Perdue Farms is the first major chicken producer to go antibiotic-free at the hatching stage.

The third-largest chicken producer announced Wednesday that now 95 percent of the chickens Perdue sells are antibiotic-free.

Chicken embryos are commonly injected with vaccines before hatching, causing a hole in the egg. To avoid bacteria getting into the hole and infecting the embryo, an antibiotic called gentamicin is also injected into the egg.

Over the past 12 years, Perdue has been phasing out the use of gentamicin in hatching chicks, including increasing cleanliness in hatcheries.

Perdue will continue to use a class of antibiotics called ionophores only by veterinarian prescription. Ionophores are not used in humans, but are common in animals.

Perdue says ionophores will only be given to sick chickens, and never to those in the "no antibiotics ever" line.

Read More:

• Perdue Says Its Hatching Chicks Are Off Antibiotics (NPR)
• Chicken Company Perdue Takes Big Steps to Reduce Antibiotic Use (Wired)