Time of ovulation in sows is not related to intravaginal dissolved oxygen levels or temperature

Abstract

Timing is a crucial factor in the success of artificial insemination (AI). In sows, the appropriate time for AI amounts 12 hours before to 4 hours after ovulation based on the period in which viable spermatozoa should be available at the site of fertilization. However, in contrast to the general period of estrus, which is associated with behavioral and physical changes, the exact time of ovulation is not visible externally. It is, therefore, important to consider and evaluate additional methods that allow a more accurate determination or prediction of the actual time of ovulation than just the occurrence of the standing reflex in sows. With this goal in mind, 14 DanBred sows (parity: 5.2 ± 2.4) were subjected to ultrasound scans of the ovaries. The examinations started 80 hours after weaning and were repeated in 8 hours intervals for up to 72 hours to monitor ovarian function and time of ovulation. Additionally, intravaginal dissolved oxygen (pO2 in mmHg) levels and temperature (in°C) were measured using a fluorescence-based technique (OxyLiteTM) to uncover possible relations between the time of ovulation and the amount of oxygen available to cells and tissue. On average, sows ovulated 121 ± 10 hours after weaning and 16 ± 9 hours (mean ± SD) after the onset of heat. There were no significant differences in the intravaginal pO2 (P=0.988) or temperature (P=0.985) between the time points and in any of the direct, pair-wise comparisons between the five respective time points (P>0.05; before ovulation: 20 hours, 12 hours, and 4 hours; after ovulation: 4 hours and 12 hours). In conclusion, intravaginal pO2 and temperature have limited usefulness in predicting the occurrence of ovulation in sows using the presented technology.