Factors affecting feed intake
Major drivers of feed intake
The amount of feed on offer must be sufficient to satisfy appetite and meet production targets. Provide equal access to feed for all cows, particularly at troughs or on a feedpad.
Optimise nutrient content in the diet for intake and milk production (e.g. energy, protein and fibre). Feed quality and the palatability of a particular feed are affected by:
High neutral detergent fibre (NDF) in individual feeds and the total diet will restrict the cow's ability to consume a high intake.
Provide feeds and total diets that are easy to eat and digest. Consider the:
- chop length
- degree and type of grain processing
- amount of green leaf available in pastures.
Ensure mixed rations are mixed thoroughly.
Neutral detergent fibre (NDF) content
NDF in forages and the total diet determines dry matter (DM) intake. Diets need to be balanced to contain sufficient and effective NDF for healthy rumen function while not providing too much fibre, as this slows down digestion and limits intake.
Other important drivers of DM intake
Other factors that influence DM intake include:
- cow size
- rumen health (see Managing for healthy rumen function for more information)
- stage of lactation (in early-lactation cows require higher DM intake)
- water quality and accessibility
- heat stress (see Heat stress and nutrition for more information)
- overall animal health
- nutrient supply (should be constant and consistent to maximise rumen microbial activity and DM intake).
NDF intake rules of thumb
There are three rules of thumb for NDF intake:
- Optimum intake is achieved when NDF content equals 28% to 34% of total diet DM.
- Maximum NDF intake from forage should equal 1% of the cow´s body weight.
- Maximum intake of NDF in the total ration should equal 1.2% of the cow's body weight (1.3% for a high-producing cow).
Estimating potential intake from NDF
The rules of thumb can be used to help evaluate the NDF content of a cow's diet and see if it falls into the optimum range. The following example shows how to calculate all the figures you will need to do this.
Estimating intake from NDF on lush, low-fibre pastures
Example: a 600 kg cow on a diet of lush, temperate pasture (45% NDF) and dairy meal (15% NDF).
In order to find the total percentage of NDF content in the cow's diet, follow the steps below.
1. Use the rules of thumb to find the different maximum intake levels of NDF.
Max. total diet intake of NDF = 1.2% of 600 kg (body weight) = 7.2kg
Max. intake of forage NDF = 1% of 600 kg (body weight) = 6 kg
Max. NDF intake from sources other than forage = 7.2 kg - 6 kg = 1.2 kg
2. Calculate how much lush, temperate pasture (45% NDF) the cow should eat.
Calculate the max. DM intake of lush, temperate pasture (forage) using the figure for the max. intake of forage NDF (step 1). That is, if a cow can eat 6 kg of forage NDF, how many DM kilograms should it eat of a forage that is 45% NDF?
Max. DM intake of lush pasture (45% NDF)
= 6 x 100 ÷ 45
= 13.3 kg DM
3. Calculate how much dairy meal (15% NDF) the cow should eat.
Calculate the max. DM intake of dairy meal using the figure for the max. NDF intake from sources other than forage (step 1). That is, if a cow can eat 1.2 kg of NDF from sources other than forage and dairy meal is only 15% NDF, how many DM kilograms of dairy meal should it eat?
Max. intake of dairy meal (15% NDF)
= 1.2 x 100 ÷15
= 8 kg DM
4. Calculate the total potential DM intake on this diet.
Calculate the total potential diet DM intake by adding together the max. DM intake of lush pasture (step 2) and the max. DM intake of dairy meal (step 3).
Potential diet DM intake
= 13.3 (max. DM from lush pasture) + 8 (max. DM from dairy meal)
= 21.3 kg DM
5. Find the total percentage of NDF in this diet and see if it falls inside the optimum NDF intake range.
Evaluate the total diet NDF by dividing the max. total diet intake of NDF (step 1) by the potential diet DM intake (step 4) and multiplying by 100 to find the percentage of NDF the diet contains.
Total diet NDF
= 7.2 ÷ 21.3 x 100%
= 33.8% = Good (inside optimum range)