Thawing boar semen in the presence of seminal plasma: Effects on sperm quality and fertility

Causes of poor fertility after insemination of frozen-thawed (FT) sperm include reduced sperm viability at thawing and a shorter longevity of surviving sperm in the female genital tract due to sub-lethal damage. The present studies examined the effect of incubating thawed boar sperm in seminal plasma (SP) on sperm membrane integrity (viability), and motility in vitro (experiment 1), and fertility in vivo (experiment 2). For experiment 1, FT sperm from five individual boars and a sperm pool from these boars were thawed and incubated for 4h in media containing 0%, 10%, or 50% autologous seminal plasma (individual boars) or pooled seminal plasma (sperm pool). At approximately 10min (0h) and again at 1h, 2h, 3h, and 4h, sperm populations were examined for percentage sperm viability and percent sperm motility. Each variable progressively decreased during the incubation period. Incubation in 50% SP increased percentages of live sperm (P <0.0001) and percent sperm motility (P <0.01) at all time points compared to incubation in either 0% or 10% SP. For experiment 2, multiparous Large white×Landrace sows (n =82) each received 900IU eCG at weaning and 750IU hCG 80h later to control time of ovulation. Sows were assigned on the basis of parity to be inseminated with pooled semen with or without SP from the boars used in experiment 1. Sows received 3×10⁹ live fresh-extended sperm (n =30) or FT sperm thawed in 80mL BTS extender (n =26) or 3×10⁹ live FT sperm thawed in 80mL BTS containing 50% SP (FT-SP; n =26). Sows were inseminated at 36h, and 42h after hCG injection. Compared to sows receiving fresh semen, the pregnancy rate of FT inseminated sows tended (P =0.06) to be lower with the FT-SP group being intermediate. Farrowing rates were not different (83.3%, 69.2%, and 65.4% for fresh, FT, and FT-SP, respectively). Inseminations with FT sperm were associated with a reduction in litter size (P <0.05), which was not evident in the FT-SP group. Taken together, these data confirm an adverse effect of inseminating FT sperm on sperm quality and sow fertility but suggest that thawing FT sperm in 50% SP may partially alleviate these adverse effects.