Developing an automated sheep weighing system

A project undertaken at the Faculty of Veterinary Science, The University of Melbourne, and managed by J Larsen

This project is developing an automated system to weigh sheep as they walk over a weigh plate placed in the paddock. If successful, the system will provide regular body-weight monitoring of sheep without the need for mustering to:

• Improve the health and productivity of young sheep, allowing more efficient supplementary feeding during summer and autumn.
• Enable accurate monitoring of the bodyweight of other classes of sheep at critical times, such as late pregnancy and lactation.
• Allow intensive monitoring of the growth of prime lambs which will facilitate better marketing strategies.

Once a system is developed for sheep, it could then be adapted to weigh cattle in the paddock.

Background

To achieve optimum production, young Merino sheep should not fall below critical target weights after weaning, usually 22-25 kg, depending on their adult body size.

Below this weight they have insufficient reserves to cope with further weight loss. If they receive insufficient energy in their ration they must use muscle tissue to provide energy for survival. This dramatically decreases production of their high value wool and puts them at a greater risk of dying.

Despite this, inefficient supplementary feeding practices and unacceptably high death rates among Merino weaners are common on woolgrowing farms.

To prevent these losses, farmers need to regularly monitor the body-weight of Merino lambs between 4 and 8 months of age. One strategy is for farmers to individually tag 30 weaners and weigh them at 4-6 week intervals during the summer and autumn. From this information they can then accurately judge when to start feeding grain supplement, increase or decrease the amount fed, and when it’s appropriate to stop feeding.

However, the experience of veterinary consultants from the Mackinnon Project is that farmers will weigh weaners after having a problem year, but gradually discontinue the practice 2-3 years later. This is because sorting out 30 tagged sheep from a mob of 1000 weaners is a pretty tedious job, and other demands on the farmer’s time tend to take precedence.

Farmers then resort to visual monitoring of the weight and condition of sheep. This is doesn’t detect early weight losses, when supplementary feeding should commence or be increased, or excessive weight gains in some sheep indicating that too much supplement is being fed, or some of the lighter sheep need to be removed into a separate mob.

Team members

The project is being led by Dr John Larsen from the Mackinnon Project, located within the University of Melbourne’s School of Veterinary Science at Werribee. Collaborators include Jim Ranken, a farmer and inventor from Ballan, 80 km west of Melbourne, and Dr Knowles Kerry, Principal Research Scientist with the Australian Antarctic Division, who has developed automated weighing and identification systems for wildlife.

Progress

A system developed by the Australian Antarctic Division to remotely weigh penguins is being modified and incorporated into the sheep weighing system.

A number of complex issues were considered, such as rejecting weights when more than one sheep is on the weigh plate. New algorithms have been incorporated into the software that drives the system to more accurately estimate the weight of sheep as they walk over the weighing platform. The software has been linked to a specially designed sheep weigh plate and trialled with sheep of known weights.

Drafting systems to ensure that animals walk over the weigh plate in the paddock in an acceptable manner have also been developed. These are placed in areas that sheep use to access water or supplementary feed. In 2003 we will link the modified weigh plate and software to the sheep drafting system, then incorporate an individual animal identification system based on radio frequency identification devices (‘microchips’).