In my part of the world, the best prices are paid for 'white' lambs of good conformation, a covering but not overfat (lean better than being a butterball), liveweight in the 40-42kg range. They are aiming for a carcase of not more than 21kg, which is what the supermarkets want. In your neck of the woods you have a lot of slaughterhouses processing for the supermarkets, so I would expect the pricing to be similarly skewed towards these well-muscled little lambs.
In terms of conformation and kill percentage (dead to liveweight ratio), a lot depends on breed and feeding.
A hill sheep is unlikely to be top conformation; a Texel, Beltex or Charollais should be. (I don't have any experience of Suffolks, Hampshires, etc, so forgive me for not knowing what conformation etc would be expected of them.)
Texel crosses from hill sheep on a hill farm, reared on grass and no cake, could have a kill percentage as low as 44%; good Texel or Charollais lambs, fed a little cake and on good grass, should be well over 50%, maybe up to 60%.
On weighing at home, use the following guidance:
- Take off 2kg for the grass and poo in their bellies and intestines
- Take off 2kg for the journey and handling
- Take off another 1kg for the abbatoir's scales never ever thinking your lambs weigh what you do
- Aim to have a good Texel in the ring weighing 38-40kg as VSS says, or a lesser animal could be a little more, up to 42kg
- Oh, and take off another kilo or two if they are wet and/or have heavy thick fleeces
So you can have them up to 45kg when you weigh them, full, at home, to be aiming for the best prices.
You can sell them heavier than this, it's just that you will certainly get less per kilo and often will get less per head, as there won't be so many buyers bidding for them.
There's no minimum age, they should go to market when they're ready. Our first lambs get away at 3 months old (poor wee souls
), most at about 4 months.
The best time to take them is when the price is highest and they are fit, not fat, and not too large. Keep an eye on your local papers' market reports and watch the lamb averages to give you an idea of what prices are doing. But be aware there is often a pendulum effect - a couple of weeks of good prices, and all the farmers will sweep up all the lambs they can possibly get away and send them off, resulting in a glut and the price falling just that very week everyone takes their lambs...
For planning for future years, prices are usually as good as they'll be while Ramadan is on, especiallly if it's early in the summer.
HTH