Superovulation in Sheep: Number and Weight of the Corpora Lutea and Serum Progesterone

To determine similarities and differences between nonsuperovulated and superovulated ewe models, data collected from several experiments (1989 through 2005) were analyzed. Mature non-pregnant non-superovulated (n = 91) or superovulated (n = 299) Western range-type ewes were used for evaluation of luteal function. To induce superovulation, ewes were injected twice daily with FSH on days 13 to 15 of the estrous cycle. At corpora lutea (CL) collection on day 5 or 10 of the estrous cycle, the number of CL was determined. For selected ewes, the CL were weighed and blood samples were collected for determination of progesterone (P4) concentration in serum. Each year, a similar (P > 0.1) number of ovulations/ewe was induced by FSH treatment (range from 12.4 ± 2.0 to 20 ± 2.5/year). Superovulated ewes had greater (P < 0.001) number of CL than non-superovulated ewes (16.2 ± 0.5 vs. 1.9 ± 0.1). Weight of CL on day 5 of the estrous cycle was similar for superovulated and non-superovulated ewes (252.2 ± 4.1 vs. 224.7 ± 15.6 mg/CL), but on day 10, weight of CL from superovulated ewes was less (P < 0.05) than from non-superovulated ewes (379.9 ± 4.0 vs. 598.7 ± 18.5 mg/CL). Luteal tissue mass per ewe was greater (P < 0.001) for superovulated than non-superovulated ewes on days 5 (3.7 ± 0.4 vs. 0.5 ± 0.1 g) and 10 (6.1 ± 0.5 vs. 1.2 ± 0.1 g) of the estrous cycle. Serum P4 concentration on day 5 of the estrous cycle did not differ statistically (P > 0.1) for superovulated vs. non-superovulated ewes (2.3 ± 1.1 vs. 1.3 ± 0.1 ng/ml), but on day 10 tended to be greater (P < 0.06) in superovulated than non-superovulated ewes (5.8 ± 1.3 vs. 3.8 ± 0.3 ng/ml). When P4 concentration in serum was expressed per g of luteal tissue mass, values were similar for non-superovulated and superovulated ewes on days 5 and 10 of the estrous cycle. Moreover, all P4 values were greater (P < 0.05) on day 10 than on day 5 of the estrous cycle. Thus, despite some differences in CL number and CL weight, the major function of the CL, P4 production does not seem to be altered in superovulated ewes compared with non-superovulated ewes. Therefore, these data indicate that our superovulated ewe model may be used for studies of luteal function.