Research underlines the benefits of 75pc-plus DMD silage for beef, dairy and sheep farms, both in terms of increased weight gain or milk output, and in reducing concentration requirement
Herbage from 1.2 million hectares (3m acres) of pasture is ensiled annually in Ireland. The feed value of the silage produced will have major consequences for ruminant performance.
The production of high feed-value silage should always be the objective of producers who feed silage to lactating dairy cows, growing and finishing beef cattle, and pregnant ewes.
For me, the target for high feed-value silage is a dry matter digestibility (DMD) of greater than 75pc.
With the dramatic increase in input costs, concentrate will be expensive next winter.
And another benefit of increasing silage feed value is that you can maintain animal performance at a reduced level of concentrate supplementation. This is known as the ‘potential concentrate sparing effect’.
Effect of silage feed value on animal performance
The feed value of grass silage is a combination of its intake potential and nutritive value. Digestibility is the key factor influencing both.
There is a substantial volume of data in the literature on the impact of DMD on the performance of stock offered silage-based diets.
The mean response expected for each 5pc unit increase in DMD of silage offered to beef cattle is an increase in silage intake of 0.35kgDM/day, leading to an increase of 0.15kg/day in liveweight gain and 0.11kg/day in carcass gain.
However the response in animal performance to improved silage DMD depends on the quantity of concentrate offered, which impacts diet forage to concentrate ration (F:C).
When silage is offered without concentrate supplementation (for example, to store cattle that will be turned out to pasture next spring) each 5pc unit increase in silage DMD increases daily liveweight gain by 0.24kg, equivalent to 36kg additional body weight following a 150-day housing period.
Finishing beef cattle are offered concentrate to achieve optimum performance.
On a silage-based diet consisting of 60pc concentrate, each 5pc unit increase in silage DMD increases carcass gain by 0.09kg/day — equivalent to 13.5kg carcass weight, valued at €70/head, during a 150-day finishing period.
The mean response expected for each 5pc unit increase in the DMD of silage offered to lactating dairy cows is an increase in silage intake of 1.0kgDM/day, resulting in an increase of 1.65kg/day in milk yield and 0.04 of a percentage point in protein concentration.
The response in animal performance to improved silage DMD depends on the quantity of concentrate offered.
When silage is supplemented with low levels of concentrate (diet F:C ratio 80:20), each 5pc unit increase in silage DMD increases milk yield by 2.9 kg/day.
For diets where the concentrate is 50pc of total food intake, each 5pc unit increase in silage DMD results in an increase in milk yield of 1.3kg/day.
In prime lamb production the objective is to produce lambs that have a high birth weight and are born alive will little assistance.
Studies at Athenry have shown that each 1kg increase in lamb birth weight results in lambs that are 3.3kg heavier at weaning.
The mean response for each 5pc unit increase in the DMD of silage offered to ewes during mid- and late pregnancy is an increase in lamb weight at birth of 0.25kg and an increase of 6.5kg in ewe body weight at lambing.
Ewes offered high feed-value silage have a higher body condition score at lambing, so can mobilise body reserves during lactation without the need for concentrate supplementation post-lambing.
Effect of silage feed value on reducing concentrate needs
When concentrate price is high relative to product price (meat or milk), one of the benefits of increasing silage DMD is the ability to maintain animal performance while reducing concentrate input.
The potential concentrate sparing effect of increasing the feed value of silage offered depends on the original silage feed value and concentrate feed level.
For example, for finishing beef cattle offered either 71 or 75 DMD silage and supplemented with 4kg concentrate daily, the concentrate feed level could be reduced by 1.8 and 2.3 kg/head per day, respectively, if silage DMD is increased by 5pc units.
So for a 150-day feeding period, total concentrate input can be reduced by up to 3.5t for every 10 cattle housed.
Increasing the DMD of silage offered increases milk yield and protein concentration.
An increase in silage DMD of 5pc units enables the yields of milk fat and protein to be maintained while daily concentrate feed level is reduced by 3.3 kg.
Based on lamb birth weight, and changes in ewe body weight, increasing in silage digestibility by 5pc units can result in a reduction in concentrate requirement of 12kg/ ewe during late pregnancy.
■ Produce high feed-value silage — DMD greater than 75pc;
■ Increasing silage feed value either:
a) increases animal performance; or
b) maintains animal performance at a lower level of concentrate supplementation;
■ A 5pc unit increase in silage DMD increases:
a) carcass gain of beef cattle by 0.11kg/day;
b) milk yield of dairy cows by 1.65kg/day;
c) lamb birth weight by 0.25kg;
■ A 5pc unit increase in silage DMD enables animal performance to be maintained while reducing concentrate input by up to:
a) 2.4kg/day for finishing beef cattle – the equivalent to 3.6t for every 10 cattle
b) 3.3kg for lactating dairy cows
c) 12kg/ewe during late pregnancy.
Dr Tim Keady is a Teagasc research officer based in Athenry, Co Galway