Influence of season in Kerala on the yield and quality of bovine oocytes obtained by ultrasound-guided transvaginal oocyte recovery

Abstract

The present study was carried out to assess the influence of three seasons in Kerala on the yield and quality of oocytes from crossbred (CB) dairy cows (n=27), subjected to ultrasound-guided transvaginal oocyte recovery (TVOR). Meteorological data including, ambient temperature (AbT) and relative humidity (RH) was recorded and Temperature Humidity Index (THI) was calculated. In each season, selected animals (n=9) were subjected to TVOR; data regarding the number of follicles available for puncture (>2mm), number of aspirated follicles, number of oocytes retrieved and oocyte recovery rate were recorded. The retrieved oocytes were subjected to morphological evaluation. Significantly higher (P<0.05) AbT and THI was recorded during summer (28.92±0.64oC and 80.61±0.76) when compared to rainy (26.95±0.17oC and 78.68±0.21) and post-monsoon (27.29±0.22 oC and 77.75 ± 0.57) seasons. However, due to the availability of rainfall throughout the year, RH did not differ significantly between seasons. The mean number of follicles imaged (available for puncture) by ultrasonography per session was significantly higher (P<0.01) during the rainy season (11.19±0.74) compared to post-monsoon (8.08±0.47) and summer (5.28±0.38). Total mean number of follicles aspirated and oocytes retrieved per session was highest during rainy season (7.86±0.49 and 3.17±0.28) and least during summer (4.36±0.29 and 1.81±0.20). However, the oocyte recovery rate and the yield of culture-grade oocytes did not differ significantly between seasons. It was observed that the THI during all the seasons was above the thermo-comfortable level suggested for dairy cows. Ovarian activity of CB dairy cows was compromised during the summer season in Kerala, as evidenced by the lowest number of follicles aspirated and oocytes retrieved per session.