Which are the best silages for dry cows?

June 13, 2022

Which are the best silages for dry cows?

There are three aspects of silage quality to consider when selecting silages for dry cows – nutritional quality, fermentation quality, and hygienic quality

Nutritional quality

The three key nutritional parameters are energy, protein, and fibre. While generally the higher the energy and protein the better for milking cows, this isn’t necessarily so for dry cows. If dry cows are at or close to their target body condition score (BCS) at dry off, they do not need an energy-dense diet. They are usually better off with lower energy and higher fibre feed, such as mature grass silage (or hay), especially during cold winters.

Photo-2-Nutritional-Quality

However, higher energy silage may be necessary if body condition gain is needed. The required daily weight gain can be calculated based on average BCS at dry off and target BCS for calving with consideration for the last month of gestation, where no improvement will occur. If you would like help putting together a diet for dry cows to ensure BCS targets are met, your Nutritech Area Manager is well placed to help with the DietCheck® program

Fermentation quality

Is a measure of the efficiency of silage fermentation. A low pH relative to dry matter % and a high lactic acid content indicate good fermentation quality. In contrast, high ammonia nitrogen and the presence of butyric acid indicate a slow, inefficient fermentation and substantial nutrient breakdown. Using a proven inoculant such as Sil-All 4×4® can help to ensure good fermentation quality.

Protein-Breakdown-Graph-01

Trials have shown that stock fed well-fermented silage from a more mature crop can perform better than those on a poorly fermented silage made from a crop with better digestibility. Silages with good fermentation are also more palatable, leading to less wastage when silage is fed out in the paddock, as often is the case for dry cows. It is essential not to feed butyric silage to springers close to calving as this increases the risk of metabolic issues at calving.

Hygienic quality

Some of the moulds that can grow in silage produce toxins that can adversely affect cow health. Some are harmful to rumen microbes, reducing feed digestibility, some impair immunity and others can cause abortion. The generalisation that ‘white moulds are safe’ is not true – there are some white moulds that do not produce toxins but there are others that can be pretty harmful. Unless you are a microbiologist with a powerful microscope, it is best to assume that all moulds may be detrimental and discard any mouldy silage.

The Silage Fermentation

Silage-Fermentation-Graph

Moulds need air to grow, so good compaction and sealing and good feed out management will reduce the risk of moulds and mycotoxins. Using a proven oxygen barrier such as Silostop® can reduce spoilage in the top metre of a stack or pit.

Silage can also contain Listeria, another possible cause of abortion. Avoiding soil contamination and achieving a low pH reduce the risk of Listeria.

Silage analyses

When more than one pit of silage or stack of bales has been made, getting samples from each pit or stack analysed can provide helpful information to help allocate the most appropriate silage to each group of stock. When looking at the analysis report, take into account the fermentation characteristics (pH, silage acids and ammonia nitrogen) as well as the energy and protein. If you would like a guide to understanding silage analyses, ask your Nutritech Area Manager.

It is also important to visually assess the silage, looking for any signs of spoilage such as moulds. Any spoilt silage should be discarded and not fed to any class of stock. Remember – if the feed is not fit for milkers, it is not fit for dry cows either!

For more information on feeding dry cows and analysing silage, contact your local Nutritech Area Manager

Grass / Lucerne / Clover Silage Feed Test Interpretation Guide

Feed ParameterRecommended Range Notes
Nitrogen

Depends on protein requirement of stock class and type of crop ensiled.

For high quality silage:

Grass: 2.5 - 2.9

Lucerne or clover: 2.9 - 4.0

The nitrogen value is what is used to calculate crude protein (CP=N x 6.25). It is the measure of all the nitrogen components in the feed including DNA, ammonia, ‘free’ nitrogen and true protein. While high true protein is good for the growth and performance of many animals, we don’t want too much ammonia or free nitrogen. Check Ammonia N as a % of total Nitrogen – this will tell you if a high proportion of the nitrogen is ammonia rather than true plant tissue protein. High nitrogen becomes surplus to animal requirements and will also increase the buffering capacity of the forage. This increases the requirement for strong front-end fermentation inoculant.

If < 2.9 check: dry matter (too high), timing of harvest (too late, mature plant), mower height (too low, so picking up too much stem).

If > 4.0 check: dry matter (too low), timing of harvest (too early), fertiliser application (high urea uptake), mower height (too high), damage to plant cell (over compaction) and any other factors that may have increased N content of the plant.

Dry Matter

Stack: 30-40%

Bale: 35-45%

Dry matter is the weight of the feed once all of the water has been evaporated. Dry matter has a significant impact on fermentation quality of the silage. It is largely influenced by timing of harvest, length of wilt and climatic conditions during the wilting period.

Low dry matter: silage is difficult to ferment due to high water content. Water is ~pH 7, which takes a lot of fermentation acids to bring it down to pH 4.5. Clostridial fermentation can also dominate in low DM silages which will increase ammonia-N % and butyric acid levels. A higher DM is required for bales due to the difficulty in reducing pH, the inability for water to escape in a bale and subsequent degradation of plasticwrap. Tedding can help increase the dry matter - ted within 0.5–2 hours after mowing while plant stomata are still open. Leave the swath as wide as possible but don’t over-wilt as field losses will increase.

High dry matter: silage is difficult to ferment due to the presence of air. Therefore the silage may not reach target pH and aerobic spoilage organisms can also grow for longer. Higher dry matter is often correlated with lower feed quality specifications e.g. protein, metabolisable energy due to plant maturity


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