Downregulation of testicular function in the goat by altrenogest

Mihsler-Kirsch et al. BMC Veterinary Research https://doi.org/10.1186/s12917-021-02845-6 (2021) 17:183 RESEARCH ARTICLE Open Access Downregulation of testicular function in the goat by altrenogest Lisa Mihsler-Kirsch1, Henrik Wagner1, Klaus Failing2 and Axel Wehrend1* Abstract Background: The present study investigated whether the administration of the progestin altrenogest provides noninvasive, temporary, and reversible suppression of gonadal function in the goat as a potential alternative to chirurgical castration, which is related with irreversibility, risks of complications till death of the animal and welfare issues. Eight sexually mature Peacock goats were randomly divided into two groups. The experimental group was administered altrenogest (0.088 mg/kg) orally once daily for 7 weeks. The remaining four goats received an oral glucose solution and served as the control group. After completing the administration period, the reversibility of the medication was evaluated for another 7 weeks (observation phase). The treatment effects were assessed by clinical examination; ultrasound examination of the testes, including one-dimensional grayscale analysis, blood testosterone levels, analysis of semen parameters and libido. At the end of the observation period, the animals were castrated and the testicles were examined histologically. Results: Altrenogest treatment had no significant effect on the physical development of the goats, the sonographic appearance of the testes, the gray values measured in the ultrasound images, or the blood testosterone levels. The effects of treatment on the testicular and semen parameters varied widely in the experimental animals; the testicle volume was significantly lower and the number of pathologically altered sperm in the ejaculate was significantly higher in treated animals. Conclusion: These findings indicate that daily altrenogest administration at a dose of 0.088 mg/kg does not reliably suppress gonadal function in the goat. Keywords: Altrenogest, Goat, Downregulation, Gonadal function, Castration Background In contrast to other species, few studies have examined the effects of temporary suppression of gonadal function in the goat [1]. Today, the chirurgical castration is a widespread method to control reproduction and behavior in the male goat, but it is irreversible, covers the risk of complications till death of the animal and is a welfare issue because of the related pain. A temporary suppression of reproduction in bucks would make it possible to * Correspondence: 1 Clinic of Obstetrics, Gynecology, and Andrology of Large and Small Animals with Ambulatory Service, Justus Liebig University Giessen, Frankfurter Strasse 106, 35392 Giessen, Germany Full list of author information is available at the end of the article keep female and male animals together without breeding potentials, so that fertile bucks do not have to be kept in isolation until reproduction is desired again at a later time [1]. Previously evaluated methods of temporary gonadal function suppression in the goat include immunization against gonadotropin-releasing hormone [2–4], the use of long-term gonadotropin-releasing hormone implants [5], and administration of the α1-adrenoceptor antagonist tamsulosin [6]. In some species, altrenogest administration results in reversible downregulation of male reproductive function. Altrenogest is a synthetic progestogen which is widely used for estrus suppression and synchronization in pigs © The Author(s). 2021 Open Access This article is licensed under a Creative Commons Attribution 4.0 International License, which permits use, sharing, adaptation, distribution and reproduction in any medium or format, as long as you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons licence, and indicate if changes were made. The images or other third party material in this article are included in the article's Creative Commons licence, unless indicated otherwise in a credit line to the material. If material is not included in the article's Creative Commons licence and your intended use is not permitted by statutory regulation or exceeds the permitted use, you will need to obtain permission directly from the copyright holder. To view a copy of this licence, visit http://creativecommons.org/licenses/by/4.0/. The Creative Commons Public Domain Dedication waiver (http://creativecommons.org/publicdomain/zero/1.0/) applies to the data made available in this article, unless otherwise stated in a credit line to the data. Mihsler-Kirsch et al. BMC Veterinary Research (2021) 17:183 Page 2 of 7 and mares by oral administration. The molecule binds to the progesterone receptors in the hypothalamus and pituitary gland resulting in inhibition of gonadotropins release [7]. In juvenile boars, daily administration of 20 mg altrenogest reduces plasma luteinizing hormone and testosterone levels, delays the onset of puberty, and reduces testicle size and weight [8, 9]. While daily altrenogest at 0.044 mg/kg has no significant effect on reproductive behavior and semen parameters in stallions and zebra stallions [10, 11], daily administration of 0.088 mg/kg altrenogest over a longer period to stallions significantly and reversibly reduces blood testosterone and luteinizing hormone concentrations, and induces a progressive decrease in testicle size and libido. Further, daily treatment with altrenogest at 0.088 mg/kg decreases the amount of ejaculate and the total sperm count in stallions throughout the treatment period [12, 13]. On the basis of these previous findings, the present study examined whether the administration of 0.088 mg/kg altrenogest has similar effects on the gonadal function in goats. Table 2 Statistical analysis of physical parameters, testicular measurements, and testosterone concentrations of goats treated with altrenogest vs. control animals Parameter Factor Group Interaction Time Time x Group Body weight 0.64 < 0.0001 0.70 Body length 0.61 < 0.0001 0.63 Body height 0.93 < 0.0001 0.94 Volume of the testes 0.02 < 0.0001 0.0005 Consistency of the testes 0.14 0.04 0.07 Testosterone 0.65 0.026 0.59 Testes gray value 0.77 0.0002 0.11 two bucks of the experimental group one time at the 7th time point, from the other two bucks in this group at any time. These two bucks showed normal ejaculate parameters (Tables 5 and 6). Time had a significant effect on the volume, density, and pH of the ejaculate, and a highly significant effect on the total sperm count (Table 7). The number of morphologically altered sperm was significantly higher in the experimental group (Fig. 1). Results Physical parameters, testicle measurements, and blood parameters Clinical examination of the goats revealed no clear differences between the two groups. Body weight, length, and height increased during the course of the study (Table 1). There was a highly significant effect of (...truncated)