With many herds reporting mixed performance in the first part of the winter, could the introduction of maize silage get cows milking better?

Is Maize the Key to getting Cows Milking this Winter?

NutriOpt LogoMost years, dairy farmers can’t wait to introduce maize silage into the diets, providing as it does a good supply of starch and, due to feeding a mix of forages, a boost to dry matter intakes. Any benefit in production from adding maize could be particularly welcome this year, but Dr Liz Homer from Trouw Nutrition GB warns that care will need to be taken to get the most from the forage.

“With many herds not really firing on grass silage based diets despite the better headline analysis of the forage, we have seen an enthusiasm to get maize into diets,” Dr Homer comments. “A significant number of the early samples received for analysis had to be rejected as they were not properly fermented, suggesting they had not been in the clamp for the minimum two weeks required to achieve a stable fermentation, yet farmers wanted to get the forage into diets.

“Now, however, we have a better picture with well-fermented samples being sent in (see table). Dry matter is slightly lower than last year at 33.1% while crude protein and ME are almost the same as last year. However, NDF is lower at 37.3% DM, but with higher lignin. Starch content is the same this year as last year but starch degradability is slightly higher than the same time last year.

“Bypass starch levels are good and with starch degradability already at 79% this has the potential to support high levels of milk production.

Dairy Cows“The average maize silage sample appears to be very fermentable with high levels of rapidly fermentable carbohydrate (RFC) and high levels of total fermentable carbohydrate (TFC). This is because maize this season has a good level of starch, and although NDF digestibility is not particularly high, the overall NDF content is slightly lower. As normal with maize silage the fermentable protein is low, so looking at the rumen balance will be important as there are a lot of fermentable carbohydrates in relation to fermentable protein.

“Due to the increased fermentability of maize silage it will be extremely important to monitor rumen health. It is known the maize silage starch degradability increases with time in the clamp, but in this instance due to the growing conditions seen this season and rapid maturing of the plant and starch, it is already much more rumen degradable. Therefore acid load is high early on in the season. This, coupled with a low fibre index due to a lower NDF content, means rumen health could be an issue.”

Dr Homer says that while on paper maize silages look like they should help increase milk production, it will be essential to look carefully at the analysis of grass silages and how the two forages will perform together. She comments that dairy performance has been very mixed as cows settle onto winter rations despite results showing that, on average, grass silages are better quality than previous years, with higher energy and protein contents, indicating a need to delve more deeply into the analysis results.

“While traditional terms such as dry matter, crude protein and even ME may describe the silage in the clamp, they do not describe how it will behave once the cow has eaten it. It is important to understand that the energy and protein actually used by the cow is not the same as the feed they eat, but what that feed becomes after it has been broken down into the end products of digestion.

“Key to this is optimising rumen performance to maximise efficiency. The rumen microbes must have an adequate supply of fermentable carbohydrates and protein, with a balance of both slowly and rapidly fermentable types. The rumen needs to be buffered to prevent falls in pH and acidosis. The fibre index and acid loading on the silage analysis will help here.

“It is also important to feed adequate structural fibre and this means looking closely at digestible NDF levels. Digestible NDF (dNDF) is the potential amount of the NDF in the forage that can be degraded in the rumen. Undigestible NDF ends up in the slurry as longer particles.”

Increasing the dNDF decreases the time required to digest the forage and reduces rumination time while increasing rumen turnover and the amount of fermentable carbohydrate in the rumen. This results in increased forage and total dry matter intakes, increased energy available to the cow and improved performance.

“If too little undigestible NDF is fed then rumen function is compromised; buffering capacity is decreased and risk of acidosis increased. Too much undigestible NDF and rumen turnover and dry matter intakes will both be reduced. The optimum level of undigestible NDF in the total diet is 8-10%. If less than 8% there is insufficient structural fibre, while more than 10% indicates an opportunity to improve intakes.

Cows Feeding“It is perfectly possible for two silages which look the same in terms of ME to behave very differently in the rumen and so affecting the performance of the entire diet. We believe that in many cases a close look at dNDF levels and what they mean for supplementary feeds could have a big impact on performance.”

If feeding a grass silage with low levels of NDF but with high dNDF, rumen effective fibre such as straw may be needed to provide undigestible fibre to slow down rumen turnover to extract the maximum value from the silage. With high rapidly fermented carbohydrates and digestible fibre in these silages, the acid load on the rumen could be increased, raising the risk of acidosis

Conversely, if using a grass silage with high NDF levels coupled with low digestibility, intakes may be reduced and lower than expected, a problem made worse with higher dry matter silages. While rumen health is unlikely to be a problem in these silages, rumen function may be slowed down. Diets may need more fermentable carbohydrates such as ground wheat to fire up the rumen.

“Making the wrong decision when cows aren’t milking as expected can make matters worse. For example adding more rumen fermentable carbohydrates such as cereals to diets based on a grass silage with high dNDF could increase the rate of rumen fermentation when it actually needs slowing down.”

Dr Homer stresses it will be particularly important to look at maize and grass silage closely. She says farmers feeding grass silage with high dNDF and very fermentable maize will need to look at ways to regulate rumen fermentation to reduce the acidosis risk, suggesting it may pay to consider rumen buffers. If, however, maize silage is being fed with low dNDF grass it is likely the high fermentable nature of maize will improve rumen function and throughput.

“Maize has the potential to improve performance this winter but it will be essential to look carefully at the analysis of all forages in the diet to ensure optimum rumen productivity. And get forages analysed regularly so you can react to changes as you work through the clamp and adjust the diet as maize starch degradability increases over the winter,”

Table - Maize Silage Analysis to End November

2016 Maize Silage Average

2017 Maize Silage Average

Dry matter (%)



Crude protein (%)



ME (MJ/kgDM)



Starch content (%)



Starch degradability (%)



Bypass starch (g/kg)



NDF (%)



dNDF (%)



Lignin (g/kg)



Rapidly fermentable carbohydrate (g/kg)



Total fermentable carbohydrate (g/kg)



Acid load



Fibre index