Dairy farmers will vaccinate for salmonella in August and September if they want to protect their herd from abortions. Later in the autumn, they will drench stock and use pour-on to protect against worms and fluke.

How to do these jobs properly is essential to getting the best use of the medicine purchased and completing the job safely. Damage to the animal or person is a big risk unless you take the necessary precautions and are prepared well in advance.

One of the biggest mistakes farmers make every year is underestimating the weight of the animal to be treated. Most drenches work on a certain volume of product per kilo of liveweight, so try and get an accurate measurement of the weight of your animals. Of course there will be a range, but you need to at least know the minimum and maximum, and treat accordingly.

Always read the label of the product used and follow the directions for required dosage and route of administration. Drug manufacturers are required by law to print instructions.

There are three main ways to give an injection: directly into the blood supply of the muscle – intramuscularly (IM); under the skin – subcutaneously (sub-cut); or directly into the vein – intravenous. Proper restraint keeps both you and the animal safe, and new crushes now have attachments to raise the animal’s head and secure the animal in place from the sides and/or behind.

If there is an option to choose between an IM and sub-cut injection, always go for the sub-cut as it is less invasive and less likely to damage valuable carcase meat.

Injections are given either by syringe or using a dosing gun. The difference between the two is that with a syringe you manually control how much of the drug gets injected into the cow, while the dosing gun dispenses preset volumes of medicine for more than one animal. This can save time.

Choose a needle based on the animal’s weight. Needle size is measured in gauges. The gauge of a needle is inversely proportional to its diameter – the lower the gauge, the bigger the needle. For instance, a calf’s skin is thinner, so a higher gauge needle will be used. You should also try to use the finest gauge possible to make sure that the cow feels as little pain as possible, but not so fine that risk of breaking the needle is increased.

Remember also to choose needle length based on the type of injections that need to be administered. Usually, shorter needles are needed for sub-cut injections and longer needles for IM and intravenous injections.

1 Always try and use pour-on when the weather is dry – even though some manufacturers claim products to be weather-proof. Once applied to control mites and lice, etc, limit mixing of groups. The product should be applied along the backline in a narrow strip extending from the shoulders to the tailhead.

2 To give an injection to a calf weighing less than 200kg, an 18-20 gauge (g) needle with a 1in (2.5 cm) length is ideal. For larger animals weighing over 200kg, you will need a 16-18g needle that is about 1½in long.

3 Instead of catching the head of each animal when drenching (especially cows), a long hook gun with a backpack can take a lot of the hassle out of the job. It makes the job safer and is less stressful on the animal.

4 Most farmers that use products wrong do so because they underestimate or overestimate the weight of the animals. The fool-proof way to solve this is to actually weigh the heaviest and the lightest animals, average the figures and then administer the medicine accordingly.