Protective effect of dietary L-carnitine supplementation on follicular development in the ovary of ewes with subclinical pregnancy toxemia

Abstract

This study examined the effects of subclinical pregnancy toxemia (SPT) on follicular development and evaluated the protective potential of dietary L-carnitine supplementation in ewes. Eighteen crossbred Hamdani ewes underwent estrous synchronization, natural mating, and pregnancy confirmation via ultrasonography on day 45 post mating. The ewes were fed according to the National Research Council (NRC) (2007) guidelines until day 100 of gestation, after which they were assigned to one of three groups: SPT (G1, n=6), SPT+L-carnitine (G2, n=6), and control (G3, n=6). Blood beta-hydroxybutyrate (beta HBA) levels were measured on days 100 and 138. Following slaughter, ovarian tissues were collected, processed, stained with Harris hematoxylin and eosin, and imaged for histometric analysis. Follicle types, oocyte diameters, and zona pellucida (ZP) thickness were recorded. Primordial follicle numbers did not differ significantly among groups (p>0.05). Primary follicles tended to be higher in G1 compared to G2 and G3, but this was not statistically significant (p<0.05). Secondary follicles differed significantly, with G2 exhibiting higher counts than G1 and G3 (p<0.05), indicating enhanced secondary follicle development with L-carnitine supplementation. Antral follicles were low across all groups, with no significant differences (p>0.05), consistent with limited preovulatory follicle formation during pregnancy. Atretic follicles were more numerous in G1 than in G2 and G3 (p<0.05), suggesting increased follicular regression in ewes with subclinical pregnancy toxemia (SPT). Secondary follicle oocyte diameters were larger in G2 and G3 than in G1 (p<0.05), while antral follicle oocyte diameters showed no significant differences (p>0.05). ZP thickness tended to be higher in G3 for both secondary and antral follicles, although differences were not significant between groups (p>0.05). Pairwise effect sizes (Cohen's d) also indicated a large effect of L-carnitine on secondary follicle and antral follicle development, and oocyte diameter; and a negative effect of subclinical pregnancy toxemia on follicle development. These results highlight the importance of adequate nutrition and metabolic support during late gestation and suggest that L-carnitine supplementation may enhance follicular growth and reproductive performance in ewes with SPT. Further studies are needed to clarify the mechanisms by which L-carnitine protects ovarian functions and follicular development.