Most sheep are vaccinated by injection, with a vaccine against five or six common infections. Lambs get a vaccination and a booster six weeks later, and sheep are vaccinated annually. You don't have to do this (and organic farmers don't vaccinate), and your sheep may not get infected if you have a small stable flock with no bad neighbours. In a valuable flock, you might not want to risk all the sheep getting infected. You can do the vaccination by yourself.

Most sheep are 'drenched' annually against worms, with a 'drench gun' that you squirt into their mouth. All sheep have intestinal worms, and a few worms are not a problem (in fact researchers now think that humans avoid some health issues if they have a small worm load). A high worm load is bad for sheep health and growth, and gives them diarrhoea ('makes them scour'). Worms live and lay eggs in the sheep's intestine, the sheep passes the eggs onto pasture in its dung, the worms hatch on the grass, the sheep eats the grass and the baby worms, and so the cycle continues. After sheep are drenched, they should be moved to a new paddock where they won't immediately eat worms again. Most worms die on dry ground in a few months of very hot weather, and they can be removed by grazing with cattle or horses (which have different worm types, so the sheep worms die inside them). You are not required to drench for worms, and some have become resistant to most drenches. You can check for worms with faecal tests which your Vet can organise, and you can control worms by pasture rotations and by getting rid of the worst affected sheep (eg sheep that scour when the others are fine). There are some organic methods that help. Check the Wormboss site for lots of information about worms.

Ovine Brucellosis is a disease of rams, passed in semen. Your Vet can check every year or so, to certify that your rams are not infected. The Vet takes a blood sample from every adult ram, feels their balls for lumps, and checks that your fences will keep out other stray rams. Ovine Brucellosis accreditation is not compulsory, but it is important if you are selling rams commercially. However once accredited, it's more difficult to bring in rams from an unaccredited flock .

Ovine Johne's Disease is a wasting disease of sheep that takes several years to show, and is fairly recent in Australia. Infection is transferred by eating grass contaminated by infected dung. Young lambs can have a once-only vaccination with Gudair, which can be dangerous for needle scratch in humans. The Vet can do it, or you can do it yourself - buy a vaccinator with a needle that retracts into a protective cover for your own safety. All farms in Australia have an OJD rating, with a point score based on the prevalence of OJD in the area, whether the lambs and the whole flock are vaccinated, and whether the flock has SheepMAP status (MN 1, 2 or 3 - established through faecal tests). There are restrictions on moving sheep with a lower OJD rating to a higher rating area, so check before you buy. Quarantine checks will stop you at a state border. Check the Internet for details, particularly about OJD area ratings.