Live yeast in feed to manage heat stress: Fact or fake news?

Balancing act for rumen health helps manage heat stress and promotes growth

Beef
Shade and access to good, clean water are more important than rumen additives in managing heat stress, say nutritionists.

Shade and access to good, clean water are more important than rumen additives in managing heat stress, say nutritionists.

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A variety of brewer's yeast added to grain rations has been shown to lead to daily weight gain but can basic management do the job just as well?

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Summer's sudden arrival has brought to mind the realities of heat stress.

At present livestock prices no one wants to see an animal slip backwards so proponents of brewers yeast added to mixed rations say it helps balance rumen pH, preventing acidosis, and helping maintain a better plane of nutrition and outcome.

Lallemand manufactures and sells a strain of Saccharomyces Cerevisiae and has been promoting its effect on heat stress management through a white paper distributed on social media titled: Assessment of heat stress risks in dairy and beef cattle and live yeast benefits.

The paper points to studies from Italy and France that have shown the addition of brewers yeast to silage rations for dairy cattle living indoors is a good thing when managing temperatures above 24C - which is something of a heat wave in Europe.

A study on beef cattle from Texas A&M AgriLife Research Center is the closest that Australian producers can look at when trying to make a decision on whether the supplement is worth a try. Those study results suggest 50g/day increase in weight gain and a 5kg increase in carcase weight over a 70 day feeding period.

Queensland based animal nutritionist Jim Wade, Wade Agriculture points out that Australia is next level when it comes to heat and stress. It is true that he has prescribed live yeast products, particularly pro and pre-biotics in certain situations depending on animal health and environment but says the introduction of live yeast to livestock feed is not a silver bullet when managing heat stress.

"Access to shade and good clean water are more important considerations," he suggests.

Mr Wade said heat stress is a management challenge for livestock producers. Grazing animals in hot weather tend to eat less which creates change in the rumen usually resulting in a lower pH. If a hot spell lasts several days and if the nights fail to cool down very much it can take weeks before animal performance is back to levels where it was before the original hot weather event.

"Live yeast stimulates the appetite and enhances digestion," he says noting that he prescribes the product in certain pelletised products used in the feedlot industry.

When cattle are resting under shade they are not eating and if the rumen is empty the resulting change in pH can have a lasting impact on animal performance.

When cattle are resting under shade they are not eating and if the rumen is empty the resulting change in pH can have a lasting impact on animal performance.

"What we can say is that live yeast may stimulate appetite and enhance digestion at a time when feed intake may go down."

He also points out that the impact of live yeast cannot be easily attributed to weight gain because of other complex factors in the rumen that cloud the results.

How cattle are weaned and backgrounded prior to entering a feedlot will also have a bearing on outcome.

"There are many factors that effect live weight gain," he says. "But one thing that can be measured in a feedlot during periods of heat stress is the intake by animals fed on a ration with live yeast versus a control without.

"You can't do this as easily in the paddock."

Livestock consultant Alastair Rayner, Tamworth warns that rumen supplements should not be used as a replacement for basic animal husbandry and that during times of heat stress animal access to shade and water is paramount.

"There has been a lot of feed studies internationally and a lot of papers not widely peer-reviewed," he warned. "There are a lot of products on the market and a lot of advertising that promotes the rumen as mysterious; like a witches brew and you add things to to eke out better performance.

"In fact the rumen looks after itself really well, provided there is enough roughage in the diet. It doesn't need the addition of secret herbs and spices.

"The rumen is a fantastic organism and adjusts very well to what is being eaten.

"However, in hot conditions it is much more important to ensure cattle have access to adequate shade and sufficient water - hot days can see consumption increase by 80 per cent and that water should be available in troughs that are deep enough to keep water relatively cool.

"When water temperature is above 18 degrees consumption does decrease and this impacts cooling and feed intake.

"My advice for heat waves is to focus on shade and water and allow cattle to feed when it is cooler."

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