Gestation length, calf birth weight, calving difficulty, perinatal mortality, and calf health following timed artificial insemination or embryo transfer with fresh or frozen in vitro-produced embryos.

The aim of this study was to determine the effect of embryo origin (artificial insemination [AI] vs. in vitro embryo production [IVP]), calf breed, and calf sex on gestation length (GL), birthweight (BiW), calving difficulty (CD) score and perinatal mortality. Lactating dairy cows (n = 1,106) were randomly assigned to be bred by timed AI (frozen-thawed semen) or timed embryo transfer (ET) with fresh or frozen IVP dairy (Holstein Friesian [HF] or Jersey [JE]) or beef breed (Angus, [ANG] or Limousin [LM]) embryos. Data were subsequently obtained from 442 calves derived from these breeding events. For all births, CD was scored on a scale of 1 to 4 (1 = unassisted, 2 = minor assistance, 3 = considerable difficulty or 4 = veterinary assistance or cesarean). Additional measurements were completed on subsets of calves. For 281 calves, weight was recorded immediately after birth. For 108 of these calves, blood samples were collected at birth for biochemical and hematological analysis. For 126 calves, blood samples were also collected 24 h after birth to measure serum IgG concentration to assess passive transfer of immunity. The effects of the independent variables (embryo origin, calf breed and sex) on GL, BiW, CD score and perinatal mortality, and the association between these dependent variables were examined using generalized linear mixed models. Overall, GL (mean days, 95% CI) was shorter for calves derived from AI (278.9; 277.0, 280.8) compared with calves derived from ET-fresh (281.8; 279.8, 283.7) and ET-frozen (282.0; 280.0, 284). Within the population of HF calves (n = 159), BiW (mean kg, 95% CI) was lighter for calves derived from AI (34.7 kg; 33.3, 36.2) compared with ET-fresh (39.7 kg; 37.8, 41.7) and ET-frozen (38.5 kg; 36.6, 40.6). Among calves derived from ET, breed affected GL, BiW, and CD: calves that were sired by the LM bull had a longer GL (290.9 d) than AA (282.0 d), HF (280.5 d), and JE calves (282.0 d). Angus calves were heavier (fresh: 46.3 kg; 44.5, 48.2, frozen: 43.5 kg; 41.6, 45.4) than both HF (fresh: 39.7 kg; 37.8, 41.7, frozen: 38.5 kg; 36.6, 40.6) and JE calves (fresh: 30.8 kg; 29.0, 32.7, frozen: 28.8 kg; 26.5, 31.2). Angus calves derived from ET-fresh had greater CD score than HF calves derived from both AI and ET-fresh. Results of biochemical and hematological analyses were within the normal range for healthy calves and concentrations were only affected by breed in a few of the variables measured. Embryo origin did not affect passive transfer of serum IgG from maternal colostrum to calf circulation. In conclusion, dairy breed calves derived from IVP-ET had similar incidence of CD as dairy breed calves derived from AI, but the incidence of CD was greater for beef breed calves derived from IVP-ET. In general, neonatal calf blood measurements were not affected by calf origin (AI or ET), and all treatments had comparable incidence of perinatal mortality.