Relationship between return to oestrus, luteal function and metabolic indicators in dairy cows.

Introduction: Many factors may disturb oocyte fertilization and embryonic development giving rise to return to oestrus. Among these factors, CL function at the time of embryo implantation has a major role, and luteal activity can be affected by nutritional and metabolic conditions. In this study, we investigated the relationship between AI outcome, CL activity and plasma metabolic indicators from AI to the time of expected embryo implantation. Methods: Whey progesterone measured every 3-4 days by RIA was used to study the ovarian cycle characteristics in 33 dairy cows from day 15 post-partum to pregnancy diagnosis performed at day 30-35 after each AI. Animals were monitored until they became pregnant or for at least three consecutive AI. The whole observation period lasted seven months. Plasma progesterone, urea, cholesterol, triglycerides, NEFA, βOH-butyrate and glucose were measured in samples taken at AI and 7, 14 and 21 days after AI. Result and discussion: 66.7% of cows became pregnant within 3 AI, 18.2% did not become pregnant within 3 AI and 15.1% did not become pregnant within the observation period. Mean plasma NEFA at the time of the first AI were at basal levels suggesting that cows were inseminated once overcome the period of negative energy balance. Plasma progesterone was significantly lower on day 14 in AI with negative outcome (5,11  0,68 vs 7,42  0,69 ng/ml; P<0,05). Negative AI were classified according to ovarian cycle length subsequent the AI (Physiological, N=11, 22,0  0,6 days; Long, N=14, 34,8  3,0 days). Plasma progesterone was significantly lower (P<0,05) after negative AI followed by a Physiological cycle only on day 21. Triglycerides and cholesterol were slightly but significantly higher in negative AI (P<0,01). These differences may imply the presence of metabolic signals affecting CL activity and/or embryo survival.