Lr. Meek et Tm. Lee, PREDICTION OF FERTILITY BY MATING LATENCY AND PHOTOPERIOD IN NULLIPAROUS AND PRIMIPAROUS MEADOW VOLES (MICROTUS-PENNSYLVANICUS), Journal of Reproduction and Fertility, 97(2), 1993, pp. 353-357
Mating behaviour and litter production of female meadow voles (Microtu
s pennsylvanicus) housed in long (14 h light:10 h dark; long day; LD)
or short (10 h light:14 h dark; short day; SD) photoperiods were monit
ored to determine whether the reduced birthrate of SD females resulted
from a lack of copulation. All females mated, but fewer SD females ga
ve birth. LD and SD females fell into three distinct groups based on m
ating latency. The rapid onset group (RO) mated between 7 min and 9 h
after pairing, the intermediate onset group (10) mated between 16-44 h
and the late onset group (LO) mated after 58-262 h of male contact. S
ixty-seven per cent of LD females were assigned to group RO, 27% to 10
, and 6% to LO. In contrast, 30% of SD females were assigned to group
RO, 35% to IO and 35% to LO. Fertility was predicted by mating latency
. Sixty-nine per cent of RO, 93% of 10 and 33% of LO animals gave birt
h. In a further experiment, a small-mouthed cup was added to the envir
onment to serve as an escape for females wishing to avoid mating. Alth
ough females did not use the cup to escape male approaches, mating occ
urred in only 66% of SD females, but was observed in all LD females. I
n a final experiment, mating latency and litter production were record
ed in primiparous LD and SD females initially observed in the first ex
periment. Group LO was eliminated in parous females; all primiparous L
D and SD females mated within 48 h. Birthrates of LD (82%) and SD (73%
) parous females were increased compared with birthrates of nulliparou
s females (LD=65%; SD=55%). These observations suggest that long day-l
ength and parity increase spontaneous oestrus in meadow voles (50% of
nulliparous and 80% of primiparous RO animals mated in less than 1.5 h
). Females in the IO and LO groups are probably induced into oestrus,
as normally described for arvicoline rodents, by direct male contact.
Rapid mating (< 48 h) predicts greater fertility for both LD and SD fe
males, while delayed mating (> 5 8 h) predicts low fertility. Parity d
ecreases mating latency and increases litter production. Short day fem
ales produce fewer litters than LD females in equivalent groups.