Monitor grass growth to avoid lamb growth checks

Lamb producers are being advised to keep a close eye on grass growth to prevent a check in lamb growth rates over coming weeks.

Grass quality has been declining due to the warm, wet weather, which has meant many farms have seen a surge in grass growth.

Kate Phillips, Adas livestock consultant, says growth has been “phenomenal” and advises farmers to get on top of grazing covers.

“What I’m seeing is lots of grass that is too long and low DM. I’ve seen quite a lot of fields where you can’t even see the lambs.

“There’s an abundance of grass and farmers are struggling to keep on top of the quantity.”

She says grass quality is only declining because grass has got away from sheep, but she warns lamb performance could drop because grass is so long and full of stem.

Pat McCambridge, beef and sheep development adviser for Cafre (College of Agriculture, Food and Rural Enterprise), says much of the slowing down of lamb growth rates in June is due to the deteriorating sward quality.

“Once grass starts heading, dry matter digestibility decreases from about 75D in mid May to about 60D in mid June.

“This happens at a time when lambs become more dependent on grass,” he adds.

He says using a rotational grazing system can help improve grass quality by cutting out seed head production and maintaining a leafy sward.

Sward height targets for lambs
 Rotational grazing  Set stocking
 Pre-graze  Post-graze  Pre-graze  Post-graze
 10-12cm  5-7cm  6-8cm    3-4cm  3-4cm

Lambs being set stocked should be entering pasture at 2,200kg DM/ha and should be taken out when grass is grazed down to about 1,600kg DM/ha (see table).

He says farmers should close up fields with excess grass for silage making to avoid wastage.

Eblex’s livestock scientist Liz Genever says DM content has also fallen from around 20% to 15%.

“Generally, this means lambs will be struggling to get the energy they need to achieve high growth rates,” she explains.

Weaning lambs

Dr Genever says if growth rates of lambs aged eight weeks and upwards falls below 200g/day, action should be taken.

“Once lambs reach eight weeks old their energy intake from grass is greater than from ewe’s milk, so competition for high-quality grass between ewes and lambs increases,” explains Dr Genever.

Consequently, it may be worth considering weaning lambs, providing you have better quality grass to move them to and they’re aged 10 weeks plus, she advises.

“If the ewes are losing condition weaning will benefit the sheep. Assess body condition of ewes and look at lamb growth rates.”

Creep feeding

For producers thinking of introducing creep to bolster lamb growth rates, Dr Genever warns economic viability should be considered carefully.

“At this time of the year we are heading into historically falling prices, so it may be a struggle to get a return on investment,” she says.

She says creep feeding should also be “strategically targeted” at lambs that will respond the best.

“If lambs have never encountered creep before it will take two to three weeks to adapt.”

Dr Genever says creep is better directed at lambs weighing 35kg that have another six to eight weeks of growing left. Anything 38kg or heavier will risk upsetting the final few weeks of growth.

“It is about monitoring what is happening on your farm. It is also worth remembering if growth rates are back it could be parasite or grass related, or a combination of both.”

See also: Are you considering weaning?