MMN September 2024 – Feeding for Milk and Condition with Late Season Grazing

As we head into September with shorter days and grass quality declining, it can be difficult to maintain milk production and body condition at this stage of the grazing season. By the time a loss in condition is seen, it is too late, and the damage has already been done to future production and fertility.

Cattle are diurnal grazers and tend to graze more during the day and less during the hours of darkness. The most intensive grazing periods are early morning and late afternoon/evening. This is why buffer feeding is recommended before afternoon milking, so that cows maximise grass intake after PM milking.

In the second half of the grazing season, grass can become more stemmy and fibrous and it is more difficult to maintain sward quality and achieve the desired residuals. Topping fields can help to encourage more palatable, leafy regrowth.

It can be difficult to know how well buffer rations are meeting cow requirements when grass quality and intake is unknown. Therefore it is important not to overestimate how much dry matter, and therefore energy, cows are getting from grass. When the dry matter of the grass is high, under dry weather conditions, the amount of milk that grass can support is considerably higher than on a wet day.

The following tables show the impact of grass dry matter content on milk yield. The predicted milk yield assumes that protein is not in short supply and calculations are based on a 650kg cow producing milk at 4% butterfat and 3.3% protein.

 

Table 1. Milk production depending on fresh grass intake and grass at 20% dry matter and 11.5ME.

 

Fresh grass intake (kg)	Grass dry matter intake (kg)	Energy intake (MJ)	Predicted milk yield from grass (litres)
40	8	92	3.2
50	10	115	7.5
60	12	138	11.9
70	14	161	16.2

 

 

On a wet day, the dry matter of grass may be only 12% – in which case milk from grass will be considerably less.

 

Table 2. Milk production depending on fresh grass intake and grass at 12% dry matter and 11.5ME.

 

Fresh grass intake (kg)	Grass dry matter intake (kg)	Energy intake (MJ)	Predicted milk yield from grass (litres)
40	4.8	55	0 - not enough for maintenance!
50	6	69	0 - not enough for maintenance!
60	7.3	84	1.7
70	8.4	97	4.1

 

While it is difficult to know how much energy cows are getting from grass, an effective way to assess the nutritional status of the cows is to carry out a metabolic profile test. This can help assess both short-term and longer-term energy status (as well as protein and mineral nutrition). Another sign that cows have been lacking in energy is a low milk protein content of around 3% or less.

 

Tips to maintain milk production and body condition at grass:

• Top fields to tidy them up and encourage higher quality regrowth.
• Test grass for nutritional value so that your nutritionist can more accurately formulate a buffer feed to meet the needs of the herd.
• Consider feeding an extra 1-2kg concentrate on wet days, if possible, either in the buffer feed or through the parlour (if intakes allow, without compromising rumen health).
• Carry out a metabolic profile test to assess energy status.
• Consider keeping newly calved cows housed to better manage condition, maximise dry matter intake and minimise weight loss in early lactation to protect fertility.

Lorna MacPherson,  lorna.macpherson@sac.co.uk; 07760 990901