Abstract

To evaluate the impact of energy restriction on embryonic survival in Bos taurus and Bos indicus genotypes, a reciprocal embryo transfer approach was used in a completely randomized design with a 2 × 2 × 2 factorial arrangement of treatments. Recipient cows were assigned randomly to 1) a diet to meet daily maintenance requirements (MAINT), or 2) restricted intake of nutrients to 70% of energy maintenance requirements (RESTR). Angus (AN) and Brangus (BN) embryo donors were superovulated and artificially inseminated with female sexed-sorted semen from the same breed. Embryos were then randomly transferred 7 d post-insemination (d 7) to either AN or BN recipients fed the respective diets for 20 d to create 8 treatment combinations (AN × AN × RESTR, n =14; AN × AN × MAINT, n = 19; AN × BN × RESTR, n = 16; AN × BN × MAINT, n = 17; BN × BN × RESTR, n = 15; BN × BN × MAINT, n = 19; BN × AN × RESTR, n = 14, BN × AN × MAINT, n = 19). Recipients remained on the dietary scheme until d 91. All cows were then submitted to the same feeding regime until calving. Pregnancy diagnosis was performed at d 28 and 91. Embryo loss was defined as a cow that received an embryo but was diagnosed as nonpregnant. There was an effect of diet (P < 0.001) and day (P < 0.001) on recipient BW. Similarly, diet altered recipient BCS (diet × day, P = 0.005). There was a recipient breed × diet interaction on embryo loss at d 28 (P < 0.001), where AN × RESTR recipients had greater embryo loss than AN × MAINT (69.0 vs 28.2%, respectively), and BN × RESTR (69.0 vs 27.9%, respectively). There was also an embryo breed × diet interaction (P < 0.021) on embryo loss by d 28, with RESTR recipients that received an AN embryo experiencing greater embryo loss than RESTR recipients receiving BN embryos (64.3 vs 31.9%, respectively). At d 91, AN × RESTR recipients had greater (recipient breed × diet, P < 0.001) embryo loss than AN × MAINT (78.4 vs 41.9%, respectively) and BR × RESTR (78.4 vs 41.0%, respectively). These results indicate that Bos taurus cattle may be more susceptible to embryonic loss than Bos indicus when submitted to a feed restriction scheme during the first trimester of gestation.

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