Description:
The spur gene in chickens causes the male birds to grow long, bony "horns" from the side of their shank (1). It is commonly seen in only males, though separate genes can also enhance the number of spurs and also cause females to grow spurs that rival males in length. Typically though, males will have long spurs, while females will only have a small bump that doesn't protrude out of the skin (2).
These spurs are made from keratin (6), the same material human fingernails are made of, and will grow continuously throughout the bird's life. It is possible to estimate the age of a bird through the length of the spur (5), though different strains can be selected for faster or slower growth. Some people suggest trimming or hooding spurs to prevent the bird from hurting itself or others, though this is controversial because of the main blood vessel that develops through the center.
Originally, it was believed that spurrless birds carried a novel gene (2), but it was later discovered that the spur gene was recessive in and of itself (4). Spur length has since also been linked to sexual traits, including overall testosterone production, egg production, and body size (1)(3)(4), with longer spurs and more obvious spurs in females leading to an increase in overall productive traits.
The APA recognizes all males to have spurs. The only breed that can show visible, lengthy spurs in females is the Sumatra. The Cubalaya and Sumatra are also allowed to have multiple spurs. There are no restrictions given for minimum or maximum spur length, nor are there any penalties for a cock that doesn't have spurs. (8).
Breeding with Spurs:
Spur x Spur = 100% Spur
Spur x No Spur = 100% Spur Carrier (appears to have no spur)
Spur x Spur Carrier = 50% Spurs, 50% Spur Carriers
Spur Carrier x Spur Carrier = 25% Spur, 50% Spur Carrier, 25% No Spur
Spur Carrier x No Spur = 50% Spur Carrier, 50% No Spur
References & Further Reading
Chen, A.; Zhao, X.; Zhao, X.; Wang, G.; Zhang, X.; Ren, X.; Zhang, Y.; Cheng, X.; Yu, X.; Wang, H.; et al. Genetic Foundation of Male Spur Length and Its Correlation with Female Egg Production in Chickens. Animals 2024, 14, 1780. https://doi.org/10.3390/ani14121780
Kozelka, A. W. "Spurlessness of the White Leghorn." (1933): 71-78.
Oguntunji, A. O., and K. I. Ayorinde. "The frequency and influence of spur gene on six metric traits in Nigeria Local Chicken." Nigerian Journal of Animal Production 36.1 (2009): 20-27.
Ukwu, H. O., T. T. Tyo, and D. J. Kuusu. "Expression of Spur Gene in the Nigerian Indigenous Chickens in the Guinea Savannah Region of Nigeria: Phenotypic Effects." Nigerian Journal of Animal Production 49.5 (2022): 59-67.
Doherty, Sean Paul, et al. "Estimating the age of domestic fowl (Gallus gallus domesticus L. 1758) cockerels through spur development." International Journal of Osteoarchaeology 31.5 (2021): 770-781.
Smoak, K. Dale, and Roger H. Sawyer. "Avian spur development: abnormal morphogenesis and Keratinization in the Scaleless (sc/sc) mutant." Transactions of the American Microscopical Society (1983): 135-144.
Kent, John P., et al. Hens (Gallus gallus domesticus) with larger spurs have higher faecal testosterone levels; evidence of female to male-like phenotype. No. e26994v1. PeerJ Preprints, 2018.
American Poultry Association. (2023). American Standard of Perfection (45th ed.)
Gallery of Images
