The effects of inbreeding on service period and pregnancy length in Holsteins and Czech Fleckviehs after the first calving

Abstract. The effects of inbreeding level on service period (SP) and pregnancy length (PL) were monitored in Holstein and Czech Fleckvieh after the first calving. The levels of inbreeding (FX) ranged from 1.25 to 25 %. SP and PL of inbred cows were compared with their outbred equals – half-sisters, sharing the same sire (n = 1824) and their first calving happened in the same farm and at the same time (± 3 month). Database with the number of 631 810 animals (year of calving 1985–2004) was used for analyses. Inbred cows were grouped according to Fx coefficient (1.5-2.3 %; 3.0-5.0 %; 8.0-12.5 %; 25 %). The GLM with fixed effects (the breed, breeding value of the sire and monitored individual for milk production, year of calving, age at first calving) was applied to all data. The effect of inbreeding depression on SP was more pronounced at higher levels of inbreeding (+2.81; +3.35; +4.53; +8.23 d, respectively according to above mentioned Fx groups) but non-significant. Differences in PL (+0.3; +0.32; -0.08 and 1.68 d) were not significant either. Average value of PL for inbred animals was 0.43 d higher. The correlation coefficient was +0.023 for SP and +0.0658 for PL. The Fx coefficient increasing by 1 % extends the SP by 0.22 day and PL by 0.063 day. There was a higher variability of SP and PL in inbred cows. The length of calving interval between the first and second lactation is affected more by SP than PL.