Refugia - Secret Weapon Against Drug Resistant Worms
"Refugia" Definition by University of Namibia in South Africa
The word "refugia" is used to denote parasitic populations that have not been exposed to a particular drug and hence still contains a large proportion of susceptible organisms.
"Refugia" is a word that is rarely heard or mentioned in the goat industry. I ran across it in a research paper while I was trying to better understand the worm problem and all of the recommendations for "pasture rotation" that I kept seeing. No one was describing exactly how to do the pasture rotation, especially when a breeder only has a small amount of acreage. I was totally surprised when I started reading about refugia and worm immunity in goats. This article will only discuss the refugia topic.
I believe that there is a vast amount of bad information being given word of mouth and through goat chat groups about worming and I have never read any of the chat group experts discuss or recommend breeders need to understand refugia. Below are some examples of worming recommendations coming from goat chat groups with a heavy emphasis on "worming the heck out of the goats and moving to a clean pasture". NOTE - there is no such thing as a "worm free" goat after worming.
Now, what does refugia mean to you and how does it work.
Before we discuss refugia related to parasites and pastures, it is good to have a basic understanding of how "biological warfare germs" are created. A scientist starts out with some germ being selected. In our example, we will take the flu germ. The scientist will take whatever the strongest antibiotic against the flu, significantly dilute it down and then put the diluted medicine in with the flu germ. This will kill most of the flu germ but a small sample will survive. The scientist allows the germ to grow and then more antibiotic is placed with it but less diluted. Again, most of the germ dies. The surviving germs are allowed to grow and other rounds of antibiotics are added with less and less dilution until the antibiotic is added full strength. It soon results in the antibiotic having no affect on the flu germ and the germ is now a serious problem because there is no known medicine for the drug resistant germ.
Worm larvae in a pasture can follow the same result. Initially, the worms were not resistant to any drugs. As more and more of the first drugs were used, the worms became resistant to that drug and the breeders started using the next drug. Again, the worm becomes resistant to the next drug and breeders continue to move to another drug until there are no more new drugs to use. At that time, breeders were recommended to rotate to "clean" pastures. Breeders were told to "worm the heck" out of the goats, hold them in the barn area for 24-48 hours and then rotate them to a "clean" pasture.
Here is the problem. Worms only breed in the goat's rumen. If you "worm the heck" out of all of your goats and then put them in a "clean" pasture, the only worms the goats will pick up as they graze, are the worse ones. The ones that the best de-wormers in the industry could not kill. What is even worse is, there can be 4-5 generation of worms in a single year.
Lets take an example of assigning a number to indicate how drug resistant the worms are. 0 = no drug resistance and 4 = the strongest worm resistance. We have already discussed the "0" resistant worms and how continual worming has now created the "4" resistant worm. Now if you worm with multiple de-wormers, increased strength or wormed over several days, you have killed much of the "4" resistant worms and now you are rotating the animals to a clean pasture where only "4.5" resistant worms will be and that is generation 1. Generation 2 will create "5" resistant worms. Generation 3 will create "5.5" resistant worms. Generation 4 will create "6" resistant worms. This all occurred in just one year.
With "refugia", you try to maintain as many low resistant worms in your animals and pastures as possible. This is done by ONLY DE-WORMING when it is absolutely necessary and culling the goats that have the biggest problem with worms. 20% of your goats, produce 80% of the worm problem. Now, when the animals go to the "unclean" pasture, there will be more of the low resistant worms and the goats are adding fewer of the most resistant worms. This means the goats are much more likely to pick up low resistant worms than the most resistant worms. When the "0" resistant worm breeds with the "4" resistant worm, the result will be "2" resistant worm eggs. You have reduced the resistance in the worms on your farm. Plus, the research states that the less resistant worms are more likes to attach to the goats rumen while the most resistant worms just coming from the drenching will still be weak from the treatment.
The other concept that goes along with this as stated in one of the research articles is related to worm immunity in goats. It states that goats have to have some worms in their system to maintain their immunity. Without any worms, the goats system will lose its immunity. Think about what you are doing when you vaccinate annually with your CD/T vaccines. If it is not done annually, to keep it in the goats system, the immunity goes away.