Hoskins, S., Brown, J. 2020. Oestrus checking – increasing productivity and embracing the 3R’s. Animal Technology and Welfare 19(2), 159-161.

Much like the menstrual cycle in humans, mice also have a cycle where the eggs ripen, ovulation takes place, the females come into heat and are receptive to mate with the male; this occurs over the space of 4-5 days and is called the oestrous cycle. ‘Oestrus checking’ is a visual check of the female’s genitalia to assess her readiness to mate. It is done by holding each female by the base of the tail in your left hand and using the thumb of your right hand, gently touch the stomach of the mouse to open the vagina to assess which stage of the cycle she is in. Selecting females for mating by visually checking for oestrus vastly increases successful plugging rates in CD-1 females. Our results show an increase from 13% to 81% by introducing this method into our daily routines. This allows us to greatly reduce the number of matings needed to produce the desired number of plugs in accordance with the 3Rs. Choosing only females that are ready to mate also reduces the stress levels of having females not suitable for mating being introduced into male cages. This is a good refinement to the process as it minimises the risk of injuries caused by aggression from the males.

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