Do professional violinists use gut strings?
Some Baroque players use wound gut core, like Eudoxas or Passiones, for the lower strings while some Baroque violinists also use the plain gut D Chorda rather than a wound gut D. Eudoxa by Pirastro for Violin, Viola, Cello and Bass.
When did violins stop using gut strings?
The pure gut A string was common until the advent of synthetic strings in 1970.