28 Limited availability of L-carnitine in the preovulatory follicle promoted by obesity can be restored by diet supplementation in mares

Maternal obesity can predispose to reproductive disturbances. Systemically, in mice and humans, obesity-induced lipid accumulation impairs mitochondrial metabolism due to excessive formation of long-chain acylcarnitines and L-carnitine insufficiency. L-carnitine is an essential cofactor for fatty acid mitochondrial transport, through formation of long-chain acylcarnitines. It also helps regulate pyruvate oxidation by forming acetylcartinine and reducing mitochondrial acetyl-CoA, a pyruvate oxidation inhibitor. The extent that L-carnitine insufficiency occurs within the ovarian follicle with mare obesity has not been determined. We hypothesised that mare obesity reduces free L-carnitine and increases long-chain acylcarnitine concentrations in the preovulatory follicle, which can be corrected by diet. Mares were grouped as normal weight (NW, n = 6, 17.8 ± 1.8 years, body condition score [BCS] 5.7 ± 0.3); obese (OB, n = 7, 18.6 ± 1.5 years, BCS 7.7 ± 0.2); and obese diet supplemented (OBD, n = 7, 18.1 ± 1.3 years, BCS 7.7 ± 0.2). For ≥6 weeks before sampling, NW were fed hay (grass/alfalfa) daily at ∼2% bodyweight; OB and OBD were free-fed the same hay mix and 3 kg corn/oats; OBD also received diet supplements designed to promote equine wellness and metabolic support (Equine GI™ [147 g] and a proprietary metabolic mix [40 g, including 15 g of L-carnitine]) (Platinum Performance^® Inc.). Follicular fluid (FF) was collected from follicles ≥ 35 mm during oestrus at 20 ± 2 h after induction of maturation; FF was stored at −80°C until absolute quantification by liquid chromatography-mass spectrometry of acylcarnitines. Free L-carnitine and 17 acylcarnitine species were quantified. Differences were analysed by one-way ANOVA with post hoc Tukey’s multiple comparison tests. Total acylcarnitines, free L-carnitine, and acetylcarnitine tended (P < 0.1) to be lower in FF from OB than NW, and were higher in FF from OBD than OB and NW (P < 0.05). No difference was noted for long-chain acylcarnitines, but short-chain acylcarnitines were more abundant in FF from OBD than NW and OB (P < 0.05). The ratio between palmitoylcarnitine and propionylcarnitine indicates ineffective β-oxidation and was lower in OBD than OB (P < 0.05); both were not different from NW (P > 0.2). Mare obesity affects acylcarnitine profiles and limits free L-carnitine in the follicle, which may cause follicular cell metabolic disturbances. Diet supplementation for obese mares with L-carnitine and other ingredients was able to improve β-oxidation efficiency, restore and increase free L-carnitine availability and acetylcarnitine concentration in the follicle, therefore, improving mitochondrial metabolic flexibility and likely contributing to a healthier follicle.

This study was funded by the Cecil and Irene Hylton Foundation, the Foundation for the Horse, the USDA NIFA Animal Health and Disease Grant No. COLV 2021-09/project accession number 1026913, and the Abney Foundation Scholarship.