Differences in Embryo Survival Between Bos Indicus and Bos Taurus Females Receiving Energy Restricted Diets during Early Gestation

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.