Biological defleecing: intravenous infusion of amino acid mixtures lacking lysine and methionine creates a weakened zone in the wool staple, which is amenable to mechanical wool harvesting

Abstract

Conventional shearing of sheep is labour-intensive, expensive and presents significant occupational health and safety risks. The only alternative at present is based on injection of epidermal growth factor, which severs the fibre at the follicle level. This technology cannot be used in pregnant animals and requires application of a net to retain the severed fleece. An alternative is to create a weakened zone within the wool staple, which would be sufficiently strong to retain the fleece on the sheep while a protective covering regrows, but sufficiently weak as to allow painless and automated removal of the fleece. We demonstrate that this approach is possible using mixtures of amino acids lacking lysine and methionine. Initially we demonstrate the relationships between staple strength, a subjective ‘harvestability’ score and a subjective ‘pain’ score, using fleeces from animals treated with varying levels of cortisol to create a wide range of strengths of wool attachment. We assigned a score to the ease with which we could manually break the staples, and also to the animal’s response to breaking the staples still attached to the skin. The relationships between these variables indicated that a staple was considered harvestable and could be removed with minimal skin flinch response at a staple strength of ~10–13 N/kTex. Staples within this range were then produced by intravenous infusion of mixtures of amino acids lacking in lysine and methionine for a 5-day period. The weak point was uniformly created across the entire fleece and when a prototype roller-pin device was applied to the weakened wool, it uniformly broke the fleece of the three sheep tested. The mode of action of the amino acid treatment on wool growth was studied. There was no effect of unbalanced amino acids on the rate of follicle bulb cell division, the number of active wool follicles, or the length of the keratinisation zone in the wool follicle. Fibre diameter was reduced by ~4 microns by treatment, and intrinsic fibre strength (strength relative to cross-sectional area of the wool fibres), was reduced by ~50%. Results of these trials are encouraging but further work is required to develop a practical, on-farm method of altering systemic amino acid supply and to design an automated, high-throughput system of severing the weakened wool.