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OFA系列文章~OFA與繁殖者 

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OFA系列文章~OFA與繁殖者

文章泡泡拔 » 2007-02-08, 12:50

Breeders and the OFA 繁殖者與OFA
________________________________________

Progress in hip joint phenotype of dogs in the United States between the 1970's and early 1990's
has been shown through results of a retrospective study using the OFA data base. This improvement
was evident as an increase in the percentage of dogs classified as having excellent hip joint phenotype
and a decrease in the percentage of dogs classified as having hip dysplasia (HD). The increase in
percentage of dogs classified as having excellent hip joint phenotype was greater for German Shepherd
dogs, Golden Retrievers, Labrador Retrievers, and Rottweilers than for all dog breeds combined.
In addition, the submission screening rate for these four breeds was higher than the screening rate
for all dogs. Within these four breeds, the improvement was greatest for Rottweilers, which also had
the highest screening rate.


Overall, low screening rates for breeds found in this study offer some insight into the problems involved
with reducing the incidence of HD. The typical dog breeder is involved in breeding dogs for about five
years. Thus, informed, experienced breeders are continually replaced with uninformed, inexperienced
breeders who may not be as aware of the problems associated with HD or of the importance of participating
in a screening program. In addition, many breeders choose which dogs they breed on the basis of the
hip phenotype of individual dogs without knowledge of the phenotype of related dogs or previous offspring.
It can be very difficult to get hip information on siblings and previous offspring due to the overall low
number of dogs radiographed in a given litter (most dogs in a litter end up in pet homes). This is the slowest
method of reducing the incidence of an undesirable trait or increasing the incidence of a desirable trait.
The use of preliminary radiographs as early as 4 months of age can be used by breeders to add valuable
information on the hip status of dogs they choose to use in a breeding program.

What can breeders do? 繁殖者能作些什麼?
________________________________________

Hip dysplasia appears to be perpetuated by breeder imposed breeding practices, but when breeders and
their breed clubs recognize HD as a problem and establish reduction of HD as a priority, improvement of
the hip status can be accomplished without jeopardizing other desirable traits. Prospective buyers should
check pedigrees and/or verify health issues with the breeder. If suitable documentation is not available,
assume the worst until proven otherwise.


Do not ignore the dog with a fair hip evaluation. The dog is still within normal limits. For example; a dog
with fair hips but with a strong hip background and over 75% of its brothers and sisters being normal is a
good breeding prospect. A dog with excellent hips, but with a weak family background and less than 75%
of its brothers and sisters being normal is a poor breeding prospect.

OFA's Recommended Breeding Principals

OFA建議的繁殖原則

1.Breed normals to normals
2.Breed normals with normal ancestry
3.Breed normals from litters (brothers/sisters) with a low incidence of HD
4.Select a sire that produces a low incidence of HD
5.Replace dogs with dogs that are better than the breed average


繁殖者與OFA

回顧過去幾年來以OFA資料庫所做的研究結果,在1970年代到1990年代這段時間,
美國犬隻的髖關節表現型已經有很大的進步。這樣的改進可以由髖關節表現型獲得“excellent(極佳)”
等級之犬隻百分比的增加,與髖關節發育不全(HD)犬隻百分比的減少來獲得證明。相較於所有犬種
的綜合統計,德國狼犬、黃金拾獵犬、拉不拉多拾獵犬與洛威那,在“excellent(極佳)”犬隻百分
比的增加,有更明顯的躍進。附帶一提,這四個品種相較於其它所有犬種,有著更高的送檢率。在
這四個品種之中,羅威那的進步最為顯著,同時也是送檢率最高的犬種。


整體看來,在這個研究中發現,送檢率較低的犬種在降低HD發生率的工作上,潛在著一些問題。
典型的繁殖者參與繁殖工作的時間大約是五年,因此熟稔且經驗豐富的繁殖者,會持續被生疏且經驗
不足的繁殖者所取代,這些缺乏經驗的繁殖者可能會忽略HD的相關問題,也會忽視建立繁殖篩檢機
制的重要性。

此外,許多繁殖者依照個體的髖關節表現型來挑選適合繁殖的種犬時,卻沒有弄清楚血緣相關犬隻或
之前所生後代的髖關節表現型。因為接受X光篩檢的犬隻數目很少,所以要取得種犬兄弟姊妹或之前所
生後代(一胎幼犬裡大多數最終都會成為家庭寵物)的髖關節資訊,有可能是非常困難的。如果只依照
個體的髖關節狀態來挑選種犬,這將是最慢的方法,用來降低非期望性狀的發生率,或增加期望性狀的
發生率。繁殖者可以利用犬齡4個月時所做的X光初步篩檢,來為自己繁殖機制下所挑選的種犬,在髖關
節的狀態上增加有價值的資訊。

繁殖者能作些什麼?

對繁殖者來說,HD是一個長久不滅的問題,在繁殖上造成他們的負擔。但是當繁殖者與他們所屬的犬種
協會都肯正視HD是一個問題,並且以降低HD發生率為首要目標,那麼犬隻的髖關節狀態就會有所進步,
同時不會伴隨其它非期望性狀的發生。即將購買幼犬的飼主應該要檢查幼犬的族譜,並且與繁殖者確認健
康上的問題,如果沒有辦法提出適當的憑證與證明,請假設最壞的結果,直到繁殖者提出證明為止。


不要忽略得到“Fair(普通)”等級判定的犬隻,這個等級的狗仍然在正常的範圍內。舉個例子,一隻狗只獲
得“Fair(普通)”等級的判定,但是他有很好的血系背景,並且有超過75%的兄弟姊妹也都有正常的髖關節
,那麼我們仍然會預期這隻狗會有不錯的繁殖結果。如果一隻狗獲得“Excellent(極佳)”等級的判定,他是
他的血系背景很衰弱,兄弟姊妹正常的比例低於75%,那麼他的繁殖結果就不會太樂觀。


OFA建議的繁殖原則

1.繁殖正常的狗,以生出正常的狗
2.繁殖直系血親也都正常的狗
3.繁殖兄弟姊妹CHD發生率低的狗
4.挑選後代發生CHD機率低的種犬來做繁殖
5.挑選後代正常比例超越品種平均的狗,來取代原本進行繁殖的種犬


本文翻譯自http://www.offa.org/hipguide.html








--------------------------------------------------------------------------------------------------------------

關於繁殖建議,指導手冊裡有作詳細解釋,以下補上指導手冊所寫的部分!!


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
紮手術的同時,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。
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