Nicotinic acid treatment improves the developmental potential of equine oocytes for cloned embryo production.

Nicotinic acid (NA) treatment during in vitro maturation (IVM) has been shown to elevate nicotinamide adenine dinucleotide (NAD+) levels and improve oocyte developmental competence. Suboptimal equine oocyte IVM systems currently limit the efficiency of viable embryo in vitro production. This study evaluated NA supplementation during IVM for cloned equine embryo production, using oocytes from abattoir-sourced ovaries and live mares via ovum pick-up (OPU). Abattoir-derived oocytes (n = 694) were treated without or with 50 or 200 μM NA during the 18 h holding period (Pre-IVM). Next, OPU-derived oocytes (n = 147) received either no treatment or 200 μM NA during Pre-IVM. Additionally, 285 OPU-derived oocytes were treated with 200 μM NA during Pre-IVM and then either without or with 200 μM NA during the final 22-24 h of IVM. While different cell lines provided the donor nuclei, all experimental groups used the same cell line in each replicate. In abattoir-derived embryos, the Pre-IVM NA treatment increased blastocyst rates compared with the control (50 μM: 27.1 ± 1.4%; 200 μM: 32.9 ± 3.0%; control: 19.9 ± 1.7%; P < 0.05). In OPU-derived embryos, the Pre-IVM NA treatment had no effect (P > 0.05), but NA supplementation during IVM improved the blastocyst rate (53.4 ± 9.6% vs 31.3 ± 8.1%; P < 0.05). The rates of nuclear maturation, couplet fusion, and cleavage were not influenced by NA supplementation. These results show that NA treatment during Pre-IVM and IVM enhanced equine oocyte developmental potential. Further research is needed to clarify the underlying mechanisms and assess embryo viability post-transfer.