How Much Hay is Needed to Make
A Difference in a Calf's Rumen?
How much hay (on a dry matter basis) is needed in a calf's ration to make an observable difference in her rumen (difference defined as rumen pH, concentration of total volatile fatty acids and plaque formation)?
In their work (Bieranvand, H. and Others, "Interactions of alfalfa hay and sodium propionate on dairy calf performance and rumen development". Journal of Dairy Science, April 2014, 97: 2270-2280) the authors compared rations with and without alfalfa hay at levels of 5 and 10 percent of concentrate ration. The "control" ration was a grain "meal" and the hay was chopped and added to get the desired feeding level.
In my reading of the results it looks as though the critical value for including chopped hay was ten percent of the starter grain ration. This was chopped to small pieces (average length only 0.1 inch). When hay was included this way the calves actually ate more "starter" during the first six weeks (over 1 pound a day compared to just under three-fourths of a pound daily - 33% more).
Using a threshold of daily "starter" intake of 2.2 pounds a day to wean calves the 10 percent hay ration calves average weaning age was 45 compared to control (no hay) calves at 59 days.
At 70 days the 10 percent hay calves averaged 196 pounds while the control calves came in at 176 pounds.
I was impressed by the microscopic images from the rumens. The keratin layer was much thinner for the 10 percent hay calves than for the control calves (keratin builds up on the rumen wall reducing the efficiency of absorption of nutrients).
These findings are from small samples of calves and from only one study. Nevertheless, they suggest that we think about how to introduce small amounts of nutritious roughage to relatively young calves. I am sure that chopping forage is only one way to accomplish this goal.