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Induction of ovulation in chronically hypophysectomized Booroola ewes
R C Fry1, I J Clarke, J T Cummins
1Animal Research Institute, Werribee, Victoria, Australia.
Journal of Reproduction and Fertility
|March 1, 1988
Summary
The Booroola fecundity (F+) gene significantly increases ovulation rates in Merino ewes. This suggests ovarian factors, not pituitary ones, are the primary drivers of high fecundity in these sheep.
Area of Science:
- Reproductive Biology
- Animal Genetics
- Sheep Production
Background:
- The Booroola Merino breed is known for its exceptional fecundity.
- The fecundity (F+) gene is associated with increased litter size in sheep.
- Understanding the physiological basis of high fecundity is crucial for sheep breeding programs.
Purpose of the Study:
- To investigate the role of the fecundity (F+) gene in ovulation rate.
- To determine whether ovarian or pituitary factors are responsible for the high fecundity in Booroola Merino ewes.
- To compare induced ovulation rates between Booroola F+ and non-F+ ewes.
Main Methods:
- Hypophysectomy was performed on Booroola Merino ewes with (F+) and without (++) the fecundity gene.
- Ewes received intramuscular injections of pregnant mare serum gonadotropin (PMSG) followed by human chorionic gonadotropin (hCG).
- Ovulation rates were assessed laparoscopically.
Main Results:
- Booroola F+ ewes exhibited significantly higher ovulation rates (8.00 ± 1.66) compared to ++ ewes (3.62 ± 1.10) (P < 0.01).
- Hormonal treatments (PMSG and hCG) successfully induced ovulation in both groups.
- The data strongly indicate a genetic influence on ovulation rate.
Conclusions:
- The high fecundity of Booroola Merino ewes is primarily attributable to ovarian factors, likely mediated by the fecundity (F+) gene.
- The F+ gene directly influences the ovary's response to gonadotropins, leading to increased ovulation.
- These findings have significant implications for selective breeding to enhance reproductive efficiency in sheep.