Breeding For Parasite Resistance
Breeding for parasite resistance has been a very enjoyable part of breeding with Katahdins, they have such great potential as far as parasite resistance goes. Everybody has their own way of doing things, this is how we do things, it works for us in our management system (100% perennial pastures during spring,summer and fall and hay in winter, no creep feed and no grain for anyone ).
Evaluating the lambs start with a fecal sample, but not just any sample. Taking fecal samples from the lambs when there’s no parasite load tells you nothing about the parasite resistance of the lambs, the samples need to be taken when there is a high enough parasite load in order to distinguish the good ones from the bad ones. As we get closer to weaning we start to take random samples and we do FAMACHA. The goal is to have a lamb crop average of at least 500 eggs per gram, that average or higher allows you to distinguish the good from the bad. We do FAMACHA because you can have lambs with a 4 FAMACHA that do not have a high fecal egg count because the parasites have not started to lay eggs yet, also we don’t want to loose lambs because of parasites. We know we are close when we start to see 4 FAMACHA scores and / or the random sample is over 500. So what happens when the average is not close to 500? Well ... we graze harder and do the opposite of what you are suppose to do when you try to avoid parasites.
Reaching that day when fecal samples need to be collected is a big milestone. This year we collected samples from about 260 lambs. We set it up in a way that the lambs can keep eating while waiting ... everybody needs to provide a sample. Lambs that don’t have a sample go back to the group waiting where they can graze and we will hopefully have better luck the next time through. No, we don’t wait for the lambs to donate samples naturally, my wife puts on a glove, add lube and goes in an takes a sample, she know how to do it. This year we weighed the lambs, recorded FAMACHA and collected fecal samples, 6 hours of work, time well spent.
Sending 260 samples in for analysis is far too expensive. Analyzing your own fecal samples is not that difficult and costs us about 10 cents in consumables per sample and some of our time. For us, time is probably the largest investment in getting the samples processed. It took my wife about 30 hours of work over 6 days to analyze all the samples.
The data is analyzed once all the fecal samples have been analyzed. This year we had an average eggs per gram of 659, above the 500 target so the results will be useful. The best 8 lambs had zero eggs per gram seen and the worst lamb had 5850 eggs per gram.
The graph above shows the cumulative eggs per gram, e.g. 17 animals (bottom, x-axis) shed 30% (vertical, y-axis) of the eggs, or 40 animals shed 50% of the eggs. Just think about the implications, if we removed 40 animals from this group of 260 lambs we will reduce the parasite eggs being shed by 50%. This is always amazing to see, the magnitude changes from year to year (based on climate and the rams we use) but the end result is always the same, a small number of lambs are shedding the majority of the parasite eggs.
We use this information to select the lambs that need to leave the farm at a lighter weight, the ones that wont be finished to our target weight and condition. This allows us to reduce the parasite load dramatically without having to use dewormer.
We also use this information to select replacements and the few lambs we sell as breeding stock. We take another fecal sample 30 days after the first sample, a second sample helps us eliminate lambs that were “lucky” when the first sample was taken. Any lambs that have above average fecal sample for either sample wont be sold as breeding stock.
Just looking at where the lambs ranked relative to the average is a good start but more analysis is required in order to quantify the parasite resistance of your ewes and the rams you used. Knowing the parasite resistance of your ewes and rams allows you to make informed breeding and culling decisions. Quantifying the parasite resistance of the ewes, rams and lambs in a way that takes their own performance as well as their family and offspring performance into account is where NSIP EBVs (Estimated Breeding Values) comes in. We are part of NSIP (National Sheep Improvement Program), we, along with other breeders submit our data to be analyzed, we get EBVs back that quantify the genetic merit of our animals for various traits measured, parasite resistance is one of the traits for which we get EBVs. We also exchange genetics with other breeders in NSIP so that animals and bloodlines can be evaluated in other management systems.
Measured parasite resistance is a must have if you are serious about parasite resistance, not having to deworm is not measured parasite resistance (it might be an indication of it but does not measure it). You can do this even if you only have a handful of sheep, get a microscope and supplies an learn how to do fecal egg count. The University of Rhode Island has a great video on how to collect fecal samples as well as how to do fecal egg counts https://web.uri.edu/sheepngoat/video/, they also have a fact sheet that includes photos of the different parasites you are likely to see in your samples https://web.uri.edu/sheepngoat/files/McMaster-Test_Final3.pdf . If you live in New England, NY, NJ, PA, WV, MD, DE you could be eligible for free fecal egg counts, look at this flyer if you are interested https://web.uri.edu/sheepngoat/files/2019_SARE-LNE15-342-Fecal-Egg-Count-Analysis-program-Announcement_FINAL.pdf .
Fecal egg counts for Katahdins is about 20% heritable (the % of variation that is because of additive genetics) so there are other factors that influence the eggs per gram, if you want to take your selection to the next level, take a look at EBVs, contact NSIP (http://nsip.org/katahdin-breeders/) Jim Morgan is our breed coordinator.