Dry matter

What is dry matter?

Every feed consists of water and dry matter. Dry matter, abbreviated DM, is the part that remains after complete drying. The dry matter holds all the nutrients: energy, protein, fat, fibre and minerals.

Why are rations calculated in dry matter?

Feeds contain very different amounts of water. A kilo of fresh grass silage supplies far fewer nutrients than a kilo of hay. To compare feeds, nutrient contents are given in grams or MJ per kg of dry matter. A cow’s feed intake is also calculated in kg DM.

Approximate dry matter contents:

• fresh pasture grass: about 15 to 20 per cent
• grass silage: about 30 to 40 per cent
• maize silage: about 30 to 35 per cent
• hay and straw: about 85 to 88 per cent
• concentrates and cereals: about 87 to 89 per cent
• cow’s milk: about 12.5 per cent

The DM content of silage varies from clamp to clamp and even within one clamp, so it pays to measure it regularly. A silage with 30 instead of 35 per cent DM means that the cows get noticeably fewer nutrients from the same fresh weight.

How do you measure dry matter?

A laboratory feed analysis gives exact values. On the farm you can also determine the DM content yourself. You weigh a sample, dry it in a microwave or a dedicated feed dryer until the weight no longer changes, and weigh it again. The remaining weight divided by the starting weight gives the DM share.

How much dry matter does a cow eat?

Dry matter intake is the most important figure in feeding, because it limits how much energy the cow gets. Guide values:

• dry cows in the close-up period: about 1.5 to 1.8 kg DM per 100 kg body weight
• in the first 60 days of lactation: about 2.5 to 2.8 kg DM per 100 kg body weight, so roughly 19 to 21 kg for a 750 kg cow
• high-yielding cows at peak lactation: often more than 23 kg DM a day

In the days before calving, dry matter intake drops naturally. After calving it rises more slowly than milk yield. This is what causes the negative energy balance. Read more in Ketosis causes major expenses.

Dry matter in the ration

The DM content of the finished ration matters too. A TMR with about 40 to 50 per cent dry matter is eaten well. If it is too dry, cows sort it more easily. If it is too wet, intake falls. When a dry ration is moistened with water, the concentrate sticks better to the fibre.

Dry matter in calves

In colostrum and calf milk, dry matter is also a measure of quality. The Brix value of colostrum estimates its dry matter content. Good colostrum is above 25 per cent DM. Milk replacer for an intensive feeding plan is often mixed at about 15 per cent DM. Read more in Colostrum management; for the right start!.

Common pitfalls

A ration is often calculated once with laboratory DM values and then mixed the same way for months. When the silage changes at the face or rain falls on the open clamp, the ration is no longer right. A weekly DM check of the main silages keeps the ration more accurate.

Frequently asked questions

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