Factors Altering Abomasal Emptying Rate

By Dr. Noah Litherland, Vita Plus dairy youngstock specialist
Let’s take a look at calf plumbing; more specifically, the calf abomasum.  If we understand how a calf’s plumbing works, we can predict how calves will respond to feeding and management programs.

The abomasum plays a very important role in dairy calves’ meal digestion.  In adult cattle, the abomasum volume remains fairly consistent as digesta continuously flows from the rumen to the abomasum.  In calves, the weight and holding capacity of the abomasum both increase with calf age and size.  Additionally, the capacity of the abomasum enlarges significantly after ingestion of a liquid meal and is dependent upon meal size.

Motility and emptying of the abomasum are under both neural and hormonal control.  The passage of ingesta through the gastrointestinal (GI) tract is primarily driven by the physical and chemical characteristics of the feed.  The GI tract senses the chemical composition of the meal, which results in increases or decreases in concentrations of key hormones.  These hormones cause nerves in the abomasum to stimulate or relax the abomasum.

Abomasum pH
After swallowing milk or milk replacer, the esophageal groove shunts milk to the abomasum where digestion begins.  The abomasum holds milk before it is slowly metered to the intestines.  The abomasum secretes acid to decrease the pH of the milk and start the digestive process.

The acidic environment also provides a barrier to prevent some bacteria from colonizing the intestinal tract.  At a pH above 5.0, the survival rate of potentially pathogenic bacteria, such as E. coli and Salmonella species, increases and, therefore, colonization of the small intestine and development of diarrhea is more likely.

Nursery calves have an abomasal pH below 2.0 before feeding and the pH increases to around 6.0 after drinking milk or milk replacer.  It does not return to the pre-feeding pH level until after two hours.  Depending on meal size and chemistry, abomasal pH can remain elevated for as long as nine hours.

Meal volume is a primary factor driving abomasal emptying rate.  The greater the volume of milk offered to a calf during each feeding, the longer the milk will remain in the abomasum. This suggests that meal size and frequency impact abomasal pH.

Perhaps abomasal emptying rate (and pH) explain, in part, why we see increased incidence and severity of scours in calves fed more than 2 percent of their bodyweight.  Calves in autofeeders typically consume more frequent meals and larger amounts of milk than conventionally fed calves.  It is plausible that autofeeder calves have both slower abomasal emptying rates and higher abomasal pH.

Osmolality of ingested meal impacts abomasal emptying rate
The osmolality (concentration of particles in a solution) of milk is about 290 milliosmoles (mOsm) per liter.  Hypertonic milk or milk replacer (greater than 300 mOsm/L) decreases the emptying rate, and solutions that are extremely hypertonic (greater than 600 mOsm/L) substantially decrease emptying rate.

A 2-liter 20/20 milk replacer meal (about 450 mOsm/L) has an average abomasal emptying time between 190 and 206 minutes.  In comparison, abomasal emptying following ingestion of 2 liters of whole milk (about 290 mOsm/kg) takes 129 to 191 minutes.   Stalling out the abomasal emptying rate may facilitate colonization of the intestine with pathogenic bacteria.

What does this mean for my calves?
Large meals, high-osmolality meals, and frequent meals all contribute to both increased abomasal pH and decreased abomasal emptying rate, which appears to increase risk for pathogenic bacteria to colonize the intestine.

The “Goldilocks theory” applies to abomasal emptying rates:  Fast and slow emptying rates are more problematic than moderate and consistent abomasal emptying rate.

I prefer to feed 2 to 2.5 quarts twice daily of a low-osmolality milk replacer or quality pasteurized milk for the first two weeks and then increase to 3 quarts twice daily of a low-osmolality milk replacer or milk from week three to week six.  In autofeeder systems, I apply the same principles by setting up the program to achieve similar meal size and solids intake.

Allow calves to eat starter grain for both rumen development and supply of additional energy and protein to complement the milk program.  In my experience, this feeding approach provides the most consistent performance.

By understanding the calf’s plumbing, we can design feeding and management programs that fit the calf’s abilities to digest milk, grow, and decrease opportunities for pathogens.