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In 2023 the Plymouth Rock was listed by the Livestock Conservancy as 'recovering', meaning that there were at least 2500 new registrations per year. [10] Worldwide, numbers for the Plymouth Rock are reported at almost 33 000; [11] about 24 000 are reported for the Barred Plymouth Rock [12] and over 970 000 for the White variety. [13]
By cross-breeding of Barred Plymouth Rock and White Leghorn birds, an autosexing breed with barred gray adult plumage was produced. As in other autosexing breeds, the sex of chicks can be distinguished at about a day old. [2]: 47
the Dorbar, an auto-sexing heavy meat breed from Dorkings and barred Plymouth Rocks, bred from 1941 to about 1949, when development stopped [1]: 59 the Rhodebar, from Rhode Island Reds and barred Plymouth Rocks, standardised in Britain in 1951; a similar cross-breed was developed in Canada [1]: 63
Figure 1. Feathering types in ten-day-old chicks.Left: Fast normal-feathering chick. Right: Delayed-feathering chick carrying sex-linked K gene. Delayed-feathering in chickens is a genetically determined delay in the first weeks of feather growing, which occurs normally among the chicks of many chicken breeds and no longer manifests itself once the chicken completes adult plumage.
The B1 allele is causing the typical sex-linked barring phenotype/ appearance and is present in most modern sex-linked barred chicken breeds. Females or male chickens carrying the B2 allele in the heterozygous condition show a defined barring pattern but in the homozygous condition, males are essentially white with very little pigmentation. [9]
Poultry shows spread interest and understanding, with 88% of all farmers having chickens by 1910. [11] Barred Plymouth Rock hen, No. 31S. laid 237 eggs in first year at the Maine Agricultural Experiment Station (1903) As the United States urbanized, demand for eggs grew.
It was created between 1946 and 1954 by Laura Kaufman, who crossed the native Polish Green-legged Partridge breed with American Plymouth Rock birds. The aim was to introduce the barred gene of the Plymouth Rock to make chicks auto-sexing – female chicks can be distinguished from males at one day old by the longer black eye-stripe. [2] [3]
In Barred Rock chickens, male chicks tend to have a large and distinct pale spot on the head, while hen chicks have a smaller and less defined spot. This is due to the effects of the incompletely dominant barred (B) gene. [7] Rhode Island Red and New Hampshire Red chicks with chipmunk stripes are almost always females. [8]