Correct starch choice critical to cow performance this winter

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Length: 1032 words; 4-5 minutes

Cows being fed image

Many winter rations have required additional fermentable energy to balance the very high lignin levels in grass silages this winter. But get the choice of energy feed wrong – particularly when it comes to high starch feeds – and the result can be a reduction in feed efficiency, not an improvement.

“The low cost of cereals has increased usage rates on many dairy units, and increased the risk of triggering sub-acute ruminal acidosis (SARA),” explains KW nutritionist Dr Anna Sutcliffe.

“Yet more fermentable energy (FME) than usual is going to be needed to support milk yields because of the very high lignin levels in this year’s grass silages. Trouw Nutrition analysis results have shown average lignin levels for 1st- through to 3rd-cut silages rising from 36.6% to 40.2% lignin (DM basis).

“Sugars from liquid feeds will be an important part of that FME balance, as they stimulate the growth of the fibre-digesting rumen bacteria that release energy from forage. However, with an ideal starch:sugars ratio of 3:1, it’s starch feeds that need to provide the majority of the extra energy.

“Understanding which are the best options – in terms of both value and SARA risk – is therefore critical to retain good rumen function and get the best possible production out of that forage.”

“Understanding…the best options…is therefore critical to retain good rumen function…”

Rumen efficiency compromised

The low price of cereals earlier this year means that there’s a temptation to overuse rolled wheat in particular to help meet that energy requirement whilst keeping feed bills low. But according to Dr Sutcliffe, the likelihood of further compromising rumen fermentation efficiency as a result could easily reduce both milk from forage and income over feed costs (IOFC), rather than improve them.

“The role of starch in driving milk yields and promoting milk protein production is well established, as is its value in helping to minimise negative energy balance in early lactation,” she states. “But the potential for starch to disrupt rumen fermentation efficiency by lowering rumen pH – the lactic acid produced following starch fermentation is the strongest acid in the rumen – means that great care is needed if good rumen function is to be maintained.

“That’s particularly true whenever the level of starch fermented in the rumen increases, or the potential acid loading in the rumen is already high because basal forages are more acidic than usual, as many low DM forages are this season.”

DairyCo figures suggest that as many as 20% of all lactating cows could be suffering from SARA at any one time even in a normal year. Defined as when rumen pH falls below 5.8 for even short periods of time during the day, bouts of SARA typically occur in the period just after meals are eaten, whether in the parlour or at the feed fence.

And as Dr Sutcliffe points out, the risk of the rumen dropping below this pH 5.8 threshold is even greater when the ration is based on forages that have a pH that might be as low as 3.6. In these situations, supplying additional energy safely without further increasing the risk of triggering SARA becomes a significant challenge.

Correctly formulated rations

“Yet when rations are formulated correctly, it’s entirely possible to feed up to 26% starch-plus-sugars for yields of 9-10,000 litres/cow or higher without any problems,” she adds. “Selecting the right starch feed is therefore about much more than just cost per tonne, or even cost per unit of energy or starch.

“The key is to choose the right level and type of starch feed to balance the release of fermentable energy in the rumen, taking into account the acidity and fibre content in the forage, plus the levels of sugar, digestible fibre and oil also being fed.”

According to Dr Sutcliffe, starch feeds can be broadly categorised into three groups: those where starch is the main energy source, those containing a more balanced supply of energy, and those where the rate of starch release is slower (figure 1). The straight starch feeds tend to be the lowest cost options per unit of starch, but also carry the highest risk of triggering SARA, so do not always offer the best option for all situations.

Starch feed value comparison graph
Figure 1 – Comparison of different starch feed value* (Click to enlarge)

“If silages are high in dry matter and fibre, then a moist feed like processed bread will work well, as long as the starch-to-sugars ratio is kept to around 3:1,” she advises. “And use high sugar liquid feeds like Stockmol 20 to maintain that balance, with the added benefit of improving palatability and intakes of the dry silages.

“If a further energy boost is needed, such as where fibrous silages are also low in D-value, consider replacing some of the straight starch feeds with a palatable confectionery blend like SugaRich Dairy or SweetStarch. These feeds have a high energy content that comes from sugars and oil as well as starch, so can increase ration energy levels whilst improving the energy balance and lowering the risk of SARA.

“Just make sure the confectionery blend chosen has been ‘manufactured’ to the same specification each time for a consistent nutrient supply, and isn’t just a mix of whatever co-products were available at the time.”

Balanced energy release

However, the greatest care is needed when silages are low in fibre and acidic. In these situations, Dr Sutcliffe recommends switching to Soda Wheat – caustic soda-treated wheat – to supply most of the starch in the ration.

SodaWheat image
SodaWheat is a more rumen-friendly source of starch energy than rolled cereals.

“The whole grain in Soda Wheat has a slower rate of fermentation than rolled or ground cereals, so is much less likely to trigger acidosis,” she explains. “If processed cereals are going to be fed, the best option is either ground maize or maize germ meal, as maize starch is more slowly fermented than other cereal starches.

These feeds do cost extra in terms of starch or energy supply (figure 1), but as Dr Sutcliffe points out, it’s about knowing when to invest in specific feed characteristics to maintain good rumen function. And if combined with a good supply of digestible fibre and sugars, the result will be a balance of energy release in the rumen that will significantly reduce the risk of acidosis.

“Remember that extracting maximum value from home-grown forage is vital if feed costs per litre are to be kept under control. This might involve choosing feeds best suited to improving rumen fermentation of forage rather than those offering the lowest cost, but the net result will be an increase in IOFC despite the potentially higher monthly feed bill.”

* Based on prices correct at the time of writing and subject to change, based on 29t tipped bulk loads delivered on-farm within 50 miles of origin.

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