Paddywhack (also spelled paddywack) or nuchal ligament (Latin: ligamentum nuchae), is a strong elastic ligament in the midline of the neck of sheep or cattle which relieves the animal of the weight of its head. It is pale yellow in colour. (The yellow colour is the elastin on the ligaments.) The name is derived from the corruption of paxwax (originally faxwax Old English hair + to grow).
The nuchal ligament is unusual in being a ligament with an elastic component, allowing for stretch. Most ligaments are mostly made of highly aligned collagen fibres which do not permit stretching.
Structurally, the nuchal ligament is formed with the association of both elastin proteins as well as type III collagen (45%). The collagen fibrils share a consistent size as well as helical pattern which gives the ligament its tensile strength. The elastin on the other hand is a protein that allows for flexibility. These two elements of the nuchal ligament maintain a complex balance which allows the constant weight bearing of the head along with multidirectional movement without damaging the durability of the ligament through over-use/stretching. 
It is eaten in several countries. It is high in protein (78%) and also contains fat (10%), crude fibre (0.7%), and crude ash (1%). The meat is taken from domestic cattle, the bison, African buffalo, the water buffalo, the yak, and the four-horned and spiral-horned antelopes.
Dried paddywhack is commonly packaged and sold as a dog treat.
In popular culture
- Morocutti, M; Raspanti, M; Ottani, V; Govoni, P; Ruggeri (1991). "Ultrastructure of the bovine nuchal ligament". Journal of Anatomy. 178: 145–154.
- Beef Carcase Grading System Meat Standards Australia
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