Archive: Maize results so far - what do they tell us?

Published 12 December 14

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Maize results so far - what do they tell us?

Adam Clay, ruminant manager at Trouw Nutrition, summarises the results from maize silage samples already received and what they mean to rationing this winter.

Maize silage analyses are well underway at the laboratory, with more than twice as many maize samples received to date in 2014, compared to the same time period in 2013.

A summer of mixed weather contributed to variable growing conditions for this year’s maize silage crop. July saw predominantly dry weather, coupled with above average temperatures. While August proved to be more unsettled, with unseasonably cooler weather and higher daily rainfalls.

Crop yields were ‘typical’ at 15 to 18 tonnes of fresh weight per acre. Analyses of the first 1,300 samples show that, on average, this year’s maize silage is of good quality, very similar to last year and will be a welcome addition to rations leading into the winter period (see table 1).

Dry matter, energy, starch and intake factor are all very acceptable and offer a timely boost to the rather mediocre grass silage quality seen on many farms. With many dairy herds failing to achieve target yields by two to four litres per head per day, the run into winter has again been very difficult for farmers and advisers alike. The introduction of maize silage should help boost performance when formulated correctly into dairy rations.

Balancing grass silage

Two major factors that seem to be limiting milk production have become apparent with this year’s grass silage; notably, forage intake and rumen energy supply, the correction of which requires careful control to minimise the risk of rumen acidosis.

The average analyses of over 11,000 grass silages shows a typical average dry matter of 30.3% and ME of 10.5 MJ/kg DM, which, on the face of it, should support good levels of milk production. The issues, however, seem to be, firstly, that the average intake factor is 95.2 g/kg0.75, which translates into a realistic maximum intake of approximately only 10kg DM/day and, secondly, rumen energy from the average grass silage supports only 46.9g/kg DMI of microbial yield (calculated from MPE minus MPB). This suggests lower rumen activity, which further drives down the rate of forage digestion and depresses feed intake. So the cow can consume less energy because rumen fill and function is compromised.

To put the microbial yield value into context, some grass silages this year achieve over 70g/kg DMI, which is 50% more than the season’s average. Clearly, the average grass silage will need careful supplementation with starch and sugar to achieve target milk yields. In these situations, rumen adicosis risk will increase and therefore, supplementing diets with buffers or yeasts, may also be required to maximise the potential of microbial activity through a healthy rumen.

Maize silage will certainly help. The average intake factor of 104 g/kg0.75 has a potential DMI of 11kg, which will boost total forage DMI while rumen energy will support a microbial yield of 62g/kg DM. Approximate calculation shows that a forage intake of 10.5kg DM/day of 50:50 grass and maize silage would support a microbial yield of 572g, which is some 22% greater than the 469g/day that could be achieved from 10kg DMI of the average grass silage alone.

Starch and rumenac

The average 2014-15 maize silage contains 1% less starch than last year (30.6% vs. 31.6%) but its higher rumen degradability (69.2% vs. 67.9%) means that it is already supplying the same quantity of rumen available starch and therefore rumen energy from starch, as 2013 (212 vs 214g/kg DM).

It is important to remember that the degradability of starch in maize silage increases with time in the clamp. In 2013, the starch degradability increased from 67.9% to 75% over the winter months, which, at the average starch level of 31.6%, increased rumen available starch from 214 to 237g/kg DM over the season. While this will raise the rumen energy supply, there is also an associated risk of rumen acidosis as the winter progresses. Maize silage will certainly need checking through the winter.

Glucogenic energy

Glucogenic energy is a key driver of milk yield, with greater supply increasing production. It originates largely from propionate produced by the rumen fermentation (significantly from starch), as well as by-pass starch absorbed as glucose directly by the small intestine. Interestingly, there is an 8% reduction in by-pass starch (94.1 vs 101.8g/kg DM) this year, compared to 2013, although glucogenic energy supply remains very similar between years (146 vs 145g/kg DM). There is, of course, a limit to the amount of starch that can be digested in the small intestine of cows.

A sensible target is 1kg per day, after which, starch passes through undigested, resulting in lost nutrient value. This year’s maize silage, when fed at 5kg DM per head per day, will supply approximately 500g intestinal starch while concentrates containing approximately 25% total starch, of which 15% is by-pass, fed at 12kg per head per day (FM), will supply a further 450g of starch into the intestine. Clearly, in this case, the total intestinal starch supply of 950g per day is near to the target upper limit for digestion. In these situations, care should be taken not to exceed this value when rationing this winter, if expected milk yields are to be achieved.

Summary

It is another difficult start to winter feeding and careful consideration of all inputs into the ration is needed to achieve the target levels of performance on dairy farms. Maximising rumen digestion, while maintaining rumen health, are the key challenges faced so far this year.

 

Table 1: Early maize silage averages summary 2014

AC table