314 EARLY PREGNANCY DIAGNOSIS USING A NOVEL TRANSRECTAL ULTRASONOGRAPHY PROTOCOL IN JAPANESE BLACK COWS

Abstract

The present study aims to establish a novel practical protocol for early pregnancy diagnosis in cows by using transrectal ultrasonography. The protocol is based on measurements of corpus luteum (CL) cross-sectional area (CL c-s area) change performed at 2 separate days before the coming estrus after AI. Fourteen cows were inseminated artificially, and transrectal ultrasonographical observation of the ovaries and blood collection for measurement of peripheral plasma progesterone (P4) concentration were carried out daily from Days 12 to 23 (Day 0 = the day of onset of estrus). Thereafter, cows were routinely diagnosed for pregnancy at Day 30 by transrectal ultrasonography. The largest CL c-s area was obtained at Day 14 in both pregnant and non-pregnant cows. Seven out of 8 non-pregnant cows showed significant CL c-s area regression between Days 14 and 20 (422 ± 112 v. 249 ± 63 mm²), whereas no regression was observed between Days 14 and 20 in pregnant cows (416 ± 65 v. 402 ± 78 mm²). The regression in the CL c-s area between pregnant and non-pregnant cows was significantly different during Day 18 (424 ± 65 v. 288 ± 88 mm²) to Day 23 (402 ± 71 v. 139 ± 64 mm²). P4 concentration was significantly low (less than 1 ng mL^–1) at Day 20 in 3 out of 8 non-pregnant cows, whereas the pregnant cows showed significant increase of P4 between Days 14 and 20 (2.6 ± 0.2 v. 3.4 ± 0.5 ng mL^–1). The pregnant cows showed significantly higher P4 concentration starting from Day 18 than non-pregnant cows. However, in non-pregnant cows, 4 cows returned to estrus on Day 20 or after, 3 cows showed no signs of estrus, and 1 cow came in estrus as early as Day 18 after AI. In conclusion, the results of the present study suggest that measuring the change in the CL c-s area at Days 14 and 20 makes it possible to detect the non-pregnant cows at Day 20 after AI. However, it was also indicated that measuring the change of P4 concentrations on the same days did not always successfully detect non-pregnant cows. The new protocol based on CL c-s area regression rate can detect almost certainly non-pregnant cows at Day 20 after AI. It is suggested that this method is advantageous in research and industrial breeding.