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VikingNews AU 2019-2
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the main point in
cross
breeding is to get all the good traits and lose the bad undesired ones! two-way or three-way rotation? the simplest model of rotational crossbreeding is the two-way cross where two different breeds are crossed. the next generation
is called f1 and if the offspring from this cross is mated back to one of the original breeds, this is called a backcross . the highest level of heterosis
is always in the first generation and the level decreases in following generations. when f1 cows are backcrossed, in generation f2 the heterosis is halved compared to the level in the f1. the heterosis rises again in the f3 generation but then levels to 67% in few generations. below you can see an example of a holstein and jersey cross and the development of heterosis level in different generations. the three-breed crossing can be seen as the optimal crossbreeding system as the heterosis stays higher than in two-way crossbreeding. with four-way crossbreeding even higher heterosis can be achieved but maintaining the correct rotation gets more complicated and it?s harder to find breeds that complement each other well and are unrelated populations. therefore, the four-way cross- breeding is not recommended. in three-way crossbreeding the first generation is also called f1, but instead of start- ing the backcrossing with the cows, the cows are mated to a third breed. the heterosis stays at 100% for the first two generations, but then drops when the first backcrossing is made to one of the original breeds in f3 generation. after a few generations the heterosis level steadies at 86%. be- low you can see an example of a goldencross cross and the development of heterosis level in different genera- tions. two-way cross three-way cross 0 20 40 60 80 100 f8 f7 f6 f5 f4 f3 f2 f1 100% 50% 75% 63% 69% 66% 67% 66% 0 20 40 60 80 100 f8 f7 f6 f5 f4 f3 f2 f1 100% 100% 75% 88% 88% 84% 86% 86% 100% heterosis 50% heterosis 75% heterosis ~67% heterosis vikingjersey viking holstein vikingjersey f1 f2 f3 f4 viking holstein 100% heterosis 100% heterosis 75% heterosis ~86% heterosis vikingred vikingjersey viking holstein vikingjersey f1 f2 f3 f4 9 september 2019 | vikingnews
cows-cross-goldencross-10.html