A number of studies demonstrated abnormalities of pregnancies and calves from in vitro produced (IVP) embryos, such as prolonged gestation, the large calf syndrome and a shifted sex ratio towards males (Merton et al, 1998; van Wagtendonk et al, 1998). Within 4 years of a commercial OPU/IVP program, we used 4 different systems for embryo culture (IVC): A) TCM199; B) CR-1; C) SOF, each supplemented with 10% estrous cow serum (ECS); and D) SOF without ECS for the first 3 days of IVC. The birth weights of 125 calves (mean±SD in kg) were A) 52.6±7.1 (n=35); B) 48.8±9.2 (n=34); C) 40.4±8.5 (n=28); and D) 46.4±7.5 (n=28). ANOVA of birth weight by IVC system, breed, sex of calf, and sire (classified according to easy, normal, or difficult calving process) with gestation length revealed significant effects of IVC system (p<0.001) and breed (p<0.05). Birth weight was not significantly influenced by sex of calf and sire (p=0.18 and p=0.70, respectively). The sex ratio (male/female) of the born calves was A) 22/13; B) 20/14; C) 12/16; and D) 11/17. Overall, sex ratio was not significantly influenced by IVC system. However, sex ratio of calves originating from embryos cultured in system A was significantly (Chi-square; p<0.05) different from that obtained after embryo culture in system D.

Our data suggest that 1) birth weight and sex ratio are influenced by IVC system; 2) IVC systems based on SOF may decrease the mean birth weight and shift the sex ratio towards females; and 3) a two-step culture of embryos in SOF without serum for the first 3 days is not advantageous with respect to birth weight of calves.