Vaginal and vestibular electrical resistance as an alternative marker for optimum timing of artificial insemination with liquid-stored and frozen-thawed spermatozoa in sows

Abstract

Development of a pen-side test to objectively determine the ideal time for artificial insemination (AI) in the sow would save producers time and money. Current processes rely on identification of oestrus via subjective behavioural and physiological markers that are indicative of high blood oestrogen concentrations. This study attempted to use measurements of electrical resistance (ER) in the cervical mucus to pinpoint timing of AI accurately enough to lead to equivalent pregnancy rates as a natural mating. Thirty-six sows were divided into 3 groups and observed for signs of oestrus. Seven sows did not show any oestrus behaviour and were excluded from the study. The remaining 29 sows were inseminated via natural mating and conventional oestrus detection (n = 14), or inseminated artificially with either liquid-stored semen (n = 8) or frozen-thawed semen (n = 7) according to timing indicated from electrical resistance measurements in the vagina and vestibule. Sows that were artificially inseminated on the basis of the electrical resistance readings had a lower pregnancy rate (P = 0.034) and less piglets born alive per litter (P < 0.05) than those that were naturally mated according to a conventional oestrus detection regime. However, the pregnancy rate and total piglets born alive did not differ between the two groups that underwent artificial insemination. Change in electrical resistance in the vagina has the potential to accurately predict ovulation timing, but more work is required to refine the timing of AI in relation to the readings before the technique can be adopted by industry.

Figure 1

Schematic of the timings of examinations conducted during oestrus in sows to identify if electrical resistance is an effective physiological marker of optimum insemination timing. Day 0 is the first time-point in the oestrous cycle and is defined as the first instance of observed behavioural oestrus. The horizontal arrows lead to time-points that exist at an appropriate time relative to oestrus events and hence will enable identification of the physiological markers that could predict ovulation accurately.

Figure 2

Mean (± S.E.M) electrical resistance recorded at two locations within the reproductive tract (vestibule and vagina) during the oestrus cycle. Time points are relative to the onset of behavioural oestrus detected by the presence of standing heat in the presence of a boar. The last data point coincides with predicted ovulation, which was defined as 30 h prior to the highest detected faecal progesterone concentration. Superscripts indicate statistical differences between time-points within one location (P < 0.05).