Importance of Rumen Development in Calves
Abby Bauer, Associate Editor at Hoard's Dairyman, wrote a useful summary of remarks made by Dr. Jud Heinrichs, Penn State Univ., at the Professional Dairy Producers of Wisconsin Calf Care Workshop in early November, 2018.
Dr. Heinrichs' emphasized the importance of developing the rumen early in the life of our dairy calves. He reminded the participants that by 3 to 4 months of age the rumen should be the main compartment of the digestive system.
He said, "Grain intake is what does it."
He explained that it takes 21 to 28 days to grow the rumen once she starts eating starch (that is, calf starter grain).
Let me note here that if on the average my calves begin regularly eating at least a small handful of grain daily at I need to add 21 to 28 days before pushing them off of milk.
Let's look at what this means for beginning to wean calves:
Start regular grain intake at 14 days, start weaning process at 35 to 42 days.
Start regular grain intake at at 21 days, start weaning process at 42 to 49 days.
Experience has shown that higher milk/milk replacer feeding rates (more than 4 quarts daily) delays the time for calves regularly eating grain. When I was feeding 8 quarts daily (15% solids) most of my calves took about three weeks (21 days) before cleaning up a handful of grain every day. So, following Dr. Heinrichs' recommendation, on the average, I did not start cutting back on milk until 40-42 days.
When I stepped down their milk nearly all of my calves compensated by increasing calf starter grain consumption.
Dr. Heinrichs observed that the time to introduce forages is after calves have a well developed rumen. My calves increased their grain intakes as milk was stepped down to the range of 4 to 6 pounds (1.8 - 2.7kg) daily. He suggested that when this level of grain intake is sustained introducing forages is appropriate - they will have a desire to balance their rumen pH and chew their cud.
Thanks to Abby Bauer, Hoard's Dairyman, for reporting on this event.