With calving season in full swing for a lot of producers or about to start, I would like to touch on the importance of newborn nutrition and the development of the rumen from newborn to mature animals. Rumen development occurs in 4 main stages. This includes the newborn stage, the pre-ruminant phase, the transitional phase, and the weaning phase into adulthood.
In newborn calves, the abomasum is the largest of the 4 chambers of the stomach. As a reminder, the abomasum is the most caudal compartment and is responsible for gastric digestion in ruminants. However, there is no HCl or pepsinogen (gastric acids) secreted from the abomasum in the first 24 hours of life. The rumen is undeveloped at birth with no microbes or papillae (hair-like structures on the surface of the rumen). Therefore, the immunoglobulins (proteins) in colostrum pass directly through the rumen without being digested. The process of pinocytosis is the passive transfer of immunoglobulins across the intestinal mucosa. This provides the calf with early immunity against infectious diseases such as a navel infection. In monogastrics, the passive transfer of immunity occurs in the womb, however, the placenta type in ruminants prevents this from happening before birth. Throughout the first 24 hours, the rumen will begin to develop papillae and microbial establishment will occur. These changes will trigger the digestion of the immunoglobulins and prevent them from contributing to the immune response of these calves. This development of the rumen is why many people suggest getting colostrum to calves in the first 6 hours after birth when possible. After those 6 hours, the rumen and the epithelial of all the stomach compartments are developing and can reduce the absorption of whole immunoglobulins, therefore, reducing immune development. As you can see from the chart below, the quality and nutritious value of colostrum also decreases significantly after the first 6 hours.
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After 24 hours, the phase is known as the pre-ruminant phase where milk becomes the principal source of nutrients. This lasts for 3 weeks. The calf needs to consume 8-10% of its body weight in milk per day and relies on glucose-based metabolism like monogastrics. The calf stomach is quite small and therefore, they will need to suckle 6 or more times per day. The act of suckling promotes salivation which contains pre-gastric esterase enzymes. These enzymes initiate the digestion of milk lipids. There is a groove, called the esophageal groove, which provides a route for the milk to bypass the reticulorumen and go directly to the omasum. This prevents the microbes from denaturing the milk before it can pass through the omasum and be properly digested and absorbed in the abomasum. Bucket-feeding calves has been shown to decrease salivation and the closure of the grove can be more erratic. However, if the esophageal groove does not close properly or the calf drinks too fast, some of the milk will leak into the rumen and get fermented to lactic acid and volatile fatty acids (VFAs). This will result in a decreased rumen pH, gas formation, and rumen distention. Ruminal acidosis is the consequence of this event and will often result in diarrhea. When the groove is functioning properly, the abomasal secretions will increase due to the presence of milk and the act of suckling. These secretions contain rennin and HCL. Rennin will form a "hard clot" of butter fat and curd which will undergo slow digestion for 12-18 hours. The remaining liquid, whey protein, and lactose will quickly pass into the duodenum (small intestine). Here protein and lactose digestion occurs and they are absorbed.
From week 3 to 8 of life, the transitional phase occurs. Normal microbial flora in the rumen begins to emerge. This allows the induction of solid feed and limits milk intake. This will shift the metabolism from glucose to VFA metabolism. The saliva production needs to be increased to promote digestion, it occurs by growth in salivary glands. The transitional phase requires dry feed to promote proper rumen development. Providing forage increases the rumen weight and development of the muscles in the rumen wall. The development of rumen papillae and omasal leaves increases which creates more surface area for absorption. The act of regurgitation (chewing cut) will begin and rumen motility will increase. However, there is a risk of food and water contamination from the act of regurgitation and feces. Therefore, feed and water sources need to be observed and maintained to prevent disease spread. The development of the reticulorumen will shift the calves' metabolism from glucose (insulin-dependent) to VFA production.
The weaning and post-weaning phase occurs from 8 weeks of age to adulthood. Milk becomes less important than dry matter. The rumen microbes are producing VFAs constantly which are then used in the body to create glucose. Gluconeogenesis is the process in which glucose is formed. This process becomes more constant (not insulin dependent) and uses VFA precursors instead of lactose. The forestomach (reticulorumen and omasum) reaches the proportions of a mature animal. This means the rumen is now responsible for 70% of the stomach. The use of transition diets becomes so important from weaning into adulthood. If the microbes are fed a new ration, without transition, they will produce VFAs at a rate that will negatively affect that animal and often result in bloat or acidosis. Using products like a calf starter, that is built for these animals, with minimal dust is a great product to use for transitioning these calves onto a full dry matter diet.
Rumen development and proper timing of ration changes are important to ensure the animal is meeting requirements and production parameters. We have milk replacers for calves and lambs in stock at the ranch. Contact us if you need these products! We also have many options for calves older than 6 weeks of age to help with the transition to a dry matter ration.