Small lambs, big lambs – what’s the difference? Plenty! Lamb liveweight (LW) at birth drives both lamb survivability and total kg of lambs weaned per ewe.
How does ewe nutrition influence lamb birthweight?
Pre-scanning feeding
The nutritional “horse has bolted” by the time ewes scan at 80-100 days of pregnancy – much of the effect of ewe nutrition on potential lamb birthweight has been and gone. Around two thirds of lamb birthweight variation is influenced by ewe nutrition from day 40 to 80 of pregnancy. Underfed ewes before day 90 have smaller placentas. Smaller placentas can’t fully support the needs of the unborn lamb, increasing risk of small lambs at birth.
Aims: Up until scanning aim to at least maintain ewe LW and body condition score. For ewes already in adequate body condition score (greater than 2.5), aim for maintenance levels of feeding. For tail ender lighter ewes (less than score 2.0), consider preferential feeding for some condition gain through mid pregnancy.
Scanning to pre-lambing feeding
Although the placenta has finished its growth by scanning, around 90% of the unborn lambs’ growth occurs between scanning and birth – so there’s still opportunity to influence lamb birthweight. Lambs born to ewes severely underfed in late pregnancy are lighter and have less reserves of body fat to handle the first few critical hoursafter birth – with lamb losses more likely. As well, ewes losing condition pre-lamb won’t produce good volumes of high quality colostrum and may not produce as much milk at peak lactation.
Aims: How much do we need to feed ewes during late pregnancy? There are plenty of references available which give us the energy demands of ewes on an energy or dry matter basis.
Helpful Tips
If the calculation of energy demands and kilograms of dry matter isn’t where you want to be, keep things simple when you set stock for lambing:
Scan
For singles or multiples and allocate feed accordingly.
Amount of pasture
For twin and triplet bearing ewes, monitor height of pasture once set stocked pre-lamb. Don’t allow heights to drop below 4 cm or you’ll increase risk of condition loss pre-lamb. If you can’t manage this, look to supplementary feeds to top up pasture on offer and for next year plan ahead with a more conservative feed budget that allows you to lamb onto higher pasture covers.
Quality of pasture
Allocate better quality pasture for twin and triplet bearing lambs. Modern pasture cultivars on fertile soils will typically yield more potentially better quality DM than older pastures. Plan ahead accordingly.