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Definitions Of Lamb And Mutton

( Originally Published Early 1900's )

Reprinted from Bulletin of the United States Department of Agriculture


Lamb is a general term which refers to the flesh of young animals of the ovine species of both sexes. The age at which the change from lamb to yearling sheep takes place in the live animals is approximately 12 to 14 months.

Lamb carcassess as a group are distinguished from mutton carcasses by their smaller and softer bones, lighter-colored fleshs, softer and whiter external and internal fats, smaller size of carcasses and cuts, and by the foreleg joints break. Of these the latter is most prominent. Lamb foreleg joints break in four well-defined ridges, and resemble somewhat the teeth of a saw. These ridges are smooth, moist and red with blood. The bones of the hind legs at this period also are streaked with blood. As lambs approach the yearling sheep stage, the bones become harder and whiter and the break joints, although retaining some of the saw tooth effect, are relatively harder and more porous, and there is only a light indication of blood at the joint. Bones in lamb carcasses are easily cut or sawed. In the better grades the flesh is fine grained, smooth and velvety, and light pink in color.

The outer covering of fat is smooth, relatively thin and evenly distributed, and has a creamy or slightly pinkish color. Interior fats are of like quality and vary in quantity and evenness of distribution according to the grade. All fats lack brittleness and possess in a greater or less degree the softness and sheen characteristic of fat produced by a milk diet.

Spring Lamb—The term "spring lamb" refers to meat from young lambs of weaning age or younger and which are usually sold for slaughter at ages ranging from 3 to 5 months. The flesh is uniformly tender and a shade lighter than that of more mature lambs. On account of the character of the feed, which almost exclusively is milk, such carcasses are referred to in some sections as "milk lambs."

Hothouse Lamb—The term "hothouse lamb" refers to carcasses from animals which are produced generally under artificial rather than natural climatic conditions. The flesh of such carcasses is considered a delicacy and they are marketed during the late winter and early spring months, principally from January to March. They are produced under the most favorable conditions and represent unusual effort, care and attention on the part of the producers. Aside from a few of the larger cities, hothouse lamb is not a factor in the lamb trade. Such lambs are generally marketed with the pelt on.


Mutton carcasses are from animals of the ovine species which have passed the lamb stage. Breed, sex, feed and handling are responsible for variation in the age limits at which maturity is reached. These variations involve months only, and at most will not show a variance greater than six months. It is, therefore, generally understood that lambs cease to be such from 12 to 14 months of age and that yearling sheep which produce mutton would there-fore correspond closely to the maximum age limit of lambs.

Yearling Mutton—Yearling mutton carcasses are from young sheep usually ranging from 12 to approximately 20 months old. Sometimes, however, the animal may be somewhat older.

Such carcasses are distinguished from lamb carcasses by harder and whiter bones, darker and somewhat coarser flesh, firmer and somewhat thicker exteiror fat, and more liberal quantities of interior fats, grade for grade. Other prominent features which distinguish yearling mutton from lamb carcasses are wider and larger abdominal cavity, and longer body and legs. The break joint of the foreleg is always a positive means of identification. This joint usually breaks in ridges similar in shape to a lamb joint, but the surface is rough, porous, dry and lacks redness. A fair percentage of yearling mutton is found on the markets which does not show the rough saw-tooth effect, when the joints are broken, but have instead a jagged and rough surface. This is because of more advanced age and becomes more apparent as the mature mutton stage is approached. The break-joint must be present, however, and if the leg fails to break at this false joint or suture the carcass is no longer yearling button but mature mutton.

The flesh of yearling mutton is dark pink, inclining to a light red in color, comparatively tender but lacking somewhat in juiciness. Exterior and interior fats are firm, somewhat brittle, and white to slightly creamy in color. They lack the resiliency and milky tinge of fat which is so pronounced in most carcasses of lamb, yet do not possess the same degree of hardness and brittleness of the fat usually found in mature mutton carcasses.

Mature Mutton—In mature mutton, the ribs show a much more pronounced spring or bow than is generally the case in either lamb or yearling mutton carcasses. This gives the sides a distended or barrel-like appearance, particularly in the case of ewes, whereas those of lamb and yearling mutton are relatively straight and are more compact, and the general outline is more uniform and even.

A feature which is peculiar to mature mutton carcasses is the appearance of the ankle joint of the forelegs. In mature mutton forelegs the saw-tooth effect is absent. When a lamb has passed through the yearling stage and has become a sheep, the Cartilage becomes ossified or hardened and the knuckle no longer breaks off the end of the bone. The separation of the foot from the foreleg is therefore made at the ankle joint. Thereafter the knuckle normally forms the extreme end of the foreleg and presents a hard, smooth, white, shiny surface with two prominent ridges.

Another distinguishing feature is the color of the flesh. The color of mutton ranges from light to dark red, compared with medium pink to light red in yearling mutton and light to dark pink in lamb. This also applies to the thin strips of lean meat extending over the exterior of the back and sides and the somewhat broader covering of lean over the breast.

Whether mutton is derived from males of the ovine species which were castrated early in life before any marked sexual characteristics had developed.

Whether mutton carcasses are distinguished from ewe mutton carcasses by the presence of cod fat, generally regular and more even conformation, a somewhat higher percentage of lean flesh to bone, less fat, and relatively smaller forequarters in proportion to hind.

Ewe Mutton is derived from females of the ovine species which were at least 20 months old at time of slaughter. In most instances the animal has lambed one or more times.

Carcasses of ewe mutton have relatively larger abdominal cavities than wethers,larger lungs and pelvic arches, and smaller necks and shanks. The presence in ewe mutton carcasses of parts of the udder is also a distinguishing feature. The bones are generally harder than those in wether mutton carcasses from sheep of the same age. Only a small percentage of ewe mutton carcasses possess the degrees of conformation required in the higher grades.

Buck Mutton is derived from mature males of the ovine species which were uncastrated at time of slaughter. Such carcasses are usually from animals 2 years old and over.

The principal characteristics of buck mutton carcasses are short, thick necks, thick shoulders and breasts, relatively small hind in pro-portion to forequarters, large bones, coarse, dark-colored flesh, and thick, oily "skin" or fell Carcasses of well-finished bucks usually have a thick, wasty covering of fat, but have only moderate quantities of interior fats.

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