American Mammoth Jackstock Registry
Former Standard Jack & Jennet Registry of America - SJJR


Breed Characteristics
AMJR Breeders
AMJR Archives
Contact AMJR



Jack Stock Characteristics

American Mammoth Jack Stock are the world's largest breed of ass.  The breed was developed in the United States through the cross-breeding of imported large European breeds (predominantly from Spain), and to a lesser degree, native American and Mexican stock.  The breeding of these animals in small numbers precedes the creation of the registry by more than 100 years, well before the Revolutionary War, according to an account written by one of the registry's founders in 1902.

Jack Stock were developed out of a need for high quality jacks to sire mules with size, strength and vitality for use in the agriculture and transportation industries.  The variety of types of mules required in each of these industries in different regions of the country provided the premise for the types of Jack Stock bred in the early years.  Breeding of various types of Jack Stock has been further influenced by the breeds, or types of mares available in different areas, the economy, war and other factors.

To identify the characteristics of Jack Stock it is helpful to understand the diverse genetic makeup that has given distinction to these animals.  There are different types of Jack Stock, just as there are different types within the various horse breeds.  Some Jack Stock may exhibit more qualities inherited from their Majorcan ancestors, while others may resemble the Andalusian, and another may exhibit characteristics of several of the breeds in its ancestral makeup.

This diversity does not reflect the original goals of the registry when it was created in 1888, at a time when the Jack Stock industry was flourishing.  The registry sought to facilitate the standardization of the breed to include only black animals, ultimately a minimum of 15 hands tall.  The records of breeding for many years reflected these goals.  Over the years, revisions to the registry rules of entry, economic factors, war, geographical considerations, and other factors altered these breeding practices, and the diverse genetic makeup of Jack Stock persevered.

Documentation of breeding prior to the Revolutionary War is lacking in detail, however, one account indicates the first jacks to be imported were from the Cape de Verde Islands, tracing back to the Portuguese.  These animals were said to have produced inferior mules that were exported to the West Indies during the time of the Peninsular wars when jacks could not be imported from Spain.  Due to their inferior quality, these animals are said to have died out from competition with better animals, and the decline in demand from West India.

The gift of an Andalusian jack and two jennets to George Washington from the King of Spain in 1785 is widely recognized as the event that revolutionized Jack Stock breeding in the United States. These foundation stock, and a Maltese jack later bestowed on Washington by his European ally, Lafayette, produced Jack Stock and mules of a quality not previously attainable with the inferior domestic stock and those imported from the Cape de Verde Islands.

Between 1785 and the start of the Civil War a number of jacks were imported from Europe.  Registry records contain relatively good accounts of the breeds of animals imported and bred during this period. Though this information is not official, it was documented by prominent individuals in the Jack Stock industry, and founders of the registry.

One of the most influential jacks in Jack Stock history was known as Imported Mammoth, imported to northern Kentucky prior to the Civil War.  Accounts of Imported Mammoth indicate he was 16 hands, of extreme length, heavy like a horse, with large feet and bone, the latter being somewhat meaty.  Said to be far superior to any other jacks at that time, he was credited with having improved the jack and jennet stock in bone and size more than any other in his nine year breeding career.  Limestone Mammoth, a descendant of Imported Mammoth is a good example of the Imported Mammoth bloodlines.

In contrast to Imported Mammoth, imported Catalonian jacks contributed style and finish.  Prized for their glossy coats ranging in color from black to brown, the Catalonian was said to be "less in size (14-1/2 to 15 hands), bone and foot but with the finest long, keen, roman heads, and thin folding, upright ears".  Offspring of early imports reportedly exhibited an excess of style and finish with superb heads and ears, and fine silky coats.  The bone and foot lacked the size of the Imported Mammoth bloodline, but the bone was flat and clean.  Great Eastern was considered by the registry in 1888 to be one of the highest type of the Catalonian breed.  The Catalonian thrived in the United States, and the produce of the imported jacks reportedly outgrew their sires in size, bone and muscle, but retained the desired style and finish.  The Starlight line descended from imported Belknap were considered by many to be excellent examples of the fine Catalonian type of jacks produced in the United States in the mid and late 19th century.  Crossing descendants of the Starlight line with descendants of the Imported Mammoth line produced excellent Jack Stock with size, bone, style and action.

Maltese jacks were some of the earliest imported to the United States.  Considered by many to be too small, their use in breeding Jack Stock declined drastically with the increased importations of Catalonian, Andalusian and Majorcan jacks.  The Maltese imported to the United States were rarely over 14 hands.  Some had good feet and bone, but were said to be lacking in their limbs.  Black or brown in color, they had attractive heads and ears.  The Maltese were a more fiery breed than the other large European breeds, and have been credited with contributing vitality to the Jack Stock breed.

The Majorcan was the largest of the European breeds used in the development of American Jack Stock.  The average height of Majorcan imports was 15-1/2 hands, with exceedingly large bone and body.  Their heads were enormous and bulky looking, with the largest, but not so erect, ears of any other breed.  The Majorcan's action was sluggish in contrast to the lively action of the Catalonian and Maltese.  They were uniform in size than the Catalonian, and considered to be not only the largest jacks in existence, but also the most pure breed of jacks in Spain.  The numbers of Majorcans imported was limited due availability.  In 1890 it was reported their native island had been literally stripped of these animals due to their desirability for the production of jennets with size.  King Inca, registered as being 15-7/8 hands was an example of a good imported Majorcan jack.

Andalusian jacks were some of the earliest imported, and considered to be one of the most distinctive breeds of jacks in existence.  It is claimed that this breed is of an ancient race used for producing mules before the time of Christ.  Andalusians are predominantly gray, though some may be almost white, and in rare instances, black or blue.  They range in size from 14-1/2 to 15 hands, with excellent legs, large firm bone, and a good head and ear.  The Andalusian was widely used in Jack Stock breeding, but lost favor due to the coat color.  Black was the preferred color, and the only color that was allowed entry into the stud books during the early years of the registry.  An interesting observation of early breeders is that the Andalusian was less prone to developing "jack sores" than any of the other breeds.

Though considered an inferior jack at the time, a fair number of Italian jacks were imported in the late 19th century.  It was felt the importation of these jacks was motivated by their cheapness and the strong demand for imported jacks in the United States at the time.  They were generally black, though occasionally gray, and believed to be related to the Maltese.  The Italian jacks were the smallest jacks imported, ranging from 13 to 14 hands.   They were a vigorous jack, considered by some to be of a vicious nature.  These jacks were shunned by serious Jack Stock breeders, and it is not clear how much they may have been used to breed jennets.

The Poitou of France was widely considered to be the most perfectly formed of all European jacks imported to America due to his immense weight, bone and muscle, ranging in height from 14-1/2 to 15 hands.  The Poitou is quite distinct in its appearance, being the only breed with a very long coat.  Other characteristics include a broad chest, deep body, full hip, and large feet and joints. They were not imported in as great a numbers as the Spanish breeds, for the most part due to high prices.  LaFleur was one of the early Poitou entries in the stud book.

In addition to the above mentioned breeds, early history indicates some jennets were imported for Jack Stock production to the mid west and southern regions of the United States from Texas and Mexico.  These animals were considered to be inferior in quality, lacking size, bone and style.  Their introduction was stated to be a great drawback to the progress of raising the standard of jacks and jennets.  L.W. Knight, in a 1902 writing makes reference to the colors of jennets that would seem to elude to the use of these Texan and Mexican jennets in Jack Stock production.  He said, "Our jennets in this country are very diverse in color. Grays, blues and mouse-colored are quite numerous".  The "mouse" color was quite common in the Texan and Mexican jennets.

The distinguishing characteristics of good quality Jack Stock are no different today than they were 200 years ago.   Registry documentation and other historical accounts consistently affirm that breeders of the 18th and 19th centuries were striving to produce animals with the same qualities as breeders in the 20th and early 21st century.

Jacks a minimum of 14.2 hands (58") tall and jennets a minimum of 14 hands (56"), plus girth and cannon bone measurements that meet the requirements, are eligible for registration, as they were when the registry was created in 1888.  Animals in these size ranges represent a significant number of the Jack Stock population.  However, the model jack 200 years ago, and today, would be no less than 15 hands (60") tall.  He should have good width, depth and length of body, a strong loin and full hip.  The neck should be well muscled, but not excessively thick, and of proportionate length.  The feet should be large and well cupped.  Bone should be of good size, flat and clean.  The legs should not be fine in appearance, resembling the leg of the Thoroughbred horse.  The head should be well shaped and not of extreme length or thickness, tapering to a relatively fine, rounded muzzle, and be in good proportion to the body, with large wide set eyes, and well placed long, thin upright ears.  The result of these combined qualities is a jack with style and substance that is well suited for Jack Stock production, as well as producing superior quality mules of any type, relative to the breeds of mares he is put to.


Home Services Breed Characteristics AMJR Breeders AMJJ AMJR Archives AMJR News Links Contact AMJR

Copyright American Mammoth Jackstock Registry.  All rights reserved.
Last modified: 08/05/2014