Forum post — MouseGenetics Forum, thread "C57BL/6J breeding pairs not producing litters" Posted by: labtech_jane We've had a C57BL/6J trio set up for almost 8 weeks now with no litters at all. The female looks healthy and cycling normally, but no plugs have been detected in the morning checks.

Another postdoc in the building mentioned that C57BL/6J females can be picky about cage mates and that switching to monogamous pairing (1 male : 1 female) instead of a trio often fixes the problem, since trios can lead to social stress that suppresses receptivity. We also started doing the plug checks right at the start of the dark cycle instead of the next morning, and swapped in slightly soiled bedding from a proven breeder cage to encourage pheromone-driven cycling (Whitten effect).