Validation of blood vitamin A concentrations in cattle: comparison of a new cow-side test (iCheck™ FLUORO) with high-performance liquid chromatography (HPLC)

Background: Plasma concentration of retinol is an accepted indicator to assess the vitamin A (retinol) status in cattle. However, the determination of vitamin A requires a time consuming multi-step procedure, which needs specific equipment to perform extraction, centrifugation or saponification prior to high-performance liquid chromatography (HPLC). Methods: The concentrations of retinol in whole blood (n = 10), plasma (n = 132) and serum (n = 61) were measured by a new rapid cow-side test (iCheck™ FLUORO) and compared with those by HPLC in two independent laboratories in Germany (DE) and Japan (JP). Results: Retinol concentrations in plasma ranged from 0.033 to 0.532 mg/L, and in serum from 0.043 to 0.360 mg/L (HPLC method). No significant differences in retinol levels were observed between the new rapid cow-side test and HPLC performed in different laboratories (HPLC vs. iCheck™ FLUORO: 0.320 ± 0.047 mg/L vs. 0.333 ± 0.044 mg/L, and 0.240 ± 0.096 mg/L vs. 0.241 ± 0.069 mg/L, lab DE and lab JP, respectively). A similar comparability was observed when whole blood was used (HPLC vs. iCheck™ FLUORO: 0.353 ± 0.084 mg/L vs. 0.341 ± 0.064 mg/L). Results showed a good agreement between both methods based on correlation coefficients of r2 = 0.87 (P < 0.001) and Bland-Altman blots revealed no significant bias for all comparison. Conclusions: With the new rapid cow-side test (iCheck™ FLUORO) retinol concentrations in cattle can be reliably assessed within a few minutes and directly in the barn using even whole blood without the necessity of prior centrifugation. The ease of the application of the new rapid cow-side test and its portability can improve the diagnostic of vitamin A status and will help to control vitamin A supplementation in specific vitamin A feeding regimes such as used to optimize health status in calves or meat marbling in Japanese Black cattle

FOXL2 is a new progesterone-regulated gene in the endometrium

In mammals, mutual actions of estrogens and progesterone on their uterine receptors are essential for endometrium receptivity and conceptus implantation. In cattle we showed that FOXL2 -a key gene for ovarian differentiation and maintenance- is expressed and regulated in endometrium during oestrous cycle, a finding confirmed in murine and human endometrium. The present study aims to determine if FOXL2 is a progesterone-target gene in the bovine endometrium. Using various experimenta models in cattle, our results indicated (i) a negative correlation between FOXL2 gene expression and progesterone (P4) blood levels (ii) a significant reduction of FOXL2 transcript level in ovariectomized cows supplemented with P4 for 6 days (2.2-fold vs. control ovariectomized cows, P < 0.05) (iii) a significant decrease in FOXL2 mRNA level in bovine endometrial explants incubated with P4 (10-5 M) for 48h (2.4-fold vs. control explants, P < 0.05). No impact of oestradiol on FOXL2 gene expression was detected in these conditions. In order to confirm the regulation of FOXL2 promoter by P4, COS7 cells were transfected with a caprine FOXL2 reporter gene and progesterone receptor (PR) A or B expression vectors. In the presence of PRA and PRB, P4 (10-7 M) stimulated the activity of FOXL2 promoter (2.8-fold). Mutation of the P4 Response Element (PRE) in the caprine FOXL2 promoter abrogated the activity of this promoter in P4-treated COS7 cells overexpressing PRA/PRB. Collectively, our data show that reduced FOXL2 expression in the endometrium during the luteal phase results from the down-regulation of PRA/B known to occur in the presence of P4. Determining the biological actions of FOXL2 will be mandatory to define the contribution of this transcription factor in the regulation of sensor and driver properties of the endometrium