Epsilon Archive for Student Projects

Abstract

Fertility and production traits of SRB and SLB cows in Swedish organic and conventional dairy production were compared in this study. Data were collected from the Swedish milk-recording system and the Swedish certification organization for organic production (KRAV). In the study 794 092 cow lactation records between year 1997 and 2002 were used. Four fertility measures were defined: number of days between calving and last insemination (cli), number of days between calving and first insemination (cfi), number of days between first and last insemination (fli) and number of inseminations per service period (nins). Three production measures were defined: 305-days milk yield (milk), fat yield (fat) and protein yield (prot). Only records from the first lactation were used. The most complete model included the effects of production system, year of lactation, herd-year size, season and milk yield as well as the two-way interactions between system and all main effects. In addition to that also the two-way interaction between year of lactation and herd-year size was analyzed. Without adjustment for milk yield in the model, both breeds had better fertility in organic production. However, when milk yield was included, only SLB had better fertility in organic production while SRB had better fertility in conventional production. The general trend over time showed that SLB has a deteriorating fertility and that fertility for both breeds was better in larger herds. The fertility deteriorates as the milk yield increases, this was a general trend except for the first milk class which deviated from the rest of the classes. There was no interaction between the effect of season and system on fertility. Cows calving in July-August were found to have best fertility, measured as calving to last insemination.