MORPHOLOGICAL EVALUATION OF BOVINE EMBRYOS RECOVERED NON-SURGICALLY FROM SUPER-OVULATED DAIRY-COWS ON DAYS 6 1/2 TO 7 1/2 - FIELD-STUDY

Ninety-two dairy cows milking 23 l milk/day at the time of superovulation and belonging to the main domestic breeds were used in this study. Their mean age was 5.5 years and they had calved a mean 3.6 times. In 71 animals the previous calving interval was 369 days, and the calving-superovulation interval was 126 days. The cows were superovulated with 1500 to 3000 IU of PMSG (mean of 2400 IU) on days 8 to 13 of the estrous cycle (mean of 10.7 days), followed 48 to 60 hrs (mean of 52 hrs) later by cloprostenol treatment (0.5 mg). The mean interval from PMSG injection to heat was 4.1 days, and that from the cloprostenol treatment was 45.5 hrs. A total of 6.0 embryos/donor were nonsurgically recovered at the farm on days 6 to 8 (mean of 7.1 days). They were evaluated under a stereomicroscope and divided into the following groups: a) embryos with the appropriate (expected) age (developmental stage), showing no signs of degeneration, lysis or swollen blastomers (vacuolization) and including compacted morulae, early expanding blastocysts, expanded blastocysts and rarely hatched blastocysts; 54.2 p. 100 of the total material (or 3.3 embryos per donor) were classified in this group: b) retarded embryos which were at an earlier stage than expected and constituted 5.8 p. 100 of the total material, (or 0.35/donor): c) obviously degenerated embryos (morulae or eary expanded blastocysts); this group was the second largest, comprising 23.7 p. 100 of the total material (or 1.4 embryos/donor); d) unfertilized eggs which constituted a minor part (16.3 p. 100, or 0.88/donor). The number, quality and distribution of these groups were examined at various dose levels of PMSG and also in the right and left horns. Stimulation with 3000 IU yielded more embryos than 2000 and 2500 IU (6.9 vs 5.9 and 5.8), but 2000 and 2500 IU yielded a significantly higher number of viable embryos than did 3000 IU. A significantly higher number of embryos was found in the right uterine horn (7/donor) than in the left horn (2.9/donor). Corresponding to this, there was also a higher number of corpora lutea in the right than in the left ovary (4.1 vs 3.7). Several batches of PMSG were employed, but no batch variation in embryo quality or number was found. PMSG injection on various days of the cycle produced the following mean number of embryos per donor: injection on day 9: 5.1 embryos (3.2 A), on day 10: 6.5(4.0 A), on day 11: 6.6(2.8 A) on day 12: 7.9(4.7 A), and on day 13: 6.1(3.1 A). We also wished to determine if the interval between PMSG treatment and estrus would influence the number, quality and relative distribution of embryos per donor. 3.5 days (9.6 embryos) appeared to be more effective than 4 days (5.6 embryos) or 4.5 days (4.2 embryos). In only 4 donors the interval was 5.0 days and the mean number of embryos was 10.0. Sixty animals (71 p.100) came in heat between 37 and 48 hrs after the cloprostenol treatment and a total of 6.0 embryos was recovered (3.3 A). Ten animals (11.8 p. 100) exhibited standing heat from 24 to 36 hrs after the injection with a total of 7.5 embryos (4.1 A) per donor. Twelve cows (14.1 p. 100)showed estrus 49 to 60 hrs after the cloprostenol treatment and only 3.9 embryos (1.7 A) were recovered. A small number (3) animals came into heat after 61 hrs. The exact time of heat was subject to human error, but it seemed reasonable to assume that more embryos of better quality were recovered when the donors came into heat before 60 hrs after cloprostenol treatment. Breed effect was examined, but no statistical difference was found between the main dairy breeds studied (SDM, Jersey). In a samll field study on beef cattle a total of 7.1 embryos (4.0 A) was recovered. Age, parity, previous calving interval, calving-superovulation interval and actual milk yiled are currently being assessed, but preliminary investigation has failed to show that they have any specific effect. Morphological assessment of embryonic viability in lactating dairy cattle was very different, and there was marked individual variation between animals and even in the same animal (left vs right horn) as to the number, quality and relative distribution of embryos into the four main groups. Based upon a 3-year study, it is concluded however that the correlation between morphological evaluation and subsequent pregnancy (survival) rate was high.