Careful balancing will be required to get the most from maize silage for the remainder of the winter according to Trouw Nutrition GB
1 January 2016
Use full analysis to get most from maize
Dr John Allen, Technical Director with Trouw Nutrition GB, says the results of the analysis of over 3000 maize silage samples are beginning to give a clear picture of how maize silages will feed this winter and what will need to be done to get the most from forage.
“The initial results based on 1000 samples showed crops were analysing quite well,” he comments. “However, as more samples have been submitted incorporating later harvested crops, so average nutritive value has declined.
“Compared to last year, we are seeing 2% lower dry matter on average and 1.7% lower starch. NDF and ME levels are similar to last year but the intake factor is lower (see table).
“Starch degradability, which will increase with time in the clamp, is already high for the time of year at 72%. This is positive in terms of supplying the rumen bugs with energy to maximise rumen digestion, particularly fibre, but comes with an increased risk of rumen acidosis. However, on the negative side, when compared to the 2014 crop, the lower starch content means that despite higher degradability the rapid and totally fermentable carbohydrate supply and acid load will be marginally lower than in 2014. This will have implications for ration formulation.”
Dr Allen says diets will need to be formulated with the correct balance and supply of rumen fermentable carbohydrates. He explains that it is vital to meet microbial energy demands if the rest of the diet, particularly forages, are to be digested efficiently and if intakes are to be maximised.
“Since 60-70 % of the cow’s ME requirement originates from VFA production in the rumen and 50-70% of the metabolisable protein requirement comes from microbial protein growth, it is vital to ensure the rumen bugs are properly fed.
“Over the winter, starch degradability will increase which will boost the rumen fermentable carbohydrate supply. This will need to be monitored closely through regular repeat forage analysis to ensure rumen acid load and acidosis do not become a problem.”
Dr Allen explains that the new NutriOpt dairy rationing system allows a better understanding of how maize silage will feed and can provide reasons for how cows are performing. In particular it allows an assessment of glucogenic energy supply, which is the energy specifically required to drive milk production and fertility.
He says that the 2015 crop has, on average, a lower glucogenic energy component than 2014. For a cow being fed 5kg DM this difference would lead to a reduction of around 0.25 litres/day.
“This can, in part explain why many herds have not kicked on as expected when maize was introduced this season. Glucogenic energy supply is largely driven by starch, with the greatest impact coming from the proportion digested in the intestine rather than the rumen. Cereals such as wheat will increase glucogenic energy supply with rolled providing more than ground wheat which is largely digested in the rumen. Maize supplies even more glucogenic energy because of its higher by-pass starch content. In relative terms maize supplies 27% and rolled wheat 13% more glucogenic energy than ground wheat. The NutriOpt dairy rationing system will identify the most cost effective way to meet daily nutrient demands for the rumen and milk production.
Dr Allen cautions there may be specific problems with later harvested crops which have been affected by delayed harvest. In general the problem crops will be those that have a lower dry matter. To date 15% of crops analysed have a dry matter below 23% which is a far higher proportion than in a ‘normal’ year. These wetter crops also have an increased fibre content and lower starch, indicative of the growing season (see table).
“While the ME is reasonable, the intake potential is only 87% of the season’s average, implying it will be a challenge to get cows to eat target quantities. On a simple energy basis, 5kg DM intake of the average maize silage will require 17.2 kg fresh matter and provide 57.5 MJ/day, equivalent to 11.5 litres. However, the intake factor suggests only 4.4 kg DM of the average ‘wet’ maize silage would be eaten, requiring 24.3kg fresh matter and this will supply 48.4MJ, sufficient for just 9.7 litres, nearly 2 litres less than this season’s average.
“Clearly, feeding this year’s wetter maize silages will require balancing with higher energy concentrate feeds with daily intakes monitored to ensure appetite is being met. Refusals must be recorded and reacted upon accordingly.”
Looking more closely at rumen and cow factors using the NutriOpt model, Dr Allen says these wetter silages have high starch degradability at 81.4% as they did not receive the sunshine required to take the crop to maturity. He suggests that increases in degradability will be much less over the winter than for the average crop.
“Overall, the lower starch content in these wetter crops means that rumen available and by-pass starch levels will be lower than for the average crop. This will reduce the rapidly fermentable starch required for rumen microbial digestive activity and means more rapidly fermentable carbohydrates will need to be fed in the diet to compensate.
“Using the intakes in the earlier example, a cow fed the wetter silage will require the equivalent of an additional 0.6kg/day fresh weight of ground wheat to balance rumen energy supply. In addition, the wetter silages are lower in glucogenic energy. The combination of lower glucogenic energy content and reduced DMI will be equivalent to three litres/cow, requiring an extra 1kg of wheat to make up the shortfall.
“This brings an increased acidosis risk. While the higher fibre content in the wetter silages will help reduce the acidosis threat, rumen buffers and yeasts could prove invaluable in these situations. In addition farmers should consider changing the form of cereals being fed. Switching from ground or rolled cereals to caustic or alkali-treated will reduce rumen acid load.
“The key to getting the most from maize silage this winter will be regular analysis of the crop so you understand the quality of feed available. Then make sure the rationing system being used by your nutritionist can make full use of the complete analysis to ensure maximum rumen performance to support efficient milk production.”