102 UNILATERAL AND BILATERAL TRANSFER OF 2 IN VITRO-PRODUCED EMBRYOS INCREASES PREGNANCY LOSS BETWEEN 30 AND 60 DAYS

Abstract

Fertility of in vitro-produced embryos is affected by embryo stage and quality. Embryos quality 1 and stage 7 result in higher fertility than embryos of earlier stages and/or lower quality. The objective was to evaluate the effect of unilateral and bilateral transfer of 2 in vitro-produced embryos of earlier stages and/or poor quality on fertility. Heifers were synchronized using a 5-day CIDR Synch or 2 prostaglandin F_2α injections 14 days apart followed by oestrus detection. Embryo transfer was performed 7 ± 1 day after gonadotropin-releasing hormone/oestrus and heifers were assigned randomly to 1 of 3 groups: single embryo ipsilateral to the corpus luteum (single; n = 188); 2 embryos in the uterine horn ipsilateral to the corpus luteum (unilateral; n = 138); 2 embryos bilaterally (bilateral; n = 128). Embryos stage 4 to 8 and quality 1 or 2 were randomly assigned to treatment groups. All embryos were 7-day fresh in vitro-produced embryos, and pregnancy diagnosis was performed by ultrasonography on Days 32 and 60. Data were analysed by logistic regression. Conception rates on Days 32 and 60 were not different (P > 0.10) between heifers receiving a single embryo [Day 32 = 30.9% (58/188) and Day 60 = 25% (47/188)] or those receiving 2 embryos [Day 32 = 36.5% (97/266) and Day 60 = 22.2% (59/266)]. However, pregnancy loss between Days 32 and 60 was greater (P < 0.01) in heifers with 2 embryos (39.2%; 38/97) than in those with a single embryo (18.9%; 11/58). Conception rate on Day 32 was not different between groups (P = 0.4) and was 30.9% (58/188) for single, 36.9% (51/138) for unilateral, and 35.9% (46/128) for bilateral. Similarly, there was no difference (P = 0.8) in conception rates on Day 60, single = 25% (47/188), unilateral = 23.9% (33/138), and bilateral= 20.3% (26/128). However, there was an effect of group on pregnancy loss between Days 32 and 60 (P = 0.04). Losses were higher (P = 0.01) in the bilateral group [43.5% (20/46)] compared with the single group [18.9% (11/58)], and the unilateral group was intermediate [35.3% (18/51)] and tended to be different from the single group (P = 0.1). Interestingly, when pregnancy loss was compared between heifers with twin or single pregnancies, as determined by ultrasonography, and regardless of the number of embryos transferred or their location, twin pregnancies had a greater pregnancy loss [62.1% (18/29)] compared with single pregnancies [24.6% (31/126); P < 0.01]. For twin bearing heifers, as determined by ultrasonography on Day 32, pregnancy loss did not differ between unilateral (62.5%; 10/16) and bilateral (61.5%; 8/13) transfers (P = 0.9). Similarly, there was no difference (P = 0.2) for heifers with single embryo pregnancies: single (18.9%; 11/58), unilateral (22.9%; 8/35), bilateral (36.4%; 12/33), although bilateral transfer of 2 embryos tended to be higher than single (P = 0.07). Transfer of 2 low quality in vitro-produced embryos results in similar conception rates, although pregnancy losses are greater. Interestingly, only 30% (29/97) of the pregnancies from heifers that received 2 embryos contained twins, indicating the loss of one of the embryos before Day 32. Furthermore, the increased losses observed with the transfer of 2 embryos were attributed to those heifers in which twin pregnancies were diagnosed on Day 32 regardless of distribution.