Influence of systematic effects on fertility traits in Swiss Brown cows

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 %).