Comparative characterization of the oestrous cycles of the grasscutter (Thryonomys swinderianus) and the guinea pig (Cavia porcellus) by the hystricomorph vaginal membrane perforation phenomenon

Abstract

The grasscutter (Thryonomys swinderianus) is a hystricomorph rodent undergoing domestication; therefore to facilitate and enhance its breeding in captivity its oestrous cycle was characterized. For better elucidation, its oestrous cycle was studied alongside that of the guinea pig (Cavia porcellus), a domesticated spontaneous ovulating hystricomorph rodent. Sexually mature grasscutters and guinea pigs were monitored for the manifestation of the periodic vaginal membrane perforation phenomenon, which is a sign of oestrous cycling in hystricomorph rodents. The oestrous cycle was characterized with respect to its time of occurrence, constituent phases and duration. The grasscutters manifested erratic oestrous cycles with significantly different lengths, while the guinea pigs manifested uniform oestrous cycles with no significant differences. The oestrous cycles in both species consisted of two phases: one of sexual activity and the other of sexual inactivity. In the grasscutter, the sexual activity phase was represented by an open or secretion-sealed vagina, while in the guinea pig it was solely represented by an open vagina. The phase of sexual inactivity in both species was represented by an inaccessible vagina closed off the exterior by an epithelial membrane. The mean length of the oestrous cycle was 17.5 ± 21.3 days and 15.9 ± 2.1 days in the grasscutter and guinea pig respectively. The grasscutter presented a mean open/sealed period of 11.1 ± 25.9 days and a mean closed period of 12.5 ± 22.4 days. The guinea pigs presented a mean open period of 3.1 ± 1.1 days and a mean closed period of 12.9 ± 1.71 days. Since the grasscutters manifested an erratic oestrous cycle while the spontaneous ovulating guinea pigs manifested a uniform cycle it could be inferred that the grasscutter is an induced ovulator like the cuis (Galea musteloides), an induced ovulating hystricomorph that also manifests the phenomenon in a sporadic manner.