The Sire Effect on Gestational Length in Wagyu Cattle.

This study investigated the factors influencing gestation length in a herd of Wagyu cattle in Rio Grande do Sul, Brazil. Fifty-five multiparous purebred Wagyu cows underwent a Fixed-Time Artificial Insemination (FTAI) protocol using semen from a bull randomly selected from five bulls representing three distinct genetic lines. Following birth, we recorded the calves' gender, weight, and gestation length. The ANOVA test was employed to assess genetic effects on calf weight and gestation length, with significance set at p < 0.05. The 55 inseminations resulted in 52 births, comprising 34 females and 18 males. The average calf weight was 25.9 kg, with 25.2 kg for females and 27.2 kg for males (p = 0.38). No significant effect was observed for birth weight concerning the sire's genetic line (p = 0.42), although there was a trend towards an effect from the maternal grandfather (p = 0.09). The mean duration of pregnancy was 283.8 ± 5.91 days, with no significant effect of gender on gestation length (p = 0.6). However, when evaluating the genetic influences on gestation length, we observed significant effects from the sire's genetic line (p < 0.0001) and the maternal grandfather (p < 0.0001). Notably, longer pregnancies resulted in heavier calves (p < 0.0001). This is the first study to identify the effects of Wagyu breed lines on pregnancy length.