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Maximising Grass in the dairy cow diet


Getting cows out on grass is better for the cows, and beneficial for the grass plant. Nutritionally, spring grazed grass is far superior to grass silage indoors with digestibility of 80 + in terms of DMD. So the more of it you can get into the diet the better, advises Ciara O’ Shea, Teagasc Macroom

Every opportunity to get grass into the cows’ diet needs to be taken, despite the weather challenges that present at this time of year. Getting the cows out on grass is better for the cows, and is beneficial for the grass plant.  Nutritionally, spring grazed grass is far superior to grass silage indoors with digestibility in the mid-eighties in terms of DMD.  So the more of it you can get into the diet the better.

Grazing in Wet Weather

There are three daily objectives for cows grazing in wet weather:

  1. Feed the cow 2. Minimise damage 3. Grazing Residuals (if possible)

The only way for you to know if a paddock is fit for grazing, is to walk your farm. Grazing decisions cannot be made in the farmyard.

Walk your farm:   Grazing decisions cannot be made in the farmyard

To get started:

  • Walk the farm and assess ground conditions and grass covers in each paddock. (Record on PastureBase).
  • Identify the driest paddocks with a lower cover (800-1000KgDM/Ha) on your farm. The target is to have these grazed first.
  • Get cows out for 2-3 hours on these paddocks after each milking (strip graze/ back-fence, temporary roadways).
  • On/off grazing is ideal for getting grass into the cows’ diet.

Cows can achieve 90% of their daily grass intake in 2-3 hours after each milking compared to cows out full-time.

  • Graze the dry, best infrastructure paddocks with lighter grass covers. Good grazing infrastructure will help to reduce damage and achieve more grazing.
  • Aim to have multiple access points in the paddock.
  • When weather improves, graze the heavier covers. (Target these after the 30% grazing target has been achieved).
  • Use the back-fence to protect areas grazed in poor conditions.

Meeting Grazing targets

A spring grass budget and spring rotation planner should be completed on PastureBase or other grazing software. The grass budget then will allow you to plan to have enough grass into the second rotation. (Do not to let AFC drop below 500KgDM/ha). The planner is designed to take the guess work out of grazing management and it relies on the principle of grazing a set area each day.

  • The target was to graze 1% of the farm every day during February
  • The advice was to target paddocks with the lowest covers initially, in order to reach 30% target
  • It’s not possible to put cows out on grass, and keep them out, unless there is grass on the farm and there is a grazing plan put in place.
  • If 30% grazed in February was not achieved,  focus on the next target of 65-70% grazed by 17th March

Aim to get as close to these targets as possible as every extra day a cow is out on grass, it is worth €2.70/day/cow.

Nitrogen is essential; 1Kg Nitrogen applied = 10Kg Grass DM in Spring.

To get the best response to N in Spring, the soil temperature needs to be 5°C and rising (at 10cm depth). Pay particular attention to the weather forecast, soil conditions and grass cover in the paddock, prior to applying Nitrogen fertiliser (N).  Fertiliser or slurry must never be spread on water logged, snow covered or frozen soils.

To check soil temperature in your area you can look up https://soiltemp.remotesignals.ie/ or buy a soil thermometer. Do not apply fertiliser if heavy rain is forecast or if rain is forecast within the next 48 hours.  Be aware that you need to maintain a 2-meter buffer zone (no fertiliser N applied) from any watercourse.

The following paddocks need to be prioritised for early N application:

  • Recently reseeded paddocks
  • Paddocks with good perennial ryegrass content
  • Paddocks with good soil fertility
  • Grass covers over 400KG DM/Ha
  • Warmer/drier ground

The rate of fertiliser will depend on your farm stocking rate and demand for grass. The target for an intensive dairy farm is to have 70 units N/acre applied by the 1st April if weather and soil conditions allow.  This can be achieved with chemical fertiliser, or a combination of chemical fertiliser and slurry.  This is generally broken down into 23 units N/acre in late January to February, followed by 46 units of N/acre around the 1st week of March.

Slurry should replace chemical N on a portion of the farm’s paddocks.

Splash plate slurry spreading will supply 6 units N/1000gal.  Using LESS will increase N content. Trailing shoe or dribble-bar slurry spreading will bring about an increase of 9 units N/1000 gallons.

  • LESS slurry spreading makes better value of the N. Spreading 2500 gallons/acre of LESS slurry will contribute 23units N. This is the same type of N as chemical fertiliser. 23 units N/acre is sufficient N for the level of grass grown from mid-January to March 1st. (To help reduce the usage of chemical N on your farm, use LESS)
  • The remaining 46 units N/acre can be applied as chemical fertiliser to achieve the 70 units N/acre by April 1st.
  • Aim to use protected Urea because it is less prone to water losses than CAN.

If there is a need for Phosphorus or Potassium on your farm, apply compounds like 18-6-12 from mid to late march, when soil temperatures are > 10°C (check your nitrates allowances).

Cows need to be on a rising plane of nutrition, to minimise BCS loss in early lactation.

The level of meal is influenced by the amount of grass and quality of silage in the cows’ diet. 

Calf Care

During calving season it is important not to forget the 1 - 2 - 3 colostrum feeding recommendations:

  1. The calf’s first feed should be colostrum
  2. The calf should be fed the colostrum within 2 hours of birth
  3. The calf should be fed at least 3 litres/(8.5% of bodyweight) of colostrum within the first 2 hours

More on Calf Rearing can be found here

The Spring Grazing Rotation Planner can be found here (PDF) 

More Grassland Information can be found on the Grass10 webpage   and check out the Grass10/PBI Webinar - Planning your Spring Grazing with PastureBase Ireland  on Wednesday 3rd March at 7pm