For a PGF2a shot to work, the animal must be in
A diestrus
B proestrus
C none of the above
D Estrus
E metestrus
The correct answer and explanation is:
The correct answer is A: diestrus.
PGF2a (Prostaglandin F2 alpha) is commonly used in veterinary medicine, especially in livestock and animals used for breeding. This hormone is primarily used to induce luteolysis, the process that causes the regression of the corpus luteum (CL) in the ovaries. The corpus luteum is essential for the production of progesterone, which maintains pregnancy. When PGF2a is administered, it effectively “terminates” the production of progesterone, thereby inducing estrus and potentially synchronizing the animal’s reproductive cycle.
For PGF2a to be effective, the animal must be in diestrus, the phase following estrus (heat). During this phase, the corpus luteum is present and producing progesterone to maintain pregnancy or prepare for a potential pregnancy. If there is no pregnancy, the progesterone levels begin to decline naturally toward the end of diestrus. Administering PGF2a during diestrus causes the corpus luteum to regress earlier than it would naturally, thus lowering progesterone levels and allowing the animal to enter estrus again.
If the animal is in proestrus (B), the hormone would not be effective, because the corpus luteum is not yet formed at this stage. Similarly, in estrus (D), the corpus luteum is absent, so PGF2a would have no effect. In metestrus (E), although the corpus luteum may have formed, the animal is transitioning from estrus to diestrus, and PGF2a is typically not used in this phase.
Thus, for PGF2a to induce estrus effectively, the animal must be in diestrus when the corpus luteum is present and can respond to the hormone’s effects.