Abstract
The objective of this study was to determine the effect of seasons on the (1) aspiration rate, oocyte yield, and oocyte quality of buffalo. 2) Oocyte maturation rate and embryonic developmental competency in buffalo. In 2022, the ovaries of buffaloes [n= 627] were collected throughout the year, including cold seasons (October-March) and hot and moderately hot seasons (April-September). The temperature humidity index (THI) was computed, the numbers of follicles and oocytes were counted, and the recovery rate and the yield of oocytes were recorded. The quality of the oocytes was categorized as high quality (good and excellent) and low quality (fair and denuded) oocytes. Good and excellent oocytes were matured in vitro in tissue culture media-199 supplemented with 10 μg/ml follicle-stimulating hormone (FSH) + 10% fetal calf serum (FCS) + 50 μg/ml gentamicin. After 22 hours of incubation with 5% CO2 at 38.5°C, the cytoplasmic and nuclear maturation of the matured oocytes was assessed. Frozen-thawed semen was utilized to fertilize mature oocytes in vitro for eighteen hours and then cultured for seven days using modified synthetic oviductal fluid (mSOF). Our investigation showed that, in comparison to hot seasons, the aspiration rates and oocyte yield during the cold seasons were significantly (P˂0.05) higher. The number and percentage of good and excellent oocytes increased during cold seasons. Additionally, the cytoplasmic and nuclear maturation of mature buffalo oocytes in vitro was significantly (P<0.05) decreased during the hot seasons. The morula and blastocyst rates were significantly (P˂0.05) greater in autumn and winter than in spring and summer seasons. In conclusion, reproduction in buffalo in the hot seasons could be impaired by reducing the oocyte quality. In Buffalo, the rates of in vitro maturation rate, morula and blastocyst rate increased significantly during the cold seasons.

Key words: Seasons, Buffalo, Oocyte Yield, Oocyte quality, maturation, embryos.