For producing gene-targeted animals, the dosage and timing of the hormone injections to produce superovulation must take into consideration which of the following factors?

• A. Staff schedule
• B. Light:dark cycle in use at the facility
• C. Location of the cage in the rack
• D. Strain of the stud

Answer: (B)

The main idea is that reproductive physiology in laboratory rodents is tightly linked to the light-dark cycle. The circadian system, entrained by the facility’s lighting schedule, governs when the hypothalamus releases GnRH, driving the LH surge that triggers ovulation. Because superovulation relies on hormonally timed triggers (to recruit multiple follicles and then induce ovulation), the dose and timing of those injections must be planned to align with the current light-dark cycle. If the lighting schedule changes, the optimal timing of injections shifts too, so adjustments are needed to maintain consistent egg yield.

Logistical factors like staff scheduling or cage location don’t alter the biology of hormonal responsiveness. The strain of the stud can affect fertility to some extent, but the critical factor for timing the hormonal plan is the photoperiod that sets the animal’s reproductive clock.