The practical problems of giving medication in water can be considerable. On many farms, the water pipes are old, and if the antibiotic powder contains sugars or acids there is a tendency for mineral deposits to form and block the pipe, or yeasts multiply, producing a jelly which does likewise. It then becomes a major problem to clean them out. Water soluble antibiotics should be used in a pure form where possible or with a minimum carrier base. Water tanks can be quite small, and it is therefore necessary to introduce the antibiotic to the water four or five times a day. If water is taken direct from the mains supply, water medication is impossible unless a proportioner is used. Some water authorities prohibit the use of water direct from the mains supply. Up to 40% of the antibiotic may be wasted through inefficient nipple drinkers. Small groups of pigs are best medicated using a 180 litre barrel with a water bowl attached to the bottom. This is a very efficient method of administration but impractical on a large scale.

Fig.4-7 shows a range of antibiotics available for water use and dose levels per tonne of live weight. For example amoxycillin powder 50% contains 50% of the active medicine amoxycillin, and 50% of a carrier, either citric acid or a sugar such as dextrose. A dose level of 15mg/kg live weight of amoxycillin requires a dose of 30g/tonne of live weight per day of total powder but in practice this level would be raised to approximately 40g/tonne to allow for the losses in the water through the nipple drinker.

How to apply antibiotic powder to water in header tanks

1. Calculate the total kg of live weight to be medicated in tonnes.
2. Calculate the g of powder required for the 24 hour period. Add 10-20% extra if nipple drinkers are used.
3. The water intake per tonne of live weight per 24 hours will be approximately 100 litres.
4. Calculate the total water used in 24 hours.
5. Divide the header tank capacity into the total water used which gives the times that the tank is emptied in 24 hours.
6. Divide the powder and add pro rata to the tank. Stir each time.

Example

Medication with Amoxycillin - 50% at 15mg/kg. Water bowls used.

• 4 tonnes of live weight at 30g powder per tonne = 120g.
• 400 litres of water consumed
• If a 200 litre tank is available then 400/200 = the tank will empty twice in 24 hours
• Place 60g or half the powder in the tank early in the morning and the other half at the end of the day.