FLEECE ROT AND BODY STRIKE IN MERION SHEEP .6. EXPERIMENTAL EVALUATION OF SOME PHYSICAL FLEECE AND BODY CHARACTERISTICS AS INDIRECT SELECTION CRITERIA FOR FLEECE ROT

Indicators of staple thickness, staple weight, staple density, wool we ight cm-2, crimp frequency, dust penetration, fibre diameter (mean, va riability), birthcoat score, and neck and body wrinkle were evaluated for their suitability as indirect selection criteria against fleece ro t and body strike. The fleece traits were assessed in 949 Merino ewe h oggets representing the progeny from 134 sires in 15 contemporarily ma naged flocks. Fleece rot and body strike were assessed following exper imental induction. In decreasing order of importance, variability (s.d .) in fibre diameter, average staple thickness, crimp frequency, varia bility (c.v.) in fibre diameter, mean fibre diameter, birthcoat score, staple density, variability in staple thickness, staple weight, and n eck wrinkle score, accounted for a significant component of the variat ion in liability of sheep to fleece rot. Body wrinkle, variability (c. v.) in staple thickness, staple length, dust penetration, and wool wei ght cm-2 were not important. Based on combined estimates of the herita bility of the indicator trait and its genetic correlation with fleece rot, variability in fibre diameter (s.d.) and birthcoat score showed t he highest potential as indirect selection criteria. Variability in fi bre diameter (s.d.) also showed a similar scope for selection against body strike. Indicators of mean staple thickness, crimp frequency, dus t penetration and wrinkle score showed little or no scope for indirect selection against fleece rot or body strike. The role of variability in fibre diameter (s.d.) as an indirect selection criterion for fleece rot and body strike in designed breeding programmes which include oth er important objectives, will need to be further evaluated, given an u ndesirable genetic correlation with clean fleece weight. High between- flock correlations were observed for a number of fleece traits and sus ceptibility to fleece rot. Susceptible flocks were characterized by fl eeces with longer, heavier, thicker staples with a lower crimp frequen cy, and higher fibre diameter with a higher variability. Predicting th e susceptibility of flocks to fleece rot and body strike, through a be tween flock index based on the measurement of simple fleece traits, is suggested.