Other Factors

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Dairy farmers continue to make additional genetic improvement by culling within the herd. Herd replacements often allow a turnover of about 30% of milking animals per year. Some culling decisions are under the manager's voluntary control, but others may be driven by fitness traits that limit the animal's ability to remain profitable and stay in the herd. A cow must be capable of timely pregnancies so that a new lactation can begin and

Table 1 Relative emphasis of traits in selection indexes from countries with large Holstein populations

Country (index)

Table 1 Relative emphasis of traits in selection indexes from countries with large Holstein populations

Country (index)

Australia

Canada

Denmark

France

Germany

Italy

Netherlands

New Zealand

Spain

Sweden

United Kingdom

United Sta

Trait

(APR)

(LPI)

(S-I)

(ISU)

(RZG)

(PFT)

(DPS)

(BW)

(ICO)

(TMI)

(PLI)

(NMS)

Protein

36

43

21

35

36

42

35

34

32

21

57

33

Fat

12

14

10

10

9

12

8

13

12

4

11

22

Milk

-19

-3

-14

-17

12

-4

-19

Protein (%)

2

4

3

3

Fat (%)

2

1

2

Longevity

9

8

6

13

25

8

12

8

3

6

15

11

Somatic cell

5

3

15

13

5

10

11

3

12

-9

score (mastitis)

Fertility

8

9

13

1

7

10

10

7

Other diseases

2

3

Udder traits

17

9

8

6

13

16

12

7

Feet and legs

11

5

1

4

6

3

10

9

4

Size

-4

4

2

2

2

-18

-3

Dairy character

2

Rump

1

1

Final score

2

4

9

Calving traits

6

4

10

12

-4

Growth (meat)

4

6

Temperament

4

2

3

Milking speed

3

<1

6

(Source'. VanRaden, P M; Animal Improvement Programs Laboratory, Agricultural Research Service, U S Department of Agriculture, Beltsville, MD; 2003 )

(Source'. VanRaden, P M; Animal Improvement Programs Laboratory, Agricultural Research Service, U S Department of Agriculture, Beltsville, MD; 2003 )

must remain free of chronic diseases and conditions such as mastitis and lameness so that lactation can be maintained.

Supplemental breeding techniques also can help to increase genetic gains. Embryo transfer has increased the number of offspring possible from individual cows and helped to assure that potential bull dams will produce a son. Nucleus herds allow direct comparison of elite females, but they have had limited use as an alternative to traditional AI progeny testing. Cloning technologies (embryo splitting, nuclear transfer, and adult cloning) also can produce some genetic gains, but their commercial use has been limited because of cost.[4] Use of sexed semen to produce offspring of a desired gender is possible, but reduced conception rates and higher production costs may limit widespread use. Producing more females would allow a farmer to increase within-herd genetic gains.

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