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Understanding how the calf digests its feed, and how the rumen develops over time will help to ensure your rearing system achieves successful growth rates, health status, weaning weights, and future production for all calves.
When the calf is born, only one of its four stomachs, the abomasum, is functional. The abomasum is where the calf holds and digests any colostrum and milk that it is fed. Milk, in comparison to pasture and other forage-based diets, is a highly digestible feed. Therefore, to help prepare the calf for their future diet, the digestive system, in particular the rumen, needs to undergo significant changes.
The aim of a calf rearing system in the first four to six weeks of life should be to help grow and develop the rumen so that the calf can start to digest solid feed.
At birth, the rumen is small, and milk has no effect on the development of the rumen, as it bypasses it to go straight to the abomasum. As the calf begins to nibble on meal, straw, or pasture, the rumen begins to develop a population of good bacteria (microbes).
Calves need to have access to fresh, clean water to help maintain and grow microbial populations in their gut.
As well as growing larger, the rumen needs to develop papillae to become functional. Calves fed grain (or meal) will develop a functional rumen much quicker than calves fed on milk only or milk and grass/hay (Figure 1). This is because the fermentation of meal or grain produces a high level of specific fatty acids that support the development of the rumen. Forage-based feeds, such as hay or pasture also produce these fatty acids, but in much lower quantities, and therefore take a longer time to achieve the same level of rumen development.
Calves given large quantities of milk will have slower rumen development. This is mainly because the milk satisfies their appetite, so they eat less forage and concentrates, which decreases the requirement for digestion in the rumen
Figure 1: Calf rumen development after 6 weeks, fed either milk, milk and hay, or milk and grain. Source Penn State University, USA
To optimise rumen development, calves should have access to meal or grain from birth.
Providing fibre, such as hay, straw or pasture will help to promote the growth of the muscular layer of the rumen and maintain the health of the rumen lining. When papillae are exposed to the high levels of fatty acids in grain, they can become too long and clumped. Fibre helps to balance this out and maintain papillae in optimal condition. When feeding grain or meal, it is important to ensure that calves also have access to fibre. With meal, this may already be balanced in the blend - be sure to check.
Be sure to choose a source of fibre that is different from the bedding used in calf sheds to minimise calves eating bedding.
Water is an important part of any animal’s diet and helps to maintain normal body function in all animals, regardless of age. Clean, fresh water should be available to all calves from birth.
Research has shown that early access to fresh, clean water encourages calves to consume more concentrate, earlier in life. This led to those calves gaining 38% more weight over a 4-week period compared with calves that did not have access to water.
It is important to have water positioned near any concentrate feed so calves can access it easily. The water will get messy and will need to be cleaned out and replaced regularly, rather than just topped up.