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Impacting digestive development in neonatal calves

John Hibma for Progressive Dairyman Published on 24 May 2016

Raising calves has been a challenge for dairy farmers for decades. Most neonatal calves on today’s dairy farms are separated from their mothers at birth and usually fed less milk solids daily than they could consume if allowed to nurse their mothers.

The modern dairy calf is fed and housed with the expectation she will grow rapidly, with her gastrointestinal (GI) tract developing at an unrealistic rate that will allow the producer to wean her as quickly as possible. The natural process of weaning takes up to 10 months. Dairy producers wean their calves in two months.



Truth be told, a solid understanding of how the rumen and the lower GI tract of a calf develops is still very limited. For the most part, calf-raising programs on dairy farms often consist of ongoing experimentation in diets and housing designs that prioritize the financial and labor management resources of the producer rather than focusing on the biology of the neonatal ruminal GI tract development.

Many brilliant minds have tackled the task of how to successfully raise healthy calves, reduce mortality and morbidity and get them weaned with the least amount of effort on the part of the dairy farm operation. Right or wrong, the typical neonatal calf is “put to the test” during its first few weeks of life.

History has shown us there are a variety of ways to successfully raise neonatal calves. If the increased milk per lactation of the average dairy cow is any indication, we are doing an increasingly better job of raising calves and getting their GI tracts up and running. However, USDA data shows us that the average mortality rate of neonatal calves is still around 10 percent, and morbidity runs near 50 percent.

Newborn calves essentially have two big hurdles to get over in the first few weeks of life. They must fight off or overcome any attack on their immune system, and they must make the transition from a monogastric GI to a ruminant GI system.

Whether or not the rumen can develop successfully and a calf can be weaned by 2 months old is first dependent upon whether it can survive a pathogenic assault during the first week or two of life.


By far, the most challenging aspect of raising baby calves is preventing digestive diseases. Calf-raising studies clearly show that GI infections are the first ailments experienced in a calf’s life, with a large percentage requiring antibiotic treatment for diarrhea.

It is well-documented that feeding colostrum within the first 12 hours of life will dramatically bolster the immune system of baby calves. Calves are born with a very limited amount of immunity. Little if any immunity is passed from mother to fetus.

The administration of colostrum is necessary for the transfer of passive immunity, and this occurs only in the first half-day of life when the immunoglobulins are readily absorbed across the abomasal lining.

The major emphasis has been to feed colostrum only for a day for the benefit of the passive absorption of antibodies and then switch to a milk replacer or whole milk.

There is emerging research, however, suggesting that rather than abruptly switching to milk replacer, the transition milk taken from cows three or four days after freshening may contain other bioactive components, such as hormones, prebiotics and immune system stimulants that may aid in the development and health of the GI tract.

In a recent study, it was determined that calves fed transition milk had an elevated health status with reduced cortisol (stressor) levels and enhanced insulin status (increased glucose uptake), translating into greater growth rates.


Feeding programs for neonatal calves on many commercial dairies incorporate a twice-per-day feeding schedule that limit feeds milk solids. Attempts at feeding more fluid milk in only two feedings has met with disfavor due in part to digestive upsets.

This is thought to be caused by abomasal overflow into the as-yet-undeveloped rumen. Undigested milk left in the rumen may lead to bacterial fermentation, ruminal acidosis, scouring and dehydration.

Feeding programs that allow calves multiple feedings per day, where they consume smaller amounts of milk per feeding, have had very good results with improved average daily weight gains and minimal digestive upsets.

Commercial milk replacers fed to neonates should contain milk proteins such as whey and milk-based fats. Milk replacers containing proteins and fats that are plant or vegetable in origin are poorly digested and should be completely avoided.

Studies indicate calves that are limit fed, with either milk replacer or whole milk, at the rate of about 10 percent of bodyweight and are weaned around 2 months old can experience depressed growth and impaired gut health even though they may begin consuming small amounts of solid food.

Limit feeding milk to neonatal calves most likely deprives them of essential amino acids found in milk protein and the energy necessary for both skeletal and GI tract development.

Group feeding scenarios allowing milk consumption ad libitum have shown that calves can easily digest fluid milk in excess of 20 percent of bodyweight when sanitation standards are kept high. Neonatal calves fed to those levels have been shown to have higher lifetime milk production.

While the baby calf is being fed as a monogastric, the rumen is rapidly developing. Colonization of rumen bacteria starts soon after birth, and the presence and proliferation of rumen microbes is not dependent on nutrient digestion in the rumen.

The transition from an all-milk diet to rumen fermentation can be accomplished when the volume of the rumen grows to and accounts for 70 percent of the total forestomach.

When calves are born, the abomasum is the largest chamber of the forestomach, accounting for 60 percent, while the rumen is only 25 percent. By the time a cow matures, the rumen dominates the forestomach, making up 80 percent of the total volume.

Weaning, by definition, is the cessation of milk as the primary nutrient, switching over to solid feeds as the primary source of nutrition. The rumen must be ready to ferment solid feed before calves can be weaned.

The process of weaning requires an extensive increase of the surface area of the rumen for the synthesis and absorption of the volatile fatty acids necessary for energy metabolism.

The calf will transition from her reliance on calories and energy being supplied by milk to the volatile fatty acids being produced through ruminal fermentation of solid feeds. If weaning is attempted too early and the rumen is not yet large enough, calves’ growth rates are drastically reduced and oftentimes the “hay belly” is evident, indicating poor digestion of feedstuffs.

Most of the research conducted on ruminant development has focused on the speed at which the rumen can develop and calves can be weaned without doing them serious harm.

Recent studies have shown that the small intestine also undergoes transformation as the calf grows and matures. The early introduction of solid feeds to the young ruminant may cause inflammation and acidosis in the small intestine due to starch left unfermented in the rumen.

The small intestine may still be lagging behind in its ability to absorb nutrients as the calf makes the transition to ruminant.

It’s clear that the full development of the rumen GI system in dairy calves is a complex process that most likely takes longer than we’d like it to. Neonatal calves that survive pathogenic challenges will naturally develop a functioning rumen. Healthy neonates should double their birthweights by 60 days old.

Dairy producers have learned that it’s as much an art as it is a science when it comes to raising calves and knowing when the young ruminant is ready for weaning.

While evidence abounds showing advanced calf-raising programs and protocols are working well, we also must be patient with Mother Nature and not push the envelope to such an extent that growth and gut health are compromised.  PD

Information for this article was taken from Dietary Factors Influencing the Development of the Ruminant Gastrointestinal Tract, M.A. Steele, et al., presented at the 2015 Cornell Nutrition Conference.

John Hibma
  • John Hibma

  • Consulting Ruminant Nutritionist
  • Connecticut
  • Email John Hibma