- Delaying Mating By 3-4 Weeks
- Advantages
- Disadvantages
- Ewe mating weights, weaning percentage and pasture intakes
- To Mate or to Wait?
Delaying Mating
Good drought management is ensuring that the maximum number of ewes retained actually conceive and produce a least one lamb next spring! For most, this means feeding sufficient supplements premating. If you need time to bring weights up, you can consider delaying mating.
Under drought conditions, the date the ram goes out has a critical influence on the profitability of next season's lamb crop. The conflict is between mating before ewe liveweights decline or gambling by waiting for expected rain to lift ewe condition.
Delaying Mating By 3-4 Weeks
(eg delaying mating from 15 March to 10 April)
Advantages
- Ewe liveweight may be increasing if it rains.
- Naturally higher ovulation rates (>10%).
- More ewes in lamb if it rains.
- Lambing more into spring growth.
- Better opportunity to set up winter rotation.
- Easier to identify those ewes that are unlikely to survive the winter and should be sold.
- With the use of harnesses, the likely spread of lambing can be easily identified; late ewes fed less and scarce feed put into the ewes that matter.
- More essential green "pick" leaf available to give higher feed quality.
- Less chance of ryegrass staggers, zearalone, facial eczema.
Disadvantages
- Ewe liveweight may be much lower.
- Lower ovulation rates.
- Later lambing and weaning.
- More dry ewes as lower conditioned ewes may not cycle or have a reduced number of ovulations.
- Longer maintenance feeding required.
- Dry ewes and late lambers not identified early enough to capture best sale prices.
- Possibly lambing into rougher weather.
- Shorter time before the onset of the summer dry.
- May mean having to wean earlier.
- Prelamb shearing could be pushed later into a less desirable feed or weather period.
- An early winter may diminish feed supplies.
- May upset sale patterns for sale ewes.
- Potentially more dystocia and bearings if prelamb feeding is not well managed.
Many of the advantages and disadvantages overlap but of prime consideration is whether a ewe is likely to get in-lamb and when is the best time to achieve this. The base liveweight at mating accounts for 60% of the variation in ovulation rate (number of eggs shed by the ovary) and the lambing rate. The actual weight before ovulation influences the number of eggs shed. Two general statements apply:
- For every 1 kg increase in liveweight, ovulation rate is increased by 2-3 eggs per 100 ewes.
- Of every 10 eggs shed, seven will develop into extra lambs born and, of these, five will survive to weaning.
Some early work by Rattray (et al 1978) at the Whatawhata Research Station, modified for this publication, identifies the production and the feed requirements of a ewe producing a lamb against that ewe being farmed dry.
Ewe mating weights, weaning percentage and pasture intakes
| Mating Weight (kg) | Lambs weaned per Ewe Mated (%) | Pasture Intake Kg Dry Matter /lambing ewe/year |
Kg Dry Matter per year for a dry ewe |
|---|---|---|---|
| 45 | 83 | 515 | 315 |
| 50 | 93 | 580 | 338 |
| 55 | 103 | 645 | 362 |
| 60 | 113 | 710 | 385 |
| 65 | 123 | 775 | 407 |
In the table, the annual feed difference between a wet versus dry ewe is from 52% at a mating weight of 65 kg up to 61% at a mating weight of 45 kg. As a rough guide, using the 55 kg ewe, the economic return from 362 kg of dry matter is simply the wool value of, say, $15 or a return of $15 ÷ 362 = $0.04 per kg of dry matter eaten. To produce the lamb takes another 283 kg dry matter. Given a $30 drought lamb, the dry matter return equals $30÷283=$0.106 plus the ewe's wool value on top of that! Thus producing a lamb, be it only a small lamb, is the most efficient and economic use of feed.
To Mate or to Wait?
Successful drought mating means making some strategic management decisions. Underlying these decisions are some important husbandry principles:
- Ewe liveweight change in the three weeks before ovulation influences the number of eggs shed per ewe or 100 ewes.
- Weight loss, especially in light ewes, is detrimental and results in poorer ovulation rates, more dry sheep and fewer oestrus periods.
- Weight gain in light ewes is extremely beneficial and may result in higher ovulation rates than heavier ewes being held at maintenance or slowly losing weight.
- Weight gains supported by high energy or protein feeds or high pasture allowances can result in 1.0 to 1.3 extra ovulations per 100 ewes per kilogram of liveweight change. This is independent of the ovulation rates associated with the base mating weight.
- Liveweight on the mature ewe depends on both the skeletal frame size and the amount of flesh or fat on that frame. Both those factors will influence ovulation rates. The higher the weight and the better the condition, the greater the number of lambs born.
- A large number of drought Corriedale or crossbred ewes that fail to mate will have low liveweights under 45 kg or condition scores under 2.5. For Merinos, the condition score is the same but the minimum liveweight is 37 kg.
- Low-conditioned ewes (condition score 2.5 or less, or light store condition) run the risk of entering anoestrus after the second cycle if the level of nutrition does not improve. Their failure to return to service in the 20-42 day period will be because they are no longer ovulating.
- Under favourable conditions, it is usual for ewes to lose up to 10% of their mating weight before lambing. Ewes mated with a condition score of 2.5 or less should not be mated unless above-maintenance winter feeding occurs. If this cannot be assured, many of these ewes will fail to rear a lamb or survive themselves.
- 70-80% of the ewes exposed to the ram should be in-lamb at the end of the first cycle. Continued under-nutrition for a further cycle will cause several of these ewes to fail to hold to service.
- The rams should be changed frequently but left out longer than usual (up to 45 days) on the basis that even a late lamb will be beneficial.
Ian Blair
Agricultural Consultant
Agriculture New Zealand
Blenheim
Contact for Enquiries
Manager
North Island Regions
Sector Performance Policy
MAF Policy
Hamilton
NEW ZEALAND
Phone: +64 7 957 8313
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