Maybe this will help you out. I found it a couple of days ago on the Tractor Supply website. *NEEDLE SIZE Needles are measured two ways. Length and Gauge (diameter). When determining the correct gauge, remember that the higher the number, the smaller the diameter. Example: an 18 gauge needle is smaller than a 16 gauge needle. *NEEDLE SIZE RECOMMENDATIONS Longer needles are used for intramuscular injections (1-1/2") and shorter needles (1/2" -1") for subQ injections. Cattle, Hogs, Sheep - generally an 18 or 16 gauge with a 1 or 1-1/2 inch length. Sows, Boars - usually given I.M., an 18 or 16 gauge with a 1-1/2 inch length. Small Pigs- 18 gauge x 1/2 inch. Dogs, Cats - 20 or 22 gauge with a 1/2 or 1 inch length. CHorses - 18 gauge x 1 inch.

Hi everyone, I'd like to know what size needles you all use for your piglet iron shots and regular swine shots and what size needles for adult sows and boars? I have a gun syringe and went to vaccinate my new piglets today and when I opened the box of needles I thought the 16 ga. needles to large for my young piglets. I bought them on the advice of the phone customer service person. Now I don' know what I'll do with 100 of them since I have to buy others. Thanks in advance.