The healthiest kids are farm kids. They are exposed to lots of allergens early on. As far as nursing and working, it can be done. I nursed for 15 months and worked. This was before good pumps were available. I had to fill up bottles, the old fashion way(by hand). Even did it at work. It just takes determination. My boy was never sick.
No doubt a matter of determination, and obviously worth it — kudos.