Abstract

Real-time (B-mode) and simple (A-mode) ultrasonic instruments were evaluated in 2 experiments to assess their potential for measuring carcass fat and muscle variables. In a third experiment, progeny of five Romney selection lines were ultrasonically scanned at regular intervals from 5 to 14 months of age to record backfat thickness (C), GR and the width (A) and depth (B) of the L. dorsi muscle. In the one calibration experiment where the Toshiba machine was used, the machine was found to be particularly appropriate for measuring GR depth achieving a weight adjusted partial correlation of 0.81 with the carcass measurement and repeatability of 0.86. Comparable figures for the AIDD scanner in two experiments averaged 0.75 and 0.82 respectively for C fat depth measurements. Prediction equations for the chemical carcass lipid content showed that including either C or GR ultrasonic fat depths provided significantly improved estimates over those using only live weight. The addition of ultrasonic muscle widths or depths provided little additional advantage. The ultrasonic C and GR measurements confirmed that the production index line, selected on an index comprising dam's number of lambs born and the animals own weaning and hogget fleece weight, was the leanest. The single trait line selected on dam's number of lambs born, was slightly leaner than the controls, while the hogget fleece weight line was similar to the control line. The ranking of the 100 day weight selection line was found to vary with year of birth measured, but on average was similar to the control line. In contrast no major differences were detected in muscle width or depth among any of the selection lines.

RW, Moore, JK Woolhouse, and MC Wilson

Proceedings of the New Zealand Society of Animal Production, Volume 49, , 81-84, 1989