Jan 30, 1975 - The LH levels rose in all the birds in March and April and reached a ... The ducks were all fully grown drakes of the Khaki Campbell strain and.
SEASONAL CHANGES IN PLASMA LH LEVELS IN DOMESTIC DUCKS E.
J. SHARP and E. PAULKE Institut für Haustierkunde der Universität, 23 Kiel, Federal Republic of Germany, * Agricultural Research Council's Poultry Research Centre, King's Buildings, West Mains Road, Edinburgh EH9 3JS HAASE,
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(Received 30th January 1975) Summary. Seasonal changes in plasma LH concentrations were measured by radioimmunoassay every month for 1 year in nine Khaki Campbell drakes kept under natural lighting conditions in Kiel, Germany. The LH levels rose in all the birds in March and April and reached a mean ( \m=+-\S.E.) maximum of 2\m=.\4\m=+-\0\m=.\2 ng/ml early in May. Thereafter, LH levels remained high in three drakes, but decreased in the other six to between 0\m=.\9and 0\m=.\4ng/ml early in June and/or July and rose to about 2\m=.\5ng/ml by the beginning of August. Plasma LH levels started to fall in all nine drakes in September and by early October had reached winter values of about 1\m=.\2to 1\m=.\5ng/ml. A small transient increase in the level of circulating LH was observed in most drakes during November or December. It has been reported that there is an asynchrony between the seasonal changes in plasma levels of testosterone and LH in Pekin drakes (Jallageas et al., 1974). Circulating levels of both hormones rose in the spring in parallel with an increase in testicular weight, but whilst LH levels remained high during the summer and did not fall until the autumn, testosterone levels fell during March and April before the testes reached maximal size. It was suggested that, as the breeding season proceeds, the testicular interstitial cells become increasingly insensitive to LH. These data were derived from samples taken from birds killed in groups of three or four at intervals of approximately 2 months throughout 1 year, and the present study was undertaken to determine the monthly changes in plasma LH levels in individual drakes during 1 year. The ducks were all fully grown drakes of the Khaki Campbell strain and were kept in a large outdoor aviary in Kiel (54°N), Germany. Blood samples were taken from the wing veins of the same nine birds during the first 5 days of each month for 1 year. The LH concentrations were measured by a radio¬ immunoassay developed for chicken LH (Follett et al., 1972). The standard and 125I-labelled tracer were a preparation of chicken LH (fraction ) purified to minimize TSH activity (Scanes & Follett, 1972). Each plasma sample was assayed in triplicate at one dilution (80 µ to 200 µ ) and all samples taken during 1 year from each drake were assayed at the same time. In the four assays needed to complete the study, the minimum detectable dose of LH was 0-04 + 0-01 591
592
E. Haase et al.
ng/ml (S.D.), and the potency of a control plasma included in each assay ranged between 9·5 and 11-7 ng/ml (mean + S.D., 10-7 + 0-9). There was parallelism between the dose-response curve of drake plasma and the chicken LH standard
curve.
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Text-fig. 1. Variations in plasma LH concentrations in nine Khaki Campbell drakes kept outdoors in Kiel (54°N), Germany. The drakes were categorized according to whether LH concentrations remained (a) high during June and July (Group I), (b) fell during May (Group II), or (c) fell duringjune (Group III). Since the annual variations in plasma LH concentrations in the four birds in Group III were similar, mean values ± S.E. are shown.
Plasma LH concentrations rose progressively in the nine drakes during March and April from mean winter levels of 1·2 to 1-5 ng/ml (Text-fig. 1) to a mean level of 2-4+0-2 (S.E.) ng/ml early in May. The subsequent changes in levels of circulating LH were such that it was convenient to consider the birds in three groups (Text-figs la to lc). Plasma LH levels remained high duringjune and July in all three drakes in Group I, and were maximal in July in two of the birds (Text-fig. la). In contrast, plasma LH levels fell during May and were below 0-4 ng/ml at the beginning ofJune in the two birds in Group II (Text-fig.
Seasonal
changes in plasma LH in ducks
593
lb), although the plasma LH concentration rose in one duringjune to reach 2-5 ng/ml at the beginning of July. In the other drake, the circulating level of LH was still very low at this time (Text-fig. lb). The variations in plasma LH concentrations in the four drakes in Group III were similar (Text-fig. lc) ; LH levels decreased duringjune and were only 0-7 + 0-1 ng/ml at the beginning of July. Thereafter, the LH levels rose and by early August reached a mean peak of 2-5 + 0-5 ng/ml. Plasma LH levels started to fall in all nine drakes in September and by early October had reached values of about 1-2 ng/ml (Text-figs la to le). A small transient increase in the level of circulating LH occurred in the Group I birds (Text-fig. la), and in one of the birds in Group II (Text-fig. lb) during Novem¬ ber or December, and in the mean value for the four Group III birds in December (Text-fig. lc). This peak may be related to changes in the drakes' sexual behaviour since there is an increase in intensity of sexual display at this time of year in mallards which are the wild ancestors of domestic ducks (Weid¬ mann,
1956).
These data suggest that in 6/9 of these domestic drakes, held under natural lighting conditions, there was a short period during May, June or July, lasting less than 8 weeks, when they became photorefractory (van Tienhoven & Planck, 1973) and continued exposure to long daily photoperiods no longer stimulated the secretion of LH. This reduction of LH secretion might be the cause of the regression of the testicular interstitium that was observed ultrastructurally by Gamier et al. (1973) in June. The failure ofJallageas et al. (1974) to observe a reduction of plasma LH levels in June may have been due to the 2-month interval of sampling or there may be differences in the LH responses of different strains of ducks. It might also be due to differences in latitude since the French study was carried out in Montpellier where seasonal variations in daylength are not as great as those in Kiel. Since domestic ducks, including the Khaki Campbell strain, have been selected intensively for increased egg production (Weiler, 1964) selection pressures would have been operative to reduce the duration of the photorefractory phase of the reproductive cycle. In some individuals, such as those in Group I and possibly in the Pekin drakes studied by Jallageas et al. (1974), the photorefractory phase may last less than 4 weeks or no longer develop. The authors are grateful to Dr C. G. Scanes and Dr . . Follett for gifts of antisera and chicken LH preparations and to the Deutsche Forschungsgemeinshaft (SPP 'Biologie der Zeitmessung', Ha 820/1 and Ha 820/3) for finan¬ cial support. REFERENCES
Follett, B.K., Scanes, C.G. & Cunningham, F.J. (1972) A radioimmunoassay for avian luteinizing hormone. J. Endocr. 52, 359-378. Garnier, D.H., Tixier-Vidal, ., Gourdji, D. & Picart, R. (1973) Ultrastructure des cellules de Leydig et des cellules de Sertoli au cours du cycle testiculaire de Canard Pekin. Z- ZeWorscn· mikrosk. Anat. 144, 369-394. Jallageas, M., Assenmacher, I. & Follett, B.K. (1974) Testosterone secretion and plasma luteinizing hormone concentration during a sexual cycle in the Pekin duck, and after thyroxine treatment. Gen. & comp. Endocr. 23, 472-475.
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Scanes, C.G. & Follett, B.K. (1972) Fractionation and assay of chicken pituitary hormones. Br. Poult. Sci. 13, 603-610. van Tienhoven, A. & Planck, R.J. (1973) The effect of light on avian reproductive activity. In Handbook of Physiology, Endocrinology, Section 7, Vol II, Pt. 1, pp. 79-107. Eds R. O. Greep & E. B. Astwood. American Physiological Society, Washington, D.C. Weidmann, U. (1956) Verhaltensstudien an der Stockente (Anasplatyrhynchos L.). I. Das Aktionssystem. · Tierpsychol. 13, 208-271. Weller, M.W. (1964) The reproductive cycle. In The Waterfowl of the World, Vol. IV, pp. 35-79. Ed. J. Delacour. Country Life Ltd, London.
