Browse by author
Lookup NU author(s): Dr Andrew Beard
Full text for this publication is not currently held within this repository. Alternative links are provided below where available.
Development and demise of luteal structures were monitored using daily transrectal ultrasonography in 2 breeds of sheep differing in ovulation rates (nonprolific Western white-faced cross-bred, n=12 and prolific pure-bred Finn sheep, n=7), during 1 estrous cycle in the mid-breeding season. Jugular blood samples were collected once a day for radioimmunoassay (RIA) of progesterone. The mean diameter of ovulatory follicles was higher in Western white-faced than in Finn ewes (6.4 ± 0.2 and 5.3 ± 0.2 mm, respectively; P<0.001). The mean volume of luteal structures was higher (P<0.05) in Western white-faced compared with Finn sheep from Days 5 to 15 of the cycle (Day 0=day of ovulation). This accounted for the higher (P<0.05) total luteal volumes recorded in Western white-faced ewes on Day 7 and from Days 11 to 15, despite the higher ovulation rate in Finn ewes (2.7 ± 0.3 and 1.7 ± 0.2, respectively; P<0.05). Mean serum progesterone concentrations were higher (P<0.05) in Western white-faced than in Finn ewes from Days 4 to 14. Daily total luteal volumes were positively correlated with daily serum progesterone concentrations throughout the cycle in Finn sheep (r≥0.40, P<0.02), and during luteal growth and regression (r>0.60, P≤0.00001) but not during mid- cycle in white-faced ewes (r=0.16; P=0.22). During the growth of the corpora lutea (CL), luteal tissue volume increased faster (P<0.05) than serum progesterone concentrations in both breeds of sheep. During luteolysis, the decrease in luteal volumes parallelled that in serum progesterone concentrations in Finn (P=0.11) but not in Western white-faced ewes, where luteal volumes decreased more slowly (P=0.02) in relation to progesterone secretion. Increased ovulation rate in prolific Finn ewes resulted in more but smaller CL, and lower serum progesterone levels compared with nonprolific Western white-faced ewes. We conclude that breed-specific mechanisms exist to control the formation of luteal tissue and progesterone secretion in cyclic ewes differing in prolificacy. The mechanisms may involve ovulation of Graafian follicles at different sizes and inhibitory paracrine effects of CL on co-existing CL.
Author(s): Bartlewski PM, Beard AP, Rawlings NC
Publication type: Article
Publication status: Published
Journal: Theriogenology
Year: 1999
Volume: 52
Issue: 1
Pages: 115-130
Print publication date: 01/07/1999
ISSN (print): 0093-691X
ISSN (electronic): 1879-3231
Publisher: Elsevier Inc.
URL: http://dx.doi.org/10.1016/S0093-691X(99)00114-4
DOI: 10.1016/S0093-691X(99)00114-4
PubMed id: 10734410
Altmetrics provided by Altmetric
