Decreased fertility with increasing parity in lactating dairy cows

Abstract

The relationships of parity and progesterone (P4) concentrations during the bred cycle with pregnancy rate (PR) were examined in this study. Breeding records of 163 Holstein heifers and cows (in 1st parity, 2nd parity, and 3rd or 4th parity) from the Uuniversity of British Columbia Dairy Education and Research Centre were used to compare PR among heifers, 1st, 2nd and 3rd/4th parity cows. Blood or milk samples collected from 10 animals of each treatment group were assayed to compare P4 concentrations among treatment groups. Statistical analysis showed that the heifers' first insemination PR (67.9%) was higher (P < 0.05) from 1st parity (42.9%), 2nd parity, (20.0%) and 3rd/4th parity cows (11.9%). P4 concentrations were not significantly different (P > 0.05). Key words: Pregnancy rate, progesterone, parity, cows, heifers