Sex Balance

This is where a bloodline is present through a son and a daughter.

Sex balancing a bloodline is about bringing the X and Y chromosome back together. In simple terms, Mares have two X chromosomes seen as XX. Females inherit one X chromosome from each parent and transmit one X to their sons and daughters. Stallions have XY chromosomes with Y determining the sex. 

And it is important to understand this point -  stallions inherit their X chromosome from their mothers only and they only pass it on only to their daughters – they can only give their Y chromosome to their sons.   (Ken Mclean) . 

So, sons of stallions do not receive the X chromosome - the sire's maternal DNA - at all. To get the sire's maternal DNA in the foal -  there must also be a daughter of his present in the pedigree

Ken Mclean points out - 

The biggest breakthrough to understanding how linebreeding can be done in the most effective way was recognising that bloodlines should be present via a son and a daughter.  It is the only way the X and Y chromosomes can be reconnected. Remembering that a stallion is XY and a mare XX - a stallion can only give his X chromosome to his daughters.

The X chromosome is far larger than the Y and it is responsible for many of the athletic functions of the horse in terms of energy production.  There is also mitochondrial DNA and any valuable sex-linked genes that are only inherited from the mother line.  This is why - when a stallion appears via one of his sons in a pedigree - it should always be balanced with a line from one of his daughters to have any hope of recreating his attributes in the foal.  And if that stallion is passing on an imprinted gene it can only be passed on and preserved by his daughters.

All pedigree experts stand together on this point.

Clive Harper " Inbreedings and linebreedings which contain both sexes tend to produce better horses than in linebreeding where all the horses are of the same sex"

Edwin Anthony says " Balanced breeding to great ancestors is a very positive factor for class and sport performance. "

Ken Mclean " If there is a concentration of a stallion only via his sons, it is a limiting factor and will automatically exclude any valuable sex-linked genes located on the X chromosome.  By reinforcing a male ancestor via both sexes, it provides an opportunity for valuable sex-linked genes to be inherited in a foal because a stallion's X chromosome is always given to his daughters. This is why I preach the concept of duplicating males via sons and daughters so as to deploy similar genes on both sides of the chromosomal pairings"

Balance and equilibrium in sex balancing is not just about having a son and daughter of a particular bloodline - although this is a start for beginners.

Stallions have many more progeny than do mares, so seeing duplications of a bloodline through a stallion's sons is far more common. 

Due to this one factor, it is clear how it can appear that linebreeding does not work - when a horse's pedigree is overloaded with a stallion's sons and appears to be linebred.

Just because a horse shows duplications to certain ancestors does not mean the linebreeding is effective - it needs to be present in a particular way for the power of that bloodline to be able to reach the foal.

So just because you look at a pedigree and see Donnerhall appear twice via say De Niro and Don Schufro - this is linebreeding to Donnerhall from two of his sons - it is not an ideal configuration especially for breeding stock.

The pedigree of stallion Pik Konig illustrates a simple example of a basic sex balance in a bloodline.

Pedigree of Pik Konig

Pik As is present at 1 x 4 through a son - Pik Konig and daughter Pike. (see image above)

The sex balance between the top horses gets a lot more complex than this and can appear via various intricate patterns.

Full siblings also need to appear in the pedigree in a sex balanced way.  As do three quarter siblings with 75% of their bloodlines in common. 

We do not want to see full brothers coming in through sons only.  Unless they are accompanied by another balancing factor.

A sex balance can be achieved by having two sons of one sire as well as having two daughter lines of different sire.

Stallion Ladykiller shows this pattern - he has sons of Phalaris at 3 x 3.  Then he has 4 daughters of the stallion Chaucer at 5 x 5 x 5 x 5. (see pedigree below)

Blu Hors Zack has a similar pattern at 6 generations - He has the full brothers Furioso II and Mexico at 5 x 5 - both are sons of the stallion Furioso.  And he has two daughters of stallion Pericles xx at 5 x 6.

Even though this is quite a complex pattern, it does seem to work. Zack and Ladykiller are both top sires.  Having the daughter lines to counteract the male duplications - even from a different bloodline - is said to create a type of remote sex balancing effect.

And this is a very common pattern in Dutch horses - Nearly all have brothers Furioso II and Mexico via sons only but they are always accompanied by two daughters of the sire Pericles xx.

I have rarely seen a daughter line of the stallion Mexico, although Furstenball does have one  - and along with Furioso II, the full brothers are one of the main power lines in Furstenball appearing at 4 x 6 .  

 He also has Donnerhall  via two daughters - two daughters of a sire are a filly factor.

Pedigree experts say that having two sons of a sire doesn't actually hurt a performance horse and there are many with sons of a sire, but Clive Harper says they are not desirable for breeding stock - this configuration does not allow the power of that inbreeding to reach the foal.

An example would be having a De Niro mare and choosing Dimaggio as the sire of the foal - these are both sons of Donnerhall.

Kathleen Kirsan says " Avoid breeding to sons of a particular bloodline - it will deaden the transmission of sport and breeding potency"

Full brothers on the other hand are excellent for both mares and stallions as it is bringing the X and Y chromosomes back together.

The evidence for these patterns  is that top mares and stallions are rarely bred to particular bloodlines via sons only - there may be some instances, but it is not a common feature and certainly will be accompanied by balancing factors further back.

Sometimes if you are trying to add an important element to a pedigree mating, it will also bring in a sire over sire factor.  If there is another balancing factor elsewhere in the pedigree it is not the end of the world.

Clive Harper says " a pedigree is able to stand something bad if there is also something good present"

Clive Harper says " If you follow these rules (on sex balancing) and don't go any deeper into pedigree theory, you will produce better horses than random or commercial matings would throw up"

Les Brinsfield said similarly " This is a drop in the ocean with all there is to know about balanced breeding, but it is more than enough to do some serious damage"

So, if your mare has several sons of Donnerhall in her pedigree - this is becoming increasingly common - you can find a stallion that has a daughter line of Donnerhall to match her with.

Small alterations such as a simple sex balance can show a big upgrade in the foal in terms of quality.

Consider Contender who came into Holstein breeding like a bolt of lightning.  He is  out of a Ramiro / Ladykiller mare.

These are lines that at that time especially were rarely seen through their daughters - Contender managed to sex balance these blood lines in all the mares that were overloaded with male lines of Ramiro and Ladykiller - and revolutionised the breed in the process

Similarly with top sire  Chacco Blue -  showjumpers are saturated with sons of Cor De La Bryere, often seen 5 or  6 times in a pedigree.

Chacco Blue comes in with a Corde daughter on his 3rd generation and a Ladykiller daughter on his 5th generation - again providing a simple sex balance to bloodlines that mainly appear via sons only.

The simple sex balance of a bloodline can bring results far beyond what one would expect