Large variation in this year’s forage maize is being reported on farm. Low DM, low starch, high lactic acid content, and high starch degradability in the fresh crop are the problems facing farmers. What implications does this have for the cow or more importantly the rumen environment and what can be done to balance this type of forage?
An average quality maize silage sample would have a DM and starch content of between 30-35%, an NDF between 35% and 40% and a starch degradability of between 62% and 65%. The maize forages that will be difficult to manage this year will have low dry matters (<30) and high starch degradability’s mainly down to the immaturity of the crop at harvest. In addition the lower starch level will result in forage with a higher NDF and as a result lower feed value.
The soluble starch, low dry matter and extensive fermentation if an immature green crop leads to increased acid load. Feeding this forage immediately post-harvest increases the negative effect this forage has on the rumen environment. Without careful supplementation acidosis can soon become an issue.
Wetter silages with a high NDF will also reduce dry matter intake. Dairy farms using a predominantly maize based diet will struggle to get the high dry matter intakes required to maintain high yields and milk quality throughout the winter period. As a result milk quality, body condition and fertility will suffer
Forage Maize – The Solutions
There are a few things that can be done to try and make the best of a difficult situation.
Usually maize silage based diets can safely be fed with wheat to complement the low degradability of the maize starch. Maize silage made from a wet forage with immature cobs are best complemented with caustic or Maxammon treated cereals. These raw materials have lower starch degradability and also have an alkaline pH which can help raise ruminal pH.
In the absence of alternative starch sources it may be advisable to reduce the starch inclusion rate in favour of more grass silage or an alternative forage. It’s worth calculating the effect of starch degradability on the requirement for rumen starch in the diet and adjusting the diet accordingly by reducing the maize silage or the other starch sources in the diet.
In instances where there is high acid load, highly degradable starch and low fibre levels it is important to ensure sufficient NDF in the diet. On a maize based diet around 23-24% forage NDF should be provided. This is essential for proper rumen function. This is easily achieved with good quality forages but including additional poor quality grass or straw may raise the total NDF too high (>33.5%) thereby reducing intake and performance.
In these situations what is needed is a concentrated form of fibre that is digestible. Nutritionally Improved Straw or NIS is straw that has been treated with caustic soda. The treatment breaks down the fibre making it an exceptional form of digestible fibre. In addition the caustic treatment produces an alkaline product which buffers the rumen.
Silages lacking in starch will need additional starch in the diet to raise the starch content to a minimum of 17%, although this will differ according to the digestibility and NDF levels of the other feed ingredients. A shortage of starch in the diet can lead to lower milk proteins and poorer conditioned cows.
Alternatively over feeding the wrong type of starch in the wrong situation can lead to ruminal acidosis. Sources of starch such as ground maize or processed cereal grains will help to balance the starch levels.
In high starch or high acid load situations the rumen may need help in maintaining a healthy pH. Live yeasts can help reduce the build-up of lactic acid in the rumen. Rumen buffers can help raise rumen pH. Fresh cows are more prone to ruminal acidosis and so care must be taken to introduce these cows slowly on to a diet containing fresh, acidic, highly soluble starch, and high lactic acid maize silage.
During the transition period it is not only important to acclimatise the rumen to starch but also to lactic acid. Some rumen bugs use lactic acid as a substrate and help to regulate rumen lactic acid concentration and acidity.
Fungal diseases on the growing plant will result in the formation of mycotoxins which will contaminate and subsist in the ensiled forage. If you think your forage is contaminated with mycotoxins a mycotoxin binder should be included. These compounds will attach themselves to the mycotoxin, which will leave them unable to cross the gut wall, and allow them to be passed through the gut harmlessly. Mycotoxins can cause a number of undesired problems including fertility issues, swelling of the hocks, raised somatic cell count and gut upsets.
If you are concerned about the quality of your maize silage, require a maize silage analysis or would like help to balance your maize diet this winter. Please contact your local member of the Wynnstay Dairy Technical Services Team.