The Wikipedia page on chick culling provides a good overview.
Note that quoted claims confuse the general practice of culling with the specific practice of maceration. Culling also includes other methods, such as gassing with carbon dioxide.
The American Veterinary Medical Association Guidelines for the Euthanasia of Animals (2020) support the use of maceration:
Maceration, via use of a specially designed mechanical apparatus having rotating blades or projections, causes immediate fragmentation and death of poultry up to 72 hours old and embryonated eggs. A review of the use of commercially available macerators for euthanasia of chicks, poults, and pipped
eggs indicates that death by maceration in poultry
up to 72 hours old occurs immediately with minimal
pain and distress. Maceration is an alternative to the
use of CO2 for euthanasia of poultry up to 72 hours
old. Maceration is believed to be equivalent to cervical dislocation and cranial compression as to time
element, and is considered to be an acceptable means
of euthanasia for newly hatched poultry by the Federation of Animal Science Societies, Agriculture
Canada, World Organization for Animal Health,
and European Union.
Smithsonian Magazine reported:
On June 9 , United Egg Producers, an egg-farming co-op that owns approximately 95 percent of the United States’ egg-laying hens, announced that it would do away with the practice. In a statement by The Humane League, an animal rights advocacy group that worked to secure the commitment by UEP, culling will stop “by 2020 or as soon as it is…economically feasible.”
[Note that the commitment was to cull the male embryos still in the egg, rather than waiting until after they hatch.]
However, in January 2020 the Sydney Morning Herald quoted
United Egg Producers president Chad Gregory said in a statement on Wednesday that his organisation remained committed to adopting new technologies aimed to stymie culling, a goal that he called both "a priority and the right thing to do".
But, he added, "A workable, scalable, solution is not yet available."
So, it isn't clear if they are still using maceration, but they haven't met their pledge to stop (post-hatch) culling.
A 2010 article from The Telegraph suggests maceration isn't the preferred method in the UK (although it is legal):
A spokesman [for the British Egg Information Service] said that male chicks are usually gassed rather than put alive into the macerating machines and the bodies are a `useful source of food' to captive reptiles and birds of prey.
A 2016 Triple J article confirmed it was "common practice":
According to John Coward from Egg Farmers Australia, maceration isn’t only common practice in the industry, it’s also considered the most humane way to “dispose” of male chicks.