abstract
This study investigated differences between phenotypes of daughters of artificial insemination (AI)-bulls
and daughters of natural service (NS)-bulls, respectively, on organic dairy farms in Switzerland. Organic
rules recommend the use of natural mating. Therefore it is of interest whether those two groups of
phenotypes show different characteristics on organic farms. Only farms using both AI and NS with sires
of the same dairy breed as the inseminated cows were included in the study. First lactations of 594 cows
from 29 farms were analysed for daily milk yield (DMY), somatic cell score (SCS), and calving interval
(CI). Furthermore, veterinary treatments and fat/protein ratios 41.5 and o1.1 in milk samples during
the first 100 days of lactation indicating risks for metabolic disorders were investigated. General linear
models and-for binary variables-logistic regression models were calculated to explore differences in
health parameters and DMY. Service method (AI or NS) and DMY (except when DMY was the target
variable) were included in the models as fixed effects and farms as random effects. Distances between
farms where the bulls had been bred and farms where their daughters lived were calculated with a
common route planning tool. Additionally it was examined whether the bull's farm of origin was organic
or not. Dairy cows descending from NS-bulls showed a lower SCS and tended to have shorter CI and a
trend to lower DMY compared to cows descending from AI-bulls. No effects of service method on other
health parameters were found. Around 70% of NS-bulls and 26% of AI-bulls had been bred in the same
regions (o100 km distance) as their daughters. No NS-bull, but 35% of AI-bulls came from abroad
(Z300 km within Switzerland or from another country). 1.8% of AI-bulls and 30.8% of NS-bulls had been
bred on an organic farm. One explanation for the effects found in cows descending from NS-bulls might
lie in their better adaptation to local conditions. However, effects of the service method and the bull’s
environment of origin cannot be distinguished and it cannot be excluded that the chosen NS bulls had
incidentally higher genetic merits for CI and SCS than AI-bulls. Further research on differences between
NS- and AI-bulls and also on genotype x environment-interactions between organic and conventional
environments is necessary.