193 Effect of clinical metritis on oocyte recovery, oocyte quality, and early in vitro developmental competence of embryos in Bos indicus dairy cattle

Abstract

Unhygienic practices at the time of parturition or AI lead to uterine infections. The uterine infections ultimately result in genetic drain by culling the elite animals. The in vivo developmental competence of embryos is compromised in clinically metritic animals. The genetic potential of problematic females could be harvested by in vitro embryo production (IVEP). Therefore, the objective of the present study was to evaluate the effect of clinical metritis on oocyte recovery, oocyte quality, and early in vitro developmental competence of embryos in Bos indicus dairy cattle. This experiment was carried out from December 2017 to April 2018. Ovaries were collected from a local abattoir (Bos indicus; 5- to 8-year-old dairy cattle, body condition score 2.75 ± 0.25, mixed parity). These ovaries (n = 982) were divided into two groups: (1) clinically metritic (n = 184), and (2) healthy (n = 798), based upon the presence or absence of pus in the uterine lumen. Oocytes were aspirated from follicles using an 18G needle attached to a 10-mL syringe. Cumulus-oocyte complexes (COCs) were categorized into A, B, C, and D grades based on the number of layers of cumulus cells and integrity of ooplasm. The oocytes of grades A and B were subsequently transferred in groups (10/group) in four-well plates containing 100-μL droplets. The droplets with oocytes were covered with prewarmed mineral oil and incubated for 24 h at 38.5°C, 5% CO₂, and 95% relative humidity. The oocytes were evaluated for IVM on the basis of cumulus expansion. Frozen semen was thawed and prepared using the sperm swim-up procedure for each group. Spermatozoa and oocytes were incubated together for a period of 18 h. The presumptive zygotes were in vitro cultured for 4 days in a CO₂ incubator under similar culture conditions. The cleavage rate, 4-cell, and 8-cell stages were recorded on Days 2, 3, and 4 after the day of insemination, respectively. Data on oocyte recovery, oocyte quality, IVM, cleavage rate, and 4-cell and 8-cell stages were analysed by Chi-squared test using SPSS software (version 20; IBM Corp.) for Windows. Results demonstrated that recovery rate was lower (63.8% vs. 71.7%; P < 0.05) in clinically metritic compared with healthy cattle. Similarly, oocytes of grade A and B quality were lower (41.0% vs. 51.1%; P < 0.05), whereas those of C and D quality were higher (59.0% vs. 48.9%; P < 0.05) in clinically metritic compared with the healthy group. Moreover, 4-cell (38.2% vs. 54.8%) and 8-cell stage embryos (11.3% vs. 29.1%), were lower (P < 0.05) in the clinically metritic compared with the healthy group, respectively. However, maturation rate and cleavage rate did not differ (P > 0.05) between groups. In conclusion, metritis in slaughterhouse ovaries negatively affects oocyte recovery rate, oocyte quality, and early in vitro developmental competence of embryos in Bos indicus dairy cattle.