40 multiparous buffalo's cows in the postpartum period were used in this study. The animals aged 6-8 years and have a history of persistent corpus lutetium (C.L.). Two groups of animals were divided, the first one was used as a control (untreated), the second one was fed a basal diet with cotton seed oil 2% from parturition till the end of the experiment. All buffaloes showed mature C.L. were injected with PGF₂α. The buffaloes (control and treated) showed estrus were artificially inseminated 72 hours post injection (timed A.I) and examined rectaly to asses pregnancy after 60 days post insemination. Blood samples were collected from all animals before injection of PGF₂α (60 days PP) and one month after injections (90 days PP) for analysis of serum glucose, triglycerides, fatty acids and cholesterol. Serum zinc and copper levels and total antioxidants were determined. Our results revealed that serum glucose concentration was not significantly affected by fat supplementation. While triglycerides and cholesterol were significantly increased with cotton seed oil supplementation compared with control group at 90 days PP. Also the results revealed that serum concentration of palmitic, stearic. oleic, linolic and linolenic fatty acids were significantly increased with cotton seed oil supplementation group, and was more markedly increased when it was added to diet for 3months. The results also illustrated a non-significant effect on serum concentration of copper and zinc by fat supplementation compared to control group Where total antioxidants was significantly increased in the supplemented group. On the other hand the overall mean of conception rates in buffaloes supplemented with cotton seed oil were significantly increased (82.3%) than non-supplemented ones.