Gestation length, calving characteristics, and early-life health of calves born following transfer of fresh in vitro-produced embryos generated using conventional or sex-sorted sperm.

The objectives of the current study were to compare gestation length (GL), calving difficulty (CD), birth weight (BiW), and early-life health of beef and dairy calves derived from in vitro-produced embryos generated using conventional (CONV) or sex-sorted (SS) sperm. Oocytes were collected once weekly for up to 4 successive weeks from the ovaries of elite beef (Angus, n = 37) and elite dairy (Holstein-Friesian, n = 51) heifers and cows. Oocytes were matured in vitro and fertilized using frozen-thawed CONV or SS sperm from a panel of proven fertility bulls (beef = 6, dairy = 9). Embryos were cultured in vitro until d 7, at which point blastocysts (n = 468) were transferred fresh to lactating dairy cow recipients that had been synchronized using a progesterone-Ovsynch protocol. Data for individual calves were subsequently obtained for GL (n = 161), CD (n = 135), and BiW (n = 153). Additional measurements were conducted on a subset of calves, which included blood sample collection at d 11 for biochemical and hematological analysis (n = 41), and again on d 26 (n = 34) for biochemical analysis only. The effects of embryo breed (beef vs. dairy) and semen type used for in vitro fertilization (CONV vs. SS) were examined using generalized linear mixed models. Gestation length was similar for beef and dairy calves (280.8 d vs. 280.6 d) and for calves derived from CONV and SS semen (280.8 d vs. 280.7 d). Mean (±SD) BiW was heavier for beef calves than dairy calves (43.3 ± 1.0 kg vs. 39.0 ± 1.4 kg), whereas calves derived from CONV semen were lighter than calves derived from SS semen (39.9 ± 1.1 kg vs. 42.4 ± 1.0 kg). Calving difficulty scores were similar for beef and dairy calves and for calves derived from CONV and SS semen. However, calving difficulty was greater in cases when parturition was induced compared with spontaneous parturition. Results of biochemical analyses on d 11 and d 26 and hematological analysis on d 11 were within reference ranges available for healthy calves of a similar age. In conclusion, GL and incidence of CD were similar for beef and dairy breed calves derived from in vitro-produced (IVP) embryos, as well as calves derived from IVP with CONV and SS sperm. Birth weight was greater for beef calves than dairy calves. Blood biochemistry and hematology variables were similar for calves derived from IVP embryos for beef and dairy breeds and for calves derived from IVP embryos that had been fertilized with CONV and SS sperm.