Effects of energy intake on the estrous cycle of the desert gerbillid, Sund
evall's jird (Meriones crassus; 80 g; n = 2) were studied. Females were off
ered either maintenance or below maintenance levels of millet seeds and ad
lib. Atriplex halimus leaves and stems; drinking water was not available. V
aginal smears were used to determine sexual stage. We hypothesized that the
estrous cycle ceases at low levels of energy intake and commences when suf
ficient energy is available. Females lost body mass linearly with a decreas
e in metabolizable energy intake. Estrous cycle averaged 4.46 d at maintena
nce energy intake but increased to an average of 7.81 d at 70% of maintenan
ce energy intake. A cessation of the cycle occurred at an energy intake bel
ow 70% of maintenance requirements, which resulted in a body mass loss of m
ore than 1% per day. More variability in the length of the different stages
of the cycle was found with lower levels of energy intake. When offered ad
lib. millet seeds and A. halimus (n = 14), recovery to the normal cycle wa
s attained within 10 d by 43% of the females and within 16 d by the rest of
the females. Recovery time was longest in females that previously had the
lowest energy intake. We concluded that the estrous cycle of M. crassus is
sensitive to energy intake. With restricted energy intake, the estrous cycl
e and reproductive activities cease but can be restored with provision of a
dequate energy. This strategy ensures that reproduction occurs when conditi
ons of food availability and body condition of the females are favorable.