Current Progressive Dairy digital edition

Precision nutrition for calves: Can we move beyond crude protein in calf starter?

Tana Dennis and Mark Hill for Progressive Dairyman Published on 24 August 2018

In our previous article, “Precision nutrition for calves: Moving beyond crude protein concentration in milk replacer,” we presented substantial evidence for utilizing synthetic amino acids to better supply building blocks for growth and reduce costs associated with overfeeding protein.

Logically, balancing for amino acids in dry feeds for calves would be warranted. However, there is very little published research regarding amino acid formulation in dry feeds for calves. This article will address what we know about crude protein in dry calf feeds and explore opportunities for formulating calf feeds in the future.



Crude protein concentration

Several years ago, researchers at Provimi fed starters equal in energy containing 18, 20, 22, 24 or 26 percent protein to calves given 1.5 pounds of a 26 percent all-milk protein, 17 percent fat milk replacer. There were no differences in bodyweight gain, starter intake, efficiency of gain or frame growth over the eight-week trial.

In weaned calves, feeding 13.5, 15, 16.5 or 18 percent protein grower feeds blended with 5 percent chopped hay resulted in weight gain maximized at 15 percent protein and feed efficiency maximized at 16.5 percent protein.

Researchers at the University of Illinois reported mixed results when feeding an 18 percent or 22 percent protein starter to calves fed a 28 percent all-milk protein, 15 percent fat milk replacer.

In one trial, calves fed 22 percent protein starter tended to be 11 pounds heavier at 10 weeks old than calves fed an 18 percent starter. However, in a related trial comparing body composition of calves fed the same starters, carcass weights were only 3 pounds heavier at 10 weeks old for calves fed a 22 percent protein starter, and frame size was similar in both trials.

In a study from Purdue University on a commercial dairy where calves were fed pelleted starters containing 18, 20, 22 or 24 percent protein with up to 2 gallons of pasteurized milk daily, feeding a 24 percent protein starter resulted in the greatest weight gain to 12 weeks old, a 12-pound advantage compared to feeding an 18 percent protein starter.


However, frame growth was similar, and increased weight gain may have been linked to greater observed starter intake post-weaning for calves consuming 24 percent protein starter.

A University of Minnesota study tested texturized starters with 15, 18, 21 or 24 percent protein in calves fed 1.25 pounds of a 20 percent protein, 20 percent fat milk replacer. Calves fed 15 and 24 percent protein starters gained the least amount of bodyweight over eight weeks, whereas calves fed 18 and 21 percent protein gained the most.

Additionally, feed efficiency plateaued at 21 percent protein, leading the authors to conclude there was no benefit to feeding greater protein levels to calves under 8 weeks old.

These controlled trials from four different research groups agree remarkably well and suggest feeding an 18 percent protein starter on an as-fed basis is ideal for calves fed conventional or high milk or milk replacer feeding rates.

However, these studies do not address how protein sources used in a starter might impact growth and efficiency. Protein sources can differ in amino acid profiles, protein digestibility and sites of digestion, which will greatly affect how the calf utilizes dietary protein.

Crude protein source

More than 35 years ago, when the understanding of rumen-degradable and -undegradable protein was developing, many nutritionists started adding sources of rumen-undegradable protein (RUP) to dry calf feeds. However, when we look to the published data, there is little to no justification for using RUP sources in feeds for pre- or post-weaning calves.


Research performed at Provimi’s Nurture Research Center has evaluated several protein sources for calf feeds, including conventional soybean meal (SBM) used as a control protein source, heat-treated SBM, blood meal with a commercial bypass methionine source, corn distillers grains with solubles and some blends of plant protein sources. The use of heat-treated SBM and blood meal with bypass methionine did not improve growth compared to conventional SBM.

Additionally, partially replacing conventional SBM with heat-treated SBM in starters containing whole or steam-flaked corn did not improve growth, efficiency or diet digestibility in weaned calves. Researchers from Penn State University reported no differences in growth rates or carcass composition when feeding diets with increasing RUP up to 25 weeks old.

More recently, researchers in Iran reported increasing RUP from 22 to 34 percent of crude protein using heat-treated SBM did not improve growth rates or feed efficiency in calves up to 70 days old.

These results are most likely due to protein degradation in the rumen being low and increasing with age post-weaning. Table 1 shows protein disappearance over 24 hours when different plant protein sources were ruminally incubated in recently weaned calves and mature cows.

Rumen digestibility measurements of different plant protein sourcesObservations indicated sources of RUP are less needed in young calves than in older animals with more developed rumen function, as more protein remained after rumen incubation in recently weaned calves compared to mature cows. Beyond these datasets, no published data is available on digestibility of other protein sources in calves around weaning, including animal bypass proteins like blood meal.

Should we account for rumen development when formulating calf feeds?

Calves experience considerable changes in rumen development, rumen function and microbial population establishment all through the weaning transition. For the most part, we have a decent grasp on how nutrition and management can affect the above-mentioned changes in physiology.

However, there is a gap in our understanding of microbial protein production when going from a non-functional to a functional ruminant. Research from the University of New Hampshire showed the proportion of microbial protein to total protein present in the abomasum increased from 2 to 11 weeks old.

Studies have also shown starter digestibility increases with age and is influenced by the milk feeding program and the starter formula. Some researchers have reported rumen microbial populations in growing heifers do not resemble mature cow populations until at least 6 months old. Dynamic changes around weaning make precision formulation of dry feeds that much more complicated.

So what is needed?

Energy is frequently more limiting to growth in calf starters and growers than protein based on the Dairy NRC (2001) calf sub-model and recently published research. Ensuring fermentable carbohydrates are available to maximize digestible energy available to both the rumen microbes and the growing calf is critical.

Researchers at Provimi have illustrated in several trials increasing dietary starch supports weight gain and frame growth in calves consistently, whereas similar responses when increasing protein in starter or grower diets were not observed.

Additionally, utilizing RUP sources is not needed and unnecessarily increases feed costs. Some RUP sources can make sense in mature cow diets, as there may be a need to increase metabolizable protein to meet production demands.

However, if we compare prices of RUP sources based on digestible RUP in calves (Table 2), bypass SBM is equal in cost to conventional SBM.

cost of digfestible rumen-undegradable proteinFurthermore, if we assume blood meal RUP values are equal in mature cows and calves, the cost of blood meal is nearly double the cost of using SBM.

Based on the available data, we believe the combination of corn and conventional SBM offers a good balance of amino acids, is free of many anti-nutritional factors, is low in fiber and is consistently digestible. Additionally, 18 percent protein (as-fed basis) in starters for calves under 2 months old and 15 to 16 percent protein (as-fed basis) in growers for calves 2 to 4 months old are appropriate and supported by published research. end mark

Mark Hill is in ruminant nutrition and research, Provimi North America. Email Mark Hill

References omitted but are available upon request. Click here to email an editor.

Tana Dennis
  • Tana Dennis

  • Calf and Heifer Nutritionist
  • Provimi North America
  • Email Tana Dennis