| Summary: | 碩士 === 東海大學 === 畜產學研究所 === 85 === Two experiments were conducted to determine effects of
bromocriptine ( a dopaminergic agonist ) injection and
photoperiod regimen on puberty in gilts. In Exp. I., 36
crossbred gilts【 Yorkshire×Landrace ( YL ) and Duroc×
Yorkshire×Landrace ( DYL ) 】born on February 10-12,1995, were
randomly allotted into control ( C? K, bromocriptine ( BRO ) or
melatonin ( MEL ) group on 60 d of age. Gilts in CTL group were
exposed to natural photoperiod. Those in BRO group were exposed
to natural photoperiod, but were injected intramuscularly with
bromocriptine mesilate ( 0.5 mg/ Kg ) on 165,195 and 225 d of
age. Those in MEL group were administered melatonin orally at
dose of 3 mg/ day from 90 d of age to the end of this Exp. All
gilts were collected blood samples twice a week from 165 d of
age for the determination of progesterone by radioimmunoassay to
evaluate whether the individual gilt ovulated before first
estrus. The proportions of gilts attaining puberty within 245 d
were 7/12, 4/12 and 3/12 for CTL, BRO and MEL groups,
respectively, without significant difference among treatments.
The proportion of gilts attaining puberty in MEL group tended to
be lower than that in CTL group ( p=0.098 ). Ages at puberty and
body weights at puberty were not different among treatments. In
Exp. II, 36 crossbred gilts born on August 27-28, 1995, were
randomly allotted into CTL, BRO or long-light ( LL ) group on 65
d of age. Treatments for CTL and BRO groups were the same as
described in Exp. I. Gilts in LL group were exposed to 16 h
photoperiod from 120 d of age to the end of this Exp. The
proportions of attaining puberty were not different among
treatments ( 6/12, 6/12 and 5/12, for CTL, BRO and LL groups,
respectively ). However, LL group ( 181.4±24.4d ) attained
puberty earlier significantly than CTL group ( 216.2±12.4d ) (
p<0.05 ). Body weights at puberty were not different among
treatments. It is concluded that the bromocriptine injection
doesn*t influence the proportion and age of puberty in gilts.
Melatonin administration decreases the proportion of puberty in
gilts during decreasing daylength, and longdays advances puberty
in gilts during increasing daylength.
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