The effect of dietary supplementation with algal docosahexaenoic acid on boar fertility

Docosahexaenoic acid (DHA) is a long chain omega-3 polyunsaturated fatty acid (PUFA) which when supplemented in the diet of humans and animals has been shown to have beneficial effects on the cardiovascular and nervous systems and, to a lesser extent, on both male and female fertility. In males, the inclusion of DHA in the diet is believed to contribute to sperm membrane fluidity and enables sperm to withstand various stresses during semen collection and processing, while also allowing sperm to undergo membrane associated events such as capacitation and the acrosome reaction. The objective of this study was to investigate the effects of dietary supplementation with a commercial algal DHA product (SP1) on (i) raw semen quality, (ii) liquid semen quality, (iii) frozen-thawed semen quality, (iv) sperm and seminal plasma fatty acid composition (v) total antioxidant capacity of seminal plasma and (vi) field fertility of sows inseminated with liquid semen. Boars (Landrace, Large White and Maxgro) were individually fed one of three experimental diets for 135 days. These diets included (i) Control (Ctl) diet (n=31 boars), (ii) Ctl diet plus 75g SP1 per day (n=31 boars) and (iii) Ctl diet plus 150g SP1 per day (n=30). On farm analysis was conducted over a 14 week period as semen was collected from boars approximately once per week and assessed for volume, sperm concentration as well as total motility and morphology (microscopy based). On 3 occasions, between Day 56 and 135 (D0 = first day of dietary supplementation), liquid diluted semen from a subset of boars (n=12 per treatment) was assessed on Days 1, 3 and 6 post collection. Liquid semen samples were assessed for total motility using a phase-contrast microscope and viability, hypotonic resistance and acrosomal integrity were assessed by flow cytometry techniques. Sows (n=689, 702 and 552 for the Ctl, 75 and 150g SP1 treatments, respectively) were inseminated with liquid semen on 30 farms and subsequent farrowing rates and litter sizes were captured. On 3 occasions, between Day 100 and 135, semen was collected and frozen from 6 boars per treatment and was assessed, post-thaw, for total motility and thermal stress using Computer Assisted Sperm Analysis (CASA) as well as viability, membrane fluidity and mitochondrial activity via flow cytometry. On Day 0, 56 and 126, ejaculates were collected from 12 boars per treatment and sperm and seminal plasma (SP) was harvested, frozen and later analysed for fatty acid composition. The SP was also analysed for total antioxidant capacity (TAC) using the 2.2’-azino-bis-3-ethylbenzthiazoline-6-sulfonic acid (ABTS·+) assay. There was an effect of treatment on semen volume and total sperm number with boars consuming 75g SP1 per day producing a larger semen volume (P < 0.05) and a higher total sperm number (P < 0.01) than the control group. However, there was no effect of treatment on sperm concentration, motility and or abnormalities, as assessed immediately post collection, over the duration of the supplementation period (P > 0.05). There was no effect of treatment on the in vitro analysis of liquid semen (P > 0.05), however, all parameters, such as viability, hypotonic resistance and acrosomal integrity, declined with duration of storage (P < 0.05). There was no effect of treatment on post-thaw motility, thermal stress, viability, mitochondrial activity and or membrane fluidity on frozen-thawed semen (P > 0.05). Palmitic acid was the most abundant saturated fatty acid (SFA) within both sperm and SP for all treatments, while DHA was found to be the most abundant omega-3 fatty acid. There was an effect of treatment on the fatty acid composition of sperm as the DHA content increased by a 1.51 and 1.58 fold for 75 and 150g treatments, respectively, in comparison to the control group. There was no correlation between sperm DHA content and motility, viability, acrosomal integrity, mitochondrial activity, membrane fluidity or farrowing rate. There was no effect of treatment on the fatty acid composition and the TAC of SP or on farrowing rate or litter size (P > 0.05). In conclusion, dietary supplementation with SP1 altered the fatty acid composition of the sperm, increased semen volume and total sperm number but had no effect on semen quality as assessed in vitro or on field fertility. This is the first animal study which has investigated the effect of dietary supplementation with an algal DHA product (SP1), on male fertility in any species.