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The aim of this study was to analyse the influence of fixed effects on somatic cell score (SCS) in Swiss dairy production. Monthly milk recording results were investigated against the background of changing housing conditions from tie-stall barns to loose housing systems. Zone, housing system and calving age within lactation number had a significant effect on SCS, as well as the covariables milk yield per day, fat and protein percentage and days in milk. Highest SCS was observed in cows of valley situated farms. Concerning housing system, best values were recorded in tie-stall barns (2.53). SCS was 0.08 higher during the changing period (2.61), and 0.12 higher in loose housing systems (2.65). SCS increased continuously with lactation number, but the differences between the age classes within lactation number were not significant. The lactation curves for SCS resembled inverted milk yield curves and were different between the first lactation on the one hand and higher lactations on the other hand.

Abstract. The study was conducted to investigate the influence of systematic effects on fertility traits in Swiss Brown cows. Days to first service (DFS), days open (DO), calving interval (CI), non-return rate 90 (NRR90), and conception rate to first service (CRFS) were analysed. The data set included records from 82,755 cows out of 1,674 farms in Eastern and Central Switzerland. The observation period lasted from January 1988 to May 2002. Housing system, lactation number, region, zone, calving/insemination season, (all fixed), and 305-day milk yield (covariable) were tested significant at a level of p < 0.05. The random effect of herd*year accounted for between 5.2 and 16.9 % of the total variance. Improved fertility results were consistently investigated in loose housing systems. DFS (67.8 vs. 71.0 days), DO (86.3 vs. 96.0), and CI (378.7 vs. 386.7) were shorter, NRR90 (66 vs. 61 %) and CRFS (52 vs. 44 %) were higher in loose housing systems compared to tie-stall barns. Cows in the first lactation had longer time intervals and lower success rates compared to cows in the second and third lactation. In higher lactation numbers, the reproductive performance consistently decreased. Cows in Eastern Switzerland had the first service 1 day later (69.7 vs. 68.8) compared to animals in Central Switzerland, otherwise the time intervals (DFS –0.9 days; CI –0.8 days) as well as the success rates (NRR90 +3 %; FSCR +4 %) were better. NRR90 and FSCR were highest in the insemination season from April to June (67 and 52 %, resp.). FSCR was lowest from January to March (48 %) and NRR90 had the lowest values from October to December (60 %).