Chasing the Blue: Part 2

This is the second post in our three part series looking at what it takes to get the elusive blue roan Brabant horse that everyone is seeking. In part one, we looked at the genes that control color in the horse and which traits are dominant or recessive. Today, we'll consider the color possibilities for different crosses.

When a stallion and a mare are bred the offspring receives genetic material from both parents. Each parent has two copies of each gene- called alleles- one inherited from each of their parents. One of the two alleles will be passed along to the offspring for every trait, and the combination of a single allele from the sire and a single allele from the dam will produce the foal's genetic code, which controls their color. A horse has a 50% chance of passing on a given allele for each trait to the foal that they produce.

In order to consider the potential color outcomes for a foal we will explore a few different color pairings using horses here at All the King's Horses. To keep things simple and allow for a consistent comparison of probabilities we will consider all crosses out of our imported blue roan stallion, Ash. Ash has been color tested and is genetically EE (black based, will never throw the red allele), aa (no chance of throwing the Agouti/bay allele), Rnrn (can produce roan or solid colored foals). The desired blue roan foal will be black based, not carry Agouti, and have at least one copy of the Roan gene. What happens when we cross Ash to different colored mares?

Blue roan x Bay roan

The majority of our mares are bay roan so this is a logical place to start our analysis. We know that Ash is always going to throw the black gene, which is dominant, so that takes care of getting a black based foal. The bay coloration is impossible to predict without knowing the mare's genetics, specifically if she carries one or two copies of the dominant A allele that leads to bay coloration. The chances of getting a solid black (no bay) foal will be either 50% (if she carries only one copy of the A allele) or 0% (if she has two copies of the A allele and is therefore guaranteed to pass it to her foals). Similarly, with Roan the exact odds depend on which alleles the mare carries. If she carries two copies of the dominant Rn allele then the foal is guaranteed to be roan (bay or black based) while if she carries only one copy of the Rn gene the odds of crossing two single Rn carriers results in a 75% chance of a roan foal. Taking the odds of solid black AND roan together, we find that the chance of getting a blue roan when crossing Ash to a bay roan mare could be 0% (0*1.00 or 0*.75), 37.5% (.5*.75) or 50% (.5*1.00).

Blue roan x Solid bay

This calculation is similar to the bay roan in regards to producing a solid black foal- depending on the mare's genes the odds are either 50% or 0%. However, in this case the mare will never throw the dominant Rn allele so the roan coloring can only come from Ash, an allele he will throw 50% of the time. This means that when we cross Ash to a solid bay mare the chance of getting a blue roan foal is either 0% (0*.5) or 25% (.5*.5).

Blue roan x Blue roan

This combination has the highest chances of producing a blue roan foal. Because Ash carries two copies of the black allele we know that his offspring will always be black based. When both parents are blue roan we can infer that neither carries the dominant Agouti gene, so there is no chance of the offspring being bay. In this case, the only real variable is the Roan gene. We know that Ash will throw roan 50% of the time. The dam may carry one or two copies of the roan gene which means that the foal has either a 75% or a 100% chance of being a blue roan. Pretty good odds here!

Blue roan x Sorrel

A sorrel mare carries two copies of the recessive e allele and will always throw the red gene, but this color will be masked by Ash's dominant E allele and produce a black based foal. Where things get tricky is with the Agouti gene. Because the mare does not carry any coding for black color she has the possibility of carrying the dominant A allele without expressing it! This means that, depending on her genetics, the odds of producing a black (non-bay) foal is 0% (if she is AA), 50% (if she is Aa), or 100% (if she is aa). As a solid colored mare she will never throw the dominant Rn gene but Ash will provide roan coloring 50% of the time. In the end, the chance of getting a blue roan foal from this pairing can be 0% (0*.5), 25% (.5*.5), or 50% (1.00*.5).

These are examples from our own herd but obviously a stallion with different genetics would result in different probabilities. If, for example, Ash carried one copy of the recessive e allele in addition to the dominant E allele he would still present as a blue roan but rather than producing all black based foals he would pass on the red coloration 50% of the time, further reducing the odds of getting a blue roan offspring unless bred to a mare with two copies of the E allele. A bay or bay roan stallion complicates matters further as they carry the A allele which is dominant and produces a bay foal rather than a solid black/blue roan. Similarly, if someone is dead set on getting a filly all of the probabilities would have to be cut in half to account for the fact that half of the blue roan offspring will be colts instead.

I know this summary has a lot of 'math-ing' but it's important to realize that the color of the foal is dependent on many separate alleles and if just one is off the color can change completely. Crossing blue roans to blue roans can improve the odds of getting the desired offspring, but requires finding the difficult-to-locate colors to begin with! Kudos to you if you made it this far... next time we will take a look at the practical side of things and how to deal with getting the right foal for your needs.

Our sorrel mare, Chestnut, is an example of the hidden bay gene- she produces bay foals despite not looking like a bay herself due to her having no coding for black coloration

Chasing the Blue: Part 1

The first conversation is almost predictable at this point... "Hi! I'm interested in a Brabant horse and wondered if you could help me?" "Sure, they are great horses! What exactly are you looking for?" "Well I want a blue roan filly, 100% Brabant." "You and everyone else ;)" It's crazy how many times I've had this conversation. And I totally understand the beauty of the majestic, blue roan Brabant horse shown in many photos. But the reality of genetics means that producing that blue roan can be a challenge. In this short 3 part series we'll explore what it takes to make that dream Brabant and the importance of keeping an open mind when tracking down your dream horse. We will begin by looking at the science of genetic inheritance, then take a look at what that means for the probability of producing a blue roan foal (doing a little math along the way) and finally we'll consider what this means for someone shopping for their dream horse. So hang with us through the start and I promise we'll get to the good stuff (or just wait for part 3).

To begin, we need to understand how color inheritance works in horses. The following summary is adapted from an article that I wrote for the American Brabant Association's Trace Chains newsletter.

A horse’s color is controlled by specific genes. A horse has two copies of each gene (called alleles), one inherited from the sire and one from the dam. An allele is either dominant- meaning that if the horse carries it they will express the correlating trait- or recessive- meaning that it will be overruled by the dominant trait if the horse carries a dominant allele. A horse will only show the recessive trait if they inherit the recessive allele from both parents. There are 3 genes responsible for the primary colors we see in Brabant horses, which are black, red/sorrel or bay all of which can be solid or roan. (The Grey gene/color is also possible in Brabants but is a relatively rare trait and does not affect the probability that the horse will be a blue roan so we're going to set that one aside for the purposes of this series).

Extension Gene (base color)

The base color for a horse is always either red or black and is controlled by the Extension gene. Black is the dominant color, denoted E, while red is recessive and is denoted e. If a horse shows any black (whether it is full body or just their points) they must carry the E allele. We cannot infer whether a black based horse carries e, as the red allele is recessive and is masked by the dominant black allele. A horse with no black must carry two copies of the e allele.

Agouti Gene (bay)

The bay coloration can be confusing as the horse’s body is red but they have black on their legs and points (ears, muzzle, mane/tail). This modification is due to the Agouti gene. Technically a bay horse is black based, but the dominant allele, A, restricts a horse’s black coloration to their points (resulting in a bay). The recessive allele, a, leaves the black coloration over the horse’s whole body (resulting in a non-bay horse). Similar to the Extension gene, a bay horse must carry at least one copy of the dominant A allele and may or may not carry the recessive a allele. A black bodied horse has two copies of the a allele. It is worth noting that a red based horse (ee) may be a carrier of the A allele, but it will show up as a sorrel rather than a bay because the Extension genes do not code for any black coloration.

Roan Gene

Any color can also show the roan pattern. The roan gene results in white hairs sprinkled through the colored hairs. The roan pattern is dominant, Rn, while solid coloration is recessive, rn. A roan horse may have one or two copies of the dominant Rn allele and a solid colored horse carries two copies of the recessive rn allele. From this we see that a roan foal must have at least one roan parent, as the dominant allele responsible for the pattern is always expressed.

Due to the effects of dominant/recessive alleles, we often can’t tell what alleles a horse carries simply by looking at them. However, there are genetic tests available that will tell what colors and patterns a horse carries by testing a hair sample. In the next post in this series we will explore how the genetics of the parents translate into different color possibilities for their offspring.

A colorful team! Left to right we have solid bay, blue roan, and solid red (sorrel)

The Hats We Wear: Breeding Manager

I've always been fascinated by the reproductive side of animal care and management. As a high schooler at 'cow camp' I was thrilled to have the chance to spend extra time with the presenters who came to demonstrate embryo transfer for us and my dad very graciously spent several evenings driving me to a class to learn how to do artificial insemination on my own animals. In college, I had the chance to spend time working on a research project tracking follicle growth on dairy cattle. So when we made the transition from cattle to horses I brought a solid foundation of knowledge about the reproductive process and a strong desire to learn and do as much as possible myself.

As it turns out, cattle and horses are very different in some important ways when it comes to breeding. Broadly speaking, cattle ovulate a set period of time after they come into heat, leading to the ability to predict with a fair bit of accuracy when is the best time to breed them, while horses ovulate a somewhat-set period of time before going OUT of heat, leading to the need for either a lot of repeated breedings or ultrasounding to see how the follicles on the ovary are growing and maturing in order to time the breeding correctly. When I bred my first mare, I had the vet out to do the ultrasounds, tell me when to breed, and confirm pregnancy. As our herd grew it quickly became apparent that repeated vet visits for breeding work were going to become cost prohibitive, as well as a scheduling nightmare given that I was working full-time at the time, and we needed to explore other options.

I found an ultrasound class through The Breeder's Assistant where we had the chance to do hands on practice and also classroom learning and in 2018 I purchased my first ultrasound and began tracking and managing my own mares. Now it's one thing to ultrasound a mare through a normal cycle, but the real challenges come in when things don't go as planned... which is more often than we like! As I grew in my ability to 'see' what was happening it also led to developing other skills such as doing uterine lavage to clear fluids, infusions to treat bacterial infections, on-farm AI and hormonal control of the estrus cycle. I love to read up on strange cases and have found a variety of helpful Facebook groups for discussion on reproductive management as well as textbooks full of good information, all of which has to be put to use practically to stick!

Our foray into the stallion side of breeding management came when our Brabant stallion, Ash, proved to be a very difficult stallion to collect for AI. After hauling him to multiple facilities only to have them give up on trying to collect him and then following up at a vet school where he was pronounced 'physically fit' but difficult we decided that it was another case of needing to do it ourselves. I travelled to Texas for a stallion oriented class with The Breeder's Assistant and came home to start amassing the equipment necessary for stallion collection and semen processing. Having done a lot of work on the female side of things with the cattle the switch to the male side of the equation was a big leap into the unknown. It has taken several years and a LOT of trial and error to get to the point where we can (mostly) collect Ash and are expanding to some of our other stallions as well. Unfortunately, with his challenges it is becoming clear that we are unlikely to be able to ship semen on Ash but the ability to do on-farm AI is a step in the right direction and so far he has done an excellent job of settling our mares this way and putting amazing foals on the ground. With the purchase of Boone earlier this year we finally have a stallion who is easy to collect and has excellent fertility so we have started slow working on shipping semen to outside mares.

Day to day, breeding management at AKH means keeping a ton of lists to stay on top of who needs to be checked (and why), when we plan to breed, stallion semen numbers, and any treatments that we're performing. It's a job I enjoy but requires all of my ability to organize, brainstorm, and focus to keep on top of the different needs of each horse. I believe that our hard work is paying off as our conception and foaling rates have improved drastically since we started taking control of the process ourselves. There are plenty of other areas of equine breeding and reproduction that we hope to explore in the future but for now we continue to plug away at managing our mares, working with our tricky stallions, and growing our ability to serve our customers through our knowledge and services.