A well-developed, fully functional rumen enables cattle to utilize forage for advanced growth, maintain adequate health, efficiently reproduce and produce optimal volumes of milk. However, a dairy calf is not born with a functioning rumen. Calf rumen development studies at Land O"Lakes Purina Feed"s LongView Research Farm have provided growing insights on dairy calf nutrition which suggest that the development of a rumen with optimal efficiency and function can be – and is – influenced by early life feeding.
The substrate, or diet provided to the young calf directly impacts the progress of rumen development. Therefore, the calf feeding program is a critical aspect in the transition of the calf from a pre-ruminant to a ruminant animal. Calves fed a milk-only diet, which is primarily transferred directly to the abomasum by the reflexive closure of the reticular groove, have shown to have a more limited rumen development since nutrients bypass the rumen. Therefore, the abomasum increases in size and the rumen remains small with restricted development of the rumen wall and papillae.
Studies have shown that by infusing milk directly into the rumen, growth of the rumen papillae could be stimulated due to the production of volatile fatty acids (VFA) by rumen fermentation. It is known that the production of VFA is essential to the development of the rumen papillae.
Calves fed forages early in life, prior to weaning, will begin to ruminate and have greater flow of saliva into the rumen along with greater muscle development of the rumen wall. However, this dietary program does not provide sufficient concentrations of VFA – especially butyrate – to promote rumen papillae development. This development is a key component to a functioning rumen.
A study by Heinrichs and Lesmeister demonstrated that calves fed milk and high-quality alfalfa hay diets over a 12-week period had high growth rates, but minimal papillae development compared to calves fed milk only. The forage-based diets resulted in the primary production of acetic acid rather than butyric acid. (Butyrate, or butyric acid, is believed to stimulate papillae growth in the rumen as the primary substrate for energy to the rumen wall.) As such, a key element to a calf"s rumen development is the ingestion of grain. The grain is necessary for sufficient VFA production, which results from microbial digestion and therefore supports papillae growth. When calves were fed milk and free-choice grain over a 12-week period, the papillae were larger and the rumen wall was thicker and more developed. Additionally, the rumens of grain-fed calves were darker in color due to greater vascularization or blood capillary growth, which allows for more absorption of VFA into the blood stream.
"During this period of time, it also is critical that adequate water be fed, along with the grain, to create the correct rumen environment that will support fermentation and production of VFA, which will in turn stimulate rumen development," says Dr. Dari Brown, young animal marketing leader with Land O"Lakes Purina Feed.
"Research has helped make progress on understanding the role of the calf"s diet through the first 12 weeks of life, to support growth and rumen development," adds Brown. And yet, the optimal nutritional program during the phase of 12 to 24 weeks of age is not as well defined. "At this time the calf is still undergoing significant growth in structure (frame) and body weight, along with additional, important rumen development. Traditionally, calves have been feed high amounts of hay or forage with limited grain during this period," Brown says. At this critical growth stage, the heifer still needs adequate nutrient supply to meet these demands. Identifying the proper grain and hay balance of a nutritional program should help her continue to develop structurally and potentially improve her production and longevity in the herd.
"The studies we have been conducting are helping us understand the important role feed plays in the rumen development of a dairy calf," concludes Brown. "These findings could have a significant influence on how calves are fed pre and post-weaning in the future."