Skip to main content
NCBI home page
Acta Veterinaria Scandinavica logoLink to Acta Veterinaria Scandinavica
. 1998 Mar 1;39(1):35–47. doi: 10.1186/BF03547805

Seasonal Variation in Live Weight, Testes Size, Testosterone, LH Secretion, Melatonin and Thyroxine in Merino and Corriedale Rams in a Subtropical Climate

Säsongsmässig variation i levande vikt, testikelstorlek, testosteron, LH, melatonin och tyroxin hos Merino och Corriedalebaggar under subtropiska förhållanden

R Pérez 14,44,✉, M Forsberg 24,44, H Rodriguez-Martinez 34,44
PMCID: PMC8050657  PMID: 9592944

Abstract

In the present investigation we studied the seasonal changes in live weight and testes and pituitary activity in Merino and Corriedale rams in a subtropical climate. Testes activity was measured as scrotal circumference (SC), plasma concentration of testosterone (T) and release of testosterone after exogenous GnRH injection. LH pulsatility and pituitary LH responsiveness to exogenous GnRH was measured as an index of pituitary activity. In addition, we wanted to characterize the seasonal pattern of thyroxine (T4) secretion and the 24 h secretory pattern of melatonin (M) at the winter and summer solstices in the 2 breeds. Nine Corriedale and 7 Merino adult (4-6 years) rams were kept on native pasture and managed in one group. Twice a month live weight (LW) and scrotal circumference (SC) were measured. To monitor plasma concentration of testosterone (T), and thyroxine (T4), 5 animals of each breed were bled every month except during autumn (March-May), when blood samples were collected with 15 day intervals and in spring (October) with 10 day intervals. To monitor pulsatile LH secretion, 3 rams of each breed were bled at 15 min intervals for 6 h at the winter and summer solstices and spring and autumn equinoxes. Pituitary LH and testicular testosterone response to GnRH injection was performed bimonthly from 2 animals of each breed. No effect of breed was found on any of the variables investigated. An interaction between breed and sampling date was found in LW (p<0.001) and total T response after GnRH challenge (pO.001). Sampling date had a significant effect (p<0.001) on all the variables studied. In both breeds SC decreased during autumn and increased during spring with minimum T concentrations in late autumn and maximum in mid-summer/early autumn. The lowest (p<0.05) number of LH pulses were observed in winter (June) and the highest (p<0.05) in early autumn (March). The highest LH and testosterone response to GnRH challenge was observed in autumn (April) (p<0.05) in both breeds. Baseline concentrations of M were similar in both breeds at the winter and summer solstices and high concentrations were observed during the dark period on both occasions. In both breeds thyroxine was high at the end of winter/spring (February-April) and low from the end of summer to mid-autumn (August-November). The results show that Corriedale and Merino rams under subtropical conditions have annual reproductive cycles. There was an association (p<0.001) between changes in LW and SC in the 2 breeds and this relationship was stronger in Merino rams (R2 = 0.68) than in Corriedale (R2 = 0.33) which indicates that nutritional factors may have more influence on the reproductive cycle of Merino than Corriedale rams.

Keywords: seasonality, reproduction

Full Text

The Full Text of this article is available as a PDF (1.3 MB).

Acknowledgments

The authors wish to thank Ing. Agr Andrés Ganzábal, Ana Nicola, Carolina Chiesa, Dr. Alvaro López, Dr. Elize Van Lier and Dr. Mariel Regueiro for technical assistance during the experimental work, Mari-Anne Carlsson and Karin Burvall for the laboratory assistance and Ing. Juan Burgueño for his excellent help with the statistical analyses. We also thank Dr. Steven Walkden-Brown for scientific support. Financial support was recieved from the International Foundation for Science (IFS) (Grant B/1917-1). Dr. Raquel Pérez Clariget is holder of a scholarship from CONIC YT of the Uruguayan Government which supports her studies in Sweden.

References

  1. J A, AM S, J E, L P, I T. How does melatonin control seasonal reproductive cycles? Reprod. Nutr. Develop. 1988;28(2B):387–397. doi: 10.1051/rnd:19880305. [DOI] [PubMed] [Google Scholar]
  2. A B, G P, MT G, JA M, A C-l, J P, M F, H R-M. Intern. Reprod. Anim., 31 de octubre - 2 de noviembre, Carlos Paz, Córdoba, Argentina. 1996. La suplementación nutricional evita la caida invernal en la reproducción estacionai dei carnero Corriedale uruguayo? (Nutritional supplement can avoid the winter decreasing of the seasonal reproduction in Uruguyan Corriedale rams?) 2do Simp; p. 247. [Google Scholar]
  3. A C, JA M, A B, T G, JR M, M F, H R-M. Onset of spermatogenesis in Corriedale ram lambs under extensive rearing conditions in Uruguay. Acta vet. scand. 1995;36:161–173. doi: 10.1186/BF03547686. [DOI] [PMC free article] [PubMed] [Google Scholar]
  4. MJ C, MJ D, BP S. Reproductive hormone secretion and spermatogenic function in thyroidectomized rams receiving graded doses of exogenous thyroxine. J. Endocr. 1986;111:245–253. doi: 10.1677/joe.0.1110245. [DOI] [PubMed] [Google Scholar]
  5. MJ D, DE B. Seasonal changes in plasma testosterone concentration and mating activity in Border Leicester, Poll Dorset, Romney and Suffolk rams. Aust. J. Exp. Agric. Anim. Husb. 1983;23:248–253. doi: 10.1071/EA9830248. [DOI] [Google Scholar]
  6. M F, R T, A M, JR M, M-A C. Radioimmunoassay of bovine, ovine and porcine luteinizing hormone with a monoclonal antibody and a human tracer. Acta vet. scand. 1993;34:225–262. doi: 10.1186/BF03548189. [DOI] [PMC free article] [PubMed] [Google Scholar]
  7. T G, A B, R P, A L, A C, R T, J F, D L, M F, H R-M. Seasonal variations in testicular morphology in Uruguyan Corriedale rams. Anim. Reprod. Sci. 1995;40:59–75. doi: 10.1016/0378-4320(95)01402-L. [DOI] [Google Scholar]
  8. A G, JG V, P W, R G. Variación estacionai de la actividad reproductiva del carnero Merino Australiano en la Patogonia. (Seasonal changes in reproductive activity of Australian Merino in Patagonia). Rev. Arg. Prod. Anim. 1991;11:449–455. [Google Scholar]
  9. TD G, MJ D ', RP M. Male life cycle and seasonality. Marshall's Physiology of Reproduction. 1990;II:213–378. [Google Scholar]
  10. MJ H, GB M, SW W-B, JS F. Twentysixth Annual Conference of The Australian Society for Reproductive Biology Inc. 1994. Nutritional effects on testicular growth and LH and FSH secretion in Suffolk and Merino rams during the breeding and the non-breeding seasons. [Google Scholar]
  11. ABMM I, RB L. Seasonal variation in testis diameter and sperm output of rams of breeds of different prolificacy. Anim. Prod. 1977;25:311–317. [Google Scholar]
  12. G A L. Changes in pituitary responsiveness to luteinizing hormone releasing in rams exposed to artificial photoperiods. J. of Endocrinology. 1977;73:519–527. doi: 10.1677/joe.0.0730519. [DOI] [PubMed] [Google Scholar]
  13. GA L, CE L, AS M. Seasonal cycles in the blood plasma concentration of FSH, inhibin and testosterone size in rams of wild, feral and domesticated breeds of sheep. J. Reprod. Fert. 1990;88:623–633. doi: 10.1530/jrf.0.0880623. [DOI] [PubMed] [Google Scholar]
  14. GA L, RV S. Seasonal breeding: Nature's contraceptive. Recent. Prog. Horm. Res. 1980;36:1–52. doi: 10.1016/b978-0-12-571136-4.50007-3. [DOI] [PubMed] [Google Scholar]
  15. GB M, JR F, IW P. Reproductive Physiology of Merino Sheep-Concepts and Consequences. Perth: The University of Western Australia; 1990. Environmental and genetic factors affecting reproductive activity in the Merino ram. [Google Scholar]
  16. GB M, SRD S, DR L. Effects of nutritional supplements on testicular size and the secretion of LH and testosterone in Merino and Booroola rams. Anim. Reprod. Sci. 1987;12:267–281. doi: 10.1016/0378-4320(87)90098-4. [DOI] [Google Scholar]
  17. GB M, DW T, MA B. Effects of nutrition on testicular size and the concentrations of gonadotrophins, testosterone and inhibin in plasma of mature sheep. J. Reprod. Fert. 1994;101:121–128. doi: 10.1530/jrf.0.1010121. [DOI] [PubMed] [Google Scholar]
  18. GB M, SW W-B, R B, S T, DW M, JS F, MJ H, BJ R, NR A. Perspective in Comparative Endocrinology, National Research Council of Canada. 1994. Non-photoperiodic inputs into seasonal breeding in male ruminants; pp. 574–585. [Google Scholar]
  19. G M, HE F. Seasonal changes in the testicular size og grazing rams. Anim. Prod, in Aust. 1984;75:444–447. [Google Scholar]
  20. WD M, LG P, JJ D. The effects of season on the scrotal circumference and sperm motility and morphology in rams. Theriogenol-ogy. 1981;16:45–51. doi: 10.1016/0093-691X(81)90112-6. [DOI] [PubMed] [Google Scholar]
  21. TJ P, JA D, BK F. Responses of prepubertal and mature rams to thyroidectomy. J. Reprod. Fert. 1995;104:51–56. doi: 10.1530/jrf.0.1040051. [DOI] [PubMed] [Google Scholar]
  22. TJ P, BK F. Effect of thyroidectomy upon seasonality in rams. J. Reprod. Fert. 1994;101:51–58. doi: 10.1530/jrf.0.1010051. [DOI] [PubMed] [Google Scholar]
  23. TJ P, BK F. Thyriodectomy abolishes seasonal testicular cycles in Soay rams. Proc. R. Soc. Lond. B. Biol. Sci. 1995;259(1354):1–6. doi: 10.1098/rspb.1995.0001. [DOI] [PubMed] [Google Scholar]
  24. J P, G A. Short light cycles induce persistent reproductive activity in Ile-de-France rams. J. Reprod. Fert. Suppl. 1987;34:215–226. [PubMed] [Google Scholar]
  25. D P, DH G, de MM R, M T, R O. Seasonal variation in LH and testosterone release in rams of two breeds. J. Reprod. Fert. 1982;64:341–436. doi: 10.1530/jrf.0.0640341. [DOI] [PubMed] [Google Scholar]
  26. R P C, A L, A C, A B, D L, T G, R T, D Q, J F, M F, H R-M. Reproductive seasonality of Corriedale rams under extensive rearing conditions. Acta vet. scand. 1997;38:109–117. doi: 10.1186/BF03548513. [DOI] [PMC free article] [PubMed] [Google Scholar]
  27. R P C, A L, A C, M F. Proc. 13th International Congress on Animal Reproduction. 1996. Effect of season and feeding level on live weight, testes size and testosterone concentration in Uruguyan Corriedale rams; pp. 1–6. [Google Scholar]
  28. AL P, TJ R. The response of rams and ewes of three breeds to artifical photoperiod. J. Reprod. Fert. 1987;79:609–626. doi: 10.1530/jrf.0.0790609. [DOI] [PubMed] [Google Scholar]
  29. AJ R, NR A, MR S. Effect of lupin feeding on LH, testosterone and testes. In: Lindsay DR, Pearce DT, editors. Reproduction in Sheep. 1984. pp. 76–78. [Google Scholar]
  30. A R. Crecimiento estacionai de la en ovinos Merino e Ideal en pastoreo (Wool seasonal growth in Merino and Polwarth sheep under forage conditions). Prod. Ovina, SUL, Paysandú, Uruguay. 1989;1:45–50. [Google Scholar]
  31. LM S, WM P, BE H. Influence of sexual activity on serum levels of LH and testosterone in the ram. Canadian J. Anim. Sci. 1974;54:579–585. doi: 10.4141/cjas74-070. [DOI] [Google Scholar]
  32. ZZ X, MF M, SN M, HT B. Seasonal variation in testis size, gonadotrophin secretion and pituitary responsiveness to GnRH in rams of two breeds differing in time of onset the breeding season. Anim. Reprod. Sci. 1991;26:281–292. doi: 10.1016/0378-4320(91)90053-3. [DOI] [Google Scholar]
  33. L Z, GH S, H K, JF Q, E G. Persistence of luteal activity in the non-pregnant ewe. Anim. Reprod. Sci. 1984;7(1–3):245–267. [Google Scholar]

Articles from Acta Veterinaria Scandinavica are provided here courtesy of BMC

RESOURCES