Measuring litter weight weaned (LWW) with EID

Electronic national livestock identification system (NLIS) sheep tags make it possible for sheep producers to measure the actual performance of an individual ewe in terms of lamb production.

Pregnancy scanning data provides an indication of the potential lamb production from a ewe, but many factors influence the actual production achieved because of lamb mortality and variations in lamb growth rates.

Measuring litter weight weaned (LWW) is not a new concept but in the past it has been restricted to use within the stud sector because of the labour involved in recording the pedigree information required.

Practical use of LWW in a commercial flock

The use of electronic (NLIS) sheep tags make it possible to assess the performance of an individual ewe based on LWW in a low-cost, low-labour manner.

All ewes and lambs in a mob are tagged with electronic (NLIS) sheep tags and a process known as Pedigree MatchMaker is used to figure out which lambs belong to each ewe.

With the pedigree known for each lamb, it is then a simple process of recording individual live weights for each lamb using electronic (NLIS) sheep tags at approximately 100 days of age.

Some commercial contractors and consultants have developed a system that takes this data and calculates the kilograms of lamb produced by each ewe and ranks them. The result is a relative ranking of ewes within the mob, based on the kilograms of lamb that each has weaned.

Practical examples

Various commercial consultants have conducted a number of litter weight weaned demonstration activities in recent years. These have illustrated enormous variation in the level of production achieved in relation to litter weight weaned per ewe. This variation simply cannot be identified without the use of electronic (NLIS) sheep tags, which then provides knowledge of lamb pedigree, and recording of individual weaning weights.

HM Prison Langi Kal Kal demonstration

Ewes in a mob were all scanned as multiple bearing, demonstrating their reproductive potential. All ewes were in condition score 3 or better, and feed quantity and quality in the paddock was excellent with approximately 2000kg/ha of phalaris and clover.

The results were as follows:

• The most productive ewe in the mob reared a phenomenal 139.5kg of lamb (lambs at average age of 113 days). She reared 3 lambs with weights of 45kg, 45.5kg, and 49kg.
• The most efficient ewe in the mob weighed in at 73kg and reared 121.5kg of lamb. That is equivalent to 166% of her body weight reared in lamb weight.
• A number of ewes only reared a single lamb with weights ranging from 42kg to 50kg.

Shelburn demonstration

A mob of 600 first cross ewes were used in the demonstration:

• The LWW recorded for ewes with lambs at an average age of 85 days ranged from 21.5kg to 115kg.
• The highest growth rates (based on assumed average birth date of 1 week into lambing period, and birth weight of 6kg for all lambs irrespective of rearing type) achieved was 560g/day up until day 85.
• The 3 highest average growth rates achieved were all in excess of 540g/day. Of these 3 lambs, one was reared as a single, one as a twin, and one as a triplet.
• Twin and triplet lambs were found to be regularly out performing some single lambs based on average growth rates throughout the 85 day period.

LWW will now form the basis of ewe selection within the maternal flock at Shelburn.