How much grass does a sheep eat?!

Christine Page

My Shetland ewes are due to lamb in three weeks time, when the weather should be milder and the lambs can be born naturally outdoors. I plan to move the ewes into the small nursery paddock (pictured above) near the house soon so that I can keep a close eye on them through the lambing period. But how do I know how much grass they will eat and how long will the grass in this field last? 

The spring flush of new growth has not yet started but this field has been rested since last autumn, so the ewes will appreciate the pasture, even though it’s a bit old and feggy (local term for past it's best). 

I have 25 ewes due to lamb, plus a couple of shearlings (last years' lambs) and a retired old ewe, so 28 sheep in total coming into this field.  By eye I’d say they would nibble through this lot in a week, so I’ll be supplementing with hay. However, I’d like to be a little more scientific, especially as later this spring I’ll need to be calculating much more accurately the amount of forage available for the animals because this year I will be adopting a mob-grazing system of pasture management. This better utilises the pasture and ensures it is enhanced by grazing and not depleted. It also means the animals get the best, most lush pasture all through the season. I’ll write more about mob-grazing in a future post but for now suffice it to say that to get it right takes some forward planning and careful monitoring. So I am taking this opportunity to practice calculating the feed value of a particular field.

Back to how much grass does a sheep eat? Or put another way, how much food is actually in this field? The best way to work this out is to find out the dry matter of the pasture, which is what is left after all the water is removed. 

Measuring Dry Matter (DM):

  1. Walk around the field and choose a spot that best represents the average pasture in the field, not the most lush or weedy or bare
  2. Measure a meter square and cut off the vegetation within this square, placing it into a plastic bag. You don’t have to cut it too tight to the ground because the sheep can’t eat every last blade of grass either, they trample and poop on some
  3. Weigh the bag with grass in it, then empty the grass into a large roasting tray and put in cool oven overnight to dry out
  4. When it is crispy dry put back in the same plastic bag and reweigh
  5. Divide the fresh weight by the dry weight to get the percentage – in my sample the fresh weight was 489g and the dry weight 121g, giving 25% DM

What does that tell me? Well, a sheep on average will eat around 2.5%-3% of her body weight in DM per day. My little Shetland ewes only weigh around 40kgs, so that means on average each would eat between 1,000g-1,200g of DM per day. If there is 121g of DM in a square meter of this field, then each ewe would need 8-10sqm of grazing per day to sustain herself. If you picture that amount, pace out 2m by 4m or 5m, and imagine a little sheep steadily nibbling away all day it makes sense and I’d say we’re pretty close.

Next, you need to measure the square meterage of your entire field and from that fairly accurately estimate how many days it will support a certain number of sheep – it might be 1 sheep for 100 days or 100 sheep for 1 day, and I’ll explain why the latter is far far preferable for the environment, soil, plant and animal health as well as that of the humans eating any resultant produce when I write my mob-grazing post!