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To evaluate how the inclusion of Bos indicus genotype influences early fetal development in cattle, a reciprocal embryo transfer approach was used in a completely randomized design with a 2 × 2 × 2 factorial arrangement of treatments to generate 55 pregnancies over 2 consecutive years (n = 55). Recipient cows were randomly assigned to (i) a diet that met daily energy maintenance requirements (MAINT) or (ii) a diet that restricted intake to 70% of the 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 to either AN or BN recipients fed their respective diets for 28 d. Recipients remained on the dietary scheme until day 91 of gestation and were then comingled and fed a common diet that met their energy requirements until calving. Measurements included pregnancy establishment at day 28 of gestation, interferon-stimulated genes (ISG) expression in peripheral blood leukocytes, pregnancy-associated glycoproteins (PAG; using two commercial [A1 and A2] and one in-house assay), and fetal crown-to-rump length (CRL). Recipients in the RESTR diet had lower BWs and BCS (diet × day; P < 0.01) than MAINT recipients. Energy-restricted AN recipients experienced greater (recipient breed × diet, P < 0.01) pregnancy failure by day 28 than the other recipient breed × diet combinations. Restricted recipients that received AN embryos experienced greater pregnancy failure than RESTR recipients receiving BN embryos (embryo breed × diet; P = 0.03). No relevant differences were observed in ISG expression (P > 0.10). Recipients that received BN embryos had greater plasma concentrations of PAG in both A1 (embryo breed × day, P < 0.01) and A2 (embryo breed; P < 0.01). Alternatively, recipients that received AN embryos had greater plasma concentrations of PAG for the in-house assay (embryo breed × day; P < 0.01). In addition, fetuses from AN recipients had greater CRL on day 91 (breed × day, P < 0.01). In summary, Bos taurus cows experienced greater pregnancy failure when nutrient restricted. Furthermore, fetal size and the profile of PAG production during early gestation differed between B. indicus-influenced and B. taurus cattle.

Our objectives were to determine the effects of the administration of recombinant bovine somatotropin (bST) at the initiation of a fixed-time AI (TAI) protocol on concentrations of plasma IGF-1, follicle diameter, embryo/fetal size, and pregnancy rates in replacement beef heifers. Four hundred and fourteen Angus-based beef heifers were enrolled in a completely randomized design at 4 locations from January to July of 2016. All heifers were exposed to the 7-d CO-Synch + controlled internal drug release (CIDR) protocol where they received a 100-µg injection of GnRH and a CIDR insert on day -9, 25 mg of PGF2α at CIDR removal on day -2, followed by a 100-µg injection of GnRH and TAI 54 ± 2 h later on day 0. Within location, all heifers were randomly assigned to 1 of 2 treatments: 1) heifers that received 650 mg of bST on day -9 (BST; n = 191); or 2) heifers that did not receive bST on day -9 (CONTROL; n = 223). Blood samples were collected on day -9, 0, 28, and 60 to determine the plasma concentrations of IGF-1. Follicle diameter was determined on day -2 and 0 by transrectal ultrasonography. Pregnancy was diagnosed via transrectal ultrasonography on day 28 or 35, and again at least 30 d after the end of the breeding season. Embryo morphometry was assessed by measuring crown-to-rump length (CRL) on day 28, and fetal size was assessed by measuring crown-to-nose-length (CNL) on day 60. Concentrations of plasma IGF-1 did not differ between treatments on day -9 (P = 0.924), 28 (P = 0.075), and 60 (P = 0.792); however, concentrations of plasma IGF-1 were greater (P < 0.001) in BST-treated heifers at TAI (372.4 ± 16.6 vs. 193.7 ± 16.6 ng/ml). No differences (P = 0.191) were detected for follicle diameter between CONTROL and BST treatments on day -2 or 0. Pregnancy rates to TAI (PR/AI) were greater (P = 0.028) for CONTROL compared to BST heifers (42.5 ± 4.0 vs. 29.9 ± 4.1%). No differences (P = 0.536) in CRL were observed on day 28 between CONTROL and BST heifers. In addition, no difference (P = 0.890) was observed for CNL between CONTROL and BST treatments. Final pregnancy rates did not differ (P = 0.699) between treatments. The administration of bST to beef heifers at the initiation of a TAI protocol increased plasma concentrations of IGF-1 at TAI; however, failed to enhance follicle diameter, embryo/fetal size, and reduced PR/AI.