Improving Lamb Survival And Growth Rates
(condensed from a presentation by Dr. Annette Litherland, AgResearch, Palmerston North)
Maximising the lambing percentage and lamb growth can substantially lift farming profitability.
Every farmer understands that, yet many sheep farmers seem to have problems in matching the desired end product and his/her particular farming system.
- Improving lamb survival
- Pre-weaning lamb growth rates
- Post-weaning lamb growth rates
- Increasing summer feed quality
- Canterbury Farmlet Studies
1. Improving lamb survival
What is your level?
- Compare the scanning percentage with the tailing percentage and calculate actual lamb loss. Lamb loss = (potential lambs - number of lambs)/ potential number of lambs.
- To get the actual potential number of lambs if you are not scanning for triplets, the number of ewes carrying triplets can be calculated from the following equation: % Triplet bearing ewes = 27.625 - 0.6921S + 0.0044S2 S= % single bearing ewes. e.g. 155%, 170%, 180%, 200% scanning (counting all multiples as 2) actual scanning% (incl. triplets) = 160%, 181%, 203%, 228%, respectively.
As the number of twins increase, lamb survival can be expected to decrease slightly.
Research established these average figures from scanning results:
| Scanning percentage: | 120 | 140 | 160 | 180 |
| % lamb loss: | 16 | 17 | 18 | 19 |
If your lamb losses are greater than these figures, work down the list and eliminate potential risks:
Inadequate vaccination programme
Protect lambs from clostridial diseases by vaccinating ewes with "5 in 1". If warranted, use Toxovax to improve lamb survival. Campylobacter abortions can be prevented by vaccinating with Campyloxvexin.
Poor mineral status
In selenium deficient areas, ewes should be injected with a supplement at mating and two weeks prior to lambing.
Look for sub clinical iodine deficiency if healthy born lambs die for no obvious reason. This is also possible when brassica crops have been fed during winter without iodine supplementation. Ask your vet for help since iodine deficiency can vary between years.
Underweight or overweight lambs at birth
If low lamb weights are a consistent problem, shear (use winter comb) twin bearing ewes at mid pregnancy (70 to 100 days pregnant) as this can increase twin lamb birth weights by 0.5 kg. Prevent extreme weight loss of ewes during pregnancy (up to 4 kg) as this can reduce twin lamb size by 0.4 kg.
A terminal sire crossed with highly fecund ewes will increase lamb survival due to increased birth weights and heterosis.
Steep slopes, poor shelter and disturbance
Bad weather can have a profound effect on lamb survival. You can increase lamb survival by giving the highest risk group the best paddocks. The ewes with the greatest risk of lamb loss are those bearing triplets, followed by young twin bearing ewes, then twinning mixed aged ewes, and so on.
Ewes like to select birth sites with a clear view, and so often lamb at the top of slopes and exposed ridges.
In the case of twin lambs ewes might not always leave the birth site to follow a lamb falling down a slope. Streams, swamps, exposed ridges etc. are potential death traps in stormy weather.
Shelter improves lamb survival, but shelter that prevents the ewe from seeing her lamb may prevent the ewe looking for the lamb. Often slopes in the lee of the prevailing storm can provide shelter.
Avoid disturbing lambing ewes since this can cause mismothering. Try to avoid lambing in paddocks you have to drive through every day. Ewes will move larger distances in flat paddocks than on steeper hills.
Poor maternal traits in the ewe
Some breeds of sheep show better mothering ability than others. Younger ewes have less developed maternal instincts than older ewes (incidentally, Coopworth's usually display a very strong maternal instinct - ed)
Poor ewe condition and nutrition
Ewes that are well fed before lambing have less clinical and sub clinical sleepy sickness, produce more colostrum and milk, have stronger lambs, and bond better with their lambs. In late pregnancy fetal growth is very rapid and the ewe has high feed requirements. For ewes bearing singles, feed requirements are 29% higher, twins 52% and triplets 73%, compared with a dry ewe two weeks before lambing.
At lambing, single carrying ewes should be set stocked at 1000 kg DM/ha and twins at 1200-1500 kg DM, depending on the lambing date. If feed is going to be short, keep ewes tight at the early stages of pregnancy rather than later.
It is unlikely that twin bearing ewes will increase their condition over the last few weeks before lambing.
Triplet ewes can not eat enough to meet the requirements over late pregnancy, and a new high protein supplement has shown some promising results in survival of triplets (G. Davis, AgResearch Invermay)
Back to the top2. Pre-Weaning Lamb Growth Rates
Actual measurements of lamb growth rates from birth to weaning on several North and South Island farms revealed:
- Average growth rates from birth to weaning are 270 grams/day for singles and 220 grams/day for twins.
- Average growth rates (twins and singles) were 310 g/day from birth to docking, 280 g/day in mid-lactation, and 220 g/day in late lactation.
- The most important factors influencing lamb growth rates pre-weaning are likely to be improved milk production from lambing to weaning (higher pasture covers, better ewe condition at lambing, improved ewe genetics) and higher pasture quality in late lactation.
Feeding ewes during lactation
Pasture quality declines by late October due to rising temperatures and longer days. The graph below shows the actual measured values of pasture growth rates for dry, southern North Island farms.
To adequately feed ewes in early lactation and insure good pasture quality in late lactation, the lambing date needs to be judiciously timed.
Improved pasture management in spring, to better match supply and demand, offers potential lamb growth rates of 300 to 350 g/day. This provides a 100 day weaning weight of around 35 kg.
Allocation of feed to ewes
Ewes won't milk well if they are in poor condition at lambing and/or underfed during lactation.
- In early lactation pasture cover should have 1500 kg/ha (4 cm height) of DM for twinning ewes, and singles not less than 1200 kg/ha of DM
- In mid lactation, ewe and lamb(s) requirements are 23% higher and in late lactation they are 33% higher for twins than singles. This adjustment is usually achieved by increased spring growth and or manipulation of the stocking rate. Be aware that in late lactation pasture quality drops due to higher bulk and starch in the pasture.
- Ewes in poor condition with twins need to be fed very well to help lactation and increase live weights.
- A combination of a later lambing date and high covers at lambing and during early lactation can lead to early loss of pasture quality and lighter ewes and lambs at weaning.
3. Post - Weaning Lamb Growth Rates
Pasture quantity and lamb growth rate
The goal of 400 grams/day lamb growth rates remains just that for many farmers - a goal. In reality maximum growth rates for weaned lambs is more like 340 g/day on very high quality forages fed at very high allowances.
Most lambs show much slower live weight gains.
Pasture quality and sheep performance
- As pasture quality declines, lamb growth rates decline, because each kg of DM has less metabolisable energy content and also the animal intake drops.
- Pasture quality management offers massive potential for improving sheep performance.
Pasture quality facts:
- The most important nutritional limitation for sheep is insufficient metabolisable energy (ME) intake.
- Fungal toxins (Facial Eczema, Fusarium, grass staggers) will reduce ewe reproductive performance and lamb weight gain.
- Contamination with parasite larvae reduces quality (energy is needed to fight the challenge)
- Trace elements can also be a problem - consult your vet.
Pasture components vary in quality
- Clover is higher quality than grass
- Leaf is higher quality than stem
- Green material is higher quality than dead material
Quality declines with age
- decline is very slow with clover leaf
- decline is significant with grass leaf
- decline is even faster with stem
- quality is lower overall at warmer temperatures
- decline in quality with age is faster at warmer temperatures
Diet selection and feed quality
- Sheep select and eat the highest quality components first, so the quality of the remainder decreases rapidly. Hence the compounding effect of lower intake and lower diet quality.
- The animal's ability to select the best pasture is therefore obviously greatest during high pasture volume (mass), so move young stock sooner rather than later.
- Low quality feed left after young stock needs cleaning up (mower/low priority stock)
Summary:
- Dead matter substantially reduces the quality of diet
- In high dead matter pastures, shift lambs more frequently to maximise their available selection
- Predominantly grass pastures grown in high temperatures have lower quality
- Predominantly grass pastures grown in high temperatures and grazed for long periods have markedly lower quality
So what constitutes high quality pasture?
- Has high content of green leaf and clover
- Has low stem and dead matter content
- The herbage is young (as in recently grown)
- The herbage has grown in cooler rather then warmer conditions
- Grazing animals have the opportunity to select a high quality diet
4. Increasing Feed Quality In Summer
Control pastures in spring:
- Better match patterns of feed supply and demand throughout the year by:
- High pasture utilisation. This minimises dead material and stem build up and maximises leaf and clover.
- Buying stock or selling grazing helps control surplus feed.
- Rotational grazing is best at high winter stocking rates.
- Increasing lambing %, lambing at the correct time, delaying weaning, all improve pasture utilisation
- Topping and conservation
- Prevent low quality and feed accumulation
- Conservation provides a saleable product
- Regrassing: new pastures have less dead material, more clover, less fungal toxins, less parasite larvae
- Feeding concentrates: may be cost effective sometimes
- Fertiliser application: changes pasture composition, clover content, content of "easily managed grasses" and mineral composition.
- Grazing strategies
- Subdivision assists in efficient clean up grazing
- Clean up with lower priority stock
- Set stocking/fast rotations maximise intake and help control pasture of feed surplus.
Grow lambs faster pre-weaning
This reduces the requirements for a high quality feed in summer.
Plant alternative forage crops
Reasons for alternatives to ryegrass:
- Post-weaning lamb growth rates should improve markedly.
- Insurance against dry summer periods and, in FE regions (North Island), to help prevent intake of toxic spores.
If you want to increase feed quality by using a crop it should:
- Grow well and reliable in your environment
- Produce a large quantity of palatable, green forage, preferable non-grass
- Result in healthy lambs
- Be flexible enough to meet other requirements
- Be economic and result in fast growing heavy lambs
5. Canterbury Farmlet Studies
(Tom Fraser, AgResearch Lincoln)
System: 12 ewes/ha, mid August lambing, mid November weaning, lambs drafted at 15 kg CW until 5 January when all remainder sold store, dryland farming. Data collected 1997 to 2000.
Cost of renewal $250/ha
Time of renewal
Chicory, red clover: 5 years
Tall fescue: 7 years
Hybrid rye grass: 3 years
Perennial ryegrass: 20 years
Farmlet Control: 12 Perennial Ryegrass paddocks Farmlet Improved: 5 Hybrid ryegrass + chicory, 3 tall fescue, 4 chicory + red clover.
Cost of renewal per hectare/year
Control $12
Improved $56
The revenue considered is only from additional lamb weight and assumes the same lambing percentages.
| Farmlet | Lamb live weight gain (g/d) | Lamb Income ($/ha) | Renewal Cost | Net Benefit ($/ha) | Birth to Weaning | Post-weaning | 1997/1998 | Improved | 300 | 292 | 704 | 56 | 648 | Control | 284 | 150 | 600 | 12 | 587.5 | 1998/1999 | Improved | 312 | 298 | 647 | 56 | 591 | Control | 289 | 133 | 553 | 12 | 540.5 |
Net benefit to the improved system was $50-$60 per hectare. In addition, the ewes on the improved pastures are also about 6 kg heavier at mating and this should increase lambing percentages by about 12%; this is not included in the analysis. The ewes also produced an extra 0.4 kg of wool.
The above should be read in conjunction with other articles on this web site e.g.. Summer feeding of sheep (by Sue Mc Kay) and Pasture quality and alternative feeding of sheep (by Tom Frazer). For more extensive information, consult the Sheep council publication : A guide to improved lamb growth "400 plus"
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