Ewes that gain condition before and during mating have higher lambing percentages than ewes that lose weight or simply stand still.
Most farmers are aware of this and try to manage their flocks accordingly. The challenge they face is working out what the condition of the flock is.
The best way to do this is by condition scoring.
When a sheep is newly-shorn most farmers can easily tell if it is skinny or fat. But it is very difficult to judge the fatness or condition of woolly sheep by eye.
Even the use of scales can be misleading, with small fat ewes the same weight as large-framed skinny ewes.
Condition scoring by hand overcomes these problems and is also quicker than weighing.
A very simple scale of 0 to 5, increasing with level of fatness, from extremely emaciated (0) to overfat (5) is generally used.
Condition scoring assesses the amount of body fat or condition by feeling the vertical (spine) and horizontal (lumbar) processes along the loin area as shown in the following diagrams. The technique measures condition regardless of body weight (for example, at 55 kg liveweight, a small framed ewe may have a condition score of 4, and a large framed ewe a condition score of 2).
As a rule, there is about 5 kg difference in liveweight between condition scores for a given sheep.
The vertical and horizontal processes are prominent and sharp. The fingers can be pushed easily below the horizontals and each process can be felt. The loin muscle is thin with no fat cover.
The vertical processes are prominent but smooth, individual processes being felt only as corrugations. The horizontal processes are smooth and rounded, but it is still possible to press the fingers under them. The loin muscle is of moderate depth but with little fat cover.
The vertical processes are smooth and rounded; the bone is only felt with pressure. The horizontal processes are also smooth and well covered; hard pressure with the fingers is needed to find the ends. The loin muscle is full, with moderate fat cover.
The vertical processes are only detectable as a line; the ends of the horizontal processes cannot be felt. The loin muscles are full and have a thick covering of fat.
The vertical processes cannot be detected even with pressure; there is a dimple in the fat layers where the processes should be. The horizontal processes cannot be detected. The loin muscles are very full and covered with very thick fat.
The higher ovulation rates and lambing percentages associated with ewes that have been well-fed before and during mating are influenced by liveweight and whether or not the ewe has been gaining condition (flushing) during this period.
Heavier ewes in good condition invariably have better lambing performances than lighter skinnier ewes. Scientists estimate lambing percentages increase by 6–10 per cent for every extra unit of body condition score at tupping.
The flushing effect may provide an additional 5–10 per cent.
To maximise lambing percentages, ewes should not lose condition during mating and should ideally have a condition score of 3 or 4.
They should be the high priority mob, but on many farms they will be competing for the best paddocks with lambs that remain to be finished. If so, it will pay to consider whether this is the best use of feed – your lamb growing and marketing policy may need adjusting.
To ensure ewes are not losing condition at this time, 55 kg ewes should have an intake of at least 11 to 11.5 MJ ME/day of high quality green pasture per day (65 kg ewes, 12.5 to 13.0 MJ ME/day).
This is provided by at least 1.0 kg (1.2 kg) of dry matter of high quality green pasture per day.
Ideally the ewe mob should be rotated rapidly on to pasture that is 5–6 cm height. Grazing below 3 cm or 1,500 kg DM/ha will result in loss of body condition and lower lambing rates.
A Guide to Feed Planning for Sheep Farmers, NZ Sheep Council
A Guide to Improved Lambing Percentage, by K. G. Geenty, NZ Sheep Council
Your local farm consultant or veterinarian will also be able to help. Alternatively, contact your local WoolPro extension specialist:
Northern North Island: Sally Hobson, tel 07-823 3321 or 025-924 751 Hawkes Bay/East Coast: Lew Willougby, tel 06-835 1888 or 025-434 417 Southern North Island: Richard Gavigan, tel 06-376 0006 or 025-499 851 Nelson/Marlborough/Canterbury: Alan Marshall, tel 03-343 7913 025 329 399 South Canterbury: Julia Mackenzie, tel 03-680 6782 or 025-782 353 Otago: Robert Pattison, tel 03-489 9021 or 025-323 094 Southland: Aaron Meikle, tel 03-203 9071 or 025-846 377