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Care needed to avoid TMR overheating in winter

Silage spoilage, caused by overheating, may be accounting for poor performance in some herds this winter. Farmers Guardian reports.


Spoilage of total mixed ration (TMR) diets due to heating has been a more common problem this winter, according to Alice Hibbert, feed additives technical manager at Trouw Nutrition GB, who believes it may explain poorer performance in some herds.


“While farmers are familiar with the problems associated with TMR heating in warm weather, few had experienced problems in the winter before this year, yet the consequences can be just as pronounced,” says Miss Hibbert.

She says as soon as silage is exposed to air and combined with other diet ingredients it begins to ferment because oxygen, which was excluded from the clamp, is reintroduced.

This allows the moulds and yeast present on silage to multiply, rapidly using up energy and protein in forage and other ration components, forming ideal conditions for the growth of spoilage micro-organisms.



While aerobic spoilage of silage will tend to be less during winter months, due to lower ambient temperatures, Miss Hibbert says problems in the last silage season mean it is a more common occurrence this year.

“The wet, late maize harvest in particular has increased soil contamination in clamps, which can increase spoilage through winter. Spoilage is a bigger issue with poorer quality forages.”

She says as the micro-organisms ferment energy in the diet, it reduces the feed value of the entire TMR, specifically reducing sugar content and total dry matter (DM).

“If TMR diets are allowed to heat up, you end up offering a smaller quantity of a lower quality feed, both of which will affect performance.



“In addition, feeds which have been subject to proliferation of yeasts develop an odour which reduces palatability and further depresses intakes.”

How temperature affects DM intakes

How temperature affects DM intakes

As a rule of thumb, 0.25 per cent of available dry matter in TMR is lost per degree increase in temperature above 20degC.


Dry matter losses of more than 5 per cent are not uncommon, as are greater levels of feed refusals.

Miss Hibbert says: “For a typical herd feeding 22kg DM of TMR per cow per day, a 5 per cent reduction in DM available would mean a loss of about 1kg DM per cow per day.

“Assuming the metabolisable energy of the TMR is 12.5MJ per kg, this would reduce energy intakes by 12.5MJ per cow per day, about enough to produce about 2kg of milk.

“This loss is on top of the risks of a lower diet ME and greater feed rejection.”

How can TMR heating be reduced?

To reduce the risk of contamination, Miss Hibbert advises clearing troughs daily and removing any refusals, which are likely to be the most contaminated material from the previous day, as this will continue to deteriorate and contaminate fresh material put on top of it.

Any silage showing signs of contamination and aerobic spoilage should be discarded at the clamp face and not put into the diet. The clamp face should be kept clean and tight.

Treating the diet can be done to delay the rate of fermentation and heating.


Miss Hibbert says: “In the clamp, in addition to the absence of oxygen, it is the low pH which helps suppress the activity of yeasts. When you mix a TMR you can not exclude oxygen, but you can do something about pH.”

Adding a blend of buffered organic acids while mixing TMR reduces the activity of yeasts, controlling the aerobic fermentation and reducing the extent of heating.

In trials, adding acids reduced a TMR’s yeast population by 40 per cent and intakes of treated ration were 6.5 per cent higher than untreated diets, according to Miss Hibbert.


She says particular care also needs to be taken when cows are buffer fed at grazing, especially as many farmers will be keen to get cows out early for at least part of the day to reduce bought-in feed cost.

Miss Hibbert advises minimising the time feed has to heat up. Leaving TMR in a trough after morning milking ready for when cows come back risks higher levels of spoilage.

She recommends mixing diets as close as possible to when they are actually fed. If cows are TMR fed at both ends of the day, consider mixing feed twice a day to keep it fresh, rather than feeding out once a day.
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