Grazed forage not always sufficient
USING grazed forage crops to finish store lambs may be cheaper than buying in supplements. But when forage is in short supply or the weather poor supplementation could be necessary to maintain growth rates. So says ADAS beef and sheep consultant Elwyn Rees.
"The first step is to assess whether there is sufficient forage. Weigh samples of the fresh crop taken diagonally across the field from several 1m square plots," says Dr Rees.
Assume dry matter (DM) is 12% and allow for 15% to 30% wastage. "The daily dry matter intake of a finishing lamb is about 2.7% of its liveweight," he says.
"Where there is a severe deficit it may be necessary to finish lambs inside on 450g a head a day of a ration comprising nine parts whole barley to one part soyabean meal."
He advises adding minerals at 2.5% with no copper and a balance of calcium, phosphorus and magnesium to avoid urinary calculi. At this level growth rates of about 130g a day should be achieved.
Outside, 1ha (2.5 acres) of stubble turnips yielding 6.3t/ha (2.5t/acre) DM would be sufficient for 200 lambs for a month and growth rates of up to 160g a day.
"Straight barley is good for supplementing leafy brassicas, but the feed rate will depend on what growth rates are required, and how wet or frosty the weather," says Dr Rees.
"If higher growth rates are required, say 180g a day, a good crop plus 225g of cereal should be supplied. But feed conversion rates will be reduced as the lambs mature and deposit increasing proportions of fat.
"In frosty weather the quality of forage crops – stubble turnips in particular – declines. So, in prolonged periods of frost offer 120g to 225g of concentrates for growth rates of 145g a head a day," he says.