Compensability of Enhanced Cytoplasmic Droplet Rates in Boar Semen: Insights of a Retrospective Field Study

SIMPLE SUMMARY: Cytoplasmic droplets (CD) represent a common sperm abnormality in boar. Their negative effect on fertility might be compensated by high numbers of morphological and functional intact spermatozoa in the insemination dose. To prove this hypothesis, a retrospective analysis of fertility data from 1497 inseminations obtained with 260 extended ejaculates of 130 boar was performed. CD rates > 11% provided a greater risk for reduced litter sizes. However, average litter sizes in the semen group with high CD rate (>15%) did not differ from groups with medium (10–15%) or low (<10%) CD rates. The farrowing rate was even slightly higher in the high CD group. This was accompanied by a higher tolerance of sperm to heat and cold stress compared to semen groups with lower CD rates. Other functional sperm parameters did not differ between the three CD groups. In conclusion, an increased rate of CD in extended boar semen portions can be compensated by a high percentage of stress-tolerant sperm so that fertility is not affected. ABSTRACT: Retained cytoplasmic droplets (CD) provide the most abundant sperm abnormality in boar and reduce fertility. It is still unclear as to whether high CD rates in semen portions are compensable. The aim was to explore the impact of CD in relation to quantitative and qualitative sperm traits on fertility performance of sows. Retrospective data analysis of 1497 inseminations was performed. Ejaculates (n = 260) were assigned to three groups with low (<10%), medium (≥10% to <15%), and high (≥15%) CD rates. Average sperm numbers were lowest in the high CD group (2.08 × 10(9)/mL). Membrane integrity and mitochondrial activity did not differ between the groups. Breakpoint analysis indicated a shift towards lower litter sizes when the CD rate exceeded 11%. Group comparisons revealed no difference in litter size (p = 0.205), together with a slightly higher farrowing rate in the high CD group (p < 0.001), which coincided with higher resistance against temperature stress in the stored semen samples (p < 0.001) and a higher sperm motility (p < 0.001). In conclusion, an increased prevalence of CD in boar semen is compensable by high tolerance against temperature stress, whereas sperm numbers per dose are less relevant.