Mustering
- Avoid severe stress on lambs, such as dogs extensively chasing lambs which break away from the mob.
- In hot weather move lambs slowly.
- Provide lambs with adequate clean water if they are yarded for more than 12 hours before loading.
- Muzzle dogs.
- Minimise the boxing together of unfamiliar lambs.
Loading
- Move lambs quietly to avoid stress.
- Muzzle dogs.
- Do not pull or lift lambs by the wool - this will cause bruising.
- Ensure that lambs are denied feed 12 hours before trucking - but provide water during this time.
- Do not use electric prodders.
Note: Unnecessary stress on the lamb at the farm, in the truck or at the abattoir can affect meat quality by lowering muscle glycogen levels. This in turn may raise pH to an unacceptable level which may result in meat that is dark, tough, less flavoursome or has shorter shelf life.
Assessing lambs to specifications
In assessing lambs for sale the aim should be to select those lambs closest to the specifications for carcase weight and fatness required by consumers. Accurate assessment helps the producer and his agent to target specific markets.
The traditional approach of visually assessing lambs as a mob or while they are running through the drafting race, often results in drafts of lambs with a 5-10 kilogram carcase weight range and a wide variation of fat scores. Successful marketing of more even lots of lean lambs requires a more careful and professional approach.
Being a good assessor means being able to estimate accurately the carcase weight, fat score and skin quality of lambs while they are still alive. These skills can be improved by experience and study of regular abattoir feedback, but are also greatly aided by the use of liveweight scales and a good handling (palpation) technique.
Assessing carcase weight
The five guide to carcase weight is liveweight adjusted by an estimated dressing percentage.
Carcase weight = Liveweight x dressing percentage (e.g. 18.2 kg = 38 kg x 48 percent)
Liveweight can be accurately and quickly measured using a modern set of lamb weighing scales.
Although Australian lambs have an average dressing percentage of around 46 - 48% they vary considerably, from as high as 54% to as low as 40 - 42%.
Guidelines for dressing percentage
These guidelines are based on accurate fat scoring and refer to weaned second cross lambs, around 2 - 3 hours off feed, with an average wool length of approximately 5 cm.
| Fat Score |
Dressing Percentages for 2nd Cross Lambs |
| 1 |
41% |
| 2 |
43% |
| 3 |
45% |
| 4 |
47% |
| 5 |
49% |
Important factors affecting dressing percentage are:
Fatness
Lean lambs have lower dressing percentages. Dressing percentage fails by an average of around 2 percentage points for every decrease in fat score.
Time off feed before weighing alive:
Dressing percentage increases by around 1 percentage point after 4 hours of emptying out, about 2 percentage points after 12 hours, and around 4 percentage points after 24 hours.
Skin weight
- short wooled and freshly shorn lambs have a higher dressing percentage than woolly lambs.
- a 75 mm skin, just too wet to shear, holds 0.2 to 0.5 kg of water. A thoroughly saturated skin holds 1.5 - 2.0 kg of water.
Sex
Ram and cryptorchid lambs dress out about 1 percentage point lower than wether lambs and about one and a half percentage points lower than ewe lambs.
Breed
The breeding of both sires and dams can affect fat cover and the dressing percentage of a lamb. Merino lambs tend to have a lower dressing percentage.
Carcase trim and chilled versus hot carcases
Define the carcase
- carcases trimmed to AUS-MEAT standards (thick skirts, kidneys, kidney knobs and channel, udder and cod fat removed) will have a dressing percentage approximately 1.5 - 2 % points lower than if these trimmings were not removed.
- chilled ('cold') lamb carcases are around 2 to 3 % points lower than 'hot' weights
Assessing fat score on live lambs
Lamb producers can readily use a simple hands-on method to assess fat score. With practice, this method can achieve a close match with carcase fat scores.
To achieve a reliable assessment, have the lamb standing in a relaxed state, preferably in a race or lightweight scales. The lamb will not be bruised if assessed in the correct manner by palpation with the fingertips. Fingers should be worked through the wool to the skin level before feling for fat cover over the long ribs.
The best site to feel when assessing fatness is over the long ribs. This area includes the GR site, where fat depth is measured 11cm from the midline over the 12th rib onn the carcase.
| Fat Score |
1 |
2 |
3 |
4 |
5 |
| GR Tissue depth (mm) |
0-5 |
6-10 |
11-15 |
16-20 |
20+ |
| Long Ribs |
Individual ribs felt very easily. Cannot feel any tissue over the ribs |
Individual ribs felt very easily, but some tissue present |
Individual ribs can still be felt, but can feel the tissue |
Can just feel the ribs and fluid movement of the tissue. |
Ribs barely felt. Tissue movement very fluid. |
Remember, at the same weight, ewe lambs will generally be fatter than wether lambs.
- Empty out lambs for 12 hours before transport.
- Muzzle dogs.
- Provide water while lambs are emptying out.
- Weigh lambs to ensure proper assessment of weight.
- Assess fat with lambs in relaxed state, preferably in the lamb scales.
- Do not spray marks or crayons on the back, use only on the head.
- Ensure trucks are clean, with no protuberances.
- Ensure final assessment is done by someone regularly assessing lambs to ensure assessment is accurate.
