2012 KULIAH pkh 8dan 9 SELEKSI animal breed manaj

(1)

Genetics and Breeding:

Konsep Dasar, Interval generasi

dan Respon

Seleksi

(2)

PENGERTIAN DASAR SELEKSI

DEFINISI SELEKSI :

1.Perbaikan mutu genetik ternak melalui perubahan rata-rata fenotip populasi agar lebih menguntungkan secara ekonomis

2. Memilih ternak untuk bibit pada generasi berikutnya

CARA :

1. Eksploitasi variabilitas genetik/fenotip Antar bangsa/populasi

Dalam bangsa /populasi

TAHAPAN:

1. Pemilihan/penentuan tujuan 2. 2. Pemilihan metode seleksi

TUJUAN :

(3)

DASAR SELEKSI: INFORMASI

PERFORMANS

• Individual selection:

selection of individuals based on their

own phenotypic values (also called mass selection).

• Family selection:

whole families are selected or rejected

based according to the phenotypic mean of the family (we

select the family with the largest mean). This method is

preferred when the heritability of the trait is low. But the

efficacy of this method is reduced when the environmental

variation common to the members of the same family is large.

• Sib-selection and progeny testing are family-selection

methods.

(4)

Seleksi berdasar Sumber Informasi

:

1. Seleksi individu: catatan individu ybs untuk evaluasi ybs - pada sapi perah/potong : kurang tepat meramal produksi

(perlu h2 _{tinggi untuk seleksi efektif)} - estimasi produksi individu : dasar NILAI PEMULIAAN (NP)

NP : h2 (₍_{Performan Indv-} _{Rata-rata Performans Pop)} 2. Seleksi pedegree (silsilah):

dasar catatan tetua/nenek moyang

dipengaruhi derajat inbreeding (jauh dekat kekerabatannya

3. Uji Kolateral:

Berdasarkan catatan anggota keluarga Ketepatan tergantung h2, Ripitabilitas.

(5)

Selection Response

• Selection response is the expected rate genetic change (genetic progress or

improvement) which results from selection.

• The effectiveness of selection is measured by the rate of genetic change

achieved.

• Selection intensity (

i

)

is the selection differential

expressed in standard deviations.

• Selection differential (S):

the difference between the

mean selection criterion of selected animals and the

mean selection criterion of all potential parents.

(6)

(7)

(8)

(9)

(10)

With phenotypic selection (individual selection or

mass selection) the formula for selection response

can be expressed as:

L

S

h

L

i

h

L

hi

G

A

P

2

2 







(11)

Generation Interval

• Generation interval is the amount of time

required to replace one generation with the next.

• More practical definition:

the average age of

parents when their offspring are born.

• (rataan umur tetua pada saat anak-anak lahir,

kelahiran 1,2,3, dst

)

(12)

Average generation interval

Species

Male

Female

Cattle

3 to 4

4.5 to 6

Sheep

2 to 3

4 to 4.5

Swine

1.5 to 2

1.5 to 3

Horses

8 to 12

Chickens

1 to 1.5

.

lahir kawin beranak

1 2 12 bln 1 bln

(13)

Selection intensity, generation interval and the additive variance may

differ between males and females.

(14)

EXAMPLE 1:

Suppose we select for six-month weight in lambs based on phenotypic values. If the average of all candidates for selection is 32 kg, the phenotypic standard deviation is 4 kg, the generation interval in sheep is three years and the heritability of six-month weight is 0.40, suppose also that the average of selected parents is 42 kg. Find: 1. The intensity of selection

2. The expected selection response per year.

Solution:

(15)

EXAMPLE 2:

Phenotypic selection for yearling weight in beef cattle.

Bulls: keep the top 3% Cows: keep the top 50%

Suppose heritability is 0.40, generation interval is 5 years for bulls and 6.5 years for cows and the additive genetic variance is 1225 in both sexes. Find the expected selection response per year.

year

(16)

Example:

suppose we are selecting dairy bulls for improving

milk yield using progeny testing and we are using the top 5% of

bulls with average accuracy of 0.90. What is the expected genetic

change in fat% given that the genetic correlation between milk

yield and fat% is

–

0.50, the heritability of fat% is 0.50 and the

phenotypic variance for fat% is 0.80. Suppose also that the

generation interval is 6 years.

(17)

Selection for multiple traits

• So far we have dealt with selection for a single

traits. However, in practice we may want to

improve several traits.

• There are three methods of selection for multiple

traits:

1. Tandem selection

2. Independent culling levels

(18)

METODE SELEKSI

:

1. Tandem : secara berurutan

cara : 1 sifat selesai diteruskan sifat kedua waktu yang diperlukan panjang

untuk sifat yang tidak berkorelasi positif

2. Independen Culling Level:

ditentukan batas produksi tertentu, jika kurang dari batas minimal maka dilakukan culling/afkir

kekurangan: tidak ada kompensasi untuk sifat-2 yang unggul

3. Indeks : metode terbaik

menghitung indeks beberapa sifat yang diseleksi perlu banyak data

(19)

Tandem Selection

• In this method we begin by selection for one trait,

after several years we start selecting for the second

trait and so forth until the desired level of

improvement is reached .

• This method is not efficient:

- it takes long time

- if unfavorable genetic correlations exist between

(20)

Independent culling levels

• A standard (a culling level) is set for each trait.

• Selected animals should meet the standard for each

trait.

• Any animal which does not meet the standard of any

one of the traits is culled even if it is excellent for one

or more of the traits.

(21)

Selection Index

• Combines information on several traits in a

single index using weighting factors.

n n

P

b

P

b

P

b

I



₁ ₁



₂ ₂



...



Where :

- b₁, …………,bn are weighting factors (partial regression coefficients) - P₁: information on trait 1

. . .

(22)

Advantages

• More efficient than tandem selection and independent

culling methods.

• It takes into account the genetic correlations between

traits.

• It takes into account the economic value for each

trait.

(23)

Kemajuan Genetik Karena seleksi

berdasarkan nilai intensitas seleksi

Contoh: Sapi

Populasi sapi lahir/thn = 8000 ekor, sex rasio 1 : 1 Jika diseleksi (kawin alam ) = 3000 pejantan

Proporsi terseleksi = 3000/4000 = 0,7 Intensitas seleksi (i =tabel) = 0.42

Atau (program breeding), diseleksi 1000 pejantan Proporsi terseleksi = 1000/4000 = 0.25 Intensitas seleksi (i =tabel) = 1. 271

Jika dg IB, misalnya hanya perlu 4 pejantan Proporsi terseleksi = 4/4000 = 0.001 Intensitas seleksi ( i =tabel) = 3.37

(24)

Progres genetik :Hubungan Seleksi dengan nilai H

dan h

2

Reproduksi

Pertumbuhan Karkas

1. h2 _{(heritabilitas)} _{Jelek (0.0}–

Progres genetik (seleksi)

Rendah Sedang Tinggi

2. H (efek heterosis) Tinggi ( 10 – 20 %)

Sedang ( 5 – 8 %)

0 %

Perbaikan genetik (persilangan)

Tinggi Sedang 0

Catatan:

1. Progress genetik =h2 _{x DS}

2. Respon seleksi = R = ih2DS