A very important aspect of calf growth is the development of the rumen. According to Taylor Yohe, a postdoctoral research fellow at the University of Guelph, the rumen will expand 1,300% in size during the first 8 weeks of life. With that growth comes the calf’s transition from a nonruminant animal on a liquid diet to a ruminant that relies on the rumen for most of its nutritional needs.
As a calf goes from a completely milk or milk replacer diet to a starter and water regime, a drop in rumen pH can occur. While the effect of rumen pH in calves has not been studied as much as it has been in cows, we know that in adult animals, low rumen pH can lead to larger systemic health issues.
During the Tri-State Dairy Nutrition Conference, Yohe shared studies that found low rumen pH in calves can cause reduced dry matter intake and a decline in growth. Other potential negative outcomes include less gut permeability and a greater incidence of ruminal parakeratosis and lesions, which can hamper rumen tissue development.
Of course, we can’t avoid the weaning process to avoid lower rumen pH. “It’s a balance between the health and growth of calves and starter intake, because you want to develop the rumen,” Yohe said. “An aspect we can control is the weaning process.”
Yohe presented a few weaning techniques that could mitigate the drop in pH. One way to increase starter intake without decreasing pH is to allow for more gradual starter consumption. Another option is to offer some forage to calves. He shared a summary of research in which 20 out of 24 studies that utilized forage in calves showed a positive effect on rumen pH, and the other four studies showed no affect. None of the studies found a negative effect caused by forage.
The drop in rumen pH can also be moderated by feeding young calves less accessible starch. He said this can be done using a texturized starter or unprocessed grains.
There is also the opportunity to utilize individualized weaning protocols. According to the most recent National Animal Health Monitoring Service (NAHMS) dairy study, Yohe said about half of U.S. dairy farms were weaning calves based on age. “This practice may leave some calves out in the dust because they may not be consuming enough starter yet to justify being weaned,” Yohe explained.
Instead, it would be beneficial to wean calves on metrics such as body weight or starter consumption. “If you want to help prevent this drop in pH, use a protocol tailored to each calf,” Yohe advised.