Sheep Industry News August 2023

selves – which ranged from >100 to -80 percent for PFEC – and their sires (Figure 1), were very accurate predictors of their FECs across the trial. While the results of these challenges suggests that NSIP EBVs can make a difference for this trait, the question still remains, when we select sheep from these notably GIN-sus ceptible breeds for a reduced FEC EBV, what are the biological changes that are occurring? We have approached answering this a couple ways.

to compare gene expression and immune differences between low PFEC EBV lambs and the highly GIN-resistant Barbados lambs. It can be challenging to compare NSIP data across breeds, but our hope is this work can shed more light on how parasite susceptibility can be altered in a breed that is not not ed for its ability to withstand a significant worm burden. Not to mention, this study will ultimately help us better understand the biological mechanisms of resistance and susceptibility to parasites.

A preliminary report of the average fecal egg count of lambs (~120 total head) from five Dorper sires (A -E) and Barbados lambs after being challenged with Haemonchus contortus larvae. Rams B, C, D and E had FEC estimated breeding values prior to this study that were developed from FEC on range where mixed parasite species were present. Ram A and the Barbados lambs did not have EBVs prior to this project.

First, we conducted a genome wide association study in all the lambs we have artificially challenged with Haemon chus contortus, as well as others from which we had FEC data while they were grazing on pasture (natural parasite challenge). In brief, a GWAS looks for associations between single nucleotide polymorphisms and a particular pheno type – in this case, FEC. When an association is identified, there is an indication that the area in the genome where that SNP is located is relevant for why the animal(s) being tested have a higher or lower FEC. Conducting a GWAS is one strategy for finding genes that are important for parasite resistance or susceptibility. In our GWAS, we identified 26 different SNP that were significantly associated with FEC and packed-cell volume – PCV is a measurement of anemia – albeit the impact of each SNP was moderate. It is generally regarded that parasite susceptibility is a polygenic trait – many genes involved – and our findings would agree. In our next approach, we also harvested a subset of lambs from this Dorper/Barbados trial three weeks after they were infected with the Haemonchus contortus larvae. From these lambs, we collected actual worm counts as well as tissue from the inner lining of their abomasums for further RNA sequenc ing analysis. This part of the project has yet to be published and admittedly the details can get pretty thick, so I’ll spare you the finer points. But from this information we will be able

In conclusion, I want to highlight the fact that our work in Dorper and Rambouillet is only possible because of the excel lent genetic and parasite science that is being conducted by many other brilliant researchers and because multiple state and federal funding sources believe in this type of research. This research continues to demonstrate the importance of buying seedstock with EBVs generated through NSIP to improve the health and productivity of sheep. We hope our findings eventu ally help contribute to a stronger, more sustainable American sheep industry with shepherds spending a little less time hav ing to drench their animals. A) Dorper and Rambouillet lambs were housed in worm-free dry lots to maintain a consistent parasite challenge throughout the duration of the trial. B) Worm larvae suspended in solution. Artificial parasite challenges are accomplished by growing the larvae in the lab to an infective stage – same stage as they would be at when sheep consume them on grass – and then orally inoculating all lambs with the same amount. C) Female and male Haemonchus contortus worms recovered from the abomasum of parasitized sheep.

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