Importance of dry matter intake
Generally, cows have a minimum requirement for protein and energy to maintain normal body functions that is known as their 'maintenance' requirement, which is approximately 2% of their body weight.
Feedstuffs differ in their moisture content; to compare them for nutritional value and intake, they are expressed on the basis of their dry matter content (i.e. their mass once all moisture has been removed).
Maximising dry matter (DM) intake provides more nutrients to rumen microbes, which in turn provide more nutrients to the cow for:
- milk production
- milk composition
- body condition.
Every day, an efficient milking cow needs a dry matter intake equivalent to at least 3% of their body weight.
Estimating dry matter intake
1. Measure how much of each feed a cow is eating
Weigh daily allocations of:
- protein meals
- conserved forages
Intake of pasture and forage crops are more difficult to estimate; however, visual estimation, cutting quadrats and/or using rising plate meters are ways of determining pasture/forage intake levels.
2. Determine the dry matter content of each feed
In order to determine the dry matter content of a feed, all the moisture in it needs to be removed. There are two common ways to determine the dry matter content of feeds:
- Weigh and dry samples of each feed in an oven or microwave.
- Obtain an approximate dry matter value from feed tables (refer to Feed Plu$ CD or pages 56-61 of Protein Plu$ checkbook).
- Place a sample (approximately 100 g) of the feed in a microwave-proof container and record the weight (wet weight).
- Place a glass of water in the corner of the microwave.
- Place sample in the microwave, set to medium/low heat and dry for 3 minutes.
- Mix sample and reheat for 30 seconds. Weigh.
- Repeat at 30-second heating/weighing intervals until sample weight no longer changes.
- Record weight (dry weight).
- Calculate DM% = (feed dry weight ÷ feed wet weight) x 100%.
Fan-forced oven method
- Weigh the feed sample (wet weight).
- Spread out in a baking tray and dry at 80-100 °C for 4-8 hours in a fan-forced oven.
- Weigh feed again when dry (dry weight).
- Calculate DM% = (feed dry weight ÷ feed wet weight) × 100%.
Indicators of adequate/inadequate daily dry matter intake
When there is enough dry matter in the diet:
- Milk yield and composition will be on target.
- Lush pasture allocation will not be fully eaten.
- Silage, grain or mixed feed will be left in troughs.
- Cows will not stand around 'waiting to be fed'.
- Body condition scores will be on target.
When there is not enough dry matter in the diet:
- Low milk yield and problems with composition will occur (mainly milk fat percentage will be variable from pick-up to pick-up).
- Cows will appear hungry, bellow and wait for feed.
- Cows will rush to fresh forage, to feed troughs, and into the dairy for grain.
- Cows will eat all feed allocated in paddocks and troughs.
- Body condition scores will be low.
Useful rules of thumb
- The heavier the animal, the higher its maintenance requirements, and the higher the intake required for production.
- An efficient milking cow needs a daily dry matter intake equivalent to at least 3% of its body weight.
Example: a 600 kg cow needs 600 kg × 3% = 18 kg DM/day.
- Higher producing cows will eat more than 4% of their body weight as dry matter.
Example: a high-producing (over 30 L/day) 600 kg cow needs 600 kg x 4% = 24 kg DM/day.