Investigation of the availability of vaginal electrical resistance during estrus synchronization in ewes

Vaginal electrical resistance (VER) value measurement, which is a noninvasive method, is used to determine the estrus, appropriate insemination or mating time in sheep. The aim of this study was to investigate the availability of vaginal resistance values to evaluate the success of estrus synchronization program and to estimate early pregnant and returning ewes. Besides, it was also aimed to reveal the pregnant and non-pregnant ewes during the first trimester of pregnancy. Thirty-four healthy Awassi ewes were used in the study. Intravaginal sponges were inserted to ewes for 11 days and 0.075 mg d-cloprostenol was injected intra-muscularly at the day of sponge withdrawn. Ewes were mated with fertile rams in estrus. Key times of the study were the day sponge insertion (D-0), the day of estrus (D-E), sixty hours after sponge removal (h(60)), eighteen days after estrus (D18(pe)), thirty-five days (D35(pe)) and fifty days after estrus (D50(pe)). VER value was measured on D-0, D-E, h(60), D18(pe), D35(pe) and D50(pe). Progesterone concentration was measured from blood samples of D-0, D-E and D18(pe). The change in VER value and progesterone concentration on different days (D-0, D-E, D18(pe)) of the estrus synchronization protocol was significant (P<0.001). While VER measurement was not significant in the early diagnosis of pregnancy (P>0.05) on D18(pe), it was found to be significant (P<0.05) in identification of returning ewes. VER cut-off value was found to be <255 ohm for determination of returning ewes. There was no significant (P>0.05) difference in VER values of pregnant and non-pregnant ewes at D35(pe) or D50(pe). As a result, VER value measurement in the first trimester of pregnancy does not seem to be useful in determining both of the presence and the day of pregnancy. On the other hand, VER measurement can be useful in evaluating synchronization success and determining the first spontaneous estrus after induced estrus in the absence of teaser rams under field conditions.