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Diet transition stress and the implications on the rumen environment and animal productivity

By Mikaela Baker, B. Ag Sci, TRAC Ruminant Productivity Consultant

Anyone who has ever had a conversation with a TRAC consultant, would have heard something along the lines of “we are feeding the microbes, not the animal…” and it cannot be emphasized enough. Yes, the individual components are being used to build strong, healthy, robust and productive animals, but the food has to pass through the gatekeepers first. The rumen microbial environment is a sensitive ecosystem where any form of change will have an influence that despite the potential long-term benefit of that change, will take readjusting to reach a new state of equilibrium.

Influencing factors can be termed as stress, and all stress will have some influence on digestion, just as it can in people. Stress can be from a combination of factors such as:

  • Nutritional Stress - Such as excessive amounts of protein, starch, or lacking critical elements such as fibre to support rumination. It can be any change to the diet or routine of that animal.

  • Physical Stress - Such as bad drovers pushing cattle or sheep too hard, or animals being confined to muddy areas reducing animals laying times.

  • ‘Eustress’ – Such as management practices we consider as good things can also fall under stress, this is referred to as ‘eustress’, which is a positive change, but still a change. Think about eustress as moving animals to a better paddock, changing calves bedding, and providing a better-quality hay or grain.

  • Heat Stress - that results in physical discomfort with changes to behaviour and metabolism, decreasing both food intake and feed conversion.

Due to the sensitivity of the rumen, these changes influence the number of microbial populations that breakdown different elements of feeds.

Rumen adjustment takes time. As a general guide we allow 3 weeks as a minimum for rumen change, such as the minimum backgrounding period before putting animals in feedlot or prior to dairy cows calving. However, a true rumen adaption takes 6+ weeks. When the timeframe to adapt is considered, a diet that has weekly changes results in the rumen microbes never adapting to the change. Farms are businesses and resources are limited. There is a happy middle point where practical management, and best practice needs to meet. Ruminants are tough. Getting highly efficient feed conversion is also tough. At each degree of ‘stress’ we put on the animals; we lose a bit of efficiency.

Going into a change too quickly can result in the animal taking longer to convert the feed to a product or, the animal can get sick. We can’t start feeding a full rate of concentrate and expect those microbes to be on standby to breakdown the grain and make it available for the animal to utilize, they simply don’t exist and that food passes through underutilized. It takes time to build up microbial populations and going too fast, can result in a rumen environment that does not support microbe survival.

The change in season is the perfect time to take diet change into consideration. The environmental change from winter to spring this year can only really be distinguished by the maturing of plants as they hit their flowering date. The sun hasn’t made a strong appearance, with weather staying mild and pasture-based systems not quite achieving the ‘spring flush’. While it still feels much like very early spring, that pasture quality tells a very different story. Preparing to set seed, the lignin and indigestible components of grass has increased, while protein is dropping.

With the aim of keeping costs down, pasture is often grazed long after it is providing a benefit and the classic drop in milk production can be seen as the energy density drops out. At this time, either mixer wagons start back up or hay feeding begins. As mentioned earlier, it is important to make minimal changes at a time to maintain a strong rumen environment, which is almost impossible to be achieved through late October and November.

The challenges seen at this time include:

  • Characteristics of pastures changing – high fibre, low protein and lower energy

  • Addition of new forages and byproducts

  • Energy density of total diet changing, due to increase in fibre

  • Increase in concentrate to contact drop in energy density

  • Change from a high starch grain mix to a higher protein starch mix

  • Change in daily routine for the animals – having to eat hay or going through a feed pad

Planning and introducing high quality conserved forages earlier to counteract the quality drop from pasture, and slowly winding up grain can help animals move through the changes and increase the appropriate rumen microbes.

Pushing to get the last goodness out of the paddocks can sometimes mean there is enough feed one day and having to fill the entire gap by opening the silage pit or bales once you hit the last day of the rotation. Silage comes with its own array of acids and low pH that will take animals longer to adapt to than hay. Transitioning animals slowly onto silage will see feed intake maintained and decreased potential of negative impacts on productivity.

The rumen is capable of adapting and changing to new feeds and quality throughout the seasons. By planning ahead and transitioning cows slowly, negative affects to production or fertility can be avoided. It is particularly important to focus on gradual changes when we are feeding less than ideal rations, and through great management of the transition and daily feeding practices, feed efficiency will be maximized to make great use of a poorer feed.

To discuss how we can apply this information on your farm,

please speak with your local TRAC consultant today,

your Experts in Ruminant Productivity or

phone the TRAC Office on 08 8733 1888


Our Consultants


Tom Thorn

0427 243 319

Owen Rees

0429 437 823

Mikaela Baker

0457 243 319


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Rumen Adaptation
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