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Digestibility of maize vital to avoid fall in milk output

Digestibility of early season maize silage can be low, resulting in nutrient wastage and even a reduction in milk production, but there are ways to mitigate this. Hannah Noble reports.

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Nick Berni, Cargill
Nick Berni, Cargill
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Could feeding maize silage too early in the season lead to a drop in milk?

Despite maize silage providing valuable nutrients to dairy cow diets, including it in the ration early in the season, up until January, can present considerable challenges.

 

Nick Berni, Cargill ruminant feed additive specialist, says energy in the form of starch in the cob and also from digestible fibre in the plant makes maize silage an important, high energy feed source for dairy cows.

 

However, he says the consequences of harvesting at the wrong stage or feeding too early in the season can potentially compromise its benefits.

 

Mr Berni says: “Early season maize always feeds differently to later season maize and this is something to always bear in mind when growing, harvesting and feeding maize silage.

 

“Starch will be less degradable just after harvest and this effectively limits the fermentable energy available in the rumen.”

 

Maize starch degradability is important as starch is a key nutrient of maize silage but the availability to the cow will change depending on the time of year.

 

“In the months after harvest, the degradability of starch will be lower which means the availability to the cow will also be lower.”

 

He says there are a number of factors which have an impact on this degradability.

 

The first is the maturity of the crop. Later harvested crops tend to have lower degradability. Variety choice also makes a difference, along with the time the maize silage is stored in the clamp and the way maize silage is processed through the forage harvester.

 

Starch

 

This, Mr Berni explains, is because starch grains are surrounded by a substance called prolamin which protects the starch granules from being degraded and broken down but similarly this also happens in the rumen. This also increases the level of starch bypassing the rumen and making its way to the small intestine.

 

As the months in the clamp increase the prolamin begins to break down through the action of the fermentation acids in the clamp. Once it has been ensiled for six to eight months the proteins which surround the maize starch granules have completely broken down, making the starch much more rumen degradable and available and decreases the level of bypass starch.

Increasing rumen digestibility of feed can ensure starch is not wasted.
Increasing rumen digestibility of feed can ensure starch is not wasted.

The degradability of early season maize is lower than in late season maize silage, and the bypass starch is higher. Digestibility increases with storage time and the bypass starch decreases.

 

“Low starch degradability will have an impact on cow health and performance and if we understand this we can put solutions in place that will allow us to maintain health and performance and adapt as maize silage changes across the season.

 

Mr Berni says the starch in maize silage early in the season is not broken down as readily in the rumen as later in the season and more makes its way to the intestine. Some of this will be broken down into glucose and absorbed and some of it will pass straight through the cow and end up in the manure.

 

Nutrients

 

“This leads to an increased level of faecal starch, which is effectively poor utilisation and a waste of nutrients but it can also cause some hind gut fermentation in extreme circumstances.”

 

He says it also has the potential to reduce cow performance, not seeing the expected jump in production associated with feeding maize silage.

 

“For every 1 per cent increase in faecal starch over 3 per cent, there is the potential to lose 0.5kg milk.

 

“In certain circumstances where high levels of maize are being fed it would not be uncommon to see faecal starch levels at 5 per cent which could potentially be up to 1.5kg lost milk,” he adds.

 

However there are several ways to determine the impact of feeding particular silages, including kernel processing scoring, ration sieving, manure sieving, or using near-infrared analysis to look at the manure.

Clamp management

 

“For many people it may be difficult to avoid feeding maize early in the season because of forage stocks or clamp management. But if you do have the option to keep maize for later in the year and are able to replace with grass silage or wholecrop that would be beneficial to save the maize silage for when it is more accessible in terms of starch and energy for the cow.

 

If this is not an option, he says farmers should look at increasing the energy feeds which are more rumen degradable or provide higher levels of rapidly fermentable energy such as barley or wheat, or by-products such as biscuit meal or confectionary products.

Mr Berni says there are also strategies from a micronutrient perspective which can be adjusted to help with feeding early season maize silage.

 

He says: “You could look to include a yeast fermentation concentrate to help increase rumen degradability and improve intestinal digestibility.”

 

These products work to increase rumen microorganisms such as fibre digesting bacteria and lactate utilising bacteria as well as fungi. They also increase starch degradability, increase microbial protein and increase starch utilisation and can also help to increase dry matter intake.

 

EARLY/LATE SEASON MAIZE SILAGE ANALYSIS
Analysis Early season maize (Oct-Jan) Late season maize (Feb-May)
Dry matter (%) 32.6 32.6

Digestibility value (% DM)

73.6 73.6
Metabolisable energy (MJ/kg DM) 11.6 11.8
Starch (% DM) 31.2 31.2
Starch degradability (%) 80.3 86
Bypass starch (g/kg DM) 60.4 50.1
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