Gypsy Vanner Horses: The Importance of the Mare in the Breeding
The problem with breeding lesser mares to great stallions is that only a small percentage of those foals will be of high quality. If there is no culling for those foals, the quality of the breed overall goes down. Only the best foals from those mares should be rebred. Thus, when you breed high-quality mares to high-quality stallions, you have a much higher percentage of great foals on the ground to maintain the quality of your breeding stock.
There is a good overview of the genetic principals underlying the science of equestrian breeding in a book called Equine Genetics and Selection Procedures written by the research staff of Equine Publications, Don M. Wagoner, editor/publisher. The following information is taken from that book.
The male normally carries within each body cell an X and a Y chromosome; the female carries two X chromosomes. During fertilization, the embryo's sex is determined by whether a sperm with an X or a sperm with a Y chromosome combines with the X chromosome of the dam's ovum. Since the presence of a Y chromosome results in the development of the male, the stallion can only transmit his Y chromosome to his sons and his X chromosome to his daughters. If the genes for his desirable traits are located on the stallion's X chromosomes, his sons cannot inherit those traits. His daughters, on the other hand, will inherit the X-linked genes; and even if they cannot express the traits, are capable of passing them both to the male and female offspring.
Distant relatives have little influence over his actual genetic makeup. An exception is in line breeding. A stallion advertised as the "great grandson of a world-famous sire" may have inherited very few of his great grandfather's genes.
Selection of the best stallions from the best families offers a far greater chance of producing superior offspring than if the breeder uses an outstanding sire from a relatively obsure family. Horses from successful families usually produce above-average offspring more consistently.
Although every foal receives half his genetic makeup from his dam and half from his sire, many feel that the dam contributes more to the nature of her foals than does the sire. This additional contribution is due to maternal influence. The theory of cytoplasmic genetics supports this theory.
The success of the culling process depends on the ability to distinguish between genetic and environmental variation and selecting only those individuals with superior gene types for breeding.
When horses are bred haphazardly without culling of inferior stock, many undesirable traits may become predominant in their offspring.
Grading is the outbreeding of a superior stallion to below-average mares, in the hope of raising the quality of each mare's offspring. Grading might be helpful to some horse breeders, depending on their situations and goals. The breeder should keep in mind that the mare is capable of limiting the quality of her foal, regardless of the quality of its sire. Therefore, the foal sired by a famous stallion, and out of a below-average mare, might not be valuable enough, and be considered a grade horse.
Gyspy Vanner Horses: But What About the Mare?
"A rule of thumb in the breeding world is that you can breed a mediocre stallion to a great mare and still have a nice foal. But breed a great stallion to an undesirable mare? The results will be disastrous." So states the EquiSearch Web site in an article which suggests that "the dam affects the offspring at a rate of 60 percent or more. In the majority of cases, breeding experts will tell you the mare's characteristics override the stallion's." The full article, entitled "The Mare Matters, is very interesting and is available to read online — just click the link."
