A vet's perspective - parasite management
Monday, 19 May 2008
By Max Newport, Bay of Islands Veterinary Services
Parasite management is of importance to all classes of livestock farmed these days, from the classical sheep and beef property to a miniature horse breeding farm or Alpaca stud.
All require a planned approach to get the best outcome.
| History has shown trying to ensure no worms on pasture does not work completely. |
Over 95 % of the worm parasites on the farm are on the pasture, not in the animals. With drenches we have only been targeting a small percentage of the worms as a whole. It is actually a mark of how effective new drenches are that we have developed as much resistance as we have.
With a few exceptions worms do very little damage to stock. They don’t take up much space, nor do they eat much.
The problem with worms is twofold. Firstly, the animals use a lot of energy trying to get rid of them, and secondly, while they are doing this they also have a reduced appetite.
The reduction in appetite begins within hours of immature worms being eaten. It is the reduced appetite that causes much of the poor growth rates.
The aim of the parasite management program is to reduce the numbers of worms being eaten as well as controlling the worms in the stock. These programs are commonly referred to as drench programmes. As you will see drenches are important, but only part of the program.
The minimum time from the time a worm egg leaves the animal to the time it is eaten, matures and begins to produce new eggs is around four weeks. Previous programs were aimed at drenching animals before the four weeks was up to try to ensure there were virtually no worms on the pasture. History has shown this does not work completely. What it means is that the only worms present will be resistant to the drench, and so will breed new resistant worms.
In Australia where true summer droughts kill all the worms on the pasture resistance has developed more quickly, and more severely than in New Zealand.
The aim now is to manage worms to get the best growth rates from the stock without reducing the effectiveness of drenches being used.
The current topical term is REFUGIA, referring to worms present in undrenched animals.
The purpose of these worms is to ensure any resistant worms present after drenching will mate with these non resistant worms and slow the development of resistance.
A growing recommendation is to leave 10 - 20% of a mob undrenched; do not drench the best animals in the mob.
The principles of drenching:
Drench only animals that need it. This is worked out from experience or testing. As a rule we are trying to limit the number of treatments to mature animals.
Use an effective drench. Try using combination drenches for both sheep and young cattle. There are a few exceptions to this. One is the use of Closantel in the autumn for sheep. This drench has the best action against Barbers Pole worm. Specific products for liver fluke are also available. In sheep we are recommending using a triple combination drench eg Matrix, Triton. (Both have a tape formulation for lambs.)
Check the drench you are using is working by doing a drench check test or a full drench efficacy test.
At least once a year take 10 faecal samples from animals 7-10 days after they were drenched. This can be done by holding the mob in the corner of a paddock for about half an hour then collect 10 fresh samples from the ground. Alternatively samples can be collected directly from the animals at the yards. Samples are then sent to a lab to see if any worm eggs are present. The presence of eggs indicates some worms have survived the drench program.
Drench Efficacy Test
In this test animals are faecal tested until we know they have worms present. They are then divided into groups. The groups of animals are drenched with different drenches, and then faecal samples are taken 10 days later. This test shows what drench is working, and what degree of resistance is present.
The drench efficacy test is more involved. It is used to determine the extent of a problem detected by a simple drench test, or to find out the status of the worms on a property to a number of different drenches.
Any eggs recovered from either of these tests can be grown in the lab to see what type of worm has survived the drench. This lets us know what worms are resistant, and gives us a guide as to how to control them.
Use a quarantine drench on all stock when they come onto your property. This drench should be a combination drench to reduce the chance of any resistant worms coming onto your property. After drenching put the new mob onto an area where stock have been grazing so they can pick up “your” worms. This way if there has been any resistant worms left they will breed with non resistant ones.
There is an exception to the quarantine drench rule. If you have a known resistance problem then buying in stock with less resistance than you have can reduce the resistance on your property.