Untersuchungen zur Eignung von Empfängertieren im Rahmen des Embryotransfers
The aim of this study was to test the possibilities of ultrasonography in the examination of recipient animals during commercial embryo transfer in cattle. Altogether 257 animals have been synchronised by a single or a double injection of Prostaglandine F2alpha, 33 potential recipients showed spontaneous heat. On 200 of the animals actually being used as embryo recipients, a rectal palpation as well as an ultrasonographic examination of the ovaries was performed on the day of the transfer and on day 21 of the cycle. The recipients were examined again for pregnancy by ultrasound on day 35 (28 days after the transfer) and by rectal palpation on day 49. A blood sample (plasma) was taken on day 0 (oestrus), 7 (transfer) and 21, in order to mesure the progesterone concentration (P4). An enzyme-based immunological assay was used to evaluate the plasma samples for P4 concentration. The ultrasonographically defined area of the largest cross-section of the corpus luteum was significantly correlated (r = 0,22 ; p < 0,001) with the corpus luteum size evaluated by rectal palpation. There was no relation between the scoring of the corpora lutea performed by palpation and the average P4- concentration (r = 0,13 ; p > 0,05), whereas on day 7 the luteal tissue area measured by ultrasonography was significantly correlated with the P4 values (r = 0,40 ; p < 0,001). In 55 % of the recipients, a sonographically detectable cavity within the corpus luteum was found on the day of transfer. Corpora lutea with a cavity were bigger than those without ( 3,8 cm2 vs. 3 cm2; p < 0,001), however the luteal tissue area of corpora lutea with or without cavity was not significantly different (p > 0,05). On day 21, 136 animals out of 200 (69 %) having received an embryo, showed no signs of oestrus. On day 35 and 49 pregnancy was diagnosed in 50 % and 47 % respectively. The highest pregnancy rate (60 %) was obtained in the group of recipients, with the best score evaluated by rectal palpation. However, there was no significant difference in pregnancy rate between animals with different corpora lutea scores. The pregnancy rate on day 35 was 56 % in animals with a compact corpus luteum and 45 % when a cavity was present in the corpus luteum. The mean P4 value on day 7 of animals later diagnosed as pregnant or not was not significantly different (2,1 ng/ml vs. 2,2 ng/ml). 54 animals showing clear signs of heat 21 days after the last oestrus, had a P4 value of < 1 ng/ml. The area of compact corpora lutea of recipients having a P4 content of < 1ng/ml on day 21 was significantly smaller than that of animals having a P4 value > 1 ng/ml (1,5 cm2 vs. 3,5 cm2 ; p < 0,001). The average area of compact corpora lutea on day 21 (3,6 cm2 vs. 2,3 cm2; p < 0,05) was significantly bigger in pregnant than in non-pregnant animals. The percentage of presumably (day 21), respectively definitely pregnant animals (day 35 and 49), was 86 %, 65 % and 63 % respectively with fresh embryos of good quality, 57 %, 38 % and 34 % respectively with fresh embryos of poor quality and 66 %, 45 % and 44 % respectively with frozen/thawed embryos. The use of ultrasonography in the evaluation of the corpus luteum quality of recipients prior to the transfer is of limited value in commercial embryo transfer. A good oestrus detection on day 21 is useful to get the animal pregnant as early as possible; the determination of the plasma progesterone content on this day could contribute to obtain this goal. The ultrasonographic examination of the recipients for early pregnancy diagnosis (day 35 and earlier) can help, to re-use the non-pregnant animals again as soon as possible.
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