Parturition following transfer of embryos produced in two media under two oxygen concentrations.

In vitro-produced blastocysts were transferred singly to 99 Angus crossbred recipients. Culture treatments were a 2 x 2 factorial of medium (KSOM or SOF) and oxygen concentration (5 or 20%). At parturition, birth weight and frame measurement before colostrum intake were recorded. Fetal membranes were collected; distribution and diameter of cotyledons was recorded. Cotyledon surface area was calculated. Culture with 5% O2 tended to yield smaller birth weights than culture with 20% O2 (39.7+/-1.3 kg versus 43.1+/-1.4 kg; P < 0.1); this effect was pronounced in KSOM, suggesting a medium by oxygen interaction (P < 0.1). When expressed on a body weight basis, calves born following culture with 20% O2 had consistently smaller skeletal measurements than those from culture with 5% O2. Culture with 20% O2 significantly increased individual cotyledon areas both overall and in the fetal horn and cotyledon surface area in the fetal horn. Overall, individual cotyledons were 32% larger when culture involved 20% O2 versus 5% O2; in the fetal horn the increase was 49%. Cotyledon surface area was greater for 20% compared to 5% O2 culture, though a medium by oxygen interaction was also significant (P < 0.05). Cotyledon surface area in the nonfetal horn was greater for KSOM fetal membranes than those from culture in SOF. There was a significant medium by oxygen interaction for total cotyledon number. These data demonstrate culture system-specific effects on calf and fetal membrane traits.