16 Stillbirth, gestation length, and birth weights from Jersey calves originated from artificial insemination vs in vitro embryo transfer

The use of in vitro-produced embryos (IVP) has increased in dairy cattle; however, farmers and practitioners still have concerns about the viability of IVP calves when compared to AI. The objective of this study was to compare stillbirth rate (SB), gestation length (GL) and birth weight (BW) from AI vs ET (IVP embryo transfer) calves in a commercial dairy herd. Data from 16 343 Jersey calves born between January 2020 and May 2023, were collected at Jer-Z-Boyz Ranch, located in Pixley, California (4500 cows in milk with a 305-days milk equivalent production of 9378 kg). Ovum pickup, oocyte classification, in vitro maturation, fertilization and culture were performed at the RuAnn Genetics laboratory as described by Demetrio et al. (2020 Anim. Reprod. 17, e20200053). The majority of embryos were transferred fresh to healthy, second and third lactating cow recipients, at the first service, 65 to 80 days after calving. Stillbirth was defined as calf mortality shortly before, during, or shortly after parturition. The sires used for AI or ET were selected by the geneticist based on his knowledge of the herd and desired genetic traits to be improved. Birth weights were only recorded for live calves. The effects of sire and parity (0, 1, 2, or 3+ lactations) on BW and GL were analysed in a group of nontwin female calves, originated from sires used in both AI (n = 2141) and ET (n = 485), using different regression models and a bootstrap method for the construction of 95% confidence intervals (R software). The male SB was 5.4% for AI (n = 1194) and 3.5% for ET (n = 257). The female SB was 6.5% for AI (n = 14 058) and 6.5% for ET (n = 834). The sire influenced GL and BW (P < 0.01). Longer GL resulted in heavier calves (+0.1 kg per additional day). Nulliparous cows produced calves 0.44 lb. lighter than multiparous cows. GL was shorter (P < 0.01) for AI calves (278 ± 4.7 days) when compared to ET (average: 281 ± 4.9 days). Birth weight was lower (P < 0.1) for AI calves (average: 26.14 ± 0.05 kg, minimum: 14 kg, maximum: 45 kg) when compared to ET (average: 27.23 ± 0.13 kg, minimum: 21 kg, maximum: 38 kg). One fact to consider is that most ET calves are born from multiparous cows whereas most AI calves were from nulliparous cows, due to selection pressure on genetic levels, which could have led to a higher difference in birthweights. Despite not having information on the birthweights from the dead calves, since there were no differences in the stillbirth rates, it is possible to infer that the 1.1 kg difference in birthweights is not a concern for this herd and does not compromise the viability of calves at birth originated from IVP embryos.