Four age-groups (3-6 months old, 13-16 months old, 23-26 months old and 30-36 months old) of a heterogeneous stock of female guinea pigs were studied. Females of this stock have been reported to have an average life span of 18 months with those living longer than three years considered reproductively “definitely senile” (J. Gerontol., 1951). The females were spayed, allowed to recover, and given hormones to bring them into estrus every two weeks for seven test sessions. The animals were caged and tested in groups of 3 to 5 per cage. Behaviour was recorded continuously for 12 hours following the injection of progesterone en the test day. The parameters measured were latency to estrus and duration of estrus as measured by a lordosis response and the incidence of mounting.

The data did not reveal significant differences in latency to heat or duration of heat among the four age groups. With respect to mounting, however, the differences between the 3-6 month old group and the 13-16 month old group was significant (P <0.05). The differences between the 3-6 month group and the 23-26 month and 30-36 month groups approached significance. No other significant differences in mounting were found among the rest of the groups.

We interpret these findings to infer that the receptive (lordosis) portions of reproductive behavior are less correlated with age than is the arousal (female mounting) portion.


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