SELECTION POSSIBILITIES FOR IMPROVEMENT O F FERTILITY IN CATTLE

Natural selection for fertility in cattle has taken place for centurie s and has reduced the genetic variation. Domestication has changed the natural reproductive cycle, adapting it to the feed supply. Modern bi otechnics (e.g. artificial insemination, embryo transfer) also have an influence on fertility, besides the selection for yield. The reproduc tive traits are heavily influenced by environmental factors and theref ore slow low heritabilities, ranging from 0.01 to 0.10. The herd has t he largest environmental effect, including fertility management, feedi ng and housing. Further systematic effects are the inseminator, the se ason, the parity and the age at first insemination. The length of the resting period between calving and first insemination is mainly determ ined by the farmer and has a pronounced negative effect before 50 days post partum. Despite of the low heritability for reproductive traits and the often mentioned opinion to ignore these in selection, newer me thods of sire evaluation could be used, making family selection possib le. From a selection point of view, the ability of the cow to conceive should be mainly considered, which is the maternal component of ferti lity. The joint estimation of the paternal and maternal fertility with an animal model give results for Al-bulls with accuracies of 40-70 pe rcent under normal testing schemes. Using the non-return results of pa ternal half sibs in connection with repeated own performances of the c ow result in accuracies of 20-25 percent, which could be applied for b ull dams. In the context of nucleus programs with maternal half sibs a nd progenies of the cow the accuracy could exceed 30 percent. The conn ection of data from artificial insemination, milk-recording and ancest ry records is a prerequisite for such an evaluation method, but this i s realised in most pacts of Germany. A computer-program was developed at the Bavarian State Institute with the financial support of the Fede ral Ministry of Agriculture, that will be used in the future for the c alculation of breeding values for the maternal and paternal NRR90 in a h parts of Germany. Fertility and milk production are antagonistic tra its and the increased selection for milk production leads to a decreas e in fertility. Signs for this effect can be observed in all breeds an d the development of the calving interval is reflecting this. In the f uture bulls with low fertility of their daughters should be used to a lower extent. Daughters and sons of these bulls should be avoided for the recruitment of the next bull generation. Finally fertility should be a part of a total index, which should be established for each breed according to the economic conditions. It should be granted, that even at the highest yield level the replacement of-the cows can take place .