Case study: Taking and interpreting grass silage sample results in Co. Cork
Grass silage – whether that be the pit or baled variety – is the predominant source of winter forage used on all the Teagasc Green Acres Calf to Beef Programme farms.
There are many factors that affect the quality of grass silage, such as: cutting date; sward quality; and weather at the time of ensiling. These all impact on the quality of the forage that is offered to cattle over the winter period.
Surplus grass harvested as baled silage is also increasingly used across these farms, with programme farmers implementing better grassland management practices – such as grass measuring, which imbues confidence when it comes to taking out surplus paddocks (in the form of bales).
When it comes to silage quality, overestimating or underestimating the feeding value can cost farmers significant amounts of money.
Farmers might then underestimate or overestimate the amount of meal and/or silage required by stock – in order to secure optimal animal performance.
Case study: Pat Collins
Pat Collins, alongside his father Matt, operates dairy calf-to-beef and tillage enterprises just outside Castlemartyr, Co. Cork.
Pat’s Teagasc Green Acres Calf to Beef Programme dedicated advisor – Seán Cummins – recently took silage samples from two pits on the Co. Cork holding; the first sample was taken from silage harvested on May 8, while the second sample was taken from silage ensiled on September 10.
After removing approximately the top 5in of forage, using a tool known as a silage sampler or ‘core’, samples were taken from five different locations on the pit. The core was driven down to the bottom of the clamp each time.
In addition, holes created in the plastic were taped up in order to prevent forage degradation.
The sample cores were mixed together and a representative sample bagged and submitted to the laboratory for analysis. A separate sample was taken for each pit.
Silage quality is very important for Pat’s system; good-quality silage is needed that is capable of achieving high dry matter (DM) intakes, to achieve optimum performance.
Producing good-quality silage also helps Pat to offset the need to purchase additional concentrates and helps to shorten the length of the finishing period, resulting in an earlier slaughter date.
There are also growing weanlings housed over the winter period; these animals need to maintain a high level of performance over the winter months.
Achieving an adequate level of weight gain over the course of the first winter is critical to ensure that weight targets continue to be met and profitability is maximised on dairy calf-to-beef systems.
The targeted average daily gain (ADG) over the first winter is 0.6kg/day, as this allows for cheap liveweight gain to be achieved at grass at the start of the second grazing season. If winter daily gain targets are not met, this will have a knock-on effect further down the line.
Having said that, Pat will aim for a target daily weight gain of 0.8kg/day for the Angus heifers over the winter period, while targeting 1kg/day for the Angus and Friesian males; all animals will be fed a total mixed ration (TMR).
By feeding grass silage higher than 70% plus dry matter digestibility (DMD), Pat needs very little purchased concentrates to achieve his targets.
As can be seen in this table (below), Pat harvested and ensiled good-quality silage in 2019. Ideally, he aims to cut his first-cut silage in early May to ensure maximum leaf content in the sward and to avoid fibrous stemmy material.
Over recent years, Pat has invested heavily in grassland. As some of the ground was previously under tillage, a large degree of reseeding has been undertaken; high-yielding perennial ryegrass varieties were chosen.
Swards on silage ground are incorporated into the farm reseeding programme to ensure that there is a high content of perennial ryegrass in the sward.
Click table to enlarge…
Looking into the analysis in more detail, well-preserved silage is more palatable and will result in higher animal intake and performance; well-preserved silage should have a pH of 4.0-4.7.
We can see that Pat’s silage has a pH of 4.4 (sample 1) and 3.9 (sample 2), indicating that his silage pH is in or around where it should be.
Ammonia – N (%)
Furthermore, Ammonia – N levels of less than 10% are also desirable, while values greater than 15% indicate bad preservation and can result in reduced intakes.
Anything coming in under 5% represents silage that has preserved very well.
Both of Pat’s silage samples are below the 10% figure, with the first sample at 7.2%. The second sample preserved excellently at 4.7%.
Dry matter (%)
Generally, intakes will be higher on DM silage of 20% plus, while silage made during broken or wet weather will have a lower DM value and will, in turn, result in lower intakes.
Pat’s first sample is a touch higher than the desired range of 20-30% DM. This is due to drier conditions encountered in early May when the silage was harvested; the second sample has a dry matter value of 29%.
Dry matter digestibility (DMD %)
Dry matter digestibility is an accurate and reliable test of forage feeding value. The result is used to estimate energy value, as well as expected liveweight and required supplement level.
Generally speaking, young perennial ryegrass swards cut early for silage after six weeks growth should have a DMD value of 75-80% and give top animal performance, while older stemmy swards (when cut) would have a DMD of 60-65%.
For example, with a 75% DMD silage weanlings should exhibit a daily liveweight gain of 0.8-0.85kg/day on silage only. This Cork-based farmer’s silage tested at 73.8% DMD (sample 1) and 70.7% DMD (sample 2).
Crude protein (%)
Crude protein reflects the quality of the grass at harvest, with young leafy grass having values of over 15%, while stemmy grass typically has a value of less than 10%. In addition, swards with incorrect fertiliser programmes can result in lower protein levels.
Silage with a crude protein value of 17% plus would be deemed too high. Crude protein levels for sample 1 and sample 2 on Pat’s farm are 14.8% and 13.6% respectively, which indicate adequate levels of protein.
This reflects the energy value of the silage. In general, the younger the grass the higher the energy and vice versa; young dryer grass will have a higher energy content.
An energy value of 9.8MJ/kg plus is desirable; both of Pat’s samples are above this target – 10.6MJ/kg and 10.2MJ/kg.
A full breakdown of silage sample results from the participating farmers will be published when all samples have been analysed…
Now that silage sample results have been obtained, with the help of his local Teagasc advisor – Ruth Fennell – and Seán, Pat will formulate winter diets based on the data.
In addition, the remaining 2018-born Friesian bulls will be slaughtered next week at approximately 21-22 months-of-age.
The slatted house in which they were housed will then be available for the 2019-born Friesian (40) and Aberdeen Angus (60) calves purchased this spring, when they complete the final round of grazing.