Early development and function of the corpus luteum and relationship to pregnancy in the buffalo.

A detailed study on the structure and function of the CL in the Day-5 to Day-10 window of development, and relationship to the likelihood of pregnancy, was undertaken in Italian Mediterranean buffaloes. In experiment 1, buffaloes underwent synchronization of estrus and fixed-time artificial insemination (n = 23). Features of the CL were measured from Days 5 to 10 after fixed-time artificial insemination, and pregnancy was confirmed on Day 70. Buffaloes that established a pregnancy (n = 14) had a larger CL area (1.31 ± 0.1 vs. 1.09 ± 0.1 cm(2); P < 0.01) and greater progesterone (P4) concentrations (1.90 ± 0.1 vs. 1.48 ± 0.1 ng/mL; P < 0.01) during Days 5 to 10 compared with nonpregnant buffaloes. In the same period, blood flow measured as time average medium velocity tended to be greater (P = 0.059) in buffaloes that were subsequently pregnant versus nonpregnant buffaloes (10.8 ± 0.8 vs. 8.4 ± 0.9). There was a relationship (R(2) = 0.136; P < 0.05) between CL area, P4, and time average medium velocity from Days 5 to 10. Logistic regression analysis showed that P4 concentration on Day 10 had a significant influence on pregnancy (odds ratio, 19.337; P < 0.01). In experiment 2, highly vascularized CLs (HVCLs, n = 3) and lowly vascularized CLs (LVCLs, n = 3) on Day 5 were examined by contrast-enhanced ultrasonography and then subjected to histologic investigation. Blood flow was greater in HVCLs than in LVCLs. Highly vascularized CLs showed intense staining for factor VIII and had many small, irregular-shaped blood vessels, whereas LVCLs had low factor VIII staining and relatively few large, regular-shaped vessels. Luteal cell expression of vascular EGF was greater for HVCLs compared with LVCLs. The study has shown that greater development and function of the CL from as early as Day 5 is related to an increased likelihood of pregnancy in the buffalo. Corpus lutea that show early development at Day 5 have greater expression of vascular EGF and factor VIII, increased vascularization, and higher blood flow.