Tool 10.7 Standard reference weight calculator

Standard reference weight is the liveweight of a fully grown, bare shorn, non-pregnant sheep in condition score three (CS3) with no gut fill (i.e. empty). Determining the standard reference weight

(SRW) of your flock provides a useful comparison across a range of animals of varying liveweights and condition scores in order to make decisions about meeting their nutritional requirements for maintenance or growth.

To determine the SRW, use scales to weigh a representative sample of your adult ewe base. The best way to do this is to let a few ewes run through the race at the start whose liveweight is not included (as the bigger ewes are generally at the front of the yard), then weigh a group of ewes (at least 50, depending on your flock size and the consistency of your ewe base). After you have determined your flock average liveweight on that day, adjust it based on the following factors:

• Deduct five per cent from the average liveweight if ewes have not emptied out to account for gut fill. If sheep have been yarded for four hours off feed and water you will not have to adjust for this.
• Add or subtract 19% from the average liveweight to account for any variation away from an average of CS3 (e.g., if average CS of the mob is CS2, and the average liveweight is 50kg, add 9.5kg, however, if the average CS of the mob is CS4 and the average liveweight is 50kg, subtract 9.5kg from the average liveweight).
• Make an allowance for fleece weight if ewes are not bare shorn (e.g., for full wool deduct your average adult fleece weight, for six months’ wool deduct half your average adult fleece weight).

Example SRW calculation

Note: One condition score is equivalent to 19% of the standard reference weight (SRW) for a sheep. The table below summarises the weight of one condition score for different sized sheep.