Crossbreeding
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Heterosis: superiority of the crossbred compared to the average of the parents (not necessarily superior to the best parent). Caused by fewer individuals with homozygous recessive alleles.
- Level of (%) heterosis: [(XB - PB)/PB]*100
- Example: Suffolk x Hampshire lambs grow at 0.85 lb/day compared to 0.82 for Suffolks and 0.78 for Hampshires. Then, heterosis for growth rate is
100*[0.85-0.5*(0.82+0.78)]/[0.5(0.82+0.78)] = 6.25%.
Average heterosis effects (from the SPH from the review of Nitter, G. 1978. Breed utilization for meat production in sheep. Animal Breeding Abstracts 46:131-143:
Trait |
Level of heterosis in the crossbred lamb |
Level of heterosis in the crossbred ewe, % |
Conception rate/Fertility |
2.6 |
8.7 |
Prolificacy |
3.2 |
|
Preweaning daily gain |
5.3 |
|
Postweaning daily gain |
6.6 |
|
Yearling weight/Body weight |
5.2 |
5.0 |
Fleece weight |
5.0 |
|
Birth weight/Lamb birth weight |
3.2 |
5.1 |
Weaning weight/Lamb weaning weight |
5 |
6.3 |
Carcass traits |
0 ? |
|
Lamb survival from birth to weaning |
9.8 ? |
2.7 |
Lambs born per ewe exposed to the ram |
5.3 |
11.5 |
Lambs reared per ewe exposed to the ram |
15.2 (?) |
14.7 |
Weight of lamb weaned per ewe exposed |
17.8 |
18.0 |
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