Reproductive efficiency at a commercial farm comparing AI versus ET at first insemination
2016
To evaluate reproductive efficiency using ET versus AI at first breeding post-calving procedures were performed on a commercial dairy farm in Spain. Eleven heifers were superovulated (Bo et al. Reprod Fertil Dev 2010 22:106-12). The same commercial frozen bull semen (Gerard, ABS) was used. Flushings were performed by the same ET-team (Nr. ES11ET05B). Quality 1 embryos were frozen in Ethylen-glycol and used. 170 primiparous (DIM=158 ± 17.9), were selected to be first-AI with the same semen (Group AI; n = 82; DIM=159 ± 16.3) or, ET with collected embryos (Group ET; n = 88; DIM=157 ± 19.4); DIM did not differ between groups (P = 0.402). Estrus of recipient/inseminated cows was detected (Westfalia Rescounter II pedometers). ET-cows were scanned (7.5-MHz linear, Ibex® Pro) and subjected to ET if at least one CL ≥18 mm diameter present. Luteal Surface (LS) was calculated. Early pregnancy diagnosis was performed at 28-34d (ED) and pregnant cows confirmed at 56-63d (CD). Data were analyzed with Chi squared test and logistic regression. Quality-1-embryos average/donor was 5.36; 32.9% of recipient cows were rejected. LS was 460 ± 223.5 mm2 and did not affect pregnancy. Two donors produced more fertile transferred embryos [88.9% (8/9) and =75% (6/8)], and two gave less fertile embryos [0% (0/4) and 14.3% (1/7) P=0.009]. These individual differences would not introduce bias into the study; the distribution of transferred embryos was 28% (17/59) of high fertility embryos, 19% (11/59) low fertility embryos and 52% (31/59) of average fertility embryos. Pregnancy loss did not differ among donors (P = 0.114). Fertility was higher for ET-cows [45.8% (27/59 P = 0.011)] than for AI-cows [24.4%; (20/82); OR of ED-pregnancy=2.616; P = 0.009]. DIM did not affect fertility (P = 0.7) with similar DIM (158.8 ± vs. 157.5 ± 18.1) for non-pregnant and pregnant cows. If rejected cows were included as non-pregnant, fertility did not differ [24.4% (20/82) and 30.7% (27/88) for AI and ET-groups; P = 0.39]. This highlights the relevance of the non-physiological ovarian activity resumption. Discarding recipients means to reject those with altered ovarian functionality. Therefore, one mean factor affecting fertility that can be overcome with ET-programs is to diagnose altered ovarian cycle-cows. 75.6% of non-pregnant cows after AI followed pregnancy diagnosis at day 28, with this date being the earliest date to treat. Rejected recipients (32.9%) could be treated at day 7. This accelerated reproductive rhythm has a positive impact on the farm pregnancy rate, and implies benefits of this first-AI ET-program. Early fetal loss did not differ among groups [5% (1/20) vs. 11% (3/27); P = 0.63], according with previous works showing similar pregnancy loss after day 42 of pregnancy. In conclusion, the ET-program resulted in a higher farm reproductive efficiency not through a higher fertility of the transferred embryos but through a better-expected global pregnancy rate. Economic implications should be further evaluated.
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