Some ewes can have horns, though many breeds are naturally hornless. The presence or absence of horns in sheep is primarily determined by their genetic makeup and specific breed.
The Genetic Blueprint for Horns
Horn development in sheep is a complex process governed by genetic factors, particularly as a sex-influenced trait. This means that the same genes can manifest differently depending on whether the animal is male (a ram) or female (a ewe). For example, an allele responsible for horn presence might be dominant in males but recessive in females, requiring two copies for a ewe to express horns.
Several genes contribute to horn growth and the polled (hornless) condition. One gene, often denoted as ‘P’, is dominant for the polled condition, meaning an animal with this gene copy will likely be hornless. Other genes also play roles in determining horn expression. Specific genes, including RXFP2, have been identified in horn formation. Male sex hormones also influence horn development, explaining why rams have larger horns than ewes.
Horned and Polled Ewe Breeds
Sheep breeds exhibit considerable diversity in horn presence, with some ewes consistently growing horns and others being naturally polled. For instance, in breeds like the Wiltshire Horn, both rams and ewes commonly develop horns. The ewes’ horns in these breeds may curve backward over their head or extend out to the sides, while ram horns tend to be thicker and spiral.
Conversely, many breeds have naturally hornless ewes, even if their rams possess horns. The Black Welsh Mountain sheep, for example, typically has polled ewes while the males are horned. Other breeds, such as the Icelandic and Dorset, can have both horned and polled strains. Some breeds, like the Jacob sheep, are known for their polycerate characteristic, growing more than two horns, often four, on both rams and ewes.
Distinguishing Horns from Scurs
True horns and scurs differ, though both appear as growths on a sheep’s head. True horns are permanent structures composed of a keratinous sheath over a bony core, firmly attached to the skull. These horns grow continuously throughout the animal’s life, with the most rapid growth occurring in the first few years.
Scurs, in contrast, are incompletely developed horn growths. They are typically smaller and more irregular in shape than true horns and are often loosely attached to the skin rather than directly to the skull. Scurs may also break off or be shed, unlike true horns which remain fixed. While scurs are also influenced by genetics, they represent an incomplete expression of the horn-growing genes, sometimes appearing as small, bony knobs or thin, loose growths.