Rules of thumb on your farm

How many MJ of ME (Mega Joules of Metabolisable Energy) are required to make 1kg Milk Solids

  • 1kg of milk solids takes approximately 70 MJME above maintenance to produce

    • How many Kg of milk solids do you get from 1 Kg of dry matter (DM)?

  • 1kg DM = 11 MJME then 1kg DM will make 11/70 or 0.16 (160gms) milk solids (this is presuming that the maintenance requirements of the cow are already met)

  • If maintenance of the cow is to be taken into account we need to consider that approximate maintenance of a 350kg cow (milking & non-pregnant) = 50 MJME
    450kg cow = 60 MJME

    So a 450kg bwt cow, producing 1.8milk solids would need 60 + 126 = 186 MJME
    At 1 kgDM = 11 MJME then 1.8milk solids would require 16.9 kgDM so each 1kg DM would produce 0.107 kg (107gms) milk solids.

    A 450kg bwt cow at 1milk solid produced would need 60 + 70 = 130 MJME and therefore at 11 MJME/kgDM would require 11.8 kgDM. So each 1kg DM would produce 0.085 kg (85gms) milk solids under these circumstances.

    How many MJ of ME per average kg DM of:

    • Grass

  • spring, leafy =11.5-12 MJME
  • summer, leafy, green = 10-11 MJME
  • dry and stalky = 8- 9.5 MJME

    •  

    Grass silage

  • good quality = 9.5-10 MJME
  • poor quality = 7-9 MJME

    •  

    Maize silage

  • good quality = 10.5 MJME
  • poor quality = 9.5 MJME

    • Dry matter requirements per year: (approximate)

     

  • 450kg Cow producing 300kg MS =4100 kgDM
  • 350kg MS = 4400 kgDM
  • 400kg MS = 4700 kgDM

    •  

  • well grown Friesian heifer = 2200-2600 kgDM
  • well grown Friesian calf = 800-1000 kgDM

    • Difference to a cow between a kg of:

    Grass

  • spring = good energy, sometimes low in dry matter (and low in fiber) preventing high dry matter intakes, and high in protein (energy cost in digesting this ).
  • summer = lower in energy, especially if it’s lost the green look. Low in protein often restricting production.

    • Silage

  • Grass silage = if good quality has energy not much lower than summer pasture, and better protein.
  • Maize silage = although lower in energy than spring grass it has starch as it’s main energy source. This and it’s low protein make it a good balancer for pasture at certain times of the year.

    • What are the different response rates to urea at different times of the year

    These vary considerably and urea is best considered as a growth multiplier, the best responses happen when conditions are right for good, natural, grass growth.

  • Winter = 7-10:1 (8:1 average?)
  • spring 10-20:1(12:1average?)
  • summer 10-12:1 (with moisture) and ?-8:1 if dry
  • autumn 8-15:1 (very variable). I tend to use 10:1 overall

     

    Expected grass yield off a hectare of land

  • depends on soil type, fertility, average rainfall pasture species to name but a few.
  • 10-16tonne DM grown, pre nitrogen is the approximate range but this is not the same as grass utilized by the herd. 12-14tonne “harvested” is aimed for.

    • Silage– weights and volumes

    In the stack -These depend on a lot of factors such as rolling time, maturity/dry matter of crop, chop size etc. So large variations are possible between farms, contractors and seasons

  • Stack silage = Grass silage – 150-170kg DM per cubic meter
  • Maize silage – 200-240kg DM per cubic meter
  • Pit silage = Grass silage – 200-240kg DM per cubic mete
  • Maize silage – 250-300kg DM per cubic meter

    • Feed out wagon weights- generally, when silage is taken from the stack to the wagon by conventional methods, about half of what is in a cubic meter in the stack will be in a cubic meter in a wagon. So a stack of grass silage @ 160kg DM/cubic meter will have around 80kg DM/cubic meter in the wagon.

    Andy Collier
    Intelact Consultant and Veterinarian (Animal Health Centre-Hamilton)