74 RELATIONSHIP BETWEEN BLOOD METABOLITES AND LUTEAL FUNCTION WITH THE PREGNANCY OCCURRENCE IN DAIRY COWS

Abstract

Some studies suggest that concentrations of blood metabolic parameters are related to the progesterone (P4) concentrations and that they could be of potential use as predictors of fertility. Moreover, in dairy cows, P4 concentrations are modulated by several factors, including the metabolic status of the female. However, the potential interaction between blood metabolites and the neural-hormonal control of reproduction isn't well understood. Therefore, the objective of this study was to evaluate the relationship between plasma P4 concentrations, plasma concentrations of metabolic parameters (total cholesterol, total lipids, total protein and glucose) and pregnancy occurrence in dairy cows. Sixty-four Friesian cows (3–9 years) were followed for at least 21 days after insemination. The free-stall with total mixed ration system was used as the management system for those cows and the average 305-day milk yield was ∼8700 kg. Blood samples were collected daily from oestrus (Day 0) until Day 28. All cows were presented for pregnancy diagnosis by rectal palpation and ultrasound on Day 21 and 28. All data were analysed using the frequency procedure (SAS Institute Inc., Cary, NC, USA). Results indicated that overall pregnancy rate to first insemination was 56% [P < 0.05; pregnant cows (n = 36) and nonpregnant cows (n = 28)]. Plasma P4 levels of inseminated cows were only significantly different (P < 0.05) between pregnant (27.58 ± 0.82 ng mL^–1) and nonpregnant (22.11 ± 0.74 ng mL^–1) cows from Day 17 onward. Ultrasound measurement of the corpus luteum (CL; diameter and area) showed that CL sizes were not significantly different on Day 7 and 14 (or Day 21 in pregnant cows). However, plasma P4 levels were significantly higher (P < 0.05) on Day 14 (7.33 ± 0.20 ng mL^–1) than on Day 7 (4.45 ± 0.15 ng mL^–1) and, in pregnant cows, on Day 21 (8.06 ± 0.29 ng mL^–1) than on Day 14 (7.43 ± 0.23 ng mL^–1). Also, plasma concentrations of metabolic parameters from Day 0 to Day 16 were not predictive of pregnancy outcome. However, plasma concentrations of total cholesterol were significantly lower (P < 0.05) in pregnant (3.3 ± 0.42 g L^–1) than nonpregnant (4.8 ± 0.60 g L^–1) cows from Day 17 onwards, suggesting that increasing P4 levels in pregnant cows might decrease the levels of total cholesterol in pregnant cows from Day 17 onward. However, the mechanisms of these processes needs more study. In contrast, no significant differences were found between the pregnant and nonpregnant cows from Day 17 onward with respect to the plasma concentration of total lipids, total protein and glucose. Furthermore, the correlation coefficients between the blood metabolites and plasma concentration of the P4 were insignificant except for the negative correlation coefficient (r = –0.36, P < 0.01) between the plasma concentrations of total cholesterol and peripheral P4 levels. In conclusion, the results of this study suggest that morphological and functional developments of the CL are partially independent events. In addition, plasma concentrations of total cholesterol may be used concurrently with P4 levels from Day 17 after breeding as indicators of pregnancy in dairy cows.