Sorry, I don't want to be combative. Apologies it it came off that way. I have a vested interest in keeping bighorn alive and on the mountain. That being said, on average strains of M. ovi from domestic goat clades are less likely to kill bighorn than those from domestic sheep. There are some studies that do talk about sub-lethal or minorly lethal pneumonia being induced by domestic goat exposure (Besser et al. 2017, Johnson et al. 2022); however, there are newer studies that show in similar captive settings that exposure to domestic goat strains of M. ovi do kill sheep (
https://www.proquest.com/docview/3149937216?fromopenview=true&pq-origsite=gscholar&sourcetype=Dissertations & Theses). This thesis shows that 3 out of 4 bighorn sheep that were inoculated with goat strains of pneumonia died following inoculation.
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The problem is that bighorn that are completely naive to M. ovi are at significant risk of pneumonia from domestic goats, but also there is no cross-strain immunity to M. ovi. Basically, bighorn can increase their immunity to a specific strain, but that immunity does not seem to translate to different strains. In that case, even if the pneumonia from an original goat introduction occurs and is fought off by the animal, a different strain from a different set of goats
could but may not kill them given that their lungs have likely already sustained damage. We do see pneumonia infections that have originated from domestic goats relatively frequently but it is less frequent that they're implicated in lethal pneumonia. I know of at least one recent epizootic where a domestic goat was found in the sheep herd about one month prior to the deaths occurring. It is possible it came from somewhere else, but I am waiting to hear about the strain typing results. That goat was sampled and all the dead bighorn were sampled so they should be able to link it if that is the true infection source.
Sorry if my initial message came off combative. That is not how I am trying to go about these things. I don't want to rain on people's parades when goats are likely the most feasible pack animal for many people, but it is something that we all have to think about when we are trying to leave minimal impact on the landscape.