Careful feed management to achieve good lamb growth and sustain ewe condition is vital to long-term profitability, as Tom Ward explains.
Weaning date should be guided by two key goals: maximising profit, and protecting ewe condition. These goals are interrelated because lambing percent is about feeding the lamb better. The better the lamb is fed the earlier it is sold. Therefore more feed for the ewe to achieve and maintain the best condition for tupping, lambing and rearing.
In a biological system it is impossible to match feed demand to supply exactly, so a “best guess” approach to annualised winter stocking rates, feeding, and lambing date is used. The point is that whatever the manager sees approaching weaning has been determined largely by decisions made many months prior, and to some extent will be forced upon him or her.
The ewe liveweight declines at lambing, then increases in late lactation. Her intake, however, increases 2-3 weeks into lactation peaking at 8 weeks, with single lamb bearing ewes consuming 2.5kg drymatter (DM)/day and those rearing multiples 3+kg DM/day. Milk production peaks at about four weeks after lambing and declines steadily by 20-25g/day thereafter. Good body condition score (BCS) and nutrition is needed to achieve peak milk, but feeding levels do not really affect the rate of decline. So the higher the peak the greater the potential total milk. Twins stimulate up to 35% more milk production in early lactation and 18% in later lactation. Ewes will put on weight more efficiently when lactating than when dry. They require more total feed to put on weight when lactating than when dry, which may be an unacceptable cost. Furthermore, getting weight back on ewes can be difficult due to quantity and quality constraints. It is cheaper to maintain liveweight than increase it. Consequently, on summer-dry farms ewes should be weaned at the target BCS for mating.
Ewe BCS is very important – wean at 3-3.5. Any thinner ones can be retained and fed preferentially (unless an obvious cull) until mating. This is in case they are thin because they have reared multiples. If not at target 3-3.5 by mating they should be culled. The point here is that all ewes need to be BCS 3-3.5. An average of 3 (or even 3.5) with some below 3 is not a good result. There is no benefit in having a BCS greater than 3.5.
With respect to the lamb, the animal can digest pasture from two weeks of age. However, if weaned before 6-8 weeks it will suffer and cannot totally make up for the lack of milk through eating more pasture. Lamb growth rate from milk peaks between 20 and 40 days of age, at 250-350gm/day on average. In order to maintain high growth rates in late lactation, pasture ME needs to exceed 10.5. Single lambs consume more milk and grow faster than multiples – about 80g/day faster than twins in early lactation and 35g/day faster in late lactation.
To make up for a lack of milk, multiple lambs are forced to eat grass earlier, so pasture quality is very, very important for multiple lambs. Although short ryegrass can be as nutritious as clover, the quality issue also highlights the advantage of sub clover pastures (early spring) in dry climates, and lucerne or other specialist lamb feeds (late spring). Do not underestimate the potential for poor pasture quality. An ungroomed pasture, appearing to be good quality at first glance, could easily be 50% dead and stem, meaning ME is only 9.0. Conversely, that apparent small margin from buying spring cattle could be surprisingly profitable when improved lamb weaning weights from cattle grooming are factored in.
Early rumen development is important because by docking, 80% of lamb intake is pasture and speed of rumen development is driven by energy – milk and quality grass. A 20kg lamb has twice the protein requirements of a 40kg lamb, and milk is an important source of that protein.
Of course, given quality pasture, bigger milking ewes (East Friesian, Poll Dorset) will feed multiples to a higher level.
If ewes and lambs are well fed, then weaning between 8-12 weeks will reduce lamb growth. Lighter lambs often suffer less of a weaning check so it may be better not to wean single lambs within 2-3kg of sale weight. If feed is short, consider early weaning; however, lambs need to be at least 16kg LW, and the quality of forage post weaning is the greatest determinant of post-weaning liveweight gain. Ideally, early-weaned lambs need access to legume based forages at a minimum cover of 7cm in height. Do not graze below 1200kg DM/ha.
Bigger lambs, more options
Obviously, having bigger lambs at weaning gives you more money, but also more options – fewer lambs onfarm after weaning mean more feed for other stock, reduced parasite challenge, opportunities to trade, and better hogget and 2-tooth mating results.
Sale value drives lamb sale date and influences weaning date. Lamb schedules traditionally fall from December to April, so if you cannot grow the lamb fast enough to keep ahead of the falling schedule, then sell it. This also applies to store lambs. Early lamb sales are generally the most positive so the manager may sell unweaned lambs, ewes and lambs all counted, or ewes. This may also be a trap in a growthy season – lamb schedules may hold up as meat companies compete for a limited supply of livestock, encouraging farmers to retain lambs onfarm. This will cause some farmers to develop an unseen feed deficit (or light ewes) as lambs compete for feed that should be given to ewes and ewe lambs. BCS scoring should therefore never be done by eye because experience shows farmers tend to underestimate the number of thin ewes. In one study in a growthy year, seven out of 10 farms had at least 50% of their ewes at BCS below 3. The profitability of keeping a ewe above BCS 3.0 for tupping is more than 40c/kg DM compared with lamb finishing at 17c.
Animal health
Briefly, for ewes and lambs remember vaccinations, drenches, micronutrients, udders, feet, teeth and age. Minimise yarding of lambs to reduce pneumonia from dust. Watch for stress on lambs from changing feed types. Don’t forget the rams and ewe hoggets – in theory it is easy to grow out hoggets but they get squeezed by the need to finish sale lambs and to tup, winter and lamb ewes. All livestock do better on troughed water than from creeks and dams. To keep lambs growing, move them before they need to be moved.
- Tom Ward is an Ashburton farm consultant 027 855 7799, email: tfward@xtra.co.nz.
