With rising costs of production it isimportant to ensure that all areas of yourproduction system are working efficiently.Some medications can be expensive, so itis vitally important that, when required,antibiotics are used correctly and in acost efficient manner to reduce the needfor further treatments.

Medication of poultry is generallyachieved by delivering the medicationthrough the feed or through the watersystem. In this series of articles we willexplore the advantages anddisadvantages associated with eachmethod of delivery to free-range poultryand consider what producers can do to

improve treatment protocols andresponses to treatment. In this article wewill look more specifically at waterapplication of medication.

Key to effective delivery of medication isensuring that the birds actually receivethe recommended therapeutic dose.Dose rates are usually published bypharmaceutical companies in milligramsper kilogram (mg/kg). This dose raterepresents the amount of activetherapeutic ingredient (in mg) which mustbe delivered to each kg of birdbodyweight. Thus accurate dosing ofmedication requires a very accuraterecord of how much the birds are eating

or drinking, how much the birds weigh,and the dose rate and concentration ofthe particular medication in question.

Fortunately the antibiotics, wormers anddietary additives available to free-rangeproducers have a wide safety marginmeaning that the drugs are relatively safeto the animal and as such dose rates aregiven in mg/kg.

So how do we calculate an accurate

dose rate?

Lets imagine that following post mortemexamination your 41 week old flock hasbeen diagnosed with an infectiouscondition and you have been

A Drop in the Ocean!

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recommended to treat them with anantibiotic. This particular antibioticcomes in a liquid formulation which isdesigned to be delivered through thewater and is intended to be dosed at25mg/kg of bodyweight per day. If wewanted to dose the birds at this rate theminimum amount of information requiredwould be the number of birds in theflock, the average weight of the birds andhow much they drink in 24 hours.

So, in this example if we imagine thatthere are 12000 birds in the flock andthey weigh 1930g each (target for thisparticular layer at 41 weeks) we wouldneed to administer 579000mg ofTiamulin in 24 hours:

Fortunately this particular product isrelatively concentrated with 125mg perml of product and so the total volumerequired is 4632ml per day:

Next we need to know how it isrecommended that the product isdelivered to the birds. Some antibioticswork best if they are delivered in a high

Medication of poultry is generally achieved by delivering the medication through the feed or through the water system

12000 birds x

1.93kg bodyweight x

25mg/kg bodyweight=

579000 mg

total daily dose

579000 mg

total dose÷

125mg/ml

drug concentration=

4632ml treatmentvolume/day

MARCH Ranger:March 2011 27/03/2011 15:54 Page 41

dose over a short period of time. Thisallows for a high concentration ofantibiotic to be achieved in the individualanimal however it may result in somebirds not receiving a therapeutic doseand other receiving a much higher dosedepending on when in the day eachindividual bird chooses to drink, and itsposition within the pecking order in theflock. Other antibiotics are best deliveredin a continuous fashion throughout theday so that there is a more consistentlevel of antibiotic within the birds. Otherfactors which affect how the requireddose of medication is administeredacross the day includes the palatability ofthe product and the solubility of theproduct. Poor palatability or poorsolubility will both reduce the

concentration at which medication can bedelivered.

In this example, lets say that the drugshould be administered continuouslythroughout the day. Therefore this flockwould require 4632mls of product to be

included in their daily water provision for5 days. If the birds are drinkingapproximately 210L per 1000 birds perday this would equate to a total waterconsumption of 2520L and thus 4632mls of product need to be added to2515L:

Water consumption:

210L/1000 birds x 12 (thousand birds)=

2520L/day

2520L of water consumption - 4632ml of treatment=

2515L of drinking water to which the treatment must be added

An accurate assessment of bodyweight will lead to more precise dosing

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The figure I have used in this calculation(of 210L drunk per 1000birds per day)is a very rough approximation which yourvet may use in the absence of any moreaccurate data however it is important torealise that water consumption can bevery variable. In very hot weather waterconsumption will go up. In very wetweather it will go down as free-rangebirds start drinking from those deliciousmuddy puddles just outside the pop-holes. Water consumption can alsochange with different diets, the presenceof the antibiotic product in the water,water temperature and if the birds are

diseased (which is presumably why youneed to treat them in the first place!). Sowhilst the 210L per 1000 birds may be agood rule of thumb, if you want toensure that your birds are getting thecorrect dose of medication over thecorrect time frame it is important thatyou use accurate bird weights andaccurate water consumption records inyour calculations.

How do we deliver this medication?Having worked out the dose rate, thenext step in the process is to considerhow you are going to combine the

necessary volume of product with thenecessary volume of drinking water.

Broadly speaking you have 3

options here:

1. You can just mix the product into the header tank.

2. You can mix up a stock solution and use an in-line medication doser.

3. You can use an active medicationdoser to mix the neat product into thedrinking water.

An accurate assessment of bodyweight will lead to more precise dosing

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into the tank, monitoring the tank, andpost-treatment cleaning particularlydifficult. Also, once the tank has nearlyrun dry it can take a very long time torefill.

Using an in-line medication doser is amore common practice. The doser usesthe water pressure to drive a little pumpwhich clicks up and down suckingmedicated water from the stock solutionand delivering it into the water lines. Thedoser is not powered by electricity but bythe flow of water. When medicating inthis way it is important to realise thelimitations of this equipment. The first isthat they are generally only accurate

When applying treatment through theheader tank, it is important to rememberthat the birds should receive a consistentconcentration of antibiotic throughout theday. This is achieved by turning off thewater supply to the header tank,determining how much water is within thetank and applying the necessary volumeof product to the tank. There are severalproblems with this approach to treatment.The first is that you header tank isunlikely to hold an entire days watersupply (in this case 2520L) and so youwill have to calculate how much water isin the tank, what proportion of the dayswater this represents and then measureout the correct amount of product. The

second problem here, is that you will thenhave to check the water level within thetank very regularly to prevent the birdsrunning out of water. When doing this itis important to realise that waterconsumption may vary significantly duringthe day. Most flocks will drink more firstthing in the morning (although there arevariations between flocks) and you willhave to check the water level veryregularly to ensure that sudden increasesin water consumption do not leave thebirds running dry. The third issue is thatheader tanks are, by virtue of mothernature, positioned high-up and access tothem can be difficult and hazardous. Thismay make administration of the product

Water-powered dosers are a common method of administering medication

r r

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to the drinking lines in a continuousmanor. As with the other methods ofdosing there are several issues. Firstlyyou will have to perform furthercalculations to determine the rate atwhich the product needs to be added (inthis case approximately 1:500). Secondlywhen using products which are powdersthat need reconstituting with water youmay run into the same solubility issuesdescribed previously and finally thenarrow pipe work and small mechanismin these machines can make them proneto becoming blocked. As before,maintenance and regular cleaning isessential.

I think that is probably enough maths forthis month! In summary, achievingtherapeutic doses when treating free-range poultry depends on accuratemeasurements of bird weights and waterconsumption followed by accuratecalculations to make the best use ofdosing modalities available.

Next time we will look at cleaning thewater lines after treatment.

Stephen Lister, Claire Knott,

Philip Hammond & Ian Lowery

Crowshall Veterinary Services

down to concentrations of 1%. What thismeans is that for every 99ml of waterwhich passes from the header to thedrinker lines, 1ml of the medicated stocksolution is added. From our previousexample we can see that we wanted toadd 4.632L of product to 2515L ofdrinking water. If we used the product inits neat form, set to 1% the doser wouldadminister over 25L of product and sowhen using these dosers the medicationproduct needs to be diluted down tocreate a stock solution which can besucked up and added to the drinkingwater over the entire day. Using ourprevious assumption that the birds are

drinking 2520L per day, if we were usingan in-line doser set to 1% this wouldmean that 99% of the birds’ drinkingwater would come from the header tank(2494.8L) and the remaining 1% wouldcome from the stock solution (25.2L).

We already know that we wish to providethe birds with 4632mls of product and sothe stock solution needs to be made upby mixing 20.57L of plain water and4632mls of product:Once we have mastered the calculationsrequired to determine how to mix up yourstock solution we next need to turn ourattention to the practical matter ofwhether the product in question willdissolve in such a small volume of water.Some products will readily dissolve in afew litres of water, others are much morestubborn and may precipitate to thebottom of you stock solution bucket. In

alkali so as it may cause damage to thebirds, the treatment or the equipment.Generally I would recommend that thiskind of change is done in closeconsultation with your vet.

Finally when using an in-line water dosersit is important to remember that thereare no electronic parts, it is a mechanicalgadget like granddad’s watch and itsaccuracy and longevity will depend onregular maintenance and calibration.Active medication dosers are similar toin-line dosers except that they areactively powered and controlled byelectronics which allows them to beaccurate down to much lowerconcentrations (often 1 in 5000). Whenliquid medications are being used (as inour example) a narrow pipe can beplaced directly into the neat product anda small volume of the treatment is added

East Anglia we struggle with particularlyhard water and we find that solubility canbe a particular issue. Depending on thechemical formulation of the product inquestion you may be able to improvesolubility by altering the pH of the water.

For some products you may need toincrease the pH (make the stock solutionmore alkali) and for others you may needto reduce the pH (make the solutionmore acidic). When altering the pH ofdrinking water you must be careful tomake the correct alteration for theproduct concerned and ensure that theresulting water is neither too acidic or too

2520L water consumption x

0.01 (ie 1% of 2520)=

25.2L (the volume of stock solution)25.2L total stock solution

– 4.632L (treatment volume)

= 20.57L of plain water to which the treatment is added

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