As the demand for cloned embryos and offspring increases, the need arises for the development of nuclear transfer procedures that are improved in both efficiency and ease of operation. Here, we describe a novel zona-free cloning method that doubles the throughput in cloned bovine embryo production over current procedures and generates viable offspring with the same efficiency. Elements of the procedure include zona-free enucleation without a holding pipette, automated fusion of 5-10 oocyte-donor cell pairs and microdrop in vitro culture. Using this system, zona-free embryos were reconstructed from five independent primary cell lines and cultured either singularly (single-IVC) or as aggregates of three (triple-IVC). Blastocysts of transferable quality were obtained at similar rates from zona-free single-IVC, triple-IVC, and control zona-intact embryos (33%, 25%, and 29%, respectively). In a direct comparison, there was no significant difference in development to live calves at term between single-IVC, triple-IVC, and zona-intact embryos derived from the same adult fibroblast line (10%, 13%, and 15%, respectively). This zona-free cloning method could be straightforward for users of conventional cloning procedures to adopt and may prove a simple, fast, and efficient alternative for nuclear cloning of other species as well.

The cloning syndrome is a continuum with the consequences of abnormal reprogramming manifest throughout gestation, the neo-natal period, and into adulthood in the cloned generation, but it does not appear to be transmitted to subsequent offspring following sexual reproduction. Most in vivo studies on bovine somatic cell cloning have focused on development during pregnancy and the neo-natal period. In this paper, we report on the viability and health of cloned cattle in adulthood. From our studies at AgResearch, we find that between weaning and 4 years of age, the annual mortality rate in cattle cloned from somatic cells is at least 8%. Although the reasons for death are variable and some potentially preventable, the main mortality factor in this period is euthanasia due to musculoskeletal abnormalities. This includes animals with severely contracted flexor tendons and those displaying chronic lameness, particularly in milking cows. In contrast, no deaths beyond weaning have so far been encountered with the offspring of clones where the oldest animals are 3 years of age. In surviving cloned cattle, blood profiles and other indicators of general physiological function such as growth rate, reproduction, rearing of offspring, and milk production are all within the normal phenotypic ranges.

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.