Heavy birth weight, increased calving difficulty, heart function defects, increased perinatal mortality and organ immaturity have been reported for calves produced from IVP embryos compared to those produced from MOET or AI (van Wagtendonk AM et al., 2000 Theriogenology 53, 575–597; Jacobsen H et al., 2002 Anim Reprod Sci 70, 1–11). In this study we examined birth weight (BWT), and blood chemistry at 1 day of age, gestation length and heart function at 7 days, and response to an ACTH challenge at 21 days of calves derived from IVP in a ‘semi-defined’ IVC system (Thompson JG et al., 2000 J. Reprod. Fertil. 118, 47–55) and of contemporary MOET or AI calves. Holstein Friesian (HF) 2- and 3-year-old recipients carrying single HF calves (101×IVP and 21×MOET) were monitored in this study. Within 1 day of birth the calves were weighed and a blood sample taken for analysis. At 7d, ultrasound measurement of the left ventricle diastolic diameter (LVEDd) and % ejection fraction (EF%) was determined. Each calf was then transported to a rearing unit. At 3 weeks of age, 30 IVP and 30 control AI calves of the same age were injected i.v. with Synacthen (synthetic ACTH, Ciba Corporation, 0.1μgkg−1 body weight). Blood samples were collected at −30, 0, 30, 60 and 90min (0min=time of injection) for cortisol measurements. There was no difference in BWT for MOET or IVP calves (40.9±4.7 v. 35.6±4.8kg, respectively). Moreover, gestation lengths (279 days v. 281 days) and calving assistance scores (1.3 v. 1.6) did not differ. Calf mortality at birth was higher for IVP calves (16%) than for MOET calves (5%). All but 7 surviving calves (6×IVP and 1×MOET) had high GGT levels at 1 day. Blood chemistry revealed no differences between the calf types, all measures being within normal ranges. For all calves, heart function analysis revealed no abnormalities with mean LVEDd=4.1±0.6cm and mean EF%=78.5±8.4%. All calves exhibited elevated cortisol following ACTH challenge. There was no difference between control and IVP calves for mean cortisol concentration at any time point (0min, 13.8±5.2; 30min, 46.6±9.8; 60min, 42.8±9.9; 90min, 28.1±8.9ngmL−1). These data suggest that, unlike calves produced in less defined culture systems, calves produced by IVP in a semi-defined culture system have birth weight and gestation lengths similar to those of MOET calves. Moreover, no abnormalities in organ (heart, adrenal) function were detected. However, of concern was the high number of unexplained deaths for IVP calves. This may be due to an overall lack of vigour in IVP calves that, in an unsupervised calving, results in calf death. More vigilence at calving may be needed to ensure calf survival. The authors thank Juliet Jensen, Waikato Hospital, for ultrasound measurements and David Stewart, Morrinsville Veterinary Services, for calf care. This study was funded by Vialactia Biosciences and FRST.