Alkaloids are bitter, nitrogan containing compounds which can reduce performance of grazing animals. Different alkaloids will affect animals differently. Hig concentrations of simple gramine aklaloids reduce palatability. The more complex tryptamine-carboline alkaloids cause diarhea as well as reduce palatability. So it really depends on which alkaloids you are dealing with. But simply put they will all reduce palatability thus reducing consumption.
Nitrate is nitrate. Simply NO3. At too high of levels nitrates will kill livestock. I don't believe that alkaloids can or will kill and animal.
