Reproduction in Domestic Animals - Facultad de Ciencias Veterinarias

16 t h International Congress on Animal Reproduction
80 Poster Abstracts
P157
Role of exogenous leptin and season on thyroxine
release from thyroid gland in ewes
Klocek-Górka, B 1 *, Szczęsna, M 1 , Sechman, A 2 and Zięba, DA 1
1Department of Sheep and Goat Breeding, Agricultural University of Krakow,
Poland; 2 Animal Physiology Dept., Agricultural University, Krakow, Poland
Through its circadian release of melatonin, the pineal gland plays a
key role in integrating circannual responses in day length within the
neuroendocrine axis of the ewe. Leptin, which synthesis and release
are sensitive to acute changes in nutritional status, acts on target sites
within the brain that regulate appetite and energy balance. The
pituitary-thyroid system is regulated at multiple levels, one or more of
which might account for nutritional adaptation. Thyroid hormones are
obligatory for the annually recurring termination of reproductive
activity in a spectrum of seasonal breeders, including sheep. The
presence of leptin receptors in the thyroid gland has been reported and
some leptin effects may be, directly or indirectly, mediated by
hypothalamo-pituitary-thyroid axis. It was shown that, in the ewe, the
interaction between the thyroid gland and reproductive
neuroendocrine axes changes dynamically throughout the year. The
present study addresses questions related to timing of the interaction
between thyroid hormone - thyroxine (T4) and leptin in seasonal
breeding ewes. Studies were carried out on thyroid glands’ explants in
short-term culture. Glands were collected from nine ewes selected
randomly during long days (LD, i.e. Apr., May and July) and from
additional nine ewes during short days (SD, i.e. Sept., Oct, Nov). The
explants (approximately 30 mg) were equilibrated in 2.5 ml of
RPMI/F12 medium with 0.5% FCS for 30-min, followed by a 4.5 h
incubation in medium containing either 0, 50 or 100 ng/ml of
recombinant ovine leptin (roleptin) with melatonin (100 ng/ml) and
with or without TSH (100 ng/ml). Concentrations of T4 were
determined by RIA and expressed as means ± SEM. Thyroxine
concentrations in explants media were affected (P < 0.05) by season,
and melatonin had inhibitory effect (P < 0.05) on T4 secretion during
both long and short days. In explants cultures from thyroid glands
collected during SD, roleptin in both doses together with TSH
stimulated (P < 0.01) T4 release, however, those effects were
diminished by melatonin. In LD, high dose of roleptin applied with
TSH increased T4 secretion in comparison to control (P < 0.01), and
this effect was again inhibited by melatonin. The data obtained
provide an evidence for seasonal interactions between leptin and
thyroxine in ewes with higher T4 secretion during long days when
thyroid hormones are necessary for quiescence of the reproductive
activity in ewes.
P158
The use of melatonin and progestagen to advance
puberty in Awassi ewe lambs
Kridli, R 1 *; Jawasreh, K 2 ; Sawalha, M 1
1Department of Animal Production, Faculty of Agriculture, Jordan University of
Science and Technology, Irbid 22110, Jordan
2The National Center for Agriculture Research and Extension, Baqaa, Jordan
Introduction Ewes are generally culled at 6 to 7 years of age after
having produced 5 to 6 lamb crops. Advancing puberty age allows
ewe lambs to enter the breeding season at around 7 to 8 months of age
thus obtaining one more lamb crop per female during her productive
life. Attempts to breed ewe lambs at an earlier age in Jordan resulted
in limited success as only 20 to 30 % of the females lambed at one
year of age (personal communication). Thus, the objective of this
study was to advance puberty and initiate the breeding season in
Awassi ewe lambs through hormonal treatments.
Methods This experiment was conducted at the Khanasry Station for
Small Ruminant Development to evaluate the effect of administering
hormonal treatments [melatonin, progestagen and pregnant mare\'s
serum gonadotropin (PMSG)] on advancing puberty in Awassi ewe
lambs. Fifty one, 6-month old ewe lambs of similar body weights
(around 28 kg) were randomly assigned into four treatment groups; no
hormonal treatment (CON; n=14), melatonin (M; n=13), progestagen
and PMSG (PP; n=13) and melatonin plus progestagen and PMSG
(MPP; n=11). Ewe lambs in the PP and MPP groups were treated with
intravaginal progestagen sponges for 14 days. Four hundred IU
PMSG were administered to each of these ewe lambs on the day of
sponge removal. Ewe lambs in the M and MPP groups received
subcutaneous melatonin implants (Regulin®, 18 mg melatonin) 36
days before sponge insertion. The melatonin implants were applied in
mid May, around 6 to 7 weeks before the natural breeding season for
Awassi. Fertile, harnessed Awassi rams were introduced at the time of
sponge removal.
Results Hormonal treatment had no effect on body weight. Estrus
expression tended to be greater (P = 0.1) in the M, PP and MPP
compared with CON ewe lambs (92%, 92%, 100% and 71%,
respectively). The duration from ram introduction to onset of estrus
was shorter (P < 0.001) in PP and MPP than in M and CON ewe
lambs (12±3.5, 5.7±3.7, 23.9±3.5 and 26.5±3.9 d, respectively).
Pregnancy rate (evaluated by ultrasonography 60 days post ram
introduction) was similar among treatments although being
numerically greater in the MPP group (50%, 61.5%, 53.8% and 81%
in CON, M, PP and MPP ewe lambs, respectively).
Conclusion Results indicate that a combination of melatonin,
progestagen and PMSG appears to be effective in advancing puberty
in Awassi ewe lambs. The lack of significant differences in estrus
expression and pregnancy rate may be attributed to the low number of
animals.
P159
Luteinizing hormone (LH) and Follicle stimulating
hormone (FSH) induce the expression of Cyclooxygenase
-2 mRNA in cervical tissue of non-pregnant ewes
Leethongdee, S 1,2 *, Khalid, M 1 and Scaramuzzi, RJ 1
1The Royal Veterinary College, University of London, United Kingdom;
2Faculty of Veterinary Medicine and Animal Sciences, Mahasarakham
University, Thailand
Introduction The ovine cervix contains both LH and FSH receptors
and their concentrations are greatest at oestrus indicating
physiological roles in relaxation of the cervix. Cervical relaxation at
oestrus is mediated by prostaglandin E 2 whose synthesis is regulated
by the inducible enzyme, COX-2. Consequently, the high level of
FSH and LH during the peri-ovulatory period may stimulate COX-2
regulated PGE 2 synthesis leading to cervical relaxation at oestrus. Our
objective was to determine the effect of intra-cervical LH and FSH on
the expression of COX-2 mRNA in the cervix of the ewe during
oestrus.
Methods Eighteen ewes were assigned to 4 groups of 5 (groups 1 and
2) or 4 ewes (groups 3 and 4). Oestrus was synchronised using
progestagen pessaries and 500 IU PMSG at pessary removal. Intracervical
hormone was applied 24h after pessary removal: Group 1:
FSH 2 mg; Group 2: LH 2 mg; Group 3: Vehicle; Group 4: Control.
Cervices were collected 54h after sponge removal or 30 h after
hormone treatment and divided transversely into 6 sections; alternate
sections were formalin fixed, wax embedded and sectioned at 7μm.
The expression of COX-2 mRNA was determined by In situ
hybridization using a digoxigenin-11-UTP labelled riboprobe. COX-2
expression in cervical tissue was analysed in five tissue layers
(epithelium, stroma, circular, longitudinal and transverse muscle) and
three cervical regions (vaginal end, middle region and uterine end).
Results The expression of COX-2 mRNA in cervical tissue of ewes
treated with FSH was greater than in the gum vehicle (P = 0.004) and
control (P = 0.003) groups. Similarly, the expression of COX-2
mRNA in cervical tissues of ewes treated with LH was also greater
than in the gum vehicle (P = 0.007) and control (P = 0.006) groups.
The highest expression of the COX-2 mRNA was at the vaginal end
of the cervix. The expression of COX-2 mRNA at the vaginal end and
the middle region were significantly greater than at the uterine end
(both P < 0.001).There was no difference in COX-2 mRNA
expression between the vaginal end and the middle region (P = 0.683).
Among the tissue layers expression was highest in the luminal
epithelium and lowest in the stroma. The expression of COX-2
mRNA in smooth muscle and luminal epithelium were higher than in
the stromal layer (both, P < 0.001).