Short-term treatment with deslorelin implants to improve the bucks’ ability to stimulate cyclic activity during the late non-breeding season
Introduction
Reproductive seasonality is a major limitation for goat production in temperate zones, as it limits the kidding period, and thus, the period in which milk and/or meat are offered (Chemineau et al., 2008). The male effect has been used to induce out-of-season ovulations, and thus, parturitions (Chemineau, 1987; Chemineau et al., 2006; Delgadillo et al., 2009). The sudden introduction of males to anestrous females stimulates a rapid increase in LH pulse frequency that ends in an LH peak, followed by ovulations (Delgadillo et al., 2009). This technique is widely used among goat farmers in extensive systems considering that it requires minimal human labor and economic costs (Rivas-Muñoz et al., 2007).
The percentage of females that respond to the male effect is related to male’ sexual behavior (Véliz et al., 2002). In this sense, males that display high levels of sexual behavior induce ovulation in a greater proportion of females than males with low levels of sexual behavior (Martínez-Alfaro et al., 2014). For example, increase of bucks nutritional plane (Walkden-Brown et al., 1993) or application of photostimulation (Delgadillo et al., 2002) enhances bucks’ sexual activity, increasing bucks’ ability to induce out-of-season ovulations. In the same direction, at least in certain conditions females would not respond if bucks are not prestimulated with light regimes (Flores et al., 2000; Delgadillo et al., 2002). However, light treatments cannot be easily applied in extensive grazing systems, in which animals remain continuously grazing outside, in big paddocks, with low human intervention.
As both androgenized buck wethers and does are as effective to induce estrus as intact bucks (Mellado and Hernández, 1996), it was proposed that the effectiveness of males as teasers is androgen dependent. Therefore, it is important to develop practical strategies to increase bucks’ testosterone concentration before joining bucks and does to induce ovulations and pregnancies in more anestrous females. In rams, a practical alternative is to administer two doses of eCG, inducing sustained increase of testosterone, and therefore, induce estrus and pregnancies in a greater proportion of females (Ungerfeld et al., 2014). Ungerfeld et al. (2014) hypothesized that testosterone concentrations should remain elevated for several days before joining rams with ewes to increase the percentage of females responding . However, as the production of eCG is under debate due to ethical concerns, is important to develop other alternative treatments. The application of implants containing GnRH agonists is used as a pharmacological contraception technique, as the continuous release of the analogue desensitizes the pituitary GnRH receptors (Lincoln et al., 1986). However, during the immediate period after inserting these implants there is a short-term flare up period, during which GnRH agonists stimulates males’ reproductive activity and thus, testosterone concentration increases (Junaidi et al., 2007). Giriboni et al. (2020) observed elevated testosterone concentrations for several weeks after insertion of deslorelin implants in bucks. Therefore, the insertion of deslorelin implants during a short period before joining bucks with anestrous does may be an alternative to maximize the response of anestrous does. Considering all this information, the aim of this study was to compare the reproductive response of anestrous does to the introduction of teaser bucks treated with or without deslorelin implants.
Section snippets
General procedures
All the procedures were approved by the Ethical Committee of the Aydın Adnan Menderes University (64583101/2018/096). The study was performed at the Research Unit of the Aydın Adnan Menderes University, Çine Vocational School (latitude 37°37ʹ N, longitude 28°04ʹ E), at Çine town located in Aydın province of Turkey. According to the historical records in this location, and in the southern Aegean region, July is the late non-breeding season. At this location the breeding period is consistently
Testosterone concentration
Considering the entire experiment, testosterone concentration was not different between Des and Con bucks. However, testosterone concentration was greater in Des (36.0 ± 7.6 nmol/L) than in Con (15.0 ± 6.8 nmol/L) bucks (P = 0.04) from Day -4.5 to Day -0.5 (Fig. 1).
Females’ response
Insignificant differences in most of the reproductive parameters in does stimulated with Des and Con bucks were observed in present study (Table 1). Overall, until Day 11, 66.3 % of the stimulated does came into estrus. All the does
Discussion
Deslorelin implants produced a fast increase of testosterone concentration, which rise rapidly (2.5 days after insertion), in consonance with recent reports in bucks (Giriboni et al., 2020). However, although Des bucks produced more testosterone during the period immediate before joining them with anestrous females, there were no differences in does’ reproductive response. This may be explained by the rapid and unexpected increase of testosterone concentration in Con bucks after Day 0, which
Declaration of Competing Interest
The authors report no declarations of interest.
Acknowledgements
We are grateful to The Council of Higher Education of Turkey, Mevlana Exchange Program (Project No: MEV-2017-039) and Aydın Adnan Menderes University Scientific Research Project Commission(ADU-KRM-17001-123). We also thank to Rosario Velázquez, who performed the hormonal measurements.
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