Dialing in Calf Starter Protein Concentration

By Dr. Noah Litherland, Vita Plus dairy youngstock technical specialist
Nursery calf growth depends on adequate solid feed intake, which is necessary for rumen development and allows calves to maintain growth through weaning and transition to the grower phase.  Variation in starter intake accounts for more than half the variation in total bodyweight (BW) gain.

Traditionally, calf starter grain is formulated to contain 18% crude protein on an as-fed basis, or about 20% protein when expressed on a dry matter (DM) basis (assuming 88% DM).  Effects of starter grain intake on calf growth are intake-dependent.  Calves require protein for maintenance and growth.  Like lactating cow diets, starter grain contains both rumen degradable and rumen bypass protein.  The calf rumen is constantly under construction.  As the calf goes through the weaning process, grain intake increases, rumen capacity increases, microbial ecology diversifies, rumination rates increase, and rate of passage through the rumen is altered.  All these factors make it complex to optimize protein metabolism in the developing calf.

How much protein is needed to support growth?
It depends!  Calf age (pre- or post-weaning), size and rate of growth are key factors impacting protein requirements.  Calculated crude protein requirements in the Dairy Cattle NRC, 2001 indicate a 132-pound calf gaining 1.8 pounds per day requires 0.6 pounds of crude protein per day.

That leads us to ask, “How much starter intake and which starter protein concentration would need to be fed to meet the required 0.6 pounds per day?”

Calculated crude protein intake from the interaction of starter grain intake and starter crude protein concentration is helpful to determine which combination of starter intake and protein concentration is needed to meet this example calf’s protein requirement.  In this example, the calf would need an approximate daily consumption of:

• 3.8 pounds of 16% starter
• 3.3 pounds of 18% starter
• 3.0 pounds of 20% starter
• 2.7 pounds of 22% starter

The protein intake goal can be achieved by either managing for greater starter grain intake or feeding greater protein concentration.

Let’s focus on the economics in this example with 18% and 22% crude protein starters.  Feeding 22% starter would require 0.6 pounds less starter per day to meet the same protein amount, but the cost is $0.02 per pound greater for the 22% versus the 18% starter.  From a protein standpoint, feeding the 22% would result in a savings of $0.11 per calf per day in this example.  The problem is we are not comparing apples to apples.  The 22% protein starter would result in 0.6 pounds less intake, which also means lower energy intake.

Concerns with feeding high-protein calf starter
Field experience has taught us that high-protein calf starter is effective up to a point.  There is a tipping point where the intake of crude protein exceeds the digestive tract’s ability to efficiently utilize dietary protein.  As a result, the calf’s manure becomes loose, perhaps due to the osmotic pull from protein reaching the lower digestive tract or fermentation of the protein by bacteria in the colon.  The result on some farms seems to be a degree of digestive upset when crude protein intake is excessive.

Additionally, excessive protein intake increases the amount of nitrogen excreted into the environment in urine, resulting in wetter pens and increased need for bedding, as well as decreased air quality.  Producers effectively using a high-protein starter manage starter intake amount, switch calves to a lower-protein starter at the end of the nursery phase, or dilute the starter with a small amount of forage to manage protein intakes in a desirable range.

Future perspective
Like all growing animals, calves require amino acids (not crude protein) for growth.  Amino acid-balancing calf starter might allow for decreased crude protein concentration, increased growth and/or efficiency of growth, cost savings to producers, and decreased release of excess air ammonia in calf facilities.  Additionally, producers typically must inventory two calf grains (starter and grower) with the primary difference being altered protein concentration (18% starter and 16% grower).  Perhaps an amino acid-balanced calf starter, such as BSF, could serve as both starter and grower since concerns with overfeeding protein would not be a constraint.