Lamb and mutton

Lamb, hogget, and mutton are the meat of domestic sheep (species Ovis aries) at different ages.

A sheep in its first year is called a lamb, and its meat is also called lamb. The meat of a juvenile sheep older than one year is hogget; outside North America this is also a term for the living animal. The meat of an adult sheep is mutton, a term only used for the meat, not the living animals. The term mutton is almost always used to refer to goat meat in the Indian subcontinent.

Lamb is the most expensive of the three types, and in recent decades sheep meat is increasingly only retailed as "lamb", sometimes stretching the accepted distinctions given above. The stronger-tasting mutton is now hard to find in many areas, despite the efforts of the Mutton Renaissance Campaign in the UK. In Australia, the term prime lamb is often used to refer to lambs raised for meat. Other languages, for example French and Italian, make similar, or even more detailed, distinctions between sheep meat by age and sometimes by gender, though these languages do not use different words to refer to the animal and its meat.

The definitions for lamb, hogget and mutton vary considerably between countries. Younger lambs are smaller and more tender. Mutton is meat from a sheep over two years old, and has less tender flesh. In general, the darker the colour, the older the animal. Baby lamb meat will be pale pink, while regular lamb is pinkish-red.

Under United States law (7 USC 1638), 'lamb' is defined in terms of 'mutton':

Under current federal regulations (2014 CFR §65.190), only the term 'lamb' is used:

The terms 'mutton' and 'hogget' are rare in the United States. Nevertheless, the exclusive use of 'lamb' in the United States may be confusing, particularly if it is assumed that only actual lambs are butchered for their meat. Under the previous definition (2010 CFR §65.190), 'lamb' meant 'meat, other than mutton (or yearling mutton), produced from sheep'.

The term "mutton" is applied to goat meat in most of these countries, and the goat population has been rising. For example, mutton-curry is always made from goat meat. It is estimated that over one-third of the goat population is slaughtered every year and sold as mutton. The husbanded sheep population in India and South Asian countries has been in decline for over 40 years and has survived at marginal levels in mountainous regions, based on wild-sheep breeds, and mainly for wool production.

The meat of a lamb is taken from the animal between one month and one year old, with a carcase (carcass in American English) weight of between 5.5 and 30 kilograms (12 and 65 lbs). This meat generally is more tender than that from older sheep and appears more often on tables in some Western countries. Hogget and mutton have a stronger flavour than lamb because they contain a higher concentration of species-characteristic fatty acids and are preferred by some. Mutton and hogget also tend to be tougher than lamb (because of connective tissue maturation) and are therefore better suited to casserole-style cooking, as in Lancashire hotpot, for example.

...
Wikipedia