Improving Purity

Are Pure Jersey Genetics
Possible in Mini Jerseys?

How Breeding Up Purity Works


By applying the science of Breed Based Representation (BBR) genomics Purebred Mini Jerseys can be produced.  If you want a Mini Jersey that will provide all the wonderful Jersey traits you’ve read about, you’re in the right place!  Purebred Mini Jersey Society wants to help you learn to use DNA science so we can have TRUE Mini Jerseys, not a mystery composite with unknown reproductive and dairy traits.  We want to help you find, breed, and enjoy Purebred Mini Jerseys.  We want to help you improve your family cow or herd so the offspring you produce are more valuable.  

DNA testing is the future of Mini Jerseys.

Standard Jerseys the world over are using genomics in their herds to reach their goals, as are beef breeds like Angus and Gelbvieh.  Mini Jerseys must move forward to gain respect and recognition as a dairy breed and not a “hobby farm fad”.  By improving conformation, consistency of udder, and dairy traits of the offspring produced, our Mini Jerseys will stand out from the crowd.  We must begin testing for purity and genomics to make educated breeding choices.

The key to improvement is testing our cows for a baseline and identifying the Mini Jersey bulls that carry the highest percent of Jersey DNA but are under the 42″ cutoff for Mini.  These bulls can be collected as an additional source of revenue.  Their Artificial Insemination straws will be in high demand by your fellow breeders looking to produce Purebred Mini Jerseys.

Meet Ruby.  She’s an AJCA registered, pure Standard Jersey but she’s NOT a Mini.  She’s 47.5″ and BBR100*.  She was bred as a heifer to a Mini Jersey bull of unknown genomics and purity.  He was BBR unknown, 41″ at 3 yrs old.  

Ruby had a heifer calf, Fern, from that breeding.  Fern was 21.5″ to the top of the hip at birth and testing shows her as BBR100. Fern’s sire did not noticeably reduce her purity.  Fern was 39″ at two years old.

Fern was bred to TDH Dino Smurf.  He previously sired a heifer, Willow, with Ruby.  Willow was tested as BBR100.  Because of this, we knew Dino would not noticeably reduce the BBR of Fern’s calf.  Their calf, Lilac, 20″ at birth, tested as BBR100.  

YES.  It is confusing!  That’s WHY we need the Purebred Mini Jersey Society.

We’ll use a Dexter cross to explain breeding in purity, breeding each future generation to BBR94+ Mini Jersey bulls.*
Generation 1 is a Jersey cross.  Generation 1 = 50% Jersey/50% Dexter
Generation 2 = 75% Jersey/25% Dexter
Generation 3 = 87.5% Jersey/12.5% Dexter
Generation 4 = 93.75% Jersey/6.25% Dexter
BBR94** and above are reported as BBR100
​Generation 5 = 96.87% Jersey/3.13% Dexter
Generation 6 = 98.43% Jersey/1.57% Dexter
Generation 7 = 99.21% Jersey/0.79% Dexter

*When breeding with Mini Jerseys of unknown BBR the results will not be the same.  ​We’re finding, once tested, that the average Mini Jersey cow is already in the 80-100% pure range.  Purity can be reached in only a couple of additional generations. 

**Any BBR of 94 or better is reported as 100 to allow for genetic diversity within the Jersey breed. 

As a PMJS Member you can be mentored by experienced breeders, if you wish, and get advice for breeding.
As Purebred Mini Jersey Society grows, and more Mini Jerseys are proven to carry pure Jersey genetics, you’ll have access to the expanding online database, accessible 24/7.  You can also register your Purebred Mini Jerseys and
breeding stock certified, increasing their value to others looking for true miniaturized Jerseys.

Pooling our genomic data will save us all time and money.

Purebred Mini Jersey Society is a community of Mini Jersey owners seeking to produce Mini Jerseys with DNA tested,
pure Jersey genetics, ​leading to consistent appearance, dairy traits, temperament, and performance.