stuff gets a 22ga.. If it's oily (Bo-Se, Ivomec, etc), I like a 20ga or maybe an 18ga, depending on how oily it is. If it's a suspension (PenG, Excenel, etc) it gets an 18ga.
Poking baby kids with 18ga needles isn't fun, but hey...ya do whatcha gotta do sometimes.
Poking baby kids with 18ga needles isn't fun, but hey...ya do whatcha gotta do sometimes.