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Wednesday 7 December 2016

A cut above the rest - the benefits of better silage digestibility

Better silage digestibility improves animal performance and cuts costs

Tim Keady

Published 11/05/2016 | 02:30

Silage digestibility levels vary widely in Ireland with figures last year going from a low of 52pc to a high of 82pc.
Silage digestibility levels vary widely in Ireland with figures last year going from a low of 52pc to a high of 82pc.
Timing is everything when it comes to making top quality silage.

What is the country's largest and most important harvest? Tillage farmers might disagree, but the answer is grass, the crop that is the staple diet for the majority of our beef cattle, dairy cows and sheep.

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The coming weeks will see the silage season get into full swing and it's a good time to look at the nutritional aspects of silage and how to maximise the value of your crop.

Dry Matter Digestibility (DMD) is a term we're all familiar with.

It is the main factor that determines the energy (ME) concentration of silage and is also a key factor in its intake by animals.

As DMD increases, so too does silage ME concentration and silage intake, which leads to improved animal performance.

In essence this boils down to digestibility is the main factor influencing silage feed value for your stock.

The average digestibility of silage last year was 69pc, but the DMD levels varied from as low as 52pc to a high of 82pc.

Because of the generally low DMD of the silage on farms, cattle and sheep are normally supplemented with concentrate and the level of supplementation depends on the feed value of the silage and the level of performance required.

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The following analysis looks at the impact of DMD on livestock performance.

Dairy cows

Increasing silage DMD increases silage intake and performance of lactating dairy cows. Based on 23 silage studies offered to lactating dairy cows, the mean milk yield response was 1.65kg per cow per day for each 5pc increase in DMD.

The response to increasing DMD to cows also offered different levels of concentrate supplementation (forage:concentrate (F:C) ratio) is detailed in the table.

As the daily concentrate feed level increased, the daily milk yield response per 5pc increase in DMD declined from 2.9 to 0.8 kg/cow.

But the data in the table shows that even at high levels of concentrate supplementation, silage with a higher DMD still increases milk yield.

Beef cattle

In beef cattle, based on 34 studies, there were daily live weight gains and carcase gains of 0.15kg and 0.12kg respectively per additional 5pc of DMD.

However the response in beef cattle performance to increasing DMD depends on the level of concentrate (F: in the diet). The response to increased DMD declines as the level of concentrate in the diet increases.

For diets with F:C ratios of 60:40 and 40:60, each 5pc increase in silage DMD improves the carcase gain of finishing beef cattle by 13kg and 6kg respectively during a 150-day finishing period.

At the current beef price,this is the equivalent of an extra €52 and €24 respectively per animal.

Pregnant ewes

The effects of silage digestibility on the performance of ewes during mid and late pregnancy were set out in nine studies.

Each 5pc increase in DMD during mid and late pregnancy increased ewe weight immediately post lambing by 6.5kg (with a consequent improvement in ewe body condition) and lamb birth weight by 0.26kg.

Lamb birth weight has a positive impact on weaning weight.

Previous studies at Athenry have shown that an increase of 1kg in lamb birth weight results in an increase of 3.2kg in weaning weight. An increase in lamb birth weight of 0.26kg from offering a silage with five units higher DMD should increase lamb weaning weight by approximately 0.8 kg.

Finishing lambs

The average response to a 5pc increase in DMD was an increase in daily live weight gain and daily carcase gain of 72g and 47g respectively based on 10 studies.

The effects of DMD on lamb performance decline as the level of concentrate in the diet increases. Even at high levels of concentrate supplementation, a 5pc increase in DMD improves carcase gain by 1.5 kg during a 50-day finishing period. This would have been worth approximately €8/lamb last winter

Dr Tim Keady is a Teagasc researcher based in Athenry

How to improve silage digestibility (DMD)

Harvest date is the key factor that affects silage DMD. Silage DMD declines by 3.3 units for every week delay in harvest date.

Decide on harvest following inspection of the sward canopy for presence of seed heads and decaying material at the base.

To deliver consistent silage DMD ensile herbage from late varieties (heading date June 12) eight days later than that from intermediate varieties (heading May 19)

If wilting silage, ensile within 36 hours and avoid soil contamination.

For each one week delay in harvest additional concentrate must be offered to maintain animal performance as follows: - 1.8kg per lactating cow daily - Between 0.9 and 1.8kg per finishing beef animal daily - 13kg per ewe during late pregnancy - 0.25kg per finishing lamb daily.

BETTER SILAGE iS GOOD FOR YOUR POCKET

Increased silage digestibility (DMD) doesn’t just improve animal performance — it can also cut concentrate consumption and costs.  Given the current milk price crisis, this is one area where dairy farmers can make savings.

Dairy cows

The mean daily milk yield response to increasing silage DMD by five percentage points is 1.65kg/cow. A second option, when high DMD silage is available is to maintain animal performance while at the same time reducing concentrate input.

Research shows that each increase of 5pc in silage DMD enables the yields of milk and of fat plus protein to be maintained when daily concentrate feed level is reduced by 2.7 and 3.3kg/cow, respectively.

Beef cattle

The mean daily carcase gain is 0.12kg per 5pc increase in DMD. Producing high DMD silage for beef cattle provides the option of maintaining performance while reducing concentrate input (see table).

For example, for beef cattle offered 71pc DMD silage and a daily concentrate feed level of 2 or 6kg, a 5pc increase in silage DMD reduces concentrate requirement by 2.0 and 1.4kg, respectively, to maintain carcase gain; the corresponding reductions when a 75pc DMD silage is offered are 2.4 and 2.1kg, respectively.

Pregnant ewes

Increasing silage digestibility by 5pc increases ewe weight at lambing by 6.5kg and lamb birth weight by 0.26kg. Producing high DMD silage provides the option of maintaining animal performance while at the same time reducing concentrate input. The research data shows that each 5pc increase in silage DMD enables lamb birth weight to be maintained whilst total concentrate input during late pregnancy is reduced by approximately 15kg.

Finishing lambs

Increasing silage digestibility by 5 units increases daily carcase gain of finishing lambs by 47gm. Results from research studies show that each 5pc increase in silage DMD enables lamb carcase gain be maintained whilst concentrate is reduced by 0.3kg/day.

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