轉貼本文請註明出處:
犬髖關節狗友會(www.dogchd.net)泡泡拔 阮振維譯自www.offa.org
Breeding based on individual phenotypes appears to be the
method used by most breeders, as available information on relatives
is somewhat limited. For traits considered to have moderate
heritability, this approach will reduce the frequency of an undesirable
trait in the progeny, but progress, while substantial, will
be slow.
Information on siblings of an individual animal, plus information on
the siblings of parents and grandparents, makes it possible for the breeder
to apply greater selection pressure against the disease. This results
in selection of animals with more ideal breeding values and provides a
more rapid reduction of the undesirable trait in the breeding program.
The following breeding selection criteria have been demonstrated
to more rapidly and effectively reduce the frequency of
undesirable traits:
1. Breed only normal dogs to normal dogs〞using hip dysplasia
as an example, Table 1 illustrates the outcome of matings based on
information extracted from the OFA database. A total of 444,451
progeny were identified where both parents had hip conformation
ratings. The percentage of dysplastic progeny increased as the sire*s
and dam*s phenotypic hip ratings decreased from excellent through
dysplastic. Reed (2000) reported equal genetic contribution on
progeny hip scores from the sire and dam.
2. Breed normal dogs that come from normal parents and
grandparents〞this employs the traditional horizontal pedigree
with emphasis on the most immediate three generations (50% genetic
contribution from each parent, 25% from each grandparent
and 12.5% from each great grandparent)
3. Breed normal dogs that have more than 75% normal siblings
〞this information is usually not available since most animals
in a litter become pets and are not screened for undesirable traits.
Breeders can add incentives to purchase contracts in an attempt
to gather this information, such as offering reimbursement for a
preliminary hip radiograph taken when the pet dog is spayed/neutered.
4. Select a dog that has a record of producing a higher than
breed average percentage of normal progeny〞if known, the
comparison of production performance between individuals is an
important criterion. For example, a stud dog with a track record
of producing 90% normal progeny is far superior to another dog
producing only 50% normal progeny.
5. Choose replacement animals that exceed the breed average
〞exert constant, consistent pressure to ensure overall breed
improvement.
In summary, achieving goals in breeding program depends upon the
ability to assess an animal*s predictive breeding value. Important information
to assist breeders in achieving their goals is available on the OFA
website through the database search option (
www.offa.org).
利用動物個體的表現型來進行繁殖篩選,是目前大部分繁殖者所採用的方式,不過若想獲得整個家族的資訊,基本上還是有所限制的。如果是一個只具有中等遺傳能力的遺傳性狀,用這種篩選方法的確可以降低不想要的性狀在後代出現的頻率,雖然很有用,但是進展卻會很緩慢。---從個體的兄弟姊妹獲得的資訊,加上從雙親、祖父母的後代獲得的資訊,將可以幫助繁殖者用更好的篩選機制去對抗疾病。經過這樣篩選的動物將具有更好的繁殖價值,同時也可以快速的降低非期望性狀,在繁殖過程中出現的機會。
以下的繁殖篩選準則,已經被證明能夠更快速且有效的降低,非期望性狀出現的頻率:
1.只繁殖正常的犬隻,讓他們生出正常的後代—以髖關節發育不全為例,《表格一》是從OFA資料庫中擷取出來,可以用來說明各種交配情形會產生的後果。總共 444,451隻受檢驗的後代,他們的雙親都有髖關節結構的評分。當種公種母在髖關節的評分由極佳(excellent)降到發育不全(dysplastic),生出CHD後代的百分比也會隨之增加。在Reed於2000年發表的研究論文中,也報告了相同的結果。
Reed AL, et al: Effect of Dam and Sire Qualitative Hip Conformation Scores on Progeny Hip Conformation. JAVMA, 2000; 217: 675-680
2.繁殖雙親與祖父母都正常,而本身也正常的狗—這個準則利用了最接近的三個世代,所建立起來的垂直遺傳族譜(50%的遺傳貢獻來自於雙親,25%來自組父母,12.5%來自於曾祖父母)。
3. 只繁殖本身正常,且其兄弟姐妹有超過75%比率都是正常的犬隻—這個資訊通常不容易取得,因為大部分同胎的動物都會被賣作寵物,而且不會對非期望性狀做篩檢。所以繁殖者可以在飼主的購買合約中加入一些激勵條款,試圖去收集這些資訊。例如提供一些補助,讓寵物在做結?手術的同時,也能對髖關節作X光顯影的初步檢查。
4. 挑選一隻在紀錄上,生出正常後代的比率,比品種平均還要高的狗來做繁殖—如果在有辦法了解的狀況下,比較不同個體在繁殖後代上的表現,將是一個重要的繁殖準則。舉個例子,在選擇種狗時,一隻可以生下 90%正常後代的狗,是遠遠優於另一隻只能生下 50%正常後代的狗的。
5. 選擇超越品種平均的動物,來取代原本進行繁殖的動物—要施加持續而穩定的篩選壓力,以確保整個品種的進步。簡單的說,要達成在繁殖機制上的目標,必須倚賴我們在推測動物繁殖價值上的能力。利用OFA網站上的搜尋選項,可以幫助繁殖者獲得重要的資訊,進而達成他們的目標。