182 Comparison of blastocyst rates by month in a commercial equine TVA/ICSI program

Equine oocytes are collected year-round via transvaginal aspiration (TVA) for production of blastocysts via intracytoplasmic sperm injection (ICSI). Mares are presented for TVA at different times of the year. Factors affecting when TVAs are performed include, but are not limited to, the mare’s show schedule, the desire to produce embryos when the mare is transitional and cannot be bred, and stallion/semen availability. Therefore, TVAs are performed during all 12 months of the year. The objective of this study was to compare blastocyst rates by month from a commercial TVA/ICSI program located in Lexington, KY, USA. The blastocyst rate was calculated as the number of blastocysts that resulted from the number of oocytes that matured and were injected. The data were collected over an 8-year period from 2016 to 2024. A total of 1514 TVAs were performed during this time, and the oocytes were sent to a commercial ICSI laboratory. A total of 16 218 oocytes were recovered, 9737 oocytes matured and had ICSI performed, 7025 injected oocytes cleaved, and 1576 blastocysts were produced. These results yielded 60.0%, 72.1%, and 16.18% maturation, cleavage, and blastocyst rates, respectively. An average of 10.69 oocytes were collected and 1.04 blastocysts were produced per TVA session. The total number of oocytes injected by month for January through December were respectively 659, 1376, 1580, 1257, 1251, 1039, 463, 333, 293, 480, 559, and 447, with the following corresponding blastocyst rates: 17.7% (SD 22.2), 19.9% (SD 22.8), 14.9% (SD 20.1), 15.4% (SD 26.0), 17.6% (SD 24.2), 13.1% (SD 21.7), 13.8% (SD 22.3), 16.1% (SD 25.0), 13.5% (SD 21.2), 17.5% (SD 22.0), 15.8% (SD 17.7), and 15.8% (SD 20.1). The blastocyst rates did not follow a normal distribution (Shapiro-Wilk test; P < 0.05). Consequently, the data were transformed using the Normal Quantile method. A Mixed Model was employed to assess the impact of month as a fixed effect, with year of aspiration, mare, stallion, breeds, and veterinarians considered as random effects. The analysis revealed a significant effect of month on blastocyst formation, with February having the highest blastocyst rate in our data set (P < 0.05). Additionally, the year, mare, and the interaction between mare (P < 0.01) and stallion (P < 0.01) had effects on the blastocyst rates. Mare age did not significantly affect blastocyst rate (P = 0.26). Further analysis of the year effect revealed that with increasing experience, the blastocyst rate significantly increased, with the lowest rate in 2016 and an increase thereafter (P < 0.001). Further studies are needed to elucidate what other factors in a given month or certain time of year affect blastocyst rates.