As yield per cow increases, sustaining high yields at grass becomes more difficult. Grazed grass is still a cheap way of feeding dairy cows as long as a strict grazing policy is in place along with excellent grassland management and appropriate supplementary feeding to high yielding cows. The key to good grassland management is matching grass growth with grazing time and stocking rate. Measuring grass heights with a grass stick or plate meter will give a guide to grass availability over the grazing season and allow for better planning of the grazing cycle. Research has shown that milk from grass could be as high as 29 litres. However this requires the cow to consume almost 20kg of grass dry matter per day! More realistically we should expect between 15 to 18 litres from grass in good grazing conditions. This milk yield requires a cow to consume 15kg dry matter of grass per day. With grass at 18% dry matter, this equates to 83kg fresh grass per day. As milk yield and supplementary feeding increases the opportunity to consume grass decreases.
Grass Quality
Many factors influence grass quality, we should concentrate on the factors that we can influence.
• Grass species
• Clover content
• Weeds
• Pests and Diseases
• Previous grazing residues
• Prolonged over grazing The aim must be to produce a young, healthy, leafy, well managed quality sward with high ryegrass content, free from pests and diseases.
Grass Intakes
A cow’s intake of fresh grass will be determined by a number of factors,
• Grass availability
• Grass quality
• Time allowed grazing
• Weather conditions
Assuming that a cow will graze for up to 10 hours per day, with unrestricted access to grass the rest of the time she would be ruminating and being milked. A cow harvests grass with her tongue, taking a bite every second. On average one bite is equal to 0.4g of dry matter (range 0.2g – 1.2g) so in 10 hours grazing a cow can consume 14.4kg of dry matter, if the grass has a ME of 12 this equates to maintenance plus approximately 18 litres of milk.
Grazing Behaviour
Cows will graze after morning milking until around 10am, then they tend to lie and cud for a couple of hours and graze periodically until afternoon milking. Weather also influences grazing behavior, unsettled wet weather or extreme heat will impair grass intakes. After evening milking cows tend to graze right up to dusk. If possible cows should be turned out to fresh pasture after evening milking, sugar levels are at their highest and research has shown an increase in intakes by 15% and milk yields by 5%.
Grassland Management
Ideally, we want to have fresh grass in front of cows on a daily basis. Cows should be turned out to pasture with a grass height of around 10-12cm (equivalent to 3000kg DM per ha). Cows should be removed from the field at around 5cm (equivalent to 1500kg DM per ha). This would mean 100 cows grazing for 10 hours eating 14.4kg DM of grass would require approximately 1ha of fresh grass per day.
In normal growing conditions this would normally take 21 days to return this paddock to a grazable height of 10-12cm. However the range could be from 14 to 25 days depending on growing conditions. While this ideal grass growth is variable, allowing for seasonal variations and having a flexible grazing policy works best.
For further information on NWF Grass Seed, click HERE.