Question 1

"I notice many wormers are recommended administered in the birds drinking water. We are told that each one should be left in the water for various amounts of time, some 2 days others 5. I have also heard that the birds only need one good drink of the wormer to be effective. Why is there are difference ? And what is the truth about how much of this wormer, diluted in water, a bird needs to take in before it is effective ?".

In water medication is a commonly used method of medication in flock birds where catching is impractical or individual dosing is difficult. The various regimes for how we use these drugs is based on several factors including :

1. The mode of action of the drug – How the drug chemically interacts within the body of the bird to exert its action on the target species i.e the parasite.
2. The toxicity of the drug – How the drug chemically interacts with the non target species i.e the bird
3. The stability of the drug – How the drug interacts with the solvent in which it is placed, the environment around it and the presence of organic matter.
4. The palatability of the drug – How likely it is that the bird will actually consume the medication and how much can we expect the bird to drink.
5. The reversibility of the mode of action of the drug – How long must the parasite be in contact with the drug for it to exert its action successfully

I will address each of these separately.

1. Mode of action – Most parasiticides (drugs that kill parasites) interact with the parasite either by immobilising it, destroying part of its life cycle , denying it an important metabolic pathway or by simply having a toxic effect on its life function. Every drug is different. Even within a broad family of drugs, improvements/modification in chemical structure may make them act in different ways. These may act differently in different species depending on their specific metabolic pathways. Many of the drugs that we use were designed for different purposes in different classes of animals e.g ivermectin is used for biting louse control in cattle. Many of the drugs we use are used as an off label product and therefore there mode of action in birds may not be well known or studied at all as there is no commercial registration for that purpose. Many modes of actions are still unclear for many drugs that have been in use for decades. Depending on the modes of action the parasite may be killed/damaged/paralysed with a single hit or it may need multiple or sustained damage to do its job. Below are listed some common drugs and their proposed modes of action.

DRUG	Common Brand name	Indication for use	Mode of action
Amprolium/Ethopobate	Coccivet, Amprolmix	Treatment of coccidiosis	Inhibits the transportation of thiamine in the body of the first stage in the parasites life cycle
Toltrazuril	Baycox	Treatment of coccidiosis	Interferes with the division of the nucleus and energy production in the parasite in 2 life cycle stages
BENZIMADAZOLES (Fenbedazole, oxfendazole)	Panacur Benzelmin/Systamex	Treatment of Numerous worms	Disrupts internal cell division by interfering with structures required for separation (microtubules). Blocks the bonding of phosphorous in muscle tissue resulting in paralysis. Blocks the use of external glucose as energy sources.
MACROCYCLIC LACTONES (Ivermectin, Moxidectin)	Ivomec Avomec Cydectin Moxidectin plus	Treatment of numerous worms, biting lice and air sac mites	Binds to Chloride channels in nerve junctions which stops them resetting (depolarising) and results in nerve paralysis. Blocks the transmission of signals in motor nerves by stimulating the release of chemicals that inhibit electrical impulses in nerves and in nerve/muscle junctions.
Praziquantel	Droncit Avitrol Plus Prazivet Moxidectin plus	Treatment of tapeworm	At low concentration, it increases muscular contraction causing detachment of the mouthparts (scolex) followed by paralysis. At higher concentration , causes damage to the outer skin of the tapeworm which activates the host immune system against it.
Levamisole	Nilverm Avitrol plus	Treatment of numerous worms	Acts on the receptors at the nerve/muscle junctions causing paralysis. Interferes with the incorporation of glucose into glycogen thereby starving the parasite of energy

2. Drug toxicity – How toxic a drug is to the non target vs. target organism depends in part on its mode of action, its specificity of action, its permanency/clearance from the system and the dose given. The better parasiticides are developed by choosing a specific life supporting function found only in the parasite and not in the host. This means it is difficult to kill the host but easy to kill the parasite. Others use shared metabolic processes but those for which the parasite has more receptors, stronger receptor binding or more need for that component in its pathway. If overdosed, these chemicals can exert the same effect on the host. Some drugs bind loosely to their chosen site, others are incorporated permanently into a metabolic pathway. Repeating a dose too soon in the latter may result in excessive retention of the drug by the host or a failure of the host to metabolise and clear the drug from its system.
3. Drug stability – Not all drugs are designed to be used as an in water medication. Many of the drugs we used are begged/borrowed/stolen from other animal species. How stable a drug is in solution may effect how often we must use it or how soon the bird must consume it . Some drugs dislike being in water and become chemically unstable. This means that they have a “short half life”. For example if a drug has a half life of 20 minutes in solution then after 20 minutes it is 50% unstable and no longer acting in its original form. In a further 20 minutes it is now 50% less active and so on. For this drug the birds may need to drink immediately to get the right dose or ,if non toxic, the dose is established to account for this. Other drugs are “in suspension” meaning that they are a solid suspended in water (like mud shaken in a bottle). Over time the drug settles and will only be found close to the bottom of the dish unless stirred regularly. Repeated doses or regular stirring may be recommended to achieve dosage.
4. Drug palatability – If something tastes bad we generally wouldn’t consume it ourselves but we often expect our birds too. Some dose regimes accept this and recommend repeated dose just in case the bird refused to drink a previous dose. Other drugs have recommendations to deprive birds temporarily of water to achieve thirst first. Few companies recommend the obvious option of making it taste better before offering it to the birds. Not everything that tastes bad to us, tastes bad to the bird however as we do have different taste sensations. With individual palatability in mind, most drug companies work on a generalised rule that a 100g bird drinks on average about 5-6 ml per day on an average day. This works well for most birds but obviously will result in overconsumption on hot days and may result in underconsumption on cold or wet days. Birds that eat a lot of fruit for instance may also need less water to provide their fluid needs.
5. Drug reversibility – This leads back to mode of action but can influence lengths of treatment and success . If a drug permanently destroy part of the parasites life cycle or metabolic processes in a short period of time then obviously a single dose if often enough to do the job. If the drug does not kill the parasite but simply immobilises it then it needs to remain immobilised long enough to be passed out of the system. If it is permanently paralysed then the parasite can take all week to be pushed out of the body and it does not matter. If the drug only paralyses for a few hours then we may rely on multiple doses to make sure it is pushed out with the faeces. If it gets jammed somewhere it is conceivable that it can “wake up” later and resume business. If the drug is partly reversible but takes a few weeks to be cleared from the body then repeat dosing may create a toxic dose once added to what is left in the system.

As can be seen above, “drugs ain’t drugs”. Most regimes have been designed with all of the above in mind. They all have there good and bad points. The best advice is follow the directions recommended by your avian vet. Deviating from these directions can cause inefficiency or overdosage. Not all drugs are without the ability to modify their use but leave these decisions up to your avian vet.