[Some aspects of fertility following artificial insemination and natural service in dairy cattle (author's transl)].
The difference between the non-return percentage (60-90 days) following 17,086 first inseminations and that after 9,776 first matings in Dutch-Friesian cattle was studied in a random sample of the Netherlands Herd Book records in 1969. The effects of the following factors on this difference in the cases studied are discussed: -- age of bulls and cows, -- frequency of natural service and artificial insemination during each oestrus, -- use of deep-frozen semem --housing and grazing periods. The difference having been corrected for these factors, it was estimated at not more than 9 per cent of non-return 60-90 days in favour of natural service.