Knowing the basis of and variety impact on specific weight I do not regard this test as an accurate measure of feeding value. Virtually all the historic feeding value research exhibits no real understanding of what the test is supposed to do.

It is certainly a measure of the physical specific density of a sample of grain and is a very accurate and repeatable measure. But given that the same trailer load of wheat can produce two very different specific weights depending on how it is handled/dried, the specific weight per se cannot provide a measure of the feeding value.

Within a single variety, specific weight will act as a measure of grain fill and energy content. But some varieties with big bold starch-filled grains have a grain shape that will not pack well and so have low specific weight. Varieties with smaller grains tend to pack better but smaller grains will tend to have more bran relative to starch (higher fibre).

On any sample of grain we can add about three points to the specific weight just by drying it one way versus another. Surely this physical adjustment of the sample is not adding to feeding value.

Problem in 2012

These things said it would be an insult to livestock producers to suggest that specific weight did not matter in 2012 – it did. Poor grain fill resulted in low starch content and low energy density, resulting in a definite reduction in feed value.

That said, a high specific weight wheat (78kph) at 72kph may have less feeding value than a low specific weight variety at 72kph.

The industry needs a better system that is fairer to the end user and to individual varieties. This might help us to bring other useful variety characteristics to the field.

Late varieties show increased risk

I see that last year’s poor quality in Britain prompted the HGCA to look at the topic and examine some of the factors which influence specific weight levels in winter wheat varieties.

The research looked at recommended list (RL) trials data from 1994 to 2012, combined with the post harvest grain quality surveys, and examined the effect of weather and variety traits on specific weights.

The results showed that later ripening wheat varieties tended to have higher yields but with lower specific weights. What was particularly interesting was that the difference between the RL specific weight and that achieved in commercial crops was much greater in later ripening varieties.

In general specific weights tend to be higher in trials than in commercial crops but this research found that this difference tends to be greater with later varieties.

So as we select for the higher yield potential associated with later maturing varieties we may well be acting to decrease specific weight, making it more difficult to achieve the minimum quality spec. So the shift to later ripening varieties in recent years could be adding to the risk of low specific weight.

However, the report indicates that the weather may still be the most important factor for the poor quality performance in 2012. This can be seen by that fact that in most other years crop specific weight was broadly similar to the variety’s RL specific weight, thus pointing to the uniqueness of 2012.