Post-mortem examination of the reproductive organs of female wild boars (Sus scrofa) in Sweden

It is time to mate: population-level plasticity of wild boar reproductive timing and synchrony in a changing environment

On a population level, individual plasticity in reproductive phenology can provoke either anticipations or delays in the average reproductive timing in response to environmental changes. However, a rigid reliance on photoperiodism can constraint such plastic responses in populations inhabiting temperate latitudes. The regulation of breeding season length may represent a further tool for populations facing changing environments. Nonetheless, this skill was reported only for equatorial, nonphotoperiodic populations. Our goal was to evaluate whether species living in temperate regions and relying on photoperiodism to trigger their reproduction may also be able to regulate breeding season length. During 10 years, we collected 2,500 female reproductive traits of a mammal model species (wild boar Sus scrofa) and applied a novel analytical approach to reproductive patterns in order to observe population-level variations of reproductive timing and synchrony under different weather and resources availability conditions. Under favorable conditions, breeding seasons were anticipated and population synchrony increased (i.e., shorter breeding seasons). Conversely, poor conditions induced delayed and less synchronous (i.e., longer) breeding seasons. The potential to regulate breeding season length depending on environmental conditions may entail a high resilience of the population reproductive patterns against environmental changes, as highlighted by the fact that almost all mature females were reproductive every year.

Atypical porcine pestivirus-A widespread virus in the Swedish wild boar population

The recently identified causative agent of congenital tremor in domestic piglets, atypical porcine pestivirus (APPV), was detected in serum from Swedish wild boar. A previous study from Sweden described APPV in domestic piglets suffering from congenital tremor, but the APPV situation in the wild boar population was unknown. In this study, 595 serum samples from wild boar originating from 13 counties in the south and central parts of Sweden, collected between 2000 and 2018, were analysed for the presence of the APPV-genome and for antibodies against the APPV-glycoprotein E^rns . The results revealed that APPV is highly abundant in the Swedish wild boar population; 12% (73/595) were APPV-genome positive in serum and 72% (433/595) of the tested wild boars displayed APPV-specific antibodies. The present study also shows that APPV has been present in the Swedish wild boar population since at least the year 2000. The viral sequences obtained from the wild boars were highly similar to those obtained from Swedish domestic pigs positive for APPV and suffering from congenital tremor, suggesting a viral exchange between wild boars and domestic pigs. The high proportion of viraemic and seropositive wild boar is indicative of wild boar being an important reservoir for APPV.

Concentrations of cadmium, lead, arsenic, and some essential metals in wild boar from Sweden

The wild boar (Sus scrofa) is becoming more common in Europe and has potential to be used as sentinel species for local contamination of heavy metals. Concentrations of nine trace elements (arsenic (As), cadmium (Cd), copper (Cu), iron (Fe), lead (Pb), magnesium (Mg), manganese (Mn), selenium (Se), and zinc (Zn)) were examined in kidney tissue of 104 female wild boars hunted at three sites in Sweden. The interrelationships between the trace elements and age dependency were investigated. Reproductive health was previously known to differ among animals at the different study sites, but could not be explained by heavy metal concentrations and no associations were found between heavy metals and reproductive parameters. Kidney concentrations of Cd (mean 4.16 mg/kg wet weight (w.w.), range 0.16–12.8) were higher than the permissible level for human consumption in 99.9% of the samples. Pb concentrations were generally intermediate or low (mean 0.14 mg/kg w.w., range 0.03–1.01) and exceeded the levels accepted for human consumption in 0.02% of the samples. Age class was significantly associated with the concentrations of Cd, Mg, and Mn. Concentrations of As were low (mean 0.02 mg/kg w.w., range <0.0001–0.08) and Cu and Se concentrations were within the ranges of suspected deficiency for 10% and 4% of the wild boars, respectively.

The reproductive pattern and potential of free ranging female wild boars (Sus scrofa) in Sweden

Background

The number and spatial distribution of wild boars (Sus scrofa) has increased remarkably in Sweden as well as in other European countries. To understand the population dynamics of the wild boar, knowledge of its reproductive period, oestrus cycle and reproductive success is essential. The aim of this study was therefore to describe the seasonal reproductive pattern and reproductive potential of a wild boar population in Sweden. The study was based on findings from macroscopic examinations of the reproductive organs from 575 hunter-harvested female wild boars (>30 kg body weight). Samples were collected between December 2011 and December 2015 in the southern and middle parts of Sweden. The age of the sampled animals was determined and dressed weight was noted. The stage of the reproductive cycle was defined according to ovarian structures and in relation to the appearance of/and findings in the uterus. The crown-rump length (CRL) of the embryos/foetuses was used to calculate the oestrus/mating month and month for the expected farrowing.

Results

The macroscopic examination revealed a seasonal variation of reproductive stages, although cyclic and pregnant females were found in all seasons. Moreover, the estimated oestrus/mating and farrowing months based on the CRL showed that mating and farrowing may occur ‘off-season’. The average litter size (no. of embryos or foetuses) per pregnant female was 5.4. Sow weight and age had significant effect on both the reproductive potential (ovulation rate and litter size) and pregnancy rate, respectively.

Conclusions

The reproductive potential in the studied wild boar population was high compared to studies from other countries and farrowing may occur ‘off-season’. This suggests that the environmental conditions in Sweden, including supplemental feeding, are favourable for wild boar reproduction.

Electronic supplementary material

The online version of this article (doi:10.1186/s13028-017-0321-0) contains supplementary material, which is available to authorized users.