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Reproductive Seasonality of Corriedale Rams under Extensive Rearing Conditions

Acta Veterinaria Scandinavica volume 38, pages 109–117 (1997)Cite this article

Abstract

The objective of the present study was to describe seasonal changes in scrotal circumference (SC), live weight (LW), sperm morphology and plasma levels of testosterone (T) and thyroxine (T4) in young Corriedale rams reared under extensive conditions typical for the southern Latin American region. A total of 31 Corriedale rams, 11 months of age and with a LW of 36 ± 1.1 kg and (SC) of 23.0 ± 0.5 cm at the beginning of the experiment (September) were kept on natural pastures. At monthly intervals LW was recorded, animals were clinically examined, and SC was measured. None of the animals were used for breeding. Fifteen animals were randomly selected and bled once a month from January to December and plasma concentrations of T and T4 were determined. In addition, one semen sample was collected by electroejaculation and morphological studies were performed. The mean individual LW increase was 18 kg (50% of the initial LW) during the experiment (p<0.01). LW decreased in autumn, with the nadir in late autumn. SC reached mean maximum levels in late summer (31.1 ± 0.4 cm, p<0.01), then decreased until the beginning of winter (26.3 ± 0.4 cm, p<0.01) and remained low until early spring (27.5 ± 0.5 cm, p>0.05) to increase again between mid-spring and the end of the experimental period the following summer (30.7 ± 0.5 cm, p<0.01). The mean SC in winter was 16% lower than that in late summer. Semen could be collected from the rams throughout the experiment. Frequencies of sperm head, mid-piece and total abnormalities showed monthly variation (p<0.05), but tail abnormalities were not affected by month. Low abnormalities were found in autumn (9.4% ± 2.2%). T was high during autumn (p<0.01). Minimal T4 concentrations were observed during late summer and early autumn (p<0.01) when T levels were high. Maximum T4 concentrations were registered in late autumn (p< 0.01), when SC was decreasing; in mid-spring (p<0.01) one month after shearing and in early summer (p<0.01). The results suggest that Corriedale rams under Uruguayan extensive management systems show a reproductive seasonality that, in general terms, coincides with photoperiodic variations.

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Acknowledgment

The authors are indebted to the working staff at “El Recreo”. Without their help this study would not have been possible. Financial support was received by IFS (Grant B/1917-1). Dr. Raquel Perez Clariget is holder of a scholarship from CSIC of the Universidad de la República Oriental del Uruguay which supports her stay in Sweden.

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Authors and Affiliations

  1. Departments of Animal Anatomy & Physiology, Faculty of Veterinary Medicine, University of Uruguay, Montevideo, Uruguay

    R. Perez C, A. Lopez, D. Laborde & D. Queirolo

  2. Departments of Histology and Embryology, Faculty of Veterinary Medicine, Uruguay

    A. Bielli & T. Gastei

  3. Departments of Nuclear Techniques, Faculty of Veterinary Medicine, Uruguay

    R. Tagle

  4. Statistics, Faculty of Agriculture, Faculty of Veterinary Medicine, Uruguay

    J. Franco

  5. Private Veterinary Clinic & Depts of Clinical Chemistry and Obstetrics and Gynaecology, Swedish University of Agricultural Sciences, Uppsala, Sweden

    A. Castrillejo & M. Forsberg

  6. Faculty of Veterinary Medicine, Swedish University of Agricultural Sciences, Uppsala, Sweden

    H. Rodriguez-Martinez

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  1. R. Perez C
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  2. A. Lopez
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  3. A. Castrillejo
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  4. A. Bielli
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  5. D. Laborde
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  6. T. Gastei
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  7. R. Tagle
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  8. D. Queirolo
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  9. J. Franco
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  10. M. Forsberg
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  11. H. Rodriguez-Martinez
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Correspondence to R. Perez C.

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Perez C, R., Lopez, A., Castrillejo, A. et al. Reproductive Seasonality of Corriedale Rams under Extensive Rearing Conditions. Acta Vet Scand 38, 109–117 (1997). https://doi.org/10.1186/BF03548513

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Acta Veterinaria Scandinavica

ISSN: 1751-0147