Does peripheral concentration of progesterone affect ovulation and lambing rates in Barbados blackbelly ewes?

Abstract

I would like to thank the members of my committee Drs. Robert Dailey and Marlon Knights for their support and guidance, which allowed me to grow as a scientist. In addition, my sincere appreciation to Dr. Knights for his tremendous support in the acquisition of the knowledge of ultrasonography at West Virginia University, with further training at Greenland Livestock Research Station, Barbados, which allowed me to successfully complete the second replicate of this study. Sincere appreciation is also extended to Dr George Seidel who was very supportive and gave me excellent cooperation in the statistical analysis of the data and Dr Brett Kenney for his adding breadth to my educational experience by exposure novel meat technologies. Special thanks to Ida Holaskova, who was supportive in my overcoming the many challenges in West Virginia that a new student is faced with. Completion of my research studies would not have been possible without the help of my fellow graduate students, particularly, Ms Aimee Wurst and Mr Justin Rhinehart. I wish to express my gratitude to the staff of the Ministry of Agriculture and Rural

Control of the Ovarian Cycle of the Sheep

“…One important hormonal influence is progesterone, with low concentrations in peripheral blood increasing ovulation rate, independent of nutritional management. 203 Anestrous ewes pretreated to produce lower progesterone before ram introduction than seen in the luteal phase had a greater ovulation rate than ewes with ram introduction alone. 26 Similarly, in a prolific breed of sheep, ovulation rate was negatively linearly correlated with concentrations of progesterone but lower progesterone did not increase lambs born.…”

“…During the early follicular phase, when LH pulse frequency is still relatively slow, elevated concentrations of FSH are required for the development and maintenance of potential ovulatory follicles. 203 It should be noted that episodic LH secretion is not essential; constant infusion of LH was capable of supporting ovulatory follicles in GnRH antagonist-treated 204 or prepubertal 205 ewes. 201 However, FSH concentrations fall as estradiol rises, so the preovulatory follicles must switch their dependence from FSH to LH during the follicular phase.…”

Effects of a Gonadotropin Mixture on Reproductive Success in Progesterone- Treated Non-Lactating Anestrous Ewes

“…In addition to the effects of FSH, LH effects might be necessary for successful maturation and ovulation of the follicle. Devonish et al (2009) observed that ovulation rate increased with decreasing concentrations of progesterone, likely caused by a greater LH pulse frequency. LH has been shown to have an effect on the maturation of follicles in ewes (McNatty et al, 1981 andMurdoch, 1985).…”

Effect of service sire on late embryonic and fetal loss in sheep

“…Booroola Merino cross ewes as well as other prolific breeds were reported to have lower embryonic and fetal survival (Robinson, 1951;Rhind et al, 1980aRhind et al, , 1980bMeyer, 1985Meyer, , 2002Bradford et al, 1986aBradford et al, , 1986b) so that litter size was increased less than expected despite the increased ovulation rate (Rhind et al, 1980b;Southey et al, 2001;Knight et al, 2003;Devonish et al, 2009). These findings are in agreement with the conclusion by Dixon et al (2007) that in sheep, partial losses of multiple embryos or fetuses were more common than complete losses of multiples or singletons.…”

“…In the present study, late embryonic and fetal losses increased with age in the same pattern as number of lambs born. This result may reflect the increase in losses seen with increased ovulation rates (Meyer, 1985;Dixon et al, 2007;Devonish et al, 2009). Although the number born increased with age, efficiency of maintenance of embryos or fetuses decreased with age.…”