Calf development stages of a ruminant

THIS week, let me digress a bit from a series of drought related stressing articles and look at an important aspect for every livestock farmer, that is calf development.

Many times, farmers lose calves due to limited understanding of some vital aspects of the development phases of a calf.

I am a livestock farmer and if there is a time when my blood pressure rises a few notches above normal is when I lose a calf. This pains me a lot as it means reduction in what I could sell that year and hence technically it is loss of potential income.

While there are a number of reasons why a farmer can lose a calf, the most common reason is due to poor management practices as a result of limited understanding of some critical calf development processes.

The first important aspect to understand is that a calf is born with the four chambers of the digestive system like any ruminant. However, at birth up to a few weeks it is called a pre-ruminant because the four chambers are not yet functional and the calf can only utilise milk which is absorbed by the abomasum which at this stage constitute close to 70 percent of the digestive tract of the calf.

At this point, the immature digestive metabolic systems function similarly to those of a young monogastric animal, and the calf depends on milk or milk replacer as an easily digestible source of carbohydrate and protein.

The act of sucking by the calf causes a fold of muscle to develop in the wall of the rumen called the reticular or oesophageal groove.

As the calf sucks, the oesophageal groove delivers milk directly to the abomasum where it is digested most efficiently.

So, it is important to make sure a calf suckles as this is not only a process of milk intake but it helps in the development of rumen muscles which is important for directing milking to the rightful chamber responsible for absorption of that milk into the blood stream.

At the early stages of the calf’s life, the digestion or conversation of milking into various products that can be used by the body of the calf, depends on a number of enzymes that are found in the digestive tract.

Enzymes such as renin enables the calf to efficiently utilise proteins found in milk while the enzyme pepsin will increase in quantity as the calf begins to intake nonmilk feed.

Pepsin allows the calf to utilise protein from non-milk sources.

The transition phase covering the move from the preruminant to the ruminant phase occurs between four and eight weeks of age, when the rumen begins to take over the main digestive function of feed. This phase may happen much earlier than four weeks depending on when the calf was introduced to non-milk feed such as grass and concentrate. At two weeks of age the calf should be encouraged to eat some concentrates, hay or grass. At this time the rumen, reticulum and omasum will begin to develop. By one month of age calves should be eating substantial quantities of grass and roughage. Calves will become less dependent on milk and the incidences of scours are reduced, calves can be weaned earlier, and labour and rearing costs are lowered. The ruminant phase begins at about six to eight weeks of age of the calf. At this point, dry feed is the sole source of feed, and the rumen accounts for approximately 70 percent of all stomach compartments. A calf will usually have full rumen development at 12 weeks of age and its ability to eat and digest dry food will then be more or less similar to that of an adult animal. Rumen development is defined as the development of the epithelium and it is critical to successful weaning and good calf growth rates.

Rumen development also involves growth of the microbial population in the rumen.

These microbes help in digestion of the rumen contents. There are a number of conditions that are needed for the growth of the rumen microbes and these include the bacteria which is introduced into the calf as it begins to ingest non-milk feed stuffs; the availability of feed in the rumen for microbes; liquid intake; rumen muscular contractions which help with feed mixing and movement. The contribution of these factors and others in rumen development may be discussed in detail in subsequent articles but it is important to point out rumen development is a critical growth phase in your calf as it can be difference between losing your calf and not; excellent growth rates and poor ones.

Attribution: This article borrows significantly from a publication by the Agriculture and Food Development Authority, whose authorship could not be properly captured.

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