16 October 1998

Get your sums right in forage estimates

WORK out root crop quality and quantity before feeding lambs to avoid running out of forage before theyre sold.

Surprisingly, wet conditions have not led to bumper catch crops. Instead, slug damage means finishers could be short of forage and over-estimating crop quality could add to concerns this winter.

Stubble turnips broadcast earlier than usual into standing crops have suffered most from slug damage, while later sown crops are better quality but growing slowly, says sheep consultant Lesley Stubbings. "This is causing difficulties as these crops are needed now to help lambs get over high worm burdens that have led to coccidiosis in some cases.

"Being able to worm and move lambs would be a great help, but producers need to assess forage quality and quantity. Where forage crops are poor, consider giving preference to ewes.

"But where ewes have ample feed, think about putting the bigger lambs on roots first because they will make the best use of available crop," she says.

Forage quality is variable this year, agrees Cotswolds-based independent consultant Alistair Bird. "Its not an easy thing to estimate but its worth the time as lamb finishers can predict whether they will need to supplement with 16% proprietary concentrate to ensure lambs finish before forage runs out.

"Knowing how much lambs will use is important. Its safe to assume that in good weather they will eat about 70% of the crop, while in poor conditions it could be half this level; 35%. Strip grazing will reduce waste."

As a rough guide, (see panel), a 30kg lamb eating 0.8kg/DM/day would have 1200 grazing days/acre (2970 days/ha) in good conditions. In poor conditions it would be 600 days/acre (1485 days/ha).

While assessing crop yield will help finishers plan winter feeding, regular drafting of lambs will help monitor growth rates and whether lambs need concentrate feeding to boost growth rates, says Mr Bird.

"Lambs need some dry fibre so give access to good-quality hay or straw. A grass run-back is important so lambs have a dry lying area. Where this isnt available, put straw bales along headlands to provide shelter and bedding.

"Ensure that foot problems are treated before moving lambs to avoid growth checks. Also, in selenium and copper deficient areas, consult your vet as they will grow less well if deficient."

He urges producers to remember that abattoirs dont want contaminated fleeces. "Its a good idea to crutch lambs and remove belly wool to avoid penalties later." &#42

ESTIMATINGROOT CROP

&#8226 Weigh roots from 1 sq/yard – take more than one weighing where crops are patchy.

&#8226 Multiply by two – to estimate fresh weight – eg 9lbs x 2 = 18t/acre fresh weight.

&#8226 Convert to dry matter -18t x 8% = 1440 kg DM.

&#8226 Lamb eats 0.8kg DM/day = 1200 grazing days/lamb/acre, assuming 70% utilisation.

&#8226 300 store lambs at 30kg = four days an acre.

*Calculations in mix of Imperial and metric units for ease.