Density and Length Profiles of Wyambeh Poll Merino Rams
Density and Length Profiles of Wyambeh Poll Merino Rams
Prepared by Dr. Jim Watts 27 October 2008
Samples received 2 August 2008
Introduction
The objective of the SRS® breeding system is to increase the density and length of fibres grown by sheep. If there are many fibres on the animal’s body, and these fibres are long, then the animal will produce a high fleece weight. Also, since high fibre (follicle) density is genetically correlated with low fibre diameter, the fleece will have a high value because it is fine and there is a lot of it.
An example of the distinctive fleece structure of Merino sheep with measurably high levels of fibre density and length are shown in Figure 1.
Figure 1. The fleece structure of a Merino sheep with high levels of fibre density and length.
In the Merino sheep, high fibre density is indicated by high crimp amplitude (deep crimp) and thin staples. High fibre growth rate (long fibres), is indicated by both high crimp amplitude and low crimp frequency (‘bold crimp).
Follicle and Fibre Patterns
Fibres grow from follicles in the skin. Follicles develop before the lamb is born. Primary follicles form first and then secondary follicles. The follicles are arranged as ‘follicle groups’ (Figure 2).
Figure 2. Diagrammatic representation of a follicle group in the skin.
There are only 3 primary follicles per group. The number of secondary follicles per group is a genetic characteristic for a particular sheep but can vary widely between animals (in our studies, from about 40 to 180). The S/P ratio, or ratio of secondary follicles to each primary follicle, defines the number of follicles per group.
Merino sheep have, on average, an S/P ratio of 20 to 1 and about 55 follicles per square millimetre. Primary fibres are usually about 1 to 3 microns coarser than the average diameter of the secondary fibres. The length growth rate of the fibres of Merino sheep is, on average, about 0.30 millimetres per day.
The SRS® objective is to breed Merino sheep that have primary fibres much finer than the secondary fibres, follicle densities above 85 follicles per square millimetre and S/P ratios above 40 to 1. The objective is also to improve fibre length to 0.70 millimetres per day and to have the fibre length to staple length ratio as high as possible (eg. 1.50 or greater).
Density and Length Profiles
The density and length results for the Wyambeh Poll Merino rams are listed in Table 1. Profiles are attached.
Table 1. Follicle and fibre characteristics of the Wyambeh Poll Merino rams. Bracketed figures are standard deviations.
Legend to Table:
Dp = primary fibre diameter in microns
Ds = secondary fibre diameter in microns
Fn = follicle density (per square millimetre)
S/P ratio = secondary follicle to primary follicle ratio
FL = fibre length growth rate in millimetres per day
FL/SL = ratio of fibre length to staple length.
Ram 060183 has low fibre density and high fibre length. The primary fibres and secondary fibres are very fine and uniform in diameter. The fibres havehigh crimp amplitude
Ram 070207 has high levels of fibre density and fibre length. The primary fibres and secondary fibres are fine and uniform in diameter.
Ram 070021 has low fibre density and moderate fibre length. The primary fibres and secondary fibres are fine and uniform in diameter.
Ram 070461, although tested at a young age, has high fibre density accompanied by extensive formation of secondary follicles. The primaryfibres and secondary fibres are very fine and uniform in diameter.
Ram 070457 was tested at a young age. Hence its fibre density is likely to be moderate, not high, as an adult. However, the fibre length is high and the primary fibres and secondary fibres are fine and uniform in diameter.
General comments
The results are encouraging. Fibre length is particularly good.
We need to continue to lift fibre density and S/P ratio.