By Ángel A. Custodio González, PhD Animal Science Genetics, Texas A&M

The Puerto Rican Paso Fino Horse Breed is notable for having a very high degree of purity in the specific set of genes accountable for these animals’ walk in the Paso Fino gait. The degree of purity in a breed is the result of a combination of factors. For example, the length of time since the breed has existed, the amount of pressure exerted by the breeders in the selection, the genetic composition of the animals from which the breed was started, geographic distance or the level of isolation from other breeds, the level of control exerted by the organization regarding the introduction of other breeds’ germplasm, historical, political, and economic events, the breed’s definition or the direction of the selection process. This last factor depends on how well defined are the main features that give fundamental purpose to the breed.

The definition of a breed is not an easy task and can change in time for different reasons such as changes in the needs of breeders or scientific findings that offer different ways of doing things. The definition of a breed is a process that may need to be adjusted as time goes on. For this reason, it is not strange for breeders to select for a specific type of animal for some time and then, years later, steer in a different direction, or that some breeders seek a specific type while others seek something different. The fewer the changes in direction, greater purity will be obtained.

The Puerto Rican Paso Fino horse population has a long history that can be traced back to the first years of Spanish colonization. When the first Spaniards came to Puerto Rico, there were no horses on the island. But they immediately brought them because horses were a very important means of land transportation at the time, and an essential resource for soldiers during wartime. It is known that don Juan Ponce de Leon brought horses to Puerto Rico during the very first years of Spanish colonization. The horses brought by Spaniards were from breeds available in Spain by the end of the fifteenth century, that adapted well to military and work uses. There may have been various introductions, some directly from Spain and some from other Spanish possessions in the New World. It can be assumed that no Paso Fino horses were brought in any of those introductions, because presumably, there were no Paso Fino horses in Spain or any of its possessions at the time. We cannot discard the possibility of the introduction of horses which displayed the ambling gait, because this type of gait did exist in some Spanish regions (the Asturcón horse, for example, which already existed in Spain, exhibits amble). There is also the possibility that no horses with ambling gait came to Puerto Rico, but that they carried ambling gait alleles in their genomes.

In Puerto Rico, horses had a very limited military use, hence, their principal use was civil. The features that make a good military horse are not necessarily those which make them adapt well to domestic uses. Genetic and phenotypic changes in a population is attained by means of selection and mating control. From these two, crossbreeding, which is a form of mating control, produces quicker changes than selection. Breeders in Puerto Rico must have practiced both. They crossbred and the product of that crossbreeding was used for work, as well as recreation and sport. The crossings combined the alleles of different breeds and these new combinations produced horses with different features than those of the original breeds. In these features, there were some that altered the rider’s comfort, which pleased the breeders and hence, through selection, they began to increase the frequency of those alleles in the population. This process of mating control and selection, which was carried out during centuries, produced the four-beat lateral gait that we know in Puerto Rico as Paso Fino which is, probably, the smoothest gait for the rider that can be executed by any horse.

Relatively recent advances in genomics have made it possible to identify a specific gene, localized in chromosome 23, that affects the movement pattern in horses’ extremities. For this gene, which scientists have named DMRT3, two forms, or alleles, have been found: a normal allele, which produces a functional protein, and a mutation allele that produces an incomplete protein. Horses bearing the normal gene exhibit the classic horse moves walk, trot, and gallop. Horses with the mutating allele can exhibit other patterns of movements in their extremities. Paso Fino horses, as well as other paso breeds throughout the globe bear the allele with the mutating gene. There must be other loci affecting the locomotive pattern of horses, because it is evident that there are many genetic differences among the spectrum of breeds that bear the DMRT3 gene mutation. Those other genes have not been identified. There are many possibilities. There may be one or two additional genes, each with various alleles, or there may be many other genes, some with great effects and others with very small effects on the gait. The innate locomotive forms exhibited by a horse, or the gaits that it may be able to learn may depend on the combination of alleles in its genome. What science still has not figured out about the genetic control of horse locomotion may be a simple situation or an extremely complex one with many interactions between alleles and genes.

A research by Marta Promerová, et. al., published in 2014 in Animal Genetics science journal, determined the frequency of the two DMRT3 alleles in 141 horse breeds around the world. This research study analyzed a sample of 78 Puerto Rican Paso Fino horses and found that the frequency of the mutated allele was 99.4%. For the mutated allele, there were 77 pure breed horses and only one heterozygous subject. In other words, among the 156 alleles in that population (each animal has two alleles), there was only one allele that did not present the mutation. Very few horse breeds presented a 100% purity for this allele and they were all represented in smaller samples, which renders less precise results. This is not definite evidence but tends to confirm that the Puerto Rican Paso Fino Horse Breed has a high grade of purity.

Let’s now take a look at some of the factors that have contributed to distinguish and purify the Puerto Rican Paso Fino Horse Breed.

The following quote is from the Book of Puerto Rico, chapter IX, subtitled The Cattle Industry of Puerto Rico, and written by Dr. Jaime Bagué. The book’s editor was E. Fernández García, and it was published by El Libro Azul Publishing Co. (The Blue Book Publishing Co.) in San Juan, Puerto Rico, in 1923. It is available on the Internet through the Virtual Library at Universidad del Turabo, in the Puerto Rican Collection of Electronic Books (page 628).

“Side by side with the cattle the horse was developed. All the southeastern portion of the island produced good-sized, well set up horses of quite bloodlike heads, feet and legs that went to decorate the stables of the rich: residents and foreign.

The Yabucoa horses. In 1840 Mr. Ramón Aponte took to the fertile plains of Yabucoa two mares sired by an Arabian Horse that was imported by a gentleman from Ponce. Mr. Aponte having a big farm where horses were selected, bred, and well cared for. It was a question of pride for this gentleman-farmer to win the prizes [andadura, paso fino, escape] offered by towns of Caguas, San Juan, etc. at their annual horse-fairs. The horse “El Manchado” is still remembered by the older generations; because he was as famous in his days as “Perla Fina” was in recent years. A big number of his colts were sold at one thousand dollars each; a thing unheard of, in those days. These stallions headed the fine studs of men like Marquis de las Claras in Arecibo. They also won for the farmers of Porto Rico the respect of the people of Venezuela, Cuba and Mexico which imported them, and consequently they made reputation for Yabucoa, the town of their origin.”

The aforementioned quote presents revealing details regarding the breeding, sports use, and the import and export of horses during mid-nineteenth century in Puerto Rico. Note that by mid-nineteenth century there were horse competitions with specific Paso Fino events. This points to the fact that there were enough Paso Fino horses to warrant the competitions. It is implied that breeders had already identified and defined Paso Fino enough to have developed specific quality criteria for these horses, which in turn lets us assume that the Paso Fino horses had been on the island for many years. It is evidenced that the selection process had direction, because of the specific criteria of good Paso Fino traits, an essential requirement to be able to declare a winner in a competition. The Arab breed horses mentioned must not have participated in the Paso Fino competitions, but in other of the competition events.

The book also reveals that Puerto Rican horses were exported to other Latin American countries. On page 626, chapter nine, of The Book of Puerto Rico it is stated that: “the Spanish vessels arrived at our ports and bought horses to be used by the squads that, at the time, fought in the conquest of Peru.” However, this quote refers to horse exportations occurring way before mid-sixteenth century. Most probably, mid-sixteenth century horse exportations did not include Paso Fino horses, because these horses did not exist yet in Puerto Rico. But the possibility that some of the alleles that determine the capability of the horses to perform Paso Fino could have already been present in the Puerto Rican population (and that they could have, hence, been exported to far away countries, like Peru) cannot be discarded. In the exportations that took place in the nineteenth century, however, Paso Fino horses, or horses bearing the Paso Fino alleles may have been present.

In other parts of South America, in Colombia and Peru, for example, there are also horses that are capable of the four-beat gait like Puerto Rico’s Paso Fino horses. It is possible that, in these countries, there were crossbreeding and selection processes similar to those occurring in Puerto Rico, stemming from horses that descended from some of the breeds brought by the Spaniards to the New World. But it is also possible that Paso Fino horses, or horses with the Paso Fino alleles arrived at those countries from Puerto Rico.

Colombia and Peru’s paso horse populations have gone through long periods of time –centuries– isolated from Puerto Rico’s breeds, with little or no genetic exchange between them. This isolation has provoked genetic differences between these populations. Some of these differences might not be evident at plain sight because they are gene frequencies or gene combination differences. To illustrate this, let us imagine that we are comparing two different animal populations, and that they both have alleles Q and q. In population #1, the frequency of Q=.05 and in population #2, the frequency of Q=.25, and the frequencies of q are .95 and .75, respectively. Both alleles are present in both populations, but there is a marked genetic difference between the populations respect to the frequency of these alleles. Breed #1 will be purer for allele q. If allele q produces a more desirable phenotype, then breed #1 will hold an advantage.

A research project carried out in Germany by K.S. Aberle, et. al. (2004) revealed that with only forty years of no genetic exchange between horses at both sides of the Iron Curtain, populations became clearly distinguishable by genetic analysis. The political situation casted such strict prohibitions, that it was virtually impossible to mate animals from the Federal German Republic with those of the Democratic German Republic. This shows that if animals from two populations do not mate, or if the mating is very scarce, genetic differences between those populations are maintained or even increased.

Geographic, as well as political factors have influenced the purity of the Puerto Rican Paso Fino Horse Breed. Puerto Rico is an island and has been a United States possession for over a century. Both countries have kept their horse population more isolated from Latin America than other paso horse populations. In the small island of Puerto Rico, horses have experienced less crossbreeding than in larger countries or countries nestled in a large continent. In continents, where it may be difficult to maintain strict control of the borders, there is horse movement from one country to another and breeders mate their horses with imported animals, reducing the purity of the breeds. The vast majority of Puerto Rican Paso Fino horses walk on the Paso Fino gait from very early stages, even before being tamed and trained. In other populations, many horses do not naturally walk in the Paso Fino gait, unless they are tamed and receive rigorous training.

There is another very important factor to be considered in the purity of the Puerto Rican Paso Fino Horse Breed, and it is the way in which the group of paso horses in Puerto Rico became a pure breed.

An important event that took place regarding this horse population was that during the second half of the nineteenth century, there were very enthusiastic breeders with economic resources, knowledge, and leadership. Because these breeders had a clear concept of quality, they identified some horses that displayed a set of traits that would make them into superior paso horses. They identified a horse by the name of Manchado, which was not only excellent in his execution, but was also a great stallion with an excellent breeding value (good genes). Dr. Carlos Gaztambide, in his book called Breeding Better Paso Fino Horses, and attorney Eduardo A. Quijano, in his book called Paso Fino, the Breed that Distinguishes a Country, both mention the influence of Manchado in Puerto Rican Paso Fino Horse Breed. According to the facts presented by both, breeders at the time developed a bloodline that descended from Manchado, which suggests something similar to what is known as linebreeding.

Linebreeding refers to the practice of creating a breed line of individuals, all in the bloodline of one or more excellent ancestors. For linebreeding to be successful, two conditions must be met: that the forebear be excellent, both phenotypically and genotypically, and that mating control be combined with the selection process to increase purity in the breed line. The idea behind linebreeding is that in the line of the individuals generated, the genetics of that extraordinary forebear –that shining star that rarely emerges in a population– be perpetuated. One of the consequences of linebreeding is that certain degree of inbreeding is inevitable and this inbreeding, along with the fact that all animals are genetically connected to the same forebear, results in an increase of purity within the breed.

Another important event took place later in the twentieth century: Another excellent horse, the famous Dulce Sueño, was identified. Again, the extraordinary quality of the stallion was combined with the leadership and good judgement of the owner, don Genaro Cautiño. With Dulce Sueño, linebreeding was also practiced, which resulted in a large bloodline of descendants of Dulce Sueño. Interestingly, Dulce Sueño was probably a descendant of the Manchado bloodline, which led to two different linebreeding successes in the same bloodline. This resulted in even more purity for the Puerto Rican Paso Fino population.

Many of Dulce Sueño’s descendants resulted in excellent animals, which in turn, bred a numerous and high-quality progeny. Due to its great influence in the size and quality of the breed, Dulce Sueño has been dubbed the father of modern Puerto Rican Paso Fino Horse Breed.

Two things must be made clear. First, it is not completely accurate to affirm that a rigorous linebreeding was carried out, because surely the breeders did not design the breeding system to be a linebreeding, or they might not have systematically executed it in practice. What we have stated is that the way that mating control was exerted, resembles that of the linebreeding system. Secondly, not all of Puerto Rico’s Paso Fino population descends from the Manchado-Dulce Sueño bloodline, and it may even be possible that Dulce Sueño is not a descendant of Manchado. There are horses that do not descend from these bloodlines, and maybe even an external genetic influence may have been introduced along these lines. But this does not exclude the great influence that these horses had in increasing the genetic purity of the population.

By early 1940’s, during Dulce Sueño’s influence, there was a horse population that walked in the Paso Fino gait and had its own identity for at least a century. Many formal events took place with those horses, but that animal population was not yet a pure breed as such. For an animal population to be called a pure breed, there must exist a duly organized breeder association. There must also exist a breed registry administrated by the breeders’ association or by the government, with regulations for animal inscription. In 1943, a group of breeders under the name of Asociación de Dueños de Caballos de Silla de Puerto Rico (later, Federación del Deporte de Caballos de Paso Fino de Puerto Rico) created the Breed Registry. Thus, Puerto Rican Paso Fino became a formal horse breed with its own official name. The registry remains “closed,” which means that no horse can be registered unless it is an offspring of registered animals (descendants of the Puerto Rican bloodlines). This restriction, along with the use of genetic technology, which provides for precise verification of the forebears’ identity, has greatly contributed to maintain, and even increase, the breed’s purity.

Many Puerto Rican pure Paso Fino horse breeders have made their selection and mating decisions emphasizing on the quality of the gait and have made little or no efforts to avoid inbreeding (the mating of animals that share the same bloodline). Even though the level of endogamy (a byproduct of inbreeding) in the Puerto Rican Paso Fino horse population has not been properly calculated, it is estimated to be fairly high. An effect of inbreeding is that it increases the purity of the animals, so it has contributed to the purity of the Puerto Rican Paso Fino Horse Breed (we warn that inbreeding has positive and negative effects).

Another important fact in the history of the pure Puerto Rican Paso Fino Horse Breed is that there have been various breeders’ associations. Many times, the organizations have rivaled, in their zeal for the breed’s purity. Furthermore, some of these organizations have been formed precisely because of that zeal. The constant oversight that those organizations exert on the breeders, and among them, has helped maintain the purity of the breed.

We affirm that the Puerto Rican Paso Fino Horse Breed is a unique breed in the world, even though there may be other breeds that share very similar traits. This breed is the result of the interaction of many different factors and thousands of decisions taken by the breeders through hundreds of years, that are impossible to replicate. This means that, if someone should try to begin a new breed, trying to mirror this one, he or she would face a very long and expensive endeavor and, with luck, he or she might end up with a similar breed, but it will very unlikely be the same. Hence, this breed is a priceless asset for the animal owners, for the country and for humanity. This invaluable resource deserves to be protected –quality wise and purity wise– and preserved for the benefit of future generations. If we ever lose this breed, we will have forever lost it.