breeding1

The Problem of the overshot and the lightly under jaw in the modern Chihuahua- breeding

The problem of the overshot and the light lower jaw in modern Chihuahua breeding of these articles is only an abbreviated part of the article preparing for publication. The goal of this article is to write in light popular form over current questions of the Chihuahua - breeding. It is written not only for experienced breeders, but also for beginners (and particularly for it). This interpretation is written there NOT in the scientific style, but in popular style with scientific remarks, I offer at the end of the article a specialized vocabulary.
NB! For biologists and veterinary surgeons: the text is not scientific! (The article, what is written in the scientific style will be published in Russian magazines on Russian with Russian specialized vocabulary. I am only one of the co-authors of the condition.)

Tooth and dentures problems by Chihuahuas are very current today not only in Germany or in Russia but also in the whole world. Young animals lose very early the teeth, have tartar, have problems with the tooth change, have "swimming" bite and many different problems. In this article are described the reasons of the problems and the ways of the problem removal, the description of the characteristics is made.
Each dog whether largely or small is to have 42 teeth. According to the standard it is permitted with Chihuahuas, to have fewer teeth. Each Chihuahua is to have a scissors bite or level bite. But not all dogs have that. This problem interests not only me, but also many breeders in the whole world. In some countries will be sent also the questionnaires and the breeders and owners will be asked regularly. As example I can teach only to statistics Swedish Chihuahua club (Chihuahua-Bladet No. 1-2002), because other countries conceal also the statistics or they close their eyes for this problem:
100 Chihuahua owners had the question "what kinds of bite types have your dogs?" and they answered in such a way:
Scissors - 52,
Level bite - 11
Undershot - 13 (more than 0,5cm - 2)
Overshot - 14 (more than 0,5cm - 4)
Not answered - 10 (We take on that the dogs of the owners have also tooth problems, otherwise the owners would have answered the question)
The statistics show that the dogs with the 37% the owner have problems with the bite, for 6% - large problem with the bite. The statistics is published and stands openly to the analysis. The problem of the overshot interests me much and in this article is not described the undershot, but you would have the possibility to read about the genetic formula in the large article. It is well-known that with the determination of the bite are regarded maxilla and mandible. The position of them shows whether the scissors, level bite overshot or undershot. For the head form and maxilla is responsible a pair of the genes (we call b-gene), for the lower jaw - other pair of the genes (we than A-gene designate).
The overshot formed such as anomaly of the bite, because of short lower jaw and are enough for upper jaw.
With the standard bite the lower jaw is enough long and substantial, which is called dominant homozygote characteristic (AA). The short light lower jaw is recessive homozygote characteristic (aa). The problem consists of the fact that in the last 20 years because of the mode, which shifted to short noses the recessive characteristic into the homozygote condition. Since the Chihuahuas with the short noses won at the largest exhibitions, these characteristics and fastened special and was bred strictly with the in-breeding. That you may imagine to yourself,
what look like the dogs with these characteristics, I wrote table Nr.1 (the undershot isn't described here). The table, which is taught down, is not full. The full table has many more characteristics, which are not described here, because the other characteristics are too heavily determined without Roentgen and other investigations.

Table 1: Comparison of the dogs with aa, Aa and AA genes.

Characteristics	aa	Aa (proband) just invisible, like healthy dog	AA (healthy dog)
1. Length of the lower jaw (difference to the maxilla)	very briefly	more briefly	a little more briefly or directly
2. Width of the lower jaw	closely	enough broadly or some closely	broadly
3. Switch of the lower jaw	soft, the jaw is very easily adjustable and goes easily into all directions (with grown-up dog!)	Softly, the jaw is easily adjustable and goes easily into all directions (with grown-up dog!)	Hard, firmly
4. Deep one of the lower jaw	flat, by the side seen	flat	low, before the side well seen
5. Being located to position of the teeth in the lower jaw	free standing inclined/slanted, loosely	free standing inclined/slanted, may be loosely	tightly standing, close standing, strong
6. Size and quality of the teeth	small ones, thin, sometimes thick, loose	medium sized or small, thinly, often loose	Large, firm, thick, firmly standing
7. Quality of the milk teeth	small teeth with long tooth roots	particularly with the fangs small teeth	large one being certain teeth
8. Tooth change	problematic, is often noticed arrangement of the teeth and the jaws, double teeth	problematic, "swimming" bite	runs from alone, one needs nearly no assistance of the veterinary surgeon

The consequences the mode are large quantity (at present that is the majority of all dogs in the breed) of the dogs with the recessive characteristic in the homozygote (aa) or heterozygote (Aa) condition. The influence of the characteristics on the health of the dogs is terrible:
1. Earlier tooth loss;
2. Growing of the tartar in the with difficulty attainable places, which brings the dogs to paradontitis & caries;
3. The dog can eat chopping meat only (the dog is a predator!);
4. Very heavy gastritis;
5. Earlier dying;
6. The gene interaction aaBB is a measurement shape because of the overshot (more than 2cm, unfit for breeding), if the quantity of the dogs with the heterozygote characteristic (Aa) and with the homozygote characteristic (aa) grows, then grows the probability of the births of the dogs with the measurement shape. The final editorship of the article is published in next days. In the second, third and fourth parts of the article will be published describes, how homogeneous characteristic is brought into heterogeneous condition and specialized vocabulary.

Svetlana Kuehnel

The Russian version has priority rules.

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