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Feeding forage to calves: Is it necessary?

Xavier Suarez and Alex Bach Published on 16 December 2015
calf eating

After birth, the gastrointestinal tract of ruminants undergoes important anatomical changes. At birth, calves possess a very small microbial population in the rumen.

Establishment of rumen microbiota is necessary for the physiological development of the rumen and for the animal’s ability to convert plant mass into products that can be utilized by the animal for maintenance and production.

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At birth, the rumen represents about 35 percent of the total stomach compartments, and it increases to approximately 65 percent by weaning. However, for these changes to take place, calves need to consume adequate amounts and types of solid feed. When calves start to consume dry feeds (especially starchy grains), bacteria use these compounds as substrates to sustain their growth and produce volatile fatty acids (VFA). The presence of these VFA, especially butyrate, will stimulate rumen papillae growth. Papillae are responsible for VFA absorption.

As VFA accumulate in the rumen, the pH of the rumen liquid declines, and the rumen pH may affect rumen microbial population. In fact, the content of rumen amylolytic, proteolytic, cellulolytic and methanogenic bacteria increases linearly with age in the young calf. In contrast, the proportion of lactate-utilizing and coliform bacteria gradually declines during the first weeks of life.

Rumen development is a key factor to ensure successful weaning of calves. Feeding only milk to calves does not stimulate papillae development, but the consumption of solid feed and the resulting increase in rumen VFA concentrations stimulate rumen morphological development. Butyrate is the main stimulatory VFA for rumen papillae development. Butyrate is produced by amylolytic bacteria, which ferment starch, and this is the main reason why grain-based starter feeds are often recommended for the milk-fed calf. On the other hand, forage is fermented by cellulolytic bacteria, which produce mainly acetate, which has little to no effect on rumen development.

Even though starch may be the most important ingredient in starters, it could negatively impact rumen microbial diversity and lower rumen pH to acidotic conditions. Rumen acidosis increases the keratin layer of papillae, which reduces the capacity for VFA absorption. Although it may seem logical to limit starch content to avoid acidosis, that is not the answer. The calf actually needs that starch not only for rumen development, but also to provide the energy needed to sustain growth. The trick lies in learning how to feed high amounts of starch without putting calves at risk for acidosis. There are two approaches:

  1. Feed a high-quality texturized starter.
  2. Feed forage along with a complete pellet starter.

But again, not any forage will do the trick and neither will every texturized starter.

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Feeding a texturized starter

Rather than eating several small starter meals over the day, calves often eat large amounts of starter in a few meals. If the starch in the dry feed is rapidly fermented to VFA, it could surpass the capacity for VFA adsorption. As VFA accumulate in the rumen, pH decreases, creating the environment for lactic acid producing bacteria to thrive and further decrease rumen pH, possibly reaching acidotic condition. When calves are fed a textured starter with half or more whole grains and a protein pellet, the starch in the whole grains will only be available for fermentation once the grain has been chewed either while eating or during rumination. Thus, starch fermentation to the rumen is slow. If the grains are ground and fed, or ground, pelleted and fed, the starch fermentation in the rumen is fast and the rumen can be subject to acidosis.

Feeding forages along with pelleted starter

For the manufacturing of a good quality pellet, grains need to be finely ground, which increases the surface area for rumen bacteria to ferment starch. Pelleting temperature further increases starch fermentability by gelatinizing the starch. Thus, feeding a complete pellet high in starch increases the risk for acidosis. For this reason and because pellets do not provide the necessary abrasiveness for preventing the buildup of keratin on rumen papillae, calves fed complete pellet starter should be supplemented with forage. However, the forage quality, particle size and quantity are important to consider.

A Spanish study evaluated the effects of feeding different forage sources (all chopped at 1 inch) to young calves from birth to two weeks after weaning (see Table 1). Calves fed forage (with the exception of alfalfa hay) consumed more concentrate and grew more compared with the non-forage supplemented calves. It is important to highlight that calves fed grass forages voluntarily consumed less than 10 percent of their dry feed diet as forage. In contrast, calves fed alfalfa hay consumed 14 percent of forage from the total solid feeds consumed, which negatively affected starter intake. Data from several studies indicate that when forage represents less than 5 percent of the total solid feed consumption, calf growth is optimized, and when forage represents more than 10 percent of total dry feed consumption, growth is reduced.

forage sources studied table

When the consumption of forage represents more than 10 percent of total solid feed intake, it can also result in the accumulation of forage in the gastrointestinal tract. When even higher proportions of forage are consumed, forage accumulation in the gut can result in calves with “hay bellies.” Body weight gain in those situations is due to gut fill, rather than carcass weight gain. However, when consumption of forage is less than 5 percent of solid feed intake and forage is chopped, forage will not play a big role in gut fill.

Calves need forage when the starter they are fed puts them at risk for rumen acidosis or when the starter does not provide sufficient abrasiveness to prevent the buildup of the keratin layer. Forage quality, quantity and particle size are important to consider because these aspects will impact the results of feeding forage. In the nursery period, calves do better when they have access to a forage of low quality (high NDF) and is finely chopped so that forage consumption is less than 5 percent of total solid feed intake. Forage may not be needed in the nursery period when calves are fed a high-quality texturized starter with at least 50 percent whole grains, which provide abrasiveness for the rumen.  PD

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Xavier Suarez is a calf and heifer nutritionist for Provimi North America. Email Xavier Suarez.

Alex Bach is the department head of the department of ruminant production at the Institute for Research and Technology in Agrifood (IRTA) in Barcelona, Spain. Email Alex Bach.

PHOTO: Staff photo.

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