Exploring The Development Of The Gastrointestinal Tract In Calves
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By Nele Leiterman, D.V.M.
Calves are the future of the dairy industry. Central to their early development is the maturation of their gastrointestinal tract (GIT), a process that lays the foundation for their ability to digest and utilize nutrients efficiently. In this article, we delve into the stages of gastrointestinal tract development in calves, focusing on the critical role of the rumen and abomasum, to optimize calf health and performance.
Neonatal Phases: Nurturing the Foundation
Upon birth, the GIT of the calf is still in its infancy, lacking the maturity of the rumen for forage fermentation and digestion. This neonatal period becomes pivotal as the calf transitions from being a functional monogastric animal (like pigs and poultry), with a diet primarily composed of milk, to a ruminant that primarily digests solid feeds and forages.
For the first three to four weeks of life, the enzyme profile that aids in digestion is largely composed of proteases (to digest milk proteins), lipases (to digest milk fat) and lactase (to digest the milk sugar, lactose). Another enzyme, rennin, helps to curdle the milk in the abomasum, allowing the milk to stay in the stomach longer for a more complete digestion. In the first few weeks of life, the GIT of a calf contains low amounts of amylase. This digestive enzyme aids in the digestion of complex carbohydrates like those found in grains. As a result, Crystal Creek® recommends meeting calorie needs with milk feedings alone for the first two weeks of a calf’s life. After the calf is two weeks old, and the amount of amylase increases, grain feeding becomes beneficial because the calf’s GIT becomes more efficient at digesting the grain.
As the calf matures, the enzyme profile within its GIT continues to undergo significant changes. The digestive enzymes gradually shift from a profile designed to digest milk (high in milk fat and protein digestion enzymes) to one more suited for complex carbohydrate and plant-based feed digestion.
The rumen, a critical component of the digestive system, undergoes rapid development during the neonatal phase. Initially undeveloped, it starts to transform within days after birth, spurred by the intake of colostrum rich in essential nutrients and growth factors. Another enzyme to pay attention to is pepsin which aids in the digestion of proteins and increases over time in the GIT. This allows the calf to become capable of utilizing non-milk sources of protein. This enzymatic shift, combined with the maturation of the rumen, facilitates the transition from a milk-based diet to a solid diet.
At birth the rumen is mostly inactive and vacant of the microbiota that ferment and digest solid feeds. One of the main ingredients in rumen development is butyric acid, a product of microbial digestion of starches, that is a direct source of energy for ruminal growth. Since the calf is not able to successfully digest starches in the first weeks of its life, the ruminal growth can be accelerated by adding sodium butyrate, the salt of butyric acid, to milk replacer. Research has shown that this leads to an earlier development of the rumen and increased daily weight gains in the pre-weaned phase. For this reason, three varieties of Crystal Creek’s Swift Start™ Milk Replacer contain sodium butyrate.
Pre-ruminant to Ruminant Transition: A Time of Transformation
The transition from a pre-ruminant to a ruminant marks a significant milestone in the calf’s gastrointestinal tract development. As the calf matures, the rumen undergoes a series of structural and functional changes.
First, the rumen has to grow in size to accommodate the primarily forage-based diet of a ruminant. Offering fresh water to calves from three days of age helps stretch out the rumen and creates an ideal environment for anaerobic bacteria to grow. Offering calves hay as a non fermented forage, also helps the rumen increase in size and stimulates the musculature of the rumen to start contracting and training its strength.
On the inside of the rumen there are the rumen papillae. These little, microscopic finger-like structures absorb the volatile fatty acids (VFA) produced by the fermentation process of the microbiota, the energy “currency” of the rumen. In a newborn calf these papillae are short and undeveloped. Their development and growth is directly linked to the calf’s diet during the first few weeks.
Butyric acid, as mentioned earlier, is one of these VFAs. The microbial digestion of grains creates butyric and propionic acids in the rumen. The digestion of forages yields in the production of acetic acids. While propionic and acetic acids get absorbed and provide energy to the metabolism of the calf, butyric acid aids directly to the growth of the rumen and its papillae. Penn State released a study that looked at the differences in rumen development with different rations. In the picture below, you can see that in the calf that was fed milk and hay, the papillae did not grow as much as they did in the calf that was fed milk, hay, and grain. The darker color of the membrane indicates a much better vascularization in the calf fed a ration with grain.
Conclusion: Nurturing Future Generations
The development of the gastrointestinal tract in calves is a multifaceted process that requires careful attention and management. From the neonatal stage to weaning and beyond, each phase plays a crucial role in shaping the calf’s ability to thrive in its environment. Dairy farmers and nutritionists serve as stewards of this development, employing proactive strategies to support rumen maturation and optimize calf health and performance. Calves fed higher levels of milk or milk replacer and a properly formulated calf starter will gain weight more rapidly and achieve better rumen maturation. Healthy calves grow to be productive cows. To learn more about how Crystal Creek® can help your calves, call 1-888-376-6777 and ask to speak to one of our knowledgeable team members.