Why Having A Consistent And Accurate Process Is So Important For Your Sheep Farm

As we approach the end of another year we wanted to conclude with a story about the variability of measurements and why having a consistent and accurate process is so important for your sheep farm. As sheep producers understanding the variability that naturally occurs in these measurements is critical.

We have used an example from a wool flock to illustrate this but across all measured traits there is inherent sampling error that can be introduced (despite best efforts) if these principles aren’t understood. Enjoy!

Average Fibre Diameter – A Statistical Myth

Medium wool Mike, a wool grower on Kangaroo Island, decided after due consideration and analysis of his current flock and the increasing trend in micron premiums for finer wool, that he would change his ram source to a finer average micron stud.

His research showed that a flock just down the road with a five year adult ewe fibre diameter average of 19.5 micron was achieving good wool cuts at that fibre diameter, so he attended their sale in October and bought fifteen rams.

These rams had been born in August of the year before and had been shorn in December of their birth year to even up the effects of birth and rearing status and time of drop. The rams were then all run as a group at the stud and shorn again in early June, at which time they were all assessed for fibre diameter and wool weights.

The rams were then ranked within their management group according to their index value for fleece weight and fibre diameter, and were offered for sale. In the catalogue were all of the details about the rams own measured performance (i.e. actual fibre diameter and fleece weight) as well as their deviation from the average for the group and index value. The rams that medium wool Mike purchased ranged between 16.5 and 17 micron at the pre- sale test in June with average wool cuts for the group, so he was pretty happy with the purchase.

Mike carted his rams home after the sale and put them into his ram paddock that was pretty flush for feed as he wanted them to “grow out” well before mating. In December, he decided that he would take a mid-side sample from his new purchases to see how they were going.

A couple of weeks later the results of the mid- side samples came back. To Mikes’ horror they were all between 21.5 and 22 microns! Mike was sure that he must have been duped and that the stud had deliberately mis-led him as to the fibre diameters published in their sale catalogue. He thought there was no way that he could put these rams out with his 22 micron average sheep and get where he wanted to go, and he was pretty upset about this foray to the new stud.

He rang his advisor, told him the story and was promptly told that they were a terrific buy and to get them out with the ewes as soon as joining time came around.

What was the basis for the advice he was given and how had the micron changed so much?

Understanding fibre diameter profiles 

The key to understanding what had happened to Mikes rams is appreciating the effects of nutrition on wool fibre growth and diameter. Figure 1 is a representation of the change in fibre diameter along each and every wool fibre grown by a sheep in southern Australia from birth to 18 months of age. 

Along fibre variation in diameter over a twelve month growing period is greater than the average fibre diameter variation between sheep in the same flock. Typically, in young sheep over a twelve month wool growing period, the fibre diameter will vary by up to five microns either side of the average (or a total of 10 microns!) Understanding that this is happening helps you interpret fibre test results and provides opportunities to astute growers.

The fibre diameter profile 

Figure 1 demonstrates what is happening to the wool fibre as the feed quality and type changes. 

When the lamb is born, it receives good nutrition from its’ mother initially and then is weaned onto good quality spring pastures. The wool grown is finer than the mature sheep because of the young age of the lamb and the demands for body growth.

By about October, the feed is drying off. In the absence of green feed, the wool fibre grows more slowly and the diameter begins to fall. This trend continues into the summer and autumn reaching its lowest point at the break of the season.

After the opening rains (or any rains that lead to green dry matter of 400 – 500 kg per hectare plus) the presence of green feed results in dramatic increases in fibre growth and the average diameter rapidly rises. This response is extremely sensitive to the presence of green dry matter.

The fibre diameter of the wool fibre continues to increase as the green feed season progresses and reaches a peak in late Spring. The sheep is now 15 – 18 months old. From here, the dry summer and autumn feed causes a decline in fibre diameter again, although generally not to the same lows as those achieved in the younger sheep.

This pattern is produced by all sheep across all wool profile grown from June after shearing, starting at about 17 micron, until December (16 months old) at which point the fibre has reached maximum diameter (around 24.5 micron) and is trending down again in the absence of green feed, finishing at about 24 microns when the samples were taken. The average fibre diameter for that 6 month period as measured by the machine is now about 22 microns. Had the rams been allowed to grow 12 months wool following the June shearing before measurement, the next 6 months of finer and below average fibre growth would have been included in the average micron measurement and the result would have been somewhere around 19 microns. This result would have been quite acceptable to medium wool Mike.

What about different locations on the sheep?

In addition to the variation along the staple, the average staple microns vary across the sheep depending on the location on the body from which the staple is taken (see picture below). Some sheep with deep body wrinkle can have adjacent mid side staple variation of up to 2 microns depending on whether the staple is growing on the top or the bottom of a wrinkle.

The fibre diameter can also vary from one side of the sheep to the other due to the location of the rumen. This highlights the importance of being consistent with where you take your mid-side samples from.

Obviously this can lead to significant error when assessing the average fleece micron. 

Side sample variations – average fleece micron of 22.1 microns

The take home messages 

The fibre diameter of wool in young sheep varies dramatically (up to 10 microns) along the fibre over a twelve month growing season. 

The response of the wool follicles to the presence of very low quantities of green dry matter in the pasture is rapid and results in increased fibre growth at an increasing diameter. Conversely, the absence of green feed will produce lower fibre growth of a finer diameter.

Average fibre diameter results for individual sheep from samples representing less than twelve months wool growth should always be interpreted with the fibre diameter curve in Figure 1 in mind. It is important to know the time of the year that the sampled wool was grown and the prevailing green feed conditions under which it was grown.

An average fibre diameter measurement for an individual sheep presented to you in isolation from the average of the management group is useless. It tells you very little about the genetic potential of that sheep. 

This effect is present in many of the measured performance traits and needs to be kept in mind when assessing your sheep or buying rams. Robust ASBV’s with good accuracies assist you to make better decisions on your sheep and avoid some of the traps associated with sampling error

2022 has been another incredible year for the BreedELITE Team. We are so privileged to continue to support our growing community of Progressive Producers, helping them to Breed ELITE Sheep and simplify their sheep farm and look forward to continuing to do so in the new year.

If you want to secure your delivery date or are interested to find out how the BreedELITE System can help you, give us a call on 08 8382 4565 and we will be happy to assist you.