|Abstract or Summary
- At weights of 81.5-90.5 kg, 187 prepuberal crossbred gilts were
subjected to specific environmental stimuli, for up to 17 days, to
determine which stimuli or combinations of various ones would initiate
onset of estrus in prepuberal gilts. The stimuli used were:
movement to new building, mixing or non-mixing of gilts, daily exercise,
and various degrees of exposure to a boar. At the end of each
trial, all gilts were slaughtered and their ovaries were examined.
Presence of corpora lutea was used to verify the occurrence of estrus.
Gilts were raised to test weights away from the sow and boar
herd. Moving gilts as a group of familiar penmates to another facility
separate from the brood stock herd did not stimulate estrus or
follicular growth. Mixing unfamiliar gilts together and moving them
to the second facility did induce puberty in gilts that were at least
209 days of age at initiation of the trial.
All remaining gilts in this series of trials were moved from the
grower facility to the brood stock facility on the initial day of
each trial and were subjected to various degrees of exposure to a
boar. Exposure for 17 days to a boar in a contiguous pen initiated
estrus in 31% of 16 mixed gilts. Contiguous boar exposure plus 30 minutes of direct contact with another boar stimulated approximately
equal percentages of gilts to attain puberty in a group of 23 exercised
and a group of 24 non-exercised mixed gilts (70%). Without the
24 hr per day contiguous boar exposure, but with 30 minutes of daily
direct boar contact, 78% of 23 exercised mixed gilts attained puberty
compared to 46% of 24 non-exercised gilts (P<.05) . No significant
differences were found between 24 mixed and 24 non-mixed gilts (87%
vs 79%) when each group was subjected to 24 hr per day direct contact
with a different boar during each 24 hr period. A high degree of
synchronization of estrus existed among gilts which mated while exposed
to the boar: 71% of those gilts mating did so between day-4
and day-10; 90% of those gilts mating did so between day-4 and day-13.
Additional studies indicate exposing gilts at too young an age
and to the same boar for extended periods will delay puberty as compared
to the previous boar stimulation procedures. Also, moving
mixed gilts to new locations separate from the brood stock herd and
exercising for 30 minutes daily did not stimulate puberty.
For gilts of the same average initial age (181 days), ovulation
and embryo survival rates were compared between stimulated gilts
attaining puberty and mating in 17-or-fewer days (average 5 days) and
of gilts attaining puberty in 18-or-more days from initial stimulus.
Stimuli used were mixing, daily exercise, and five minutes daily boar
exposure. The 30 gilts mating within 17 days had fewer corpora lutea
(11.7 vs 13.4, P<.05) and fewer live embryos (8.8 vs 12.0, P<.05) than
the nine other gilts at slaughter 30 days postmating. No stastically
significant differences existed between embryo survival rates and per centage of gilts conceiving. Sixteen additional gilts, exposed to the
same stimuli, experienced 2-4 estrous cycles before an elapse of 30
days occurred without returning to estrus. Fifty percent of these
gilts were either infertile or had six or fewer live embryos at 30