Article looks interesting, though I've only skimmed the summary.

A different forum's piece about chicks.
Suitability of day-old chicks as food for captive snakes - Reptile Forums

Day old chicks generally are not fed before disposal. That is, if they come directly from the hatchery. If not from a commercial hatchery, they could be several days old and been given food and water during that time. If hatchery killed chicks contain antibiotics, they came through the mother during egg development. Commercial food generally does contain low levels of antibiotics.

IMO, day old chicks are too big for most garters. So suitability as food is moot. On the other hand, I've fed plenty of adult birds to a variety of larger colubrids, boids, and at least rattlesnake. No obvious problems.