Umbilical Cords: What's "Normal?"
Just in case you ever wondered what is a normal size umbilical cord, as part of a trial on navel dipping a person did this work for you.
The diameter of umbilical cords on 60 Jersey calves were measured within 30 minutes after birth and again at 24 hours of age.
At birth the average diameter was about 7/8"(22.8mm). Two-thirds of the calf navels fell between 3/4" and just over 1".
At 24 hours the average diameter was about 1/4"(7.64mm). Two-thirds of the calf navels fell between 1/8" and just under 1/2".
So, that gives us an estimate of the "normal shrink" rate. It also suggests that even though an umbilical cord is still 1/2" in diameter at 24 hours this size, while somewhat unusual, does not necessarily mean an infection has begun. I would just tag this calf to be watched over the course of the following week to see that the umbilical cord continues to shrink as it dries up.
A.L. Robinson and Others, "The effect of four antiseptic compounds on umbilical cord healing and infection rates in the first 24 hours in dairy calves from a commercial herd." Journal of Dairy Science Vol. 97, E-Suppl 1, p. 430.