The Ratminator: Rapid Birth Machine

Reproduction

Everyone knows how fast a rat can multiple. Next thing you know, your favorite restaurant is being shut down due to rat infestation. How is this possible?

To understand this, the estrous cycle, which lasts only four to five days, needs to be explored. The cycle consists of four stages: proestrus, estrus, metestrus and diestrus. During the proestrus phase and estrus phase, the female will accept male to mate with them. However, during the metestrus and diestrus, they will no longer mate and their Vaginal smear morphology shows that they produce leukocytes. The estrus phase also produces lordosis, which is a characteristic mating behavior of female rats. Several environmental factors affect the estrous cycle such as temperature and light (Hamid & Zakaria, 2013).Mating induces a prolactin, which increases LH and signals the corpus luteum to produce progesterone. Progesterone signals to the female rat that she is “pregnancy-ready”. Fertilization is achieved during the estrus phase and is regulated by the epididymal 37 kDa protein. The embryo doubles in two cells and undergoes a series of mitotic divisions into four cells, eight cells, and a morula (Hamid & Zakaria, 2013).The blastocyst then forms and gives rise to the placenta and embryo. They have a fast pregnancy period only lasting 20-24 days. Delivery takes place in one to four hours depending on the litter size. The babies can start eating and drinking at around age 21 (Hamid & Zakaria, 2013). Rats can start reproducing after 9 nine weeks from their birth and they can give birth to 12 babies, 6 times a year (Admin, 2020). Since rats have a short life span, they begin to slow down giving birth during their midlife period. There estrous cycle length increases and they have a lot of repetitive pseudopregnancy because of a prolonged luteal phase (Westwood, 2008).