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Norwegian Red x Holstein crossbreds in Holland. - Photo: Elly Geverink
Line of Norwegian Red x Holstein crossbreds in Holland. Photo: Elly Geverink
10.11.11

Heterosis in dairy production

Heterosis is a bonus that dairy crossbreeding producers can expect in addition to the positive effects of individual genes obtained by using top A.I. bulls within a breed.

 

The bonus from heterosis should be about 5% for production and at least 10% for mortality, fertility, health, and survival. Heterosis comes on top of the average genetic level of the 2 parent breeds. Therefore, the impact of heterosis on profit should be substantial for commercial dairy producers.

 

Inbreeding

The global Holstein population has become more inbred over time. Inbreeding is increasing at about 0.1% per year in the Holstein breed. This is causing increased inbreeding depression, especially for mortality, cow fertility, cow health, and survival. As relationships between individuals rise, it becomes more and more likely that bulls and cows that are mated to each other will be closely related. Inbreeding robs dairy producers of income by increasing stillbirths, reducing cow fertility, reducing disease resistance, and shortening herd life. Reducing cow fertility should be a major negative consequence of inbreeding, because highly inbred embryos are not as viable.

 

Why crossbreeding?

Concerns about inbreeding are eliminated with crossbreeding. The effects of heterosis are the opposite of the effects of inbreeding depression. Old research has indicated that heterosis is greatest for traits related to mortality, fertility, health, and survival. Commercial pig, beef cattle, and sheep production have relied on crossbreeding to improve mortality, fertility, growth, and disease resistance for the last 50 years! 

 

Number of breeds to use in dairy crossbreeding systems

Extent of heterosis realized from crossbreeding systems differs based on the number of breeds included in the rotation. Table 1 reviews the extent of heterosis for each generation in crossbreeding systems that include 2, 3, or 4 unrelated breeds.

 

Table 1. Heterosis by generation for crossbreeding using 2, 3, and 4 unrelated breeds.

 

Generation

2 breeds

3 breeds

4 breeds

 

 

 

%

%

%

 

 

1

100

100

100

 

 

2

50

100

100

 

 

3

75

  75

100

 

 

4

63

  88

  88

 

 

5

69

  88

  94

 

 

6

66

  84

  94

 

 

7

67

  86

  94

 

 

8

67

  86

  93

 

 

9

67

  86

  93

 

 

 

 

Generally speaking, finding more than 3 breeds that are especially well-suited for a specific environment or management system might be difficult. 

 

Practical system for crossbreeding

TWOPLUS™ is a rotational crossbreeding system using two breeds, whereby for instance the Holstein and the NRF breeds are used alternately to produce the next generation. Thus, F1 heifers from NRF sires should be mated to purebred Holstein bulls; their progeny to NRF; the progeny of those to Holstein; and so on.

 

Crossbreeding systems using three breeds do not need to be confusing:  When 3 breeds are used in a simple 3-breed rotation, a color tagging system could eliminate the need for paper or electronic records for choosing service sire breed. Calves sired by breed "A" are tagged with a blue tag, calves sired by breed "B" are tagged with a yellow tag, and calves sired by breed "C" are tagged with an orange tag. Then, whenever employees see a blue tag, they know that semen from breed "B" goes in that heifer or cow, and calves from that heifer or cow are sired by breed "B". Similarly, whenever employees see a yellow tag, they breed the animal with semen from breed "C", and calves from that animal are sired by breed "C". Finally, animals with orange tags are always bred to semen from breed "A", and all calves from those animals are sired by breed "A". This is an extremely simple mating and identification system, and it is much simpler than calculating inbreeding coefficients at the time of mating, which is essential when using only same-breed matings.

 

Norwegian red x Holstein in Italy.         Photo: Elly Geverink 

 

Use highly ranked progeny tested bulls

Crossbreeding should be regarded as a mating system that complements genetic improvement within breeds. Continuous use of progeny-tested and highly-ranked A.I. bulls is critical to genetic improvement regardless of mating system (purebreeding or crossbreeding). Unfortunately, some dairy producers might interpret the merit of crossbreeding as justification to use natural service, “different-breed” bulls rather than A.I. That would be an unfortunate consequence of dairy producers’ interest in crossbreeding and will result in low merit offspring a majority of the time.

 

Crossbreeding program

Dairy crossbreeding systems should make use of the number of breeds optimal for conditions at each specific dairy operation. Every dairy farmer should make a plan and choose a crossbreeding system that suits their facilities, climate, milk market, nutritional regime and level of management.

 
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