Birthweight leads to seminal and testicular morphofunctional commitment in sexually mature boars.

Given the importance of males as semen donors for artificial insemination (AI) and the high incidence of low birthweight piglets at commercial farms, the impact of birthweight on fertility in boars deserves special attention. The aim of this study was to evaluate testicular morphofunctional parameters and semen characteristics in different birthweight boars. Forty littermate males were selected at birth and divided into two experimental groups, according to birthweight: high (HW, birthweight ranging from 1.80 to 2.15 kg, n = 20) and low (LW, birthweight ranging from 0.75 to 1.10 kg, n = 20). At 170 days of age, a sub-set of 24 littermate boars (n = 12 HW and n = 12 LW) were randomly selected for semen collection, which was performed once a week, at a 15-day interval, during five weeks. At 300 days of age, boars were orchiectomized, and the testis processed for histological and molecular analyses. The HW group was heavier and presented larger testes compared to LW animals (P < 0.05). Despite that, birthweight did not significantly affect semen volume or sperm quality parameters (concentration, motility, vigor or morphology), although LW boars produced 38.2% fewer total sperm and 24% lower semen concentration, leading to 36.8% less inseminating doses. The histomorphometrical evaluation showed that seminiferous tubules diameter and germinal epithelium height were similar between experimental groups. However, LW boars presented shorter seminiferous tubules and, consequently, fewer Sertoli cells per testis (P 0.05). Even though plasma testosterone levels were equivalent in both birthweight groups, LW testis presented less androgen receptors (P < 0.05). Additionally, birthweight was positively correlated with total seminiferous tubule length and number of Sertoli cells (P < 0.01), and with body and testis weights (P < 0.01). Taken together, even though adult LW boars showed no evident semen pathologies or spermatogenesis commitment, mature HW males have the potential to produce more spermatozoa, consequently more semen doses per ejaculate, being more valuable to an industry that relies on AI.