On the reproduction of female wild boar (Sus scrofa) in Sweden

Free-ranging wild boar (Sus scrofa) have been part of the Swedish fauna for thousands of years. Due to high hunting pressure and domestication, the species became extinct in the 17th century. After escapes from enclosures during the 1970-1980s, the numbers of wild boar in the southern part of the country increased steadily and today likely exceed 200,000 animals. To understand the population dynamics of wild boar, understanding of its reproductive period, oestrous cycle and reproductive potential is essential. The aim of this work was to increase the knowledge on female wild boar reproduction in Sweden. The study was based on macroscopic examinations of reproductive organs (ovarian structures in relation to the appearance of, and findings in, the uterus) from 617 hunter-harvested female wild boar (>30 kg body weight), sampled in 2012 to 2015 on seven private estates, located in four Swedish regions. The age of the animals was determined, and body weight noted. The crown-rump length (CRL) of the embryos/foetuses was used to calculate the oestrous month and timing of expected farrowing. Sera were analysed by commercial enzyme-linked immunosorbent assays (ELISA) in order to investigate the prevalence of nine selected pathogens. Uterus weight and length mirrored the present reproductive stage. In approximately10 % of the examined animals, reproductive abnormalities such as return to oestrus, disturbed oestrous cycle, endometritis and embryo/foetal mortality were found. Of animals aged < 12 months, 11.4 % were classified as post-pubertal which was low compared to previous European studies. The proportion of post-pubertal animals increased with age and weight, and from summer to spring, suggesting a seasonal reproductive pattern. Although, the majority of all studied animals showed a seasonal reproductive pattern, farrowing also occured ‘off-season’. The reproductive potential was high compared to other countries, and increased with age and weight, as did pregnancy rate. High sero-prevalence of Porcine parvo virus, Porcine circo virus type 2, Erysipelotrix rhusiopathiae, and Mycoplasma hyopneumoniae was found. No antibodies were detected against Porcine respiratory and reproductive syndrome virus, Brucella suis, or Mycobacterium bovis. In total, this work contributes to improved knowledge about wild boar reproduction in Sweden, which is of importance for wild boar management.Keywords: oestrous stage, puberty, reproductive potential seasonality, serology.