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Managing the ration of dairy cows before they are turned out to pasture

The key takeaways from this article

  • Optimal use of grass silages before turn out is crucial to ensure dairy cows produce milk efficiently once they are on pasture
  • Quality of grass silages for dairy cows can vary considerably, therefore, silages should be analysed before a diet is being calculated
  • It is important to feed the correct source of trace minerals at the correct level to reduce the environmental footprint of dairy farming

Optimal use of grass silages to manage dairy cows efficiently

Milk prices are variable, but farm income from milk will not always cover all the input price increases. This means that the focus must remain on managing dairy cows efficiently to avoid loss of farm income. Before cows are turned out, it is worth considering the key objectives to be reached at turnout:

  • Keep dairy cows milking as well as possible with high milk quality when they hit spring grass.
  • Ensure cows are in calf and that calving intervals are not dragging out as this will have implications for the next lactatio of dairy cows.
  • Keep dairy cows healthy and ensure they are not lame, making them ready to graze.

If these objectives are met, dairy cows should be capable of driving good margins at grass as long as milk prices rise or at least remain at the current levels.

Quality of grass silages for dairy cows can vary considerably

For many dairy farmers the challenge has been getting cows to milk when grass silages for dairy herds vary in quality, which is often is the case. This variation is a barrier to consistent dairy cow performance. Feed value of grass silages for dairy cows can vary as we move through and across clamps, especially clamps with a big face. This can lead to variable intakes and changes in the diet which can be minimised if silage clamps for dairy cows are analysed more often. It can also allow purchased feeds to be trimmed back which can help reducing feed costs of dairy herds. Alternatively, it can allow dairy supplements to be changed to better balance the rumen and keep cows performing.

Why is regular sampling of silage clamps so important?

A grass silage clamp is not a single, homogeneous product but a composite of different swards, different fields and different cuts, made in different conditions and weather. At any point in the clamp, there are variations in dry matter, protein, energy, NDF, lignin and fermentation quality. All of these factors have an impact on the quality of the nutrients supplied to the dairy cow and on dry matter intakes. The feed value of maize silage will also change with time in the clamp as starch degradability will increase, changing the proportion that is rumen fermentable.

Silage Forage Weight (kg) 33 33 33
Dry matter (%) 25 30 35
Dry matter fed (kg) 8.25 10 11.5
ME intake @ 10.5MJ/kg DM 87 105 121
Difference compared to 30% DM (MJ) -18 +16
M+ (Litres/day) 1 5 8
Silage Forage Weight (kg) 33 33 33
Dry matter (%) 25 30 35
Dry matter fed (kg) 8.25 10 11.5
ME intake @ 10.5MJ/kg DM 87 105 121
Difference compared to 30% DM (MJ) -18 +16
M+ (Litres/day) 1 5 8

Table 1: Effect of changes in silage dry matter within a clamp on intakes and milk production of dairy cows from forage.

What is the impact of differences in silage quality?

Changes in the headline figures of dairy silages can have a significant impact on the production from forage (see table 1). If the dry matter percentage is unknown, it is easy for dairy cows to be over or underfed.

The dry matter percentage also influences how quickly feed material ferments in the rumen. In wet silages, the feed has a low DM and will ferment more quickly. It could also be higher in fermentable carbohydrates and proteins. This can increase the risk of rumen acidosis of dairy cows.

Changes in ME content of grass silage can have a serious impact on milk production of dairy cows.

Assuming 10 kg DM of silage is being fed, a change of 0.5 MJ/kg DM will affect the energy intake from silage by 5 MJ per cow per day, which is enough to produce a litre of milk. Therefore, the actual energy content of the silage should be known before the dairy ration is being formulated.

Impact of fibre and lignin levels on DMI and feed efficiency of dairy cows

High levels of NDF, lignin or slowly fermentable carbohydrates will also affect how quickly the diet ferments. This can have an impact on rumen throughput and total dry matter intakes of dairy cows. Marked changes in lignin content have affected feed efficiency of dairy cows. While NDF content can remain unchanged, variations in lignin can affect dairy cow performance.

Impact of crude protein levels on rumen fermentation

Crude protein in the silage can vary greatly between fields and cuts. This will affect the supply of fermentable protein and can further upset rumen balance. The rumen microflora craves consistency, so ensuring a healthy rumen balance is important for optimum fibre digestion and feed efficiency.

The impact of feed management of a dairy herd

Armed with frequent analysis of all forages, it will be possible to fine tune the diet of a dairy herd. It will be important to go beyond ME and crude protein and look at all the nutrients the cows need, including dynamic energy and digestible intestinal protein. Make sure the rumen is balanced. Check that acid load and fibre index will support an efficient rumen and do not increase the risk of rumen acidosis of dairy cows. Alongside regular analysis and re-rationing, it is important to push feed up regularly, to ensure there is sufficient space per cow and adequate time to eat. A dairy cow should eat 12-14 meals per day. Diets can be sieved to check if the diet feeder is delivering a consistently presented diet.

Figure 1: NDF digestibility in dairy cows fed sulphate trace minerals sources compared to Intellibond, in dairy cows on a low forage diet and in dairy cows on a high forage diet.

Don’t cut corners with trace mineral management of dairy cows

It is important to keep a close watch on trace mineral management of dairy cows, considering both the amount fed and the type of mineral. Any shortfall can compromise health, fertility and performance. Equally, if mineral feed rates are too high, money is being wasted, there is a negative impact on the environment and in some cases, over-supply of trace minerals can cause problems with toxicity. A mineral analysis should be carried out on all forages. Grass in particular is a variable source of minerals depending on factors including sward composition, season and soil type. Grass is commonly a poor source of some important minerals for dairy cows. To supplement dairy cows correctly and cost-effectively, one needs to know what is in every part of the diet. This is especially true for forages which typically supply over 50% of total dry matter intakes of a dairy herd. The sources of minerals can make a huge difference. Cheaper supplements may contain higher levels of inorganic sources. Some of these are highly soluble and can interact with other ingredients in feeds and premixes as well as in the gastro-intestinal tract. Others are highly insoluble and not available to the animal. Sulphates, for example, are very reactive in the rumen which reduces their bioavailability. At the same time, the free metal which is released harms rumen microbes. The impact of sulphates in the rumen is significant because they have been shown to reduce the efficiency of fibre digestion1 so compromising the use of forage (see figure 1).

The most cost-effective way to feed minerals at any time of the year will be to take full account of all feeds in the diet and to supplement forages with bioavailable sources. Cutting back on minerals can be a false economy as any short-term gain will be wiped out by poorer performance, fertility and health.

References about responsible trace mineral management in dairy cows

  1. Faulkner, M.J. and W.P. Weiss (2017). Effect of source of trace minerals in either forage- or by-product-based diets fed to dairy cows: 1. Production and macronutrient digestibility, Journal of Dairy Science, 100:5358-53-67.

Find out more about sustainable dairy farming...