Two groups of 20 cows received similar late-gestation feed while researchers measured uterine blood flow.
Twenty cows in each group
An abstract published in the Journal of Animal Science on 29 September 2026 describes 40 multiparous MARC II beef cows selected by their previous calves’ birth weights. Twenty cows in the higher group had a historical average of 43.1 kilograms; the other 20 averaged 35.0 kilograms. The groups had similar maternal weight, body condition and calf sex ratios. All cows received a ration designed to meet maintenance and pregnancy needs in late gestation.
Blood flow and placental measurements
Doppler measurements showed greater total uterine blood flow in the higher birth-weight group at all three sampling times. Placental tissue on the side of pregnancy was also heavier in that group, while placental efficiency did not differ. The work is a conference abstract based on selected cows. Its authors say it remains unclear whether the extra blood flow drove fetal growth or reflected the growth of the fetus.