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Cross breeding in Dairy Cattle (Cross-breeding systems (DairyCo breeding:…
Cross breeding in Dairy Cattle
Why the need for cross breeding?
Most dairy cattle in the UK are pure breed with the majority being black and whites
These breeds have extensive problems which are worsening, the level of cows culled by there 4th lactation has increased dramatically over the last 50 years
Moves towards breeding based on £PLI has improved the situation slightly but not by significant amounts
Levels of imbreeding in holsteins are a problen- 2004 cattle where 3% inbred with the rate increasing at 0.17% per year
A 1% increase in inbreeding can depress milk yield by 10-30kg, as well as alter fat and protein yields and effect calving interval
Recomended to avoid mating if inbreeding (F) will be more than 6%
inbreeding depression builds up deleterious recessive genes reducing overall fitness of the animal
Cross-breeding can introduce new desirable genes, has the benefit of heterosis, avoids inbreeding depression as well as increasing the genetic pool from which bulls can be selected
Heterosis = Better than the average of the parents
Cross-breeding systems
Two breed rotational cross - Heterosis of offspring stabilises in the high 60s by the 5th cross
This is realistically not high enough to be worth the loss in production
Three breed rotational cross - Heterosis stabilises at high 86 after 7 generations
Ideal cross-breeding system
Four breed rotational cross - Heterosis stabilises at 94%
This would improve animals but is not realistic as a system due to difficulties managing crosses and limited breeds that work well together/are genetically different enough - would most likely have to rely on breeds not widely available in the UK therefore adding the extra cost of importing semen
DairyCo breeding: Recommended breeds
High input system= Holstein, Swedish Red, Montbeliarde
Low input Systems = Holstein, Jersey, Normande
Benefits of Crossbreeding
Most notable effects on health parameters and sometimes reproductive traits
Effects on production limited
When cross breeding milk yield is always lower than if a pure bred Holstein was used
Is some evidence to suggest that cumulative milk yield is higher in cross breeds
Can have positive effects on milk fat and protein yields
Main benefit is in the longevity of the cows, Genus report that 49% of HX swedish red cattle survive to 4th calving compared to 34% of pure breed Holsteins.
Studies have also shown reduction in cumulative somatic cell counts
Norwegian red crosses shown to be significantly better when fertility traits are considered
This has also been seen in Jersey crosses,
Expected F1 Heterosis: Danish data
Production traits - 3%
Fertility - 10%
Calving ease maternal - 10-15%
Longevity - 10 to 15%
Establishing a Cross breeding programme
Cross breeding is a long term commitment, requiring a set plan. Selection of breeds is important, there needs to be a large number of high quality bulls that have been genetically tested, the breeds need to be genetically different enough.
Also must consider the variability of the herd. Cross breeding can produce many different animals, considerations for differing sizes and needs must be made