"Eddie Cackler" is a parody of Eddie Cantor. The "boy wanted" sign and the five hatching eggs were references to all five of his children being girls, which was a running joke on his radio show. Then along comes a chicken resembling Bing Crosby, whose (then) four children were all boys. (Crosby later had a daughter and two more sons from his second marriage, long after this cartoon was made.)
Although the short seems dated nowadays, it was full of popular entertainment character sight gags of the era. The humor was decidedly adult slanted as well, since most cartoons were shown at a movie show, along with a newsreel and a travelogue. The kids would have liked the silly slapstick.
As they forage, chickens naturally consume pieces of gravel, which pass through their digestive system and lodge in their gizzard. The grit helps the gizzard grind up the seeds, grains, bugs and grasses that they eat, just as molar teeth grind our food.
Before the cow answers Porky, she briefly resembles Clarabelle Cow, a character from rival studio Disney.
The five girl chicks were likely a nod to the famous Dionne quintuplets, born in 1934.