Precocious puberty in male wild boars: a possible explanation for the dramatic population increase in Germany and Europe

Abstract

Background The wild boar population in Europe is steadily growing, one of the reasons for this increase probably being the high reproductive potential of this large mammal. Population management is important to stabilise wild boar numbers and a great deal of attention is focusing on the reasons, which might contribute to the high reproductive rates. Understanding the timing of puberty attainment provides information required for proper management practices. Knowledge of the earliest expected time of sexual maturation in male wild boars is limited, research being mostly focused on females. Previous hunting references indicate that sexual maturity in males occurs in the second year after birth. In contrast, male domestic pigs become sexually mature from about seven months of age. Thus, aims of this study were to investigate (1) whether there is a physiological ability for reproduction also in male wild boars of a younger age and (2) whether the body weight of wild boar males has a more important role than age in driving the maturation of the testis. Methods Male wild boar individuals were sampled during hunting drives in the eastern part of Lower Saxony in Germany. Testes with epididymides from 74 males were collected and prepared for histological examination and immunohistochemistry. The reproductive status could be ascertained based on development/occurrence of different germ cell populations using histology and based on the immunohistochemical detection of the anti-Müllerian hormone and androgen receptor. Results In this study, male wild boars aged nine to ten months already passed puberty and were able to reproduce if they had reached the appropriate body condition of about 29 kg dressed weight. Immunopositivity to the anti-Müllerian hormone in Sertoli cells was evident only in prepubertal animals and decreased with the onset of puberty. No immunoreaction was evident at postpuberty. The androgen receptor was detected in Sertoli cells, peritubular cells and Leydig cells, surprisingly already in Sertoli cells of prepubertal wild boars as well depending on body weight. Moreover, two-thirds of young males aged about ten months were precociously reproductively mature, showing histologically the presence of spermatozoa in testes and epididymides. Conclusions As piglets are mostly born in spring, also these young male individuals could target the heat of female wild boars in the winter months, resulting in the observed population increase. Therefore, a reduction in wild boar numbers should also focus on piglets of both sexes.

Fluctuations in serum steroid hormone concentrations and body mass during growth and sexual maturation in captive northern fur seals (<i>Callorhinus ursinus</i>)

“…One possible reason for the delay of sexual maturation in SEAL3 is her slower initial growth and lower body mass at age compared with normal individuals. It is reported that body weight has a more important role than age in driving the maturation of testes in wild bores (Sus scrofa) [33]. Nutritional condition is known to work as a permissive factor for the timing and progression of pubertal development in humans (Homo sapiens) [2].…”

An Approach for Investigating Sexual Maturity in Wild Boar Males: Testosterone and 17β-Estradiol Analysis

“…In addition, we also relied on the classification and results obtained in a previous publication in which the attainment of puberty was defined according to the stage of spermatogenesis [ 8 ]. We categorized males as prepubertal when the weight and the age of the animal were less than 26 kg and 8 months, i.e., 29.6 ± 3.6 kg, and 9.3 ± 1.2 months, which correspond to the limits for pubertal animals [ 7 , 8 ]. On the other hand, individuals whose weight and age were more than 34 kg and 10 months were defined as postpubertal, these values being typical of sexually mature individuals [ 5 , 7 , 8 ].…”

“…In Germany, the wild boar breeding season occurs between autumn and winter, i.e., from about October until January [ 6 ] when the day length is shortened, with farrowing approximately four months later between the end of winter and spring, which coincides with February until May. Recent investigations showed that piglets of both sexes reach puberty from about six to nine months of age and sexual maturity already in their first year of life; however, almost none of these studies evaluated sex hormones [ 6 , 7 , 8 ]. In fact, puberty was assessed macro- and microscopically in wild boar females by determining the diameter and presence of follicles/corpora lutea, i.e., the stage of the estrus cycle [ 6 , 9 ], whereas in males, it was determined by assessing the stage of spermatogenesis by means of histology and immunohistochemistry of the anti-Müllerian hormone and androgen receptor [ 8 ].…”

“…Recent investigations showed that piglets of both sexes reach puberty from about six to nine months of age and sexual maturity already in their first year of life; however, almost none of these studies evaluated sex hormones [ 6 , 7 , 8 ]. In fact, puberty was assessed macro- and microscopically in wild boar females by determining the diameter and presence of follicles/corpora lutea, i.e., the stage of the estrus cycle [ 6 , 9 ], whereas in males, it was determined by assessing the stage of spermatogenesis by means of histology and immunohistochemistry of the anti-Müllerian hormone and androgen receptor [ 8 ]. In the rut season, wild boar males of the previous year (sub-adults, i.e., from 12 to 24 months of age) and adults (over 2 years of age) attempt to reproduce.…”

“…In the rut season, wild boar males of the previous year (sub-adults, i.e., from 12 to 24 months of age) and adults (over 2 years of age) attempt to reproduce. Juveniles (under 12 months of age), which passed puberty during the breeding season develop sexual maturation at about the end of the breeding season, consequently [ 8 ].…”