Farm Tech

In The Paddock
Seasonal sheep and beef management tips March 2003

Management around mating – The key to optimising next year's lambing percentage

PDF version (180 Kb)

Key points

• Put the rams out near the peak of the breeding season
• Lambing date should coincide with the onset of the spring pasture growth flush
• Ewes should have a condition score of 3 or better
• Avoid taking weight off ewes between weaning and mating
• Androvax can increase lambing percentages by about 20 per cent
• Vaccinate against the abortion diseases toxoplasmosis and campylobacter
• Rams must be fit and healthy

The lamb production potential of a farm is greatly influenced by management before and during mating.

Farmer decisions may determine the number of ewes cycling, ewe fertility, ovulation rates, the number of ewes mated and embryo survival.

Of these, ovulation rate is most important. It's largely determined by the ewe's weight, condition, and when in the season she is mated.

Breeding season

Ewes from most breeds cycle from mid-March until mid-August. The number of ewes cycling, fertility and ovulation rate all increase toward the middle of the breeding season, then decline as the season progresses.

To maximise the potential lambing percentage, rams should be joined near the peak of cycling activity. For most ewes this is from mid-April until late-May.

In practice, the choice of a joining date can be something of a juggling act. The resulting lambing date needs to coincide with the onset of the spring flush of pasture growth, and allow sufficient time for lambs to reach target selling weights.

Ewe feeding issues

Ovulation rate and lambing percentages increase by 5–10 per cent for every 5 kg increase in the mob's mating weight. It is extremely important that ewes do not lose weight over mating.

The aim is to have ewes at a good mating weight and at a condition score of at least 3. To improve ewes by one condition score they need to gain about 5 kg liveweight.

Ewes also increase ovulation rates in response to flushing — an improvement in feeding levels in the lead-up to mating. Light, thin ewes respond better than ewes at CS 3 or better.

Good flushing pasture will have an ME content of more than 10 MJ/kg DM and a post-grazing residual of 1200 kg DM/ha.

However, flushing should not be relied upon for a good lambing percentage. A dry late summer or autumn may result in ewes competing for quality feed with other classes of stock.

Also, it is safer and more efficient to maintain ewes at good condition scores from weaning until mating. Deliberately taking weight off ewes or working them hard over summer, then flushing them up before mating, is not recommended.

However, if ewes are too light — possibly as a result of drought — it can be economic to flush them on peas and lupins, grains such barley, or good quality pasture silage.

Sixty to 70 kg ewes need 11–12 MJ ME/day for maintenance. Feeding 500 g of barley/ewe/day will contribute 5.3–5.8 MJ/day if it is all eaten.

Feeding 250–500 g/ewe/day, depending on pasture levels, is typical. For economic reasons, feeding more than this is rare.

Because of the risk of grain overload (acidosis), ewes should be gradually introduced to grains including barley, maize, oats, peas and wheat. Lupins do not cause acidosis, even when large amounts are fed.

Pasture silage is much cheaper than grain and there are no acidosis problems. When good quality wilted silage (over 30 per cent DM) is fed ad lib, intakes of up to 1–1.5 kg DM/ewe/day can be achieved, in addition to any pasture eaten.

Very good liveweight gains and lambing percentages have been obtained from ewes fed on good quality silage. If silage quality is mediocre, ewe gains can be good, but lambing percentages can be disappointing.

Crops such as kale and turnips can also be used very successfully to flush ewes, so long as utilisation levels are not too high. Large flushing responses have also been achieved on tannin-containing feeds such as birdsfoot trefoil, poplar and willow.

Androvax

Androvax is a vaccine that can increase lambing by about 20 per cent. Best results are obtained from good conditioned ewes.

This vaccine is a tool for very good management situations — it is not a substitute for poor management. Consider it where normal litter size is 1.0–1.4, when all the response will be as twins.

Where ewes are already achieving 150 per cent it should not be used, as much of the response will be as triplets or quads, which are likely to have poor survival rates. For the same reason, the vaccine should not be used in high fecundity breeds like the Finn or Booroola.

In the first year, two injections are given eight to 10 weeks and six weeks before joining. In subsequent years only one shot is needed about six weeks before mating.

Abortion diseases

The contagious diseases toxoplasmosis (toxo) and campylobacter (vibrio) are the most common causes of abortion in sheep. Younger ewes are most susceptible.

Toxo is a parasite spread in cat faeces and ingested by ewes along with hay or pasture. Ewes can be infected at any stage of pregnancy, resulting in embryonic or foetal death, or the death of newborn lambs.

One dose of Toxovax vaccine gives lifetime protection against toxo. Lambs or hoggets should be vaccinated as early as practicable (after 12 weeks of age), as natural infection makes the vaccine ineffective. The latest date for vaccination is one month before joining with teasers or entire rams.

Campylobacter infections occur in the last six to eight weeks of gestation and can cause abortion or the death of the lamb soon after birth. The disease is spread by ewes grazing pasture infected by bacteria spread from aborted material or from discharges from infected ewes.

Campylovexin vaccination is very effective. Campylovexin should be administered twice before mating, with a four week interval between vaccinations. A booster is needed before mating in later years. Failure to boost may leave ewes with limited protection.

Ask your vet for up-to-date vaccination advice when ordering your vaccine requirements.

Don't forget the rams

Active healthy rams are essential for good fertilisation rates, especially when ewe:ram ratios are high (>100:1). Check your rams about 10 weeks before joining and again the day before.

At the 10-week check, look for wounds, foot problems (abscess, foot rot), fly strike and health problems in the genitals (Brucella ovis, epididymitis, scrotal mange, pizzle rot and penis problems). Isolate any rams that are of concern and get the vet to check them out.

Rams should be physically fit, especially for hill country. Fit, healthy rams should have a pink flush around the wool-free areas near the scrotum and inside the rear legs.

More information

200 by 2000; A guide to improved lambing percentage, edited by K.G. Geenty. Chapters 2&3.

Your local farm consultant or veterinarian will also be able to help. Alternatively, contact your local Meat & Wool Innovation extension specialist: