Determination of the ovulatory mechanism of the grasscutter (Thryonomys swinderianus)

The ovulatory mechanism of the grasscutter was determined in two phases. Phase one was the histological examination of ovaries of sexually mature grasscutters in various reproductive conditions (non-mated, mated, pregnant) for Corpora lutea (an indicator of ovulation). The second phase was an evaluation of the reproductive performance (female's acceptance to mate, ability to conceive and deliver) of sexually mature grasscutters in oestrus (open vagina, sealed vagina) and anoestrus (closed vagina). The ovaries for the histological studies were obtained from 25 grasscutters comprising nine females that had been paired with males for 1 week prior to the collection of their ovaries, nine that had not been exposed to males for a minimum of 6 months and carcases of seven pregnant grasscutters. Thirty sexually mature female and eight sexually mature male grasscutters were used for the reproductive study. The females were in three groups of ten in three different sexual states namely; open vagina (oestrus), sealed vagina (oestrus) and closed vagina (anoestrus). The animals were hand-mated in pairs and separated when a definitive sign of mating was observed. Thereafter, the females were diagnosed for pregnancy and observed until parturition. The histological examinations showed an unequivocal absence of Corpora lutea in the ovaries of the grasscutters that had not been exposed to males, but their presence in the ovaries of the mated and pregnant grasscutters. In the reproductive study, 96.7% (29/30) were successfully mated, 96.6% (28/29) of those mated conceived and 89.3% (25/28) of those pregnant carried their pregnancies to term. None of these outcomes was affected by the sexual status. The histological and reproductive findings confirm the suggestion that the grasscutter is an induced ovulator. This information is important for the commercial exploitation of the animal for human food production.