TMR diets can overheat in the winter too

1 February 2016

Spoilage of 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 heating of TMR rations in warm weather, fewer have experienced problems in the winter before this year, yet the consequences can be just as pronounced,” she comments.

Miss Hibbert says that as soon as silage is exposed to air and combined with other ingredients in the diet it begins to ferment because oxygen, which has been excluded in the clamp, is reintroduced. This allows the moulds and yeast present on silage to multiply rapidly using up energy and protein in the forage and other components in the ration, promoting ideal growth conditions for spoilage micro-organisms in the total mixed ration.

While aerobic spoilage of silage will tend to be less during the winter months due to lower ambient temperatures, Miss Hibbert explains that problems 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 throughout the winter. Spoilage is a bigger issue with poorer quality forages.”

She explains that as the micro-organisms ferment energy in the diet this reduces the feed value of the entire TMR, specifically reducing both sugar content and total dry matter.

“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 that have been subject to proliferation of yeasts develop an odour which reduces palatability and further depresses intakes.

She says as a rule of thumb, 0.25% of available dry matter is lost per degree increase in temperature in the TMR above 20°C. Dry matter losses in excess of 5% are not uncommon. To this can be added greater levels of feed refusals.

“Heating leads to losses in dry matter and a decline in feed value as energy is used up. For a typical herd feeding 22kgDM of TMR per cow per day, a 5% reduction in dry matter available would mean you are losing around 1kgDM per cow per day. Assuming the ME of the TMR is 12.5MJ, this would reduce the energy intakes by 12.5MJ per cow per day, enough to produce around two litres of milk. To this can be added the risks of a lower diet ME and greater feed rejection.

To reduce the risk of contamination, she advises clearing troughs out daily, removing any refusals which are likely to be the most contaminated material from the previous day and which 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 and at the clamp face and not put into the diet.

She stresses the importance of keeping the clamp face clean and tight and says the other strategy which is proven to work is to treat the diet to inhibit the activity of the yeasts which ferment lactic acid, allowing the pH to increase, making the silage more hospitable for growth of spoilage micro-organisms and so delay the rate of fermentation and heating.

“In the clamp, in addition to the absence of oxygen it is the low pH that helps suppress the activity of yeasts. When you mix a TMR you can’t exclude oxygen, but you can do something about pH.”

She says adding Selko-TMR, a blend of buffered organic acids during the mixing of the TMR reduces the activity of yeasts, so controlling the aerobic fermentation and reducing the extent of heating. In trials, adding buffered acids reduced the yeast population on the TMR by 40%. Intakes of treated TMR were 6.5% higher that untreated diets.

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 purchased feed cost.

She advises minimising the time the feed has to heat up. Leaving a TMR in the trough after morning milking ready for when the cows come back in is risking higher levels of spoilage. She recommends mixing diets as soon as possible before 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.

For more information, contact the Trouw Nutrition GB Feed Additives Team.