The impact of omega-3 nutritional manipulation on semen cryosurvival and quality post thawing is controversial. Our aim was to examine how feeding bulls with omega-3 supplementation from different sources affects the spermatozoa quality parameters. Fifteen Israeli Holstein bulls were fed for 13 weeks with a standard ration top-dressed with encapsulated-fat supplementation: fish or flaxseed oil or saturated fatty acids (control). Ejaculates were collected before, during, and after the feeding trial. Frozen–thawed samples were evaluated by a flow cytometer for spermatozoa viability, mitochondrial membrane potential, the level of reactive oxygen species (ROS), acrosome membrane integrity, DNA fragmentation, phosphatidylserine translocation, and membrane fluidity. Both fish and flaxseed oil treatment resulted in lower ROS levels vs. control groups, during and after the feeding trial. Fewer spermatozoa with damaged acrosomes were observed in the fish oil group after the feeding trial. The spermatozoa membrane fluidity was altered in both the fish and flaxseed oil groups throughout the feeding trial, but only in the flaxseed oil group after the feeding trial. The proportion of spermatozoa with fragmented DNA was lower in the flaxseed oil group after the feeding trial. The spermatozoa fertilization competence did not differ between groups however, blastocyst formation rate was higher in the fish and flaxseed oil groups relative to the control. This was associated with differential gene expression in the blastocysts. Overall, the omega-3-enriched food improved the spermatozoa characteristics; this was further expressed in the developing blastocysts, suggesting a carryover effect from the spermatozoa to the embryos.

Intensive reproductive management in dairy herds is mostly based on AI using high-merit bulls. Therefore, semen quality of bulls is of high importance. An association between semen quality and fatty acid content in feed has been suggested. Accordingly, the aim of this study was to examine the effect of omega-3 supplementation on sperm traits and fertilization competence. Fifteen Israeli Holstein bulls were assigned to three experimental groups. Bulls were fed over 13 weeks with a standard ration top-dressed with encapsulated-fat supplementation-fish oil (FO) or flaxseed oil (FLX; i.e. omega-3 sources), or saturated fatty acids (SFA, control). Ejaculates were collected before initiation of the study, during the feeding trial, and 1 month after feeding trial. Ejaculates were treated according to the routine procedure of the Israeli AI centre (Sion Ltd.), frozen, and stored in straws. Frozen-thawed samples were subjected to “swim-up” procedure, and spermatozoon viability, mitochondrial membrane potential, reactive oxygen species (ROS) level, acrosome membrane integrity, and DNA fragmentation were evaluated via flow cytometry, using sperm-specific kits (EasyCyte, IMV Technologies). Feeding with FO, FLX, or SFA did not affect the viability or mitochondrial membrane potential of sperm collected before, during, or after the feeding trial. On the other hand, a reduced proportion of sperm with ROS expression was recorded in the FLX samples compared to the SFA sample at the end of the feeding trial (42.2±1.2 vs. 47.3±4.3%, respectively; P<0.05) and one month later (36.3±2.2 vs. 41.6±4.6%, respectively; P<0.05). A low proportion of sperm with damaged acrosomal membrane was observed in both FLX and FO samples compared with SFA at the end of the feeding trial (48.8±3.4 and 41.7±2.7 vs. 59.8±3.4%, respectively; P<0.05). The proportion of sperm with fragmented DNA was lower in the FLX group than in the SFA group, collected one month after the end of the feeding trial (2.3±0.6 vs. 5.4±1.2%, respectively; P<0.05). To examine fertilization competence, oocytes were aspirated from ovaries collected from a local abattoir, then matured (n=216; 3 replicates) and fertilized invitro with a pool of samples from each group, collected one month after the end of the feeding trial (n=5 samples per group). The proportions of 2- to 4-cell-stage embryos and of blastocysts were determined 42h and 8 days after fertilization, respectively. Although the proportion of cleaved embryos did not differ between groups, a higher blastocyst formation rate was recorded in the FLX group (P<0.05), and a moderate increase was noted in the FO group, relative to the SFA group (28.1±4.4, 19.1±2.6, and 11.9±3.4%, respectively). Results imply that feeding bulls with omega-3 originating from FLX improves sperm quality, most likely due to improved redox status and decreased DNA fragmentation. This nutritional approach seems to be an effective tool for improving bull fertility competence. Nevertheless, invivo examination is required.