I'll first start with this... There is no actual highland breed standard for a micro, mini, or mini-mid highland. The vast majority of these animals are cross bred highlands.
So regardless of anything else you read or hear, these smaller height designations are industry terms rather than an actual highland breed standard.
We expect that the bulk of our calves will fall into the mini and mini-mid range (38"- 45") as this encompasses the height ranges of all of our mini-highland cross cattle.
Micro = under 36 inches. These tiny little cows are frequently third and fourth generation crossbred highlands; most commonly a dexter/highland cross, but some may also be crossed with jersey, zebu, and other small breeds as well. They are most likely to be used as pets. As breeding cows, their small size comes with a great many complications. Dexters carry a dwarf gene mutation referred to as BD1, or chondrodysplasia (chondro) that many breeders and buyers find appealing. The highlands don't carry this gene which is the primary reason for crossing these two breeds. A dwarf cow will pass on the dwarf gene to roughly half its offspring. You can't safely breed two chondro positive animals without the risk of producing a stillborn or deformed calf called a "bulldog" so the practice of intentionally breeding for this gene at all has been the subject of many fear mongering. Dwarfism reduces the adult height of a cow by an estimated 4-5 inches, which for a highland is still not "micro" size, but rather a first step in that direction. The tiny stature of these "micro-mini" highlands are the result of selective breeding over multiple generations and/or through genetic engineering to reach heights under 36 inches.
Miniature = between 37 & 42 inches - Mini's in this size range are typically first and second generation highland crosses. Highland / dexter crossbred highlands are sometimes referred to as highdex, but more times than not they are just called mini-highlands which is a point of contention and confusion for many. The breeds are crossed for the same reason as the micro-mini; the dexters are a smaller cow, and for those breeding chondro positive cattle. Occasionally, there are pure highlands in the upper end of this "mini" range with AHCA registration to support this claim. In this case, they are simply small Highlands (but may also called mini-highlands). This can occur for a variety of reasons; intentional downsizing through multiple generations of selective breeding, illness, and gestational starvation of the calf's dam... to name a few. The key takeaway is that mini highlands may or may not carry the chondro gene, they may or may not be pure blooded highlands, and they may or may not produce mini sized calves. A mini-highland that is small due to environmental reasons will still have full size genetics that pass on to thier calf. If it's mini and it looks highland, it's simply called a mini-highland. Confusing huh? Many people believe they have miniature pure blooded highlands that probably don't because of this. And for the occasional pure blooded, mini sized AHCA registered highland, it's not always considered a desirable thing until they can provide a calving history that supports thier small genetics.
Mini-Mid = between 43 & 48 inches - Mini-mid make up the largest represented category of "mini-highlands”. This height range is typically the smallest of the pure AHCA registered highlands. But again, most of what you see for sale are unregistered crossbred highlands. Some breeders will call the upper end of this size range "small framed" verses "mid" if they are closer to the 48" height, but given how generous people are on their measurements, I always think of that as a standard size highland that someone wants to call mini to sell for more money... so consider that a word of caution. Heifers and cows in the 43-45 inch range are quite popular breeding stock for programs with mini bulls. A little larger female is thought to have fewer calving issues than mini sized cows, and particularly those that are chondro+.
Standard Size = between 48- 62 inches - These is your typical pure bred AHCA highland height range.