Effect of Weaning to Oestrus Interval and Equine Chorionic Gonadotropin on Vaginal Electrical Impedance During Peri‐oestrus in Sows

Abstract

The influence of weaning to oestrus interval, its interaction with parity and equine chorionic gonadotropin (eCG) on changes of vaginal impedance in sows after weaning was examined. The impedance measurements were carried out by a four-terminal method. Sows were monitored for oestrus via exposure to a sexually mature boar. The interval from weaning to oestrus was longer in primiparous than multiparous sows (p<0.01). A significant negative correlation was found between the interval from weaning to oestrus and parity. Repeated measures analysis showed that the interval from weaning to oestrus and parity and their interactions had a significant effect on the vaginal impedance in peri-oestrus. The vaginal impedance during pro-oestrus gradually decreased in all groups of sows with the weaning to oestrus interval from 4 to 8 days (p<0.05). In the subsequent period, the vaginal impedance increased and was significantly lower from 1 to 3 days after oestrus onset in sows with the weaning to oestrus interval 7-8 days than 4-6 days. Similarly, the vaginal impedance during pro-oestrus gradually decreased in all groups of sows with parity 1-5 (p<0.01). In the next period, the vaginal impedance increased and was significantly lower from 2-3 days after oestrus onset in sows of parity 1 than parity 2-5. Repeated measures analysis showed that eCG treatment had a significant effect on the vaginal impedance in peri-oestrus. Sows treated with eCG displayed the decrease and increase of vaginal impedance due to oestrus onset earlier than untreated sows. The results indicate that the weaning to oestrus interval, its interaction with parity and eCG markedly affect the vaginal impedance in sows during peri-oestrus.

Estrategias en el manejo reproductivo de la cerda para la mejora de la fertilidad = Reproductive management strategies for improving sow fertility

“…The decrease in VER levels has been associated with the peak of estradiol which occurs prior to the LH surge, while the electrical resistance increased gradually around the LH peak (8). Changes in VER levels in the current study took place over a 4 to 5 day period, while the time difference between sows with an early and late ovulation was less than 30 h. As such, it is likely that changes in VER at different ovulation times are too small to be detected accurately, especially since VER seems not to be directly associated with ovulation itself, but to changes in sexual hormone levels (8,6). In addition to the lack of periovulatory changes, VER values were highly variable between sows at any given time point.…”

“…In the present study, we assessed whether VER provided a reliable tool to predict time of ovulation in weaned sows. Numerous studies have shown that VER fluctuations reflect changes in steroid and gonadotrophic hormone levels (6,8,14). Consequently, vaginal probes have been employed during the periestrus period or throughout the estrous cycle for non-invasive monitoring of VER in cyclic gilts and sows in order to detect estrus but, to our knowledge, there is no information in the potential use of VER to detect ovulation.…”

“…In addition to the lack of periovulatory changes, VER values were highly variable between sows at any given time point. This variability is likely due to the effect of external factors on the sow, such as season, parity or WEI, that act directly at the vaginal level and also through changes in the sexual hormones levels (6,15). A previous study indicated that shorter WEI were associated with lower VER values earlier in the estrus period (6).…”

“…El patrón de crecimiento folicular en la cerda cíclica entre los días 8 y 15 del ciclo estral, coincidente con las etapas media y final de la fase luteal, se caracteriza por un continuo crecimiento de los folículos reclutados (asociado a los niveles basales de FSH en esta fase del ciclo estral) y por la atresia de los folículos ováricos no reclutados (Guthrie and Cooper, 1996). A partir del día 2 o 3 del ciclo estral, tiene lugar un descenso de la concentración plasmática de FSH a niveles basales (5)(6)(7) ng/mL; Guthrie and Bolt, 1990;Sacristán et al, 1996;Knox et al, 2003), permaneciendo en dichos niveles hasta el siguiente pico preovulatorio de LH. Finalizado el pico preovulatorio de LH, se da un aumento transitorio de la concentración en sangre de FSH hasta alcanzar su concentración máxima (8-10 ng/mL) entre los días 2 y 3 del ciclo estral (liberación periovulatoria de FSH; Sacristán et al, 1996).…”

“…However, the estrous response to hormonal treatments is affected by parity and season 3, and often results in lower farrowing rates and litter sizes (2,4). Previous studies have reported the use of vaginal electrical resistance (VER) as a tool to predict the estrous response in sows (5,6,7), given that changes in electrical conductivity of vaginal mucus seem to be related to changes in sexual hormone levels during the estrous cycle (8). In pigs 5, cattle 9, sheep 10, buffaloes (11) and rats (12), a decrease of VER was observed during proestrus, followed by a gradual increase during estrus until ovulation.…”