29. BEKEOVÁ,Eva, KRAJNICÁKOVÁ, Mária, HENDRICHOVSKÝ,B: The effect of thyroid gland on sheep reproductive functions during out of seasonal period (A pajzsmirigy hatása a juh ivari mûködésére szezonon kívüli idõben)
29. Bekeová
érk: 97.10.16.
UEVM, 04001 Kosice, Hlinkova 1/A, Slovak Republic
INTRODUCTION
The loss of sexual activity in spring and automnal months can be observed in most important farm animal species - i.e. in dairy cows (Mc NATTY et al., 1984), mares (BESOGNET et al., 1996), pigs (HENESSY and WILLIASON, 1984), and sheep which are typical, seasonally anestrous animals (ROBINSON et al., 1984).
The seasonal sheep anoestrus is characterized by a loss of the secretion of sexual hor-mones as well as T4 and T3. The depression of sexual hormones in non-mated sheep can be observed as early as in the first third of the out-of-seasonal period. The depres-sion of systemic concentrations of T4 and T3 in sheep as well as in other animal species has been found out in the course of postpartal anoestrus (RIIS and MADSEN, 1985; BEKEOVÁ et al., 1989). as well as in the last two thirds of the out-of-seasonal period (WEBSTER et al, 1991). The question is raised whether the depression of T4 and T3 is connected with a loss of sexual hormone secretion. Another question is whether the depression of iodothyronines influences in return the production of hormones of hypothalamic-adenohypophyseal-ovarian axis. According to present knowledge, iodo-thyronines participate in the stimulation of the synthesis of both LH and cholesterol which is a primary substrate of steroid synthesis (ANDERSEN and DIETSCHY, 1978). Furthermore, iodothyronines regulate the direct entry of Ca into intra-cellular areas at cellular level. Calcium, among other things, participates in the role of a messenger in GnRH-stimulated LH release (HANSEN et al., 1987), and also in oocyte maturation (GOREN et al.,1990).
Objective of the study
The objective of this study was to verify:
the effect of the treatment with oxytocin-, FSH- and LHRH-based preparations on systemic concentrations of T4 and T3 in sheep postpartal period;
the dependence of the changes in serum Ca and P on the changes of T4 and T3 concentrations after treatment of sheep with above-mentioned preparations;
the effect of changes of observed parameters on the quality of getting pregnant and number of liveborn lambs.
MATERIALS AND METHODS
The experimental study was conducted in 4 groups of Slovak Merino ewes lambed from 1st to 10th February. The ewes of all groups were treated according to the same scheme. The scheme of the treatment consisted in a repeated administration of selected preparations. The first treatment was carried out on h 24 p.p. (i.m.), the second one on h 72 p.p. (s.c.)
Scheme of the treatment
Control group (n=10), injection a 1 ml of saline per treatment
Experimental group 1 (n = 9), injection a 0.07 mg Carbetocin (2-methylthyrosin- deamino-1-karba) - oxytocinum, Depotocin, Léciva)
Experimental group 2 (n = 10), injection a 200 Þg of synthetic LHRH (Dirigestran, Léciva)
Experimental group 3 (n=5), injection a 160 m.u. of adenohypophyseal FSH (Folicotropin, Léciva)
Blood sampling was carried out 12 hours prior to the first treatment (i.e. 12 h p.p.) and after the treatment on days 4, 7, 14, 17, 21, 25, 34, 42, and 51 p.p.
On day 51 p.p., the ewes of all groups were synchronized with a combined treatment with gestagens and PMSG. The ewes were mated with rams.
RESULTS
From day 7 to day 21 p.p., T4 (Graph 1) in control ewes showed a predominant de-crease. In Depotocin- and/or Dirigestran- treated ewes, T4 showed an increase by day 17 and 21 p.p. The increase on day 21 p.p. in ewes after Dirigestran was significant (P<0.01) compared to control. In ewes treated with Folicotropin, T4 showed a regular increase after day 17 p.p.
GRAPH 1 Concentrations of serum thyroxine (T4, +40,0 nmol.l-1) in ewes
LHRH - (Dirigestran)
oxytocin - (Depotocin)
FSH - (Folicotropin
Triiodothyronine (Graph 2) in control ewes showed a similar decrease as T4 from day 7 to day 21 p.p. On day 21 p.p., the decrease was significant (P<0.05) compared to h 12. In three experimental ewes, despite decreasing tendency, T3 showed higher values than in controls. The significance of differences after Depotocin in comparison with controls was found out on day 4 p.p. (P,0.05) and from day 17 to day 25 p.p. (P<0.05; P< 0.01), after Dirigesteran from day 4 to day 25 p.p. (P<0.05; P< 0.001) and after Folicotropin from day 4 to day 25 p.p. (P<0.05; P<0.001).
GRAPH 2 Concentrations of serum triiodothyronine (T3, nmol.l-1) in ewes of the control and experimental groups
The dynamics of Ca (Graph 3) in control group was similar to that of T4 and T3. In Depotocin- and Dirigestran-treated ewes, Ca showed an irregular increase from day 7 to day 51 p.p. The significance of differences after Depotocin in comparison with control was found out on day 21 p.p. (P<0.05), after Dirigestran on day 7 p.p. (P<0.05), and from day 17 to day 25 p.p. (P<0.05; P<0.01). After Folicotropin, serum Ca did not change significantly.
GRAPH 3 Concentrations of serum calcium (Ca, 2,0+nmol.l-1) in ewes of control and experimental groups
In control group, inorganic P (Graph 4) showed relatively well-balanced values after a slight increase on days 4 and 7. In Depotocin- and Dirigestran- treated ewes, inorganic P showed a gradual increase. After Depotocin, the increase in ewes from day 14 onwards was irregular. The significance of differences in ewes in comparison with control after Depotocin was found out on day 4 p.p. (P<0.05), from day 14 to day 21 p.p. (P<0.05; P<0.01), on day 34 and 51 p.p. (P<0.05; P<0.01), in Dirigestran-treated ewes, on day 42 p.p. (P<0.01). After Folicotropin, inorganic P did not change signifi-cantly.
GRAPH 4 Concentrations of serum phosphorus (P, nmol.l-1) in ewes of the control and experimental groups
According to the number of lambed ewes, the conception ability in ewes treated with oxytocin, GnRH, and FSH in comparison with control (Table 1.) was higher by 44.5%, 22.2%, and 4.5%, respectively. The numbers of liveborn lambs in so treated ewes were higher by 111.1 %, 33,4%, and 13.4%, respectively.
Table 1.
Number and percentage of conceptions and number of live-born lambs
Substance Number and percentage of
administered Ewes Lambed Newborn Birth per ewe
at 24 and 72 treated ewes lambs 1 lamb 2 lambs 3 lambs
h p.p.
Control 9 5 6 4 1 -
(55,5 %) (66,6 %)
Depotocin 9 9 16 3 5 1
(100 %) (177,7 %)
Dirigestran 9 7 9 5 2 -
(77,7 %) (100 %)
Folicotropin 5 3 4 2 1 -
(60 %) (80 %)
DISCUSSION
The postpartum depression of T4 and T3, the similar one to that found out in cont-rols was observed in most species of farm animals. It is likely connected with energetic malnutrition during this period (RIIS and MADSEN, 1985; TVEIT et al., 1991).
The increase in T4 and T3 found in experimental ewes could be induced by a direct thyroid-stimulation action of the preparations administered (TALIADOVROS et al., 1978) or through the primary stimulation of prostaglandins (SHELDRICK and FLINT, 1990) and/or gonadotropins (ROBINSON and EVANS, 1990).
In ewes treated with Depotocin and Dirigestran, concentrations of Ca and P signifi-cantly changed from day 7 to day 21. The role of Ca in the quality of reproductive parameters is likely determined by its participation in the processes of the secretion of adenohypophyseal and ovarian hormones (CONN, 1986; ELIKPLIMI et al., 1987) and oocyte maturation (GOREN et al., 1990). Phosphorus is an essential element of oxidative processes connected with energy transformation. According to HUNTER (1977), the changes in energetic potential are one of the reasons of infertility.
The loss of serum Ca that we found out in control ewes post partum was reported by a number of authors in dairy cows post partum (BOSTEDT et al., 1979; �EVCÍK et al., 1980). The loss of serum Ca is more profound with the increase in milk produc-tion. Ca deficiency reduces the fertility (HUNTER, 1977) and it is closely connected with the pathology of puerperium (KACMÁRIK and ELECKO, 1978; KACMÁRIK et al., 1981).
CONCLUSION
Our results suggest that the loss of sexual functions in spring and summer months is connected with a depression of secretion of thyroid hormones. The depression of thyroid hormones is likely due to the primary changes of the secretion of sexual hor-mones. The changes in Ca and P homeostasis represent a form of the mani-festation of the decrease in iodothyronines. These changes are necessary for normal function of reproductive organs.
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